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Shifts in characteristics of the plant-soil system associated with flooding and revegetation in the riparian zone of Three Gorges Reservoir, China
Abstract
The operation of the Three Gorges Reservoir (TGR), the largest hydropower dam in the world, has triggered a dramatic shift in the flooding regimes of sites upstream of the reservoir. Little is known about how disrupted flooding regimes and consequent management approaches might affect the ecological and biogeochemical characteristics of riparian ecosystems. In this study, we evaluated the effects of disruptions to natural flooding regime on basic soil properties, soil nutrient and heavy metal levels, and key characteristics of riparian plant and soil microbial communities. To do this, we used an elevational gradient that encompassed four flooding duration zones (0 (i.e., control), 169, 237, 286 days of flooding per year on average). The disrupted flooding regimes were associated with levels of soil total N and P that were on average 17% and 24% lower, respectively, than those in the non-flooded areas. On the other hand, the concentrations of heavy metals (Hg, Pb, Cu, Zn and Mn) were higher in flood-affected areas than in the non-flooded areas. Increased flooding frequency was also associated with lower plant diversity and species richness relative to non-flooded areas. Thus, disruption of the natural flooding regime had strong and often negative consequences for the ecological and biogeochemical properties of the riparian ecosystems in our study. There was some evidence that riparian plant communities were able to partially recover from prior flooding during a single growing season, even after nine years of repeated flooding, and these recovery trajectories were associated with shifts in soil chemical properties during the same period. However, revegetation efforts had few effects on ecosystem properties or their recovery trajectories following flooding events, suggesting that natural regeneration could be a useful option for the management of these sites. We conclude that the unnatural flooding regimes associated with large scale reservoir development are likely to have profound impacts on the structure and functioning of riparian ecosystems, and these will pose a considerable challenge for environmental management and biodiversity conservation.
... In riparian ecosystems, frequent flooding results in plant organ mortality, exacerbating soil nutrient loss, and altering soil nutrient ratios Zheng et al., 2021b). Under conditions of flood stress and nutrient co-limitation, the physiological processes of C, N, and P in riparian plants are constrained, including photosynthesis and nutrient mineralization (Ye et al., 2020;Cao et al., 2022). Inundation-induced changes in plant composition and soil properties may impact nutrient interactions in riparian plant-soil systems (Yu et al., 2019;Ye et al., 2020). ...
... Under conditions of flood stress and nutrient co-limitation, the physiological processes of C, N, and P in riparian plants are constrained, including photosynthesis and nutrient mineralization (Ye et al., 2020;Cao et al., 2022). Inundation-induced changes in plant composition and soil properties may impact nutrient interactions in riparian plant-soil systems (Yu et al., 2019;Ye et al., 2020). Therefore, investigating plant C:N:P stoichiometry patterns and their drivers can enhance the insights into plant adaptation strategies and ecosystem functioning in dynamic riparian habitats. ...
... Interestingly, N and P contents in the different organs of riparian plants were significantly higher than those observed in grassland and forest ecosystems globally and in China (see Supplementary Table S3). One possible explanation is that prolonged inundation in the TGRR accelerates soil mineralization, facilitating N and P uptake by plants (Ye et al., 2020). Furthermore, frequent summer precipitation in the TGRR may transport upland surface pollutants like N and P to the adjacent zone (Zheng et al., 2023), enhancing nutrient recharge for riparian plant growth (Huang et al., 2019). ...
Carbon (C), nitrogen (N), and phosphorus (P) stoichiometry serve as valuable indices for plant nutrient utilization and biogeochemical cycling within ecosystems. However, the allocation of these nutrients among different plant organs and the underlying drivers in dynamic riparian ecosystems remain inadequately understood. In this study, we gathered plant samples from diverse life forms (annuals and perennials) and organs (leaves, stems, and roots) in the riparian zone of the Three Gorges Reservoir Region (TGRR) in China—a novel ecosystem subject to winter flooding. We used random forest analysis and structural equation modeling to find out how flooding, life forms, plant communities, and soil variables affect organs C, N, and P levels. Results showed that the mean concentrations of plant C, N, and P in the riparian zone of the TGRR were 386.65, 19.31, and 5.27 mg/g for leaves respectively, 404.02, 11.23, and 4.81 mg/g for stems respectively, and 388.22, 9.32, and 3.27 mg/g for roots respectively. The C:N, C:P and N:P ratios were 16.15, 191.7 and 5.56 for leaves respectively; 26.98, 273.72 and 4.6 for stems respectively; and 16.63, 223.06 and 4.77 for roots respectively. Riparian plants exhibited nitrogen limitation, with weak carbon sequestration, low nutrient utilization efficiency, and a high capacity for nutrient uptake. Plant C:N:P stoichiometry was significantly different across life forms and organs, with higher N and P concentrations in leaves than stems and roots, and higher in annuals than perennials. While flooding stress triggered distinct responses in the C, N, and P concentrations among annual and perennial plants, they maintained similar stoichiometric ratios along flooding gradients. Furthermore, our investigation identified soil properties and life forms as more influential factors than plant communities in shaping variations in C:N:P stoichiometry in organs. Flooding indirectly impacts plant C:N:P stoichiometry primarily through alterations in plant community composition and soil factors. This study underscores the potential for hydrologic changes to influence plant community composition and soil nutrient dynamics, and further alter plant ecological strategies and biogeochemical cycling in riparian ecosystems.
... In addition, Nmin is regulated by redox frequency change under environment of alternating drying and flooding (Zha et al. 2022). Recently, it was found that sediment physicochemical properties, such as sediment organic carbon (C, SOC), total N (TN) and C: N ratio, are inconsistent at different water-level elevations of riparian zone due to differences in hydrological stress and intensity of human activity (Li et al. 2020;Ran et al. 2020;Ye et al. 2020;. However, spatial distribution of Nmin and its driving factors based on changes of sediment physicochemical properties are still unclear at waterlevel elevation in riparian zone. ...
... On the one hand, N in the sloping farmland is released to the TGR through interflow under runoff erosion , and spatial distribution of sediment N has been changed by hydrological stress ). On the other hand, SOC, TN, pH (Ye et al. 2020;Shen et al. 2022), suspending solid deposition (Tang et al. 2018;Tang et al. 2016), particle-size distribution (Li et al. 2019) and aggregate size (Ran et al. 2020) have been changed by hydrological stress and human activities. However, the relationship between N loss and the changes in sediment physicochemical properties is unclear in the riparian zone at present. ...
... Since sediment TN decreases with submergence frequency (Li et al. 2020;Ye et al. 2020) and labile substrate input is higher at higher water-level elevation (Garssen et al. 2015;Ye et al. 2020), we hypothesized that Nmin and its Q10 vary chiefly with sediment organic N content and SQ, respectively, at water-level elevation of the riparian zone. Objectives of this study are: (1) to investigate spatial distribution characteristics of Nmin and its Q10 at water-level elevation of the riparian zone during drying period; ...
Inorganic nitrogen (N) loss through sediment N mineralization is important for eutrophication surrounding riparian zone. Sediment physicochemical properties have been changed at water-level elevation in riparian zone of the Three Gorges Reservoir (TGR) due to differences in hydrological stress and human activity intensity. However, spatial distribution and driving factor of net N mineralization rate (Nmin) and its temperature sensitivity (Q10) based on the changes in sediment physicochemical properties are still unclear at water-level elevation in the riparian zone. A total of 132 sediment samples in the riparian zone were collected including 11 transections and 12 water-level elevations on basin scale of the TGR during drying period, to conduct a 28-day incubation at 15°C, 22°C, 29°C and 36°C. Nmin, total N (TN) and substrate quality (SQ) increased with water-level elevation, while Q10 showed an opposite trend (P<0.001). Results of the structural equation model showed that water-level elevation had direct positive effects on TN and SQ (P<0.01). In addition, TN was the major factor that had a direct positive effect on Nmin, and SQ was the crucial factor that had a direct negative effect on Q10 (P<0.001). In conclusion, increases in TN and SQ were major driving factors of Nmin and its Q10 at water-level elevation, respectively, in riparian zone of the TGR during drying period.
... This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Wang et al., 2017;Ye et al., 2020). The increased amounts of these elements reflected the imbalance in exogenous inputs and endogenous outputs of RHB (Ye et al., 2019b). ...
... Reservoir hydro-fluctuation belts may be affected by the presence of certain trace elements in the Three Gorges Dam, China (Sang et al., 2019;Zhang et al., 2022). Studies have reported accumulation of soil-associated P, Zn, Cd, Cr, and As in RHB in the case of low water level Ye et al., 2019a;Ye et al., 2020). Other studies have shown a significant and positive correlation of selected trace elements in soils and organisms (Xiang et al., 2018). ...
... An alkaline-hydrolysis diffusion method was used to measure the concentration of available nitrogen (AN) (Xiang et al., 2018). Total phosphorus (TP) was digested with HF-HClO 4 in Teflon tubes (Zhao et al., 2014;Ye et al., 2020), and available phosphorus (AP) was extracted by a NaHCO 3 solution (Ye et al., 2020). A molybdenum-antimony anti-spectrophotometric method was used to quantify both TP and AP in the extract. ...
To examine the role of dam impoundment in elevating the levels of soil‐associated phosphorus (P) and trace elements in reservoir hydro‐fluctuation belts (RHB), soil samples in RHB and adjacent uplands (non‐flooded area, NFA) in the Three Gorges Reservoir, China, were collected and analyzed. Concentrations of available P, copper (Cu), chromium (Cr), and zinc (Zn) were found to be higher in RHB than in NFA (p < .05), whereas organic carbon was comparable in RHB and NFA (p > .05). The elevated levels of Cu, Cr, and Zn in RHB were probably associated the repeated drying–rewetting cycles created by the dam impoundment. The 95th percentile of the single‐factor pollution index and geo‐accumulation index in RHB were 1.29 and −0.21 for Zn, 3.21 and 1.15 for Cu and 3.37 and 1.17 for Cr. Elevated pollution potential of soil‐associated Zn, Cu, and Cr existed in RHB of the Three Gorges Reservoir.
Core Ideas Dam impoundments decreased total C and total N concentrations in reservoir flooded soils.
Cu, Zn, and Cr concentrated in the reservoir flood areas.
Variability of Cu, Zn, and Cr was captured in single‐factor pollution index and geo‐accumulation index
... There is also a need to understand how riparian insect communities respond to efforts to mitigate the consequences of altered hydrology in the TGD's drawdown zone have affected. In particular, there was a significant effort in 2008 to revegetate several areas of abandoned farmland in the TGD's drawdown zone with flood resistant native plant species (Ye et al., 2020), but it is unclear whether this revegetation has had any net effects on riparian insect abundance and/or diversity. Thus, we carried out a longitudinal study into the insect communities associated with riparian vegetation along an approximately 600-km stretch of the Yangtze, upstream of the main TGD reservoir. ...
... dactylon and Hemathria sibirica), shrub species (Hibiscus syriacus, Morus alba and Salix variegate) and tree species (Salix chaenomeloides and Taxodium distichum). These species were selected based on their resistance to the periodic flooding events that characterise the drawdown zone (Ye et al., 2020). Revegetation was carried out in 2008 and the plantings remain intact and productive at the time of publication. ...
... At each of the 18 sampling sites, 15 subplots (each 5 m  3 m) were established along an elevation gradient that ran roughly perpendicular to the river. These elevation gradients were established as part of our broader research into riparian ecosystem responses to the changes in flooding regimes associated with the construction and operation of the TGD (e.g., Ye et al., 2020). The elevation gradients ranged from 145 to 175 m above sea level (a.s.l) and were divided into On some occasions, it was not possible to carry out field work in certain subplots, mostly due to flooding of the lower elevations. ...
The establishment of hydroelectric dams can lead to major changes in hydrology for habitats within the reservoir drawdown zones. The Three Gorges Dam (TGD) in China is the world’s largest hydroelectric facility, with a reservoir covering 1080 km2 and a drawdown zone covering 350 km2. Since the TGD’s establishment in 2008, the formerly terrestrial habitats within the dam’s drawdown zone have effectively been converted to riparian habitats. A strong understanding of ecological dynamics in these novel habitats is critical to their ongoing management. Given the major contribution of insects to ecosystem function and biodiversity, we surveyed riparian insect communities semi‐annually from 2011 to 2018 across a 600 km network of eighteen sites in the TGD’s drawdown zone. During this period the total abundance of insects increased 4.4–fold, and the composition of insect communities shifted significantly, with Diptera increasingly dominant in later years. Insect abundance trajectories were coupled with concomitant changes in local climate and soil chemistry, which have in turn been brought on by the novel hydrological regime in the drawdown zone. Revegetation efforts had limited impacts on riparian insect abundances. Overall, riparian insect communities have undergone marked shifts since the TGD started operating. We cannot explicitly attribute these effects to the TGD’s establishment, but our results indicate that they might have been shaped by – or are at least coupled with – the profound changes in hydrological conditions associated with the TGD’s establishment.
... Due to their high denitrification rates, riparian ecosystems can reduce nitrogen (N) transferral from land to adjacent water bodies by removing N up to 90%, thus preventing aquatic N eutrophication (Burgin & Hamilton, 2007;Deng, Pan, et al., 2020;Ranalli & Macalady, 2010;Vidon & Hill, 2004). Nevertheless, riparian ecosystems are increasingly subject to frequent hydrological change and reduced biodiversity due to human activities, such as climate change and dam construction, posing a threat to the ecosystem structure and function (Baskerville et al., 2021;Sawyer et al., 2009;Ye et al., 2020). It has been reported that up to 90% of riparian ecosystems in Europe and North America are disturbed (Tockner & Stanford, 2002). ...
... It has been reported that up to 90% of riparian ecosystems in Europe and North America are disturbed (Tockner & Stanford, 2002). To restore the degraded riparian ecosystems, several restoration approaches have been put forward, such as active revegetation with water-tolerant plant species or natural regeneration (Chazdon, 2008;Ye et al., 2020). However, little is known about how different restoration approaches and/or hydrological changes impact denitrification processes in riparian ecosystems, which leads an uncertainty to accurately predict the N removal efficiency of the riparian zone. ...
... The Three Gorges Dam project drastically altered wetting-drying cycles throughout the water-level fluctuation zones (New & Xie, 2008), and is therefore likely to have a profound consequence on denitrification processes on a regional scale. Two restoration approaches, that is, natural regeneration and active revegetation, have been carried out at the Zhongxian Revegetation Station in the riparian zone of the Three Gorges Reservoir since 2008 to restore and protect the riparian ecosystems (Chazdon, 2008;Ye et al., 2020). Here we present the results of a study that compared in situ denitrification rates and related functional genes among different flooding intensities and frequencies in the natural regeneration and active revegetation areas (with different vegetation types). ...
Riparian zones, an aquatic‐terrestrial interface, can intercept more than half of nitrogen (N) exported from terrestrial ecosystems to adjacent rivers, primarily by denitrification processes. However, damming has disrupted natural patterns and processes of flooding and vegetation community assemblages, and yet little is known about how hydrological changes and ecosystem restoration affect the biogeochemical functioning in the riparian ecosystems.
We conducted an in situ experiment to evaluate the effects of hydrological change (e.g. altering flooding intensity and frequency) and restoration approaches (e.g. natural regeneration and active revegetation) on denitrification rates and the abundance of denitrifier genes in the riparian zone of the Three Gorges Reservoir, China.
Our results showed that active revegetation did not significantly increase denitrification rates compared to the natural regeneration, but their underlying mechanism was different. At the natural regeneration area, the denitrification rate was primarily regulated by soil properties and abundance of nosZ gene, while at the active revegetation area, it was controlled merely by the abundance of nosZ gene. In addition, vegetation types showed little effect on the soil denitrification process, and the denitrification rate decreased with flooding intensity by reducing denitrifier gene abundance.
The periodic flooding treatment doubled the denitrification rate compared with the no flooding treatment, which might be attributed to the enhancement of soil carbon availability. Our results suggest that in terms of N removal via denitrification processes, natural regeneration is a priority approach to restoring degraded riparian ecosystems.
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... To restore and protect riparian ecosystems, active revegetation has been carried out for at least 10 years. Flooding-resistant plants like Cynodon dactylon, Hemathria sibirica, Hibiscus syriacus, Morus alba, Salix variegate, Salix chaenomeloides, and Taxodium distichum were selected for this revegetation [19]. Our investigation included four essential ecosystem functions, i.e., plant productivity, microbial habitats, soil carbon stocks, and fertility [20]. ...
... The riparian ecosystem can be divided into three distinct zones based on the flooding intensity: the extreme flooding zone (EFZ), the severe flooding zone (SFZ), and the moderate flooding zone (MFZ). They experienced ~286 days, ~237 days, and ~169 days of flooding per year, respectively [19]. Active revegetation has been conducted, accompanying natural rewilding, at three restoration sites (Zhongxian, Wanzhou, and Zigui). ...
Vegetation and microbial diversity play an essential role in ecosystem function. Active ecosystem restoration costs millions of dollars to increase biodiversity, yet when and how this restoration is effective when aiming at restoring multiple ecosystem functions (EMF) is still under debate. Here, we investigated the influence of a decade of restoration practices (i.e., active revegetation vs. natural rewilding) on the recovery of the ecosystem multifunctionality (EMF) provided by a riparian ecosystem. The experiment was conducted within the region of China’s Three Gorges Dam, and the area was subjected to a gradient of flooding disturbance. We found that active revegetation increased the plant diversity by 13~57% and EMF by ~2.6 times at the extreme flooding zone (~286 flooding days/year) of the riparian ecosystem, when compared with natural rewilding. Moreover, the positive relationship between plant diversity and EMF was weak, and abiotic factors (soil aggregate, pH, soil water content, and heavy metal content) were the dominant predictors for EMF, explaining 52% of the EMF variation. Revegetation impacted EMF both directly and indirectly via altering the soil properties. In addition, we also observed important trade-offs between plant biomass and soil functions (carbon storage and fertility). This study provides critical insights into whether and how a decade of active restoration is effective to recover the EMF supported by riparian ecosystems, and it highlights the importance of active revegetation in conservation and management programs for riparian ecosystems under future extreme flooding conditions.
... Plant species zonation is a characteristic feature of water depth gradients in wetland environments and lake shorelines due to the wide availability of water for growth in these areas [15]. It has been reported that plant diversity and species richness are negatively affected by frequent flooding [16]. With the severe stress of a riparian zone, riparian vegetation species must complete their life cycles under a limited growth period, which can be as short as three months [17]. ...
... Research linking flood factors with riparian vegetation have shown the importance of flooding depth [29,30]. Current research focuses on the effects of long-term flooding [16,31] on riparian plants and the effects of flooding depth on plant traits in the laboratory [32,33], but the plant community's response to flooding depth lacks attention in the field, especially regarding the extreme flooding caused by big dams. Inundation with seasonal variation presents a different impact compared to flooding events over a long period [34]. ...
The hydraulics of flows, especially the flooding process, influence the patterns of riparian plant zonation. Different characteristics of the flooding process should be analyzed to correlate plant zonation with flooding due to their different effect modes. The effects of flooding characteristics on riparian plants have yet to be studied, especially in the field. Thus, two elements of the flow regime, flooding duration and depth, were analyzed in relation to the riparian plants of the Three Gorges Reservoir. The taxonomic indices and the functional diversity of the riparian plants in three seasons in 2019 and the corresponding inundation character were surveyed. Our results showed that the riparian plant diversity and functional diversity varied by season. A significant negative relationship between plant diversity and flooding depth was observed, while flooding duration was not a significant predictor in different seasons. The greater explanatory capacity of flooding depth than that of flooding duration suggests that flooding depth could be a better indicator of the zonation of the riparian vegetation in this area. Concerning the vital component of flow hydraulics, growing opportunities to study flooding depth and strategies that consider both flooding time and flooding depth in a reservoir should be offered, as they will assist in refining process-based river restoration.
... Particularly, there are more crystalline minerals in fine and silty sand that allows heavy metal contaminants to be easily adsorbed and fixed on mineral surfaces (Maity and Maiti, 2016;Fu et al., 2020). Additionally, plant diversity and species richness decreased markedly under the long-term periodic hydrodynamic disturbance (Ye et al., 2020). The flooding-tolerant plants survived to become the dominant species, and differed significantly at different elevations in some belt transects (e.g., Zhong County, Kaizhou and Xiangxi river) (Yin et al., 2020;Zhu et al., 2020). ...
... During the high water-level period, flooded plants decomposed to aggravate anaerobic states and release nutrients that altered the morphology and bioavailability of heavy metals (Hall and St. Louis, 2004;Yin et al., 2020). However, microbial community properties of soil/sediment seemed to be less affected by the hydrological regimes, suggesting that microbes were more resilient than plants (Ye et al., 2020). ...
Dam construction interfered with the original environment of the river system and greatly affected the geochemical behaviors of trace metals. Thus, a set of toxic metals of Cr, Ni, Cu, Zn, As, Cd, Pb and Hg in soil/sediment of the Three Gorges Reservoir (TGR) during the period of 2008–2020 were analyzed and summarized. The results showed that levels of trace metals (except Cr) were apparently higher than the soil background in the TGR and China, in which Cu, Zn, As, Cd, Pb and Hg corresponded to the moderately to highly contaminated grade. As expected, most trace metals (except Ni and As) were observed an evident increase after the full impoundment stage of 2008–2014, suggesting the dam construction of the TGR that promoting the sediment adsorption effects for trace metals. For spatial patterns, metal levels largely depended on the sampling sites, that intensive anthropogenic activities might well be the primary contributors. Main stream with higher concentrations of trace metals in comparison with tributaries reflected the larger loads of metal pollution. In the water-level-fluctuating zone, hydrological regime induced by damming played a critical role on the redistribution of trace metals through eroding soil/sediment particles or bedrocks and altering the physiochemical characteristics and vegetation coverage of soil/sediment. Finally, submerged sediment seemed as a major sink of trace metals that had greater concentration than that in the water-level-fluctuating zone.
... The TGR riparian zone is subject to periodic flooding caused by fluctuations in water levels. Specifically, the water level reaches its lowest point at 145 m above sea level in the summer and its highest point at 175 m in the winter (Ye et al., 2020;Ye et al., 2019). The riparian soils at different elevations within the TGR have experienced varying degrees of periodic flooding, which has been shown to have significant impacts on soil's physical and chemical properties (Wang et al., 2018;Ye et al., 2020;Ye et al., 2019). ...
... Specifically, the water level reaches its lowest point at 145 m above sea level in the summer and its highest point at 175 m in the winter (Ye et al., 2020;Ye et al., 2019). The riparian soils at different elevations within the TGR have experienced varying degrees of periodic flooding, which has been shown to have significant impacts on soil's physical and chemical properties (Wang et al., 2018;Ye et al., 2020;Ye et al., 2019). However, the mechanisms by which physical and chemical factors stabilize soil organic carbon and the dominant factor involved under periodic flooding regimes are still not fully understood. ...
The stabilization of soil organic carbon is closely linked to edaphic properties and environmental variables. Despite this, the mechanism of soil organic carbon stabilization, as well as the primary factor controlling soil organic carbon in riparian ecosystems, remains unclear. To address this gap, our study investigated the impact of flooding regimes on soil organic carbon fractions and other chemical properties in the riparian zone, focusing on the dominant intrinsic factors controlling soil organic carbon content within the three soil types (Anthrosols, Luvisols, and Regosols). Our results demonstrated that flooding regimes significantly affect soil chemical properties in the riparian zone, with varying effects among the three soil types. Specifically, Regosols showed an increase in the particulate organic carbon with flooding intensity. Organic carbon fractions in Anthrosols and Luvisols are found to respond similarly to flooding regimes. The effects of soil chemical properties on organic carbon fractions varied across the three soil types. The variations in POCc, POCf, and MOC for Anthrosols were explained by path models by 43 %, 95 %, and 33 %, respectively. Similarly, for Luvisols, the path models accounted for 66 %, 90 %, and 29 % of the variations, whereas for Regosols, the variations were explained by 43 %, 93 %, and 21 %. Overall, for all tested soils combined, the path models explained 36 %, 89 %, and 12 %, respectively. Therefrom, under flooding regimes, soil oxides played a more significant role in stabilizing soil organic carbon for the three soil types than clay, silt, and cations. Specifically, in Anthrosols, Luvisols, and Regosols, the path coefficient for soil oxides was 0.90, 0.95, and 0.97, respectively, for POCf; while it was 0.30, 0.21, and 0.22 for POCc. In conclusion, we revealed that flooding regimes enhance the role of soil oxides in stabilizing organic carbon. Therefore, we recommend that soil oxides shall be included in organic carbon saturation models for riparian zones subjected to flooding regimes.
... Soil N:P is reported to correlate with plant growth rate and nutrient availability (Peñuelas et al., 2013;Sardans et al., 2012). Furthermore, plant and microbial communities could develop several strategies to cope with or recover after flooding regime (Ye et al., 2018;Ye et al., 2020), and these responses may alter the ecological processes of the surrounding environment affected by flooding. For example, the aerenchyma tissues formed by plants allow larger air space and gas diffusion, which is beneficial for plants surviving flooding stress (Jackson and Armstrong, 2008;Yuan et al., 2013). ...
... The fungal community was negatively influenced by a prolonged flooding regime, whereas several taxonomic groups of bacteria (Gram-positive bacteria, Gram-negative bacteria and aerobic bacteria) were found to be more sensitive to flooding stress than fungi (Unger et al., 2009). Several lines of evidence have suggested that the restoration of vegetation or soil microbial communities after flooding events might be directly related to biogeochemical processes (Huang et al., 2019;Ye et al., 2020). ...
Extreme climate events such as flooding have profound impacts on the nutrient stoichiometry and function of terrestrial ecosystems. This study aimed to investigate the influencing mechanisms of flooding on C:N:P stoi-chiometry in different terrestrial ecosystems, which mainly focused on abiotic factors and their linkages with biotic factors. A global meta-analysis of 69 published studies (885 paired observations) was conducted to examine the effects of flooding on the C:N:P stoichiometry of plants, soil and microorganisms in different terrestrial ecosystems. The collected data included broad variations in climate parameters and flooding durations. Flooding was found to significantly elevat the C and N contents of the whole ecosystem. The responses of overall (across plant-soil-microorganism) C, N and P contents to flooding were pronounced among different ecosystem types or components. Flooding markedly increased the ratios of overall C:N, C:P and N:P ratios by 9.7%, 20.1% and 7.4%, respectively. Flooding with a short duration elevated the overall C:P ratio more than C:N and N:P ratios. Flooding regulated the ecosystem components of C and N, with both elements were also being affected by duration times and climate parameters to some extent. These results provide new insights into understanding the impacts of extreme climate events on ecosystem nutrient turnover under the circumstance of global climate change.
... Globally, extreme land-water alternation, driven by human activities and climate change, has escalated two dominant stresses, flooding and nutrient loss, during plant production (Boyer 1982;Ye et al. 2019). The stresses are profoundly affecting plant community structure, function, and biogeochemical cycles, particularly in riparian ecosystems (Saint-Laurent et al. 2014;Ye et al. 2020). Considering that plants often exhibit phenotypic plasticity, enabling them to modify their morphology, physiology, architecture, allocation, and symbiotic relationships with mycorrhizal fungi in response to environmental changes, which can enhance their survival under varying conditions (Chapin 1991;Violle et al. 2007), investigating phenotypic adjustments in plant functional traits is crucial for understanding the links between ecosystem function and environmental change (Reich 2014). ...
Aims
Plants respond to stress gradients by modifying various aspects of their morphology, physiology, architecture, allocation and mycorrhizal fungi. Yet, understanding how plants adapt to resource stress requires a comprehensive, integrated perspective that considers not only the consistency and variability of individual trait adjustments, but also the interplay between two key mechanisms: phenotypic plasticity (the direction and magnitude of trait adjustment) and phenotypic integration (the degree and pattern of trait covariation). Despite their importance, the coordination of these mechanisms in driving adaptive responses remains poorly understood.
Methods
To address these gaps, we measured the adjustment of 27 above- and below-ground traits across three dominant species (Cynodon dactylon, Xanthium strumarium, and Bidens tripartita), and explored trait networks, and the relationship between phenotypic plasticity and phenotypic integration in response to flooding and/or nitrogen in riparian habitats on the Three Gorges Reservoir area, China.
Results
The results show that both flooding and nitrogen stress induced shifts in species traits towards more acquisitive strategy, characterized by larger leaves, higher leaf nutrient concentrations, finer roots, larger specific root lengths, greater branching intensity, and elevated carboxylate concentrations. Flooding altered the hub trait with the highest centrality in the trait network from root branching intensity to leaf phosphorus content, while nitrogen stress shifted the hub trait from leaf area to root phosphorus content. Furthermore, a positive correlation was observed between phenotypic plasticity and integration, indicating that higher plasticity of functional traits facilitated better integration with other traits under flooding and nitrogen stress.
Conclusions
These findings suggest that plants exhibit more acquisitive traits in habitats experiencing flooding and/or nitrogen stress. Furthermore, a comprehensive assessment of phenotypic plasticity and its integration under compound stresses underscores the critical role of synergies between plasticity and integration in enhancing plant adaptability to environmental changes.
... Riparian zones represent the interface where terrestrial and aquatic ecosystems converge, playing a crucial role in maintaining the ecological balance between water and soil, facilitating material and energy exchanges, and enhancing water quality et al. (Gao et al. 2015;Vidon et al. 2019;Ye et al. 2019). The surrounding land of reservoir were undergone periodic flooding and exposure, resulting a water-levelfluctuation zone (WLFZ) based on the water level operation mode of Three Gorges Reservoir (TGR) (fluctuates periodically between 145 and 175 m) (Gao et al. 2015;Ye et al. 2020). Various pollutants attached on the surface soil can enter the riverway through the WLFZ due to the fluctuating water level of the TGR (Nsabimana et al. 2020). ...
Purpose
Polycyclic aromatic hydrocarbons (PAHs) had been detected in most soils of water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR), but there were few investigations on the distinct shifts of the PAHs degradation and microbial communities in these soils under different water level conditions. This study aims to investigate the effect of water level fluctuation on the PAHs degradation and microbial communities.
Material and methods
Soil samples were collected from different altitudes and depths in the WLFZ of the TGR at the end of the flooding period and drying period respectively. The content of PAHs (∑16PAHs) were determined using gas chromatography-mass spectrometer. The feature of PAHs degradation and nitrogen cycling using enzyme-linked immunosorbent assay and polymerase chain reaction method. The shifts of microbial communities were characterized by sequencing the bacterial 16S rRNA and fungal ITS rRNA gene. The analysis of linear discriminant, molecular ecological network and correlation were used to evaluate the details of PAHs degradation, nitrogen cycling and microbes.
Results
The ∑16PAHs in the WLFZ soil were higher in flooding conditions, and that of tributary stream were higher than main stream. The genes of PAHs degradation were stimulated in drying conditions. The PAHs was closely positively correlated with nitrogen cycling process in the flooding period. Both bacteria and fungi contribute to the degradation of PAHs. The biomarkers were more abundant in drying conditions, and the interaction between microorganisms during the flooding period were stronger than those during the drying period.
Conclusion
This study has demonstrated the distinct differences of the PAHs degradation and microbes in the WLFZ soil under different water level conditions. The results are of interest to understand the characteristics to PAHs distribution and degradation in the WLFZ soil of TGR in Yangtze River, China.
... Under the hydrological fluctuation, the riparian zone of the Three Gorges Reservoir (TGR) can be categorized into the water level fluctuation (WLF) area and the adjacent non-flooded (NF) area (Ye et al. 2020). The WLF area is about 349 km 2 formed by annual water level fluctuation ranging from 145 to 175 m a.s.l. and is utilized for power generation, irrigation, and flood control . ...
Aims
The soils of riparian ecosystems harbor a significant amount of organic carbon (C) and are susceptible to anthropogenic disturbances. However, the warming response of soil organic carbon (SOC) decomposition in riparian ecosystems has received limited attention.
Methods
In this study, we quantified the thermal sensitivity (Q10) of SOC decomposition across a mean annual precipitation (MAP) gradient ranging from 1270 to 1416 mm in the riparian zones of the Three Gorges Reservoir.
Results
Our findings indicate that the Q10 ranged from 1.1 to 2.1. Notably, MAP exerts a negative effect on Q10 by positively affecting the decomposability of SOC (DSOC) and soil pH, collectively explaining 52.5% of the variation in Q10. Among the factors studied, DSOC emerged as the most critical determinant of Q10 variation. The observed negative correlation between DSOC and Q10 suggests that stable SOC is more susceptible to loss under warming compared to active SOC.
Conclusions
Consequently, MAP-driven changes in DSOC significantly influence the soil C cycle feedback to climate warming in riparian zone ecosystems. Specifically, locations with greater MAP are likely to experience stronger positive feedback from SOC loss in response to warming.
... These biotic and abiotic variables collectively contribute to SMF (Sendek et al. 2021;Ma et al. 2022). Dam-regulated water level fluctuations alter soil functions (e.g., carbon storage and biomass production) and simplify plant community composition (Ye et al. 2020;Zheng, Arif, Zhang, Yuan, Zhang, and Li 2021). Additionally, different river flows affect soil functions at different sites, with degradation rates varying depending on the vertical gradient of the riparian ecosystem (Zhao et al. 2014). ...
Understanding the biodiversity-ecosystem multifunctionality relationship is critical for predicting the consequences of species loss on the sustainable provision of ecosystem services. Both theoretical and empirical studies generally demonstrate a positive biodiversity-ecosystem multifunctionality relationship. However, the underlying mechanisms linking soil multifunctionality (SMF) to plant diversity remain unclear, particularly in dynamic riparian habitats. In this study, we investigated the plant community , 10 soil functions, and their drivers within the riparian zone regulated by the Three Gorges Dam in China. Our results showed that taxonomic, phylogenetic, and functional diversity affect SMF at alpha and beta scales in both positive and negative ways. Notably, most diversity metrics are negatively correlated with SMF, especially at lower elevations and in areas near the dam. Alpha and beta diversity contribute equally to SMF, whereas functional diversity explains SMF better than taxonomic or phylogenetic diversity. Furthermore, abiotic variables explain 24% of the variance in SMF, significantly exceeding the 3% explained by biotic variables. Dam inundation has both direct effects on SMF and indirect effects mediated by soil pH, bulk density, and functional dispersion, all of which are critical variables in elucidating SMF changes. Our findings indicate that dam inundation modulates the effect of plant diversity on SMF and underscore the roles of biotic factors and functional diversity in mediating this effect. This study challenges the prevalent notion that biodiversity universally positively affects ecosystem mul-tifunctionality and broadens our understanding of the linkages between plant diversity and SMF, as well as its drivers under dam-induced hydrological changes.
... While previous research has highlighted microbial community structure or individual bacterial groups, it has not fully explored the functional implications of soil bacteria-vegetation linkages across different seasons. Most studies on plant-soil relationships in riparian zones have focused on nutrients (Ren et al., 2015;Shen et al., 2022;Zhong et al., 2018), microbial abundance (Fantini and Guries, 2007;Ren et al., 2018;Ye et al., 2019), and organic acid metabolism (Jiang et al., 2020;Yin et al., 2018). Despite this, there is a lack of in-depth exploration of the seasonal response (e.g., spring, summer, and autumn) of riparian soil to artificial plantations. ...
Riparian soils, together with vegetation, play a crucial role in supporting biodiversity and driving biogeochemical processes within river ecosystems. Conservation of riparian soils and artificial planting are essential for river ecosystem recovery following land degradation. Researchers focus on examining soil nutrients, microbial biomass, and organic acid metabolism in the interactions between plants and soil along riverbanks. However, the seasonal responses of riparian soils to artificial plantations have been infrequently reported in the existing literature. This study investigates the influence of seasonal variations on soil conditions and the growth of artificially planted species in the riparian zones of the Three Gorges Dam Reservoir (TGDR) in China. The species sampled include Cynodon dactylon, Hemarthria altissima, and Salix matsudana. These species provide valuable insight into soil properties along riparian zones, assessing interactions across different seasons: T1 (spring), T2 (summer), and T3 (autumn). The results demonstrated significant seasonal changes in soil organic matter, ammonium nitrogen, nitrate nitrogen, and other indicators between T1 and T3. Apart from invertase activity in H. altissima soil, enzyme activity peaked during T1. Dominant soil bacteria were examined using high-throughput 16S rDNA sequencing, revealing that the available bacteria belong to 62 phyla and 211 classes. Among the most abundant were Proteobacteria and Actinobacteria, averaging over 60 % across all soil samples. Principal component analyses accounted for 62.81 % (T1), 50.57 % (T2), and 54.08 % (T3) of the variation observed in the study, indicating that soil properties were predominantly influenced by the different seasonal phases, assuming all other factors remained constant. Pearson correlation analysis (p < 0.05) identified strong positive correlations between physical properties and all three plant species during T1 (r ≤ 0.94), as well as significant negative correlations with bacterial communities in T2 and T3 (r ≤ −1.00). These findings suggest that the selected plant species are well-suited to cultivation in the riparian zone of the TGDR. This study enhances our understanding of seasonal dynamics in riparian environments, offering practical insights into their management.
... Corroborando com Silva et al. (2023), que ao estudarem área de inundação sazonal também encontram pH elevado. Como relatado por Ye et al. (2020), que ao avaliar os componentes químicos do solo, destacaram que o pH tende a ser maior nas áreas ribeirinhas inundadas em comparação a outras regiões. ...
A distribuição espacial dos atributos químicos, físicos e suscetibilidade magnética do solo pode mostrar o nível de concentrações e suas relações, indicando a melhor formar de manejar o solo, consequentemente, melhorando a produtividade da área. Dessa forma, objetivou-se com presente trabalho, mapear e avaliar a variação dos atributos químicos, físicos e suscetibilidade magnética em área inundada sazonalmente utilizada para pastoreio no município de Monte Alegre, Piauí. Foi montando uma malha amostral com espaçamentos 10 X 10m, sendo coletado 18 pontos amostrais, na profundidade de 0,0 – 0,20m, totalizando um total de 18 amostras georreferenciadas. Foram determinados: pH, matéria orgânica do solo (MO), fósforo (P), potássio (K), cálcio (Ca), magnésio (Mg), acidez potencial (H+Al), soma de bases (SB), capacidade de troca catiônica (CTC), saturação por base (V%), condutividade elétrica (CE), suscetibilidade magnética (SM), areia, silte e argila. Os dados foram avaliados pelos métodos da estatística descritiva e geoestatística. Houve variabilidade espacial, permitindo a elaboração de mapas de fertilidade. Os mapas apontaram valores elevados de P, Ca, Mg, SB, CTC e V%; e baixos teres de MO e K. O mapa de SM apresentou similaridade com os mapas de K, Ca, Mg, SB e CTC. O diagnóstico da fertilidade do solo mostra o K como deficiente. Os valores elevados de Ca e Mg podem estar relacionados a deposição de sedimentos nos períodos de inundação. A interpolação de Krigagem para gerar mapas mostrou-se eficaz para determinar a distribuição espacial dos nutrientes do solo em área de pastagem natural. Palavras-chaves: Inundações sazonais, dinâmica de nutrientes, variação espacial, atributos químicos do solo, atributos físicos do solo.
... The annual average temperature registers at 18.22 ± 0.56°C (mean ± SD), while precipitation ranges from 1000 to 1300 mm annually . Rainfall is distributed unevenly across the seasons, with 60-80% occurring between April and September (Ye et al., 2020). The TGD area's yearly. ...
Dams worldwide have significantly altered the composition of riparian forests. However, research on the functional traits of dominant herbs experiencing flooding stress due to dam impoundment remains limited. Given the high plasticity of leaf traits and their susceptibility to environmental influences, this study focuses on riparian herbs along the Three Gorges Hydro‐Fluctuation Zone (TGHFZ). Specifically, it investigates how six leaf physiological traits of leading herbs—carbon, nitrogen, phosphorus, and their stoichiometric ratios—adapt to periodic flooding in the TGHFZ using cluster analysis, one‐way analysis of variance (ANOVA), multiple comparisons, Pearson correlation analysis, and principal component analysis (PCA). We categorized 25 dominant herb species into three plant functional types (PFTs), noting that species from the same family tended to fall into the same PFT. Notably, leaf carbon content (LCC) exhibited no significant differences across various PFTs or altitudes. Within riparian forests, different PFTs employ distinct adaptation strategies: PFT‐I herbs invest in structural components to enhance stress resistance; PFT‐II, mostly comprising gramineous plants, responds to prolonged flooding by rapid growth above the water; and PFT‐III, encompassing nearly all Compositae and annual plants, responds to prolonged flooding with vigorous rhizome growth and seed production. Soil water content (SWC) emerges as the primary environmental factor influencing dominant herb growth in the TGHFZ. By studying the response of leaf physiological traits in dominant plants to artificial flooding, we intend to reveal the survival mechanisms of plants under adverse conditions and lay the foundation for vegetation restoration in the TGHFZ.
... The TGR serves as a vital source of drinking water for numerous residents (Zhou et al. 2011). Following the TGR project's commencement in 2008, the reservoir's water levels have displayed seasonal fluctuations, ranging from 145 m above sea level (ASL) during summer to 175 m ASL in winter (Ye et al. 2020). Consequently, the operation of the TGD results in distinct limnological characteristics in the main stem of the Yangtze River (Wetzel 2001). ...
Although the Three Gorges Dam (TGD) is the world’s largest hydroelectric dam, little is known about the spatial–temporal patterns and community assembly mechanisms of meio- and micro-eukaryotes and its two subtaxa (zooplankton and zoobenthos). This knowledge gap is particularly evident across various habitats and during different water-level periods, primarily arising from the annual regular dam regulation. To address this inquiry, we employed mitochondrial cytochrome c oxidase I (COI) gene-based environmental DNA (eDNA) metabarcoding technology to systematically analyze the biogeographic pattern of the three communities within the Three Gorges Reservoir (TGR). Our findings reveal distinct spatiotemporal characteristics and complementary patterns in the distribution of meio- and micro-eukaryotes. The three communities showed similar biogeographic patterns and assembly processes. Notably, the diversity of these three taxa gradually decreased along the river. Their communities were less shaped by stochastic processes, which gradually decreased along the longitudinal riverine-transition-lacustrine gradient. Hence, deterministic factors, such as seasonality, environmental, and spatial variables, along with species interactions, likely play a pivotal role in shaping these communities. Environmental factors primarily drive seasonal variations in these communities, while hydrological conditions, represented as spatial distance, predominantly influence spatial variations. These three communities followed the distance-decay pattern. In winter, compared to summer, both the decay and species interrelationships are more pronounced. Taken together, this study offers fresh insights into the composition and diversity patterns of meio- and micro-eukaryotes at the spatial-temporal level. It also uncovers the mechanisms behind community assembly in various environmental niches within the dam-induced river-reservoir systems.
Key points
• Distribution and diversity of meio- and micro-eukaryotes exhibit distinct spatiotemporal patterns in the TGR.
• Contribution of stochastic processes in community assembly gradually decreases along the river.
• Deterministic factors and species interactions shape meio- and micro-eukaryotic community.
Graphical Abstract
... o K total do solo(YE et al., 2019). Dessa forma, o mapa mostra claramente a necessidade de correção dos teores de K em toda a área de estudo.Os teores de cálcio (Ca) foram classificados como muito bons, dm -3 foi a mais expressiva em termos de teor de Ca.Em relação aos teores de magnésio (Mg), na profundidade de 0,0-0,20 m, a maior parte do mapa encontrou-se entre 1,6 a 2,6 cmolc dm -3 , enquanto na profundidade de 0,20-0,40 m, os teores principais ficaram entre 0,7 a 1,4 cmolc dm -3 (Figura 1), enquadrando-se como muito bom e bom, respectivamente (Tabela 1). ...
O estudo da variabilidade espacial auxiliar no conhecimento mais detalhado da área, possibilitando a aplicação de insumos de forma mais aplicada, evitando perda e consequentemente danos ao meio ambiente. Este estudo teve como objetivo avaliar a variabilidade espacial dos atributos do solo em área de pastagem na margem do Rio Gurgueia na região de Monte Alegre do Piauí, procurando fornecer subsídios ao manejo correto da área. Foi realizado coleta de solo em duas profundidades e análise de parâmetros químicos em vinte e sete pontos de amostragem, totalizando 54 nas duas profundidades (0,0-0,20m e 0,20-0,40m). Os dados foram analisados pela estatística univariada e geoestatistica. Na análise descritiva dos atributos químicos em duas profundidades, houve normalidade dos dados em ambas as profundidades, confirmado pela média e mediana próximas, já na assimetria e curtose, verificou-se que todos os atributos analisados estão com valores próximos à zero, com exceção de Potássio e Cálcio. Identificou-se modelos em todas as variáveis investigadas, sendo estes o esférico, exponencial e gaussiano. O diagnóstico do solo da área de pastagem, apresenta uma fertilidade adequada. Apenas o potássio mostrou-se como nutriente deficiente. A boa fertilidade do solo está relacionada principalmente as inundações sazonais que depositam sedimentos ricos em nutrientes. Todas as variáveis apresentaram variabilidade espacial com graus de dependência espacial forte. Os mapas de variabilidade ilustram claramente a distribuição e concentração dos nutrientes no solo. Essa abordagem possibilita a aplicação de insumos em taxas variadas, visando oferecer uma distribuição homogênea de nutrientes à pastagem, principalmente potássio.
... Following the TGR project's commencement in 2008, the reservoir's water level exhibited periodic seasonal variations, ranging from 145 m to 175 m above sea level, demonstrating a counter-seasonal impoundment pattern (Ye et al. 2020). This regulation of water levels may have adverse impacts on biodiversity, as it inevitably alters the hydrodynamics of space, and weakens the water body's self-purification ability (Tan et al. 2022). ...
Effective and standardized monitoring methodologies are vital for successful reservoir restoration and management. Environmental DNA (eDNA) metabarcoding sequencing offers a promising alternative for biomonitoring and can overcome many limitations of traditional morphological bioassessment. Recent attempts have even shown that supervised machine learning (SML) can directly infer biotic indices (BI) from eDNA metabarcoding data, bypassing the cumbersome calculation process of BI regardless of the taxonomic assignment of eDNA sequences. However, questions surrounding the general applicability of this taxonomy-free approach to monitoring reservoir health remain unclear, including model stability, feature selection, algorithm choice, and multi-season biomonitoring. Here, we firstly developed a novel biological integrity index (Me-IBI) that integrates multitrophic interactions and environmental information, based on taxonomy-assigned eDNA metabarcoding data. The Me-IBI can better distinguish the actual health status of the Three Gorges Reservoir (TGR) than physicochemical assessments and have a clear response to human activity. Then, taking this reliable Me-IBI as a supervised label, we compared the impact of selecting different numbers of features and SML algorithms on the stability and predictive performance of the model for predicting ecological conditions in multiple seasons using taxonomy-free eDNA metabarcoding data. We discovered that even with a small number of features, different SML algorithms can establish a stable model and obtain excellent predictive performance. Finally, we proposed a four-step strategy for standardized routine biomonitoring using SML tools. Our study firstly explores the general applicability problem of the taxonomy-free eDNA-SML approach and establishes a solid foundation for the large-scale and standardized biomonitoring application.
... The biodiversity in the riparian zone is significantly affected by hydrological disturbances. Large-scale, unnatural water level fluctuations severely disrupt the original distribution of plant communities, resulting in a reverse succession in the riparian zone [4][5][6]. After the water impoundment operation of the Three Gorges Reservoir in 2003, the riparian zone gradually formed a vegetation succession pattern dominated by a few species including the plant Cynodon dactylon (L.) Pers, accompanied by Atractylodes macrocephala Koidz. ...
The cyclical process of water storage and recession in the regular operation of the Three Gorges Reservoir creates a unique habitat stress that alters the structural and functional attributes of vegetation ecology within the riparian zone. The stress-tolerant plant Cynodon dactylon (L.) Pers is the dominant plant species in the riparian zone of the Three Gorges Reservoir. In this study, the riparian zone of the Daning River, a tributary located in the center of the Three Gorges Reservoir, was selected as our study area. To identify the drivers of the morphological traits of C. dactylon in the riparian zone of Daning River, we examined plant biomass and plant characteristics across different elevation gradients, with reference to abiotic factors to determine the distribution patterns of plant morphological traits. Results indicated that in the two main soil types of the riparian zone, plant biomass showed a consistent trend along the elevation gradient, with a “middle-height expansion” pattern; biomass increased and then decreased with rising water levels. Plant biomass positively correlated with soil total nitrogen and negatively correlated with soil pH, electrical conductivity, and total phosphorus. C. dactylon adapted to prolonged flooding in the riparian zone by having a significant negative correlation between plant height and erect stem length with soil moisture content to facilitate root respiration.
... Such complex microbial interactions are of crucial importance for ecological processes and ecosystem functions (Yuan et al., 2021). Yet, global changes, such as climate warming, decline in biodiversity, frequent and severe flooding, can have substantial effects on soil microbial networks (Ren et al., 2007;Su et al., 2020;Ye et al., 2020;Yuan et al., 2021). ...
Soil microorganisms play a crucial role in ecosystem processes and functions, but how their co‐occurrence networks respond to restoration of degraded ecosystems remains poorly understood.
Here, we examined the effects of revegetation on the structure and function of the soil microbiome, including soil microbial network complexity and stability, in a novel riparian ecosystem with winter submergence opposite to the natural hydrological regime.
We found that extreme flooding intensity (30 m submergence up to 286 days per year) reduced microbial α‐diversity and network stability (robustness) but increased network complexity including network connectivity, connectance and average clustering coefficient over a 3‐year period, and those effects were mitigated by active revegetation in comparison with natural regeneration. Revegetation increased microbial network stability directly by decreasing network complexity, while extreme flooding regulated network stability indirectly by changing the soil total carbon content. Nevertheless, those dynamics of microbial network were coupling with soil microbial functions such as greenhouse gas (e.g. CH4, CO2 and N2O) fluxes and nutrient cycling.
Synthesis and applications: This study provides evidence to support the critical role of revegetation in preserving soil microbial network stability and functions under changing hydrological regime.
... Soil water determines the dominance of species in diverse communities by improving the availability of surface water and groundwater, and differences in groundwater depth determine the species composition and distribution of other communities. It is important to note that the contribution of soil water depends on the recharge of surface water and dynamic changes in groundwater depth, and cannot constrain plant growth alone (Ye et al. 2020;Malik et al. 2021). Therefore, considering the evolution of surface processes in arid areas, strengthening the protection of groundwater depth can play a positive role in promoting and restoring vegetation. ...
An oasis is a unique natural landscape in arid and semi-arid areas, significant for regulating regional microclimates and hydrological processes in deserts. However, little is known regarding the response of natural oasis plants communities to various environmental factors. Nineteen sample plots (50 m × 50 m) were selected in the Daliyabuyi Oasis in the Taklimakan Desert hinterland based on the location of groundwater monitoring wells and 76 vegetation quadrats (25 m × 25 m) were established. A two-way indicator species analysis, Mantel test, detrended correspondence analysis, canonical correspondence analysis (CCA), and hierarchical partitioning were used to provide an in-depth analysis of community classification, species composition, and environmental interpretation of the oasis. A generalized linear model was used to verify the results which showed that the current oasis community could be divided into four types according to the dominant species, which is controlled by soil moisture. Measurement of species composition and distribution of communities showed significant differences between species diversity of individual community types. Variations in groundwater depth affects patterns of species diversity which is sensitive to richness, while the degree of surface water disturbance affects the pattern of species evenness. Moreover, the CCA ordination map showed that community distribution and diversity characteristics have their own preferences in habitat gradients. The study concluded that the species dominance of the community and the composition and distribution are not dominated by a single factor. There are differences in the scale and effect of different water resource types in maintaining community characteristics.
... Consequently, the hydrological regime facilitates aggregate hydration and slacking along the decreased elevation gradient. Secondly, the hydrological regime has direct or indirect impacts on vegetation by altering the temperature, humidity, and oxygen in the soil environment [42][43][44]. It is commonly accepted that plant roots play an extraordinarily important role in aggregate stability through their penetration, entanglement, decomposition, and root exudates [45,46]. ...
The impoundment of the Three Gorges Reservoir (TGR) has greatly altered the hydrological regime and thus formed a distinctive riparian zone with anti-seasonal inundation and exposure, which may affect the soil aggregate properties in this riparian zone. Yet, the soil aggregate size distribution and stability influenced by the hydrological regime along the step-impounded elevation have rarely been documented. This study aimed to elucidate how the hydrological regime of the TGR affected the aggregate size distribution and stability in the riparian zone. Based on the step-impounded elevation, topsoil samples were collected from four elevation-dependent transects in a middle section of the TGR. Dry-sieving and wet-sieving methods were employed. The results showed that, with a decrease in the elevation gradient, the mass percentage of the >5 mm aggregates significantly decreased, while the proportions of the other size classes presented an increasing trend. Additionally, the mean weight diameter (MWD), geometric mean diameter (GMD), aggregate stability rate (ASR), and percentage of aggregate destruction (PAD) of the fractal dimension showed a successive decrease with a decrease in the elevation gradient, whereas PADMWD, PADGMD, PADASR, and the fractal dimension demonstrated a reverse trend. It can thus be deduced that the hydrological regime of the TGR significantly modified the aggregate size distribution and dramatically reduced the aggregate stability, which may provide a crucial basis for assessing the soil erosion in similar riparian zones.
... Similarly, the understory vegetation in forest ecosystems' recovery and regeneration is also heavily dependent on the severity and level of flooding (Friedman et al., 1996). Importantly, high-level adaptation, dominance, and resistance to external disturbances factors such as floods have enabled forest plants to recover at a high rate than some other vegetative land uses (Ingrisch & Bahn, 2018;Wen et al., 2018;Ye et al., 2020). Forest plants with a higher basal area and higher strands have higher recovery rates. ...
Global climate change scenarios such as frequent and extreme floods disturb the river basins by destructing the vegetation resulting in rehabilitation procedures being more costly. Thus, understanding the recovery and regeneration of vegetation followed by extreme flood events is critical for a successful rehabilitation process. Spatial and temporal variation of biochemical and biophysical features derived from remote sensing technology in vegetation can be incorporated to understand the recovery and regeneration of vegetation. The present study explores the flood impact on vegetation caused by major river basins in Sri Lanka (a model tropical river basin) by comparing pre-flood and post-flood cases. The study utilized enhanced vegetation index (EVI), normalized difference vegetation index (NDVI), the fraction of photosynthetically active radiation (FPAR), and gross primary productivity (GPP) of the Moderate Resolution Imaging Spectroradiometer (MODIS) platform. A remarkable decline in EVI, LAI, FPAR, GPP, and vegetation condition index was observed in the post-flood case. Notably, coupled GPP-EVI and GPP-LAI portrayed dependency of features and showed a significant impact triggered by the flood episode by narrowing the feature in post-flood events. EVI depicted the highest regeneration (0.333) while GPP presented the lowest regeneration (0.093) after the flood event. Further, it was revealed that 1.18 years have been on the regeneration. The regeneration of GPP and LAI remained low comparatively justifying the magnitude and impact of the flood event. The study revealed successful implications of vegetation indices on flood basin management of small to large tropical river basins.
... In the drying stage, NH 4 þ -N was rapidly oxidized by increasing oxygen and NO 3 À -N also increased faster than that in the wetting stage. The TN concentration in AC was slightly lower than that in CK, and the concentration of NO 3 À -N and NH 4 þ -N decreased at the early stage of wetting, which may be because the AC, as a submergence tolerant plant, could maintain normal physiological activities in shallow water and accelerate the formation of adventitious roots and stem growth to obtain external oxygen (Yang et al. 2012;Ye et al. 2020;Lin & Lin 2022). ...
Water-level changes in the water-level fluctuating zone (WLFZ) promoted soil and plants to release nutrients into the water, threatening the water health in the reservoir. Plant restoration in the WLFZ is also an important way to reduce the nutrient release in order to select plants that can effectively reduce the release of soil nutrients under changing water levels. This study conducted a flooding experiment to reveal the difference in the change in soil physico-chemical properties and microbial communities planted with various plants under different water-level conditions. The flooding experiment began at the end of September 2020 and was planted with three dominant plants common to reservoirs, namely Cynodon dactylon, Alternanthera philoxeroides, and Acorus calamus. Our study found the three common dominant plants along the reservoir, and C. dactylon had a good adsorption capacity for nitrogen and phosphorus when it was flooded with shallow water, decreasing soil nutrients during the drying period. After a wetting–drying cycle, there was an obvious and significant (p < 0.05) divergence among soil microbial community structures between N0 and D1, D2, and D3, respectively. This study could provide sufficient reference information for plant selection and the assessment of nutrient release of WLFZ in restoration work.
... Maintaining a continuous and competitive (functional) vegetation zone (i.e., ecological adaptation zone) in the riparian zone is necessary for realizing important ecological functions, such as material exchange and energy flow in terrestrial and aquatic ecosystems and water purification (Janssen et al., 2019;Ye et al., 2020;Arif et al., 2021b;Xia et al., 2021). The cloning property of bamboo, especially Phyllostachys heteroclada, an important waterlogging-tolerant bamboo species, gives bamboo an obvious advantage when applied to riparian zone restoration and enhances its application prospects when coupled with its once-planted, everlasting use (Cao et al., 2015). ...
The abnormality of seasonal water level fluctuation in the riparian zone causes various ecological and environmental problems, such as vegetation degradation, biodiversity reduction, soil erosion, and landscape transformation, thereby critically modifying the ecosystem structure and functions. This necessitates the development of a dominant vegetation zone with competitive potential. In this study, we investigated the content and distribution pattern of nutrient elements in each organ of the dominant bamboo species, Phyllostachys heteroclada, in the riparian zone. We also analyzed the morphological characteristics, root aeration tissue structure, root oxygen exchange capacity, ATP supply situation, and leaf PSII photosynthetic mechanism of two bamboo species (P. heteroclada and P. nigra) in the riparian zone. Compared with P. nigra, the roots of P. heteroclada formed well-developed oxygen storage and transport structure, i.e., aeration tissue, and exhibited root oxygen secretion in the waterlogging environment of the riparian zone, whereas the roots maintained a high ATP content through energy metabolism, thus benefiting mineral absorption and transport. Moreover, the accumulation of N, P, Ca, Mg, and Fe in the leaves of P. heteroclada was greater under waterlogging conditions than under non-waterlogging conditions, which is the basis for the efficient operation of the photosynthetic mechanism of the leaves. Compared with waterlogged P. nigra, the PSII electron acceptor QA of P. heteroclada leaves had a vigorous reducing ability and showed higher efficiency of light uptake energy as well as higher quantum yield indexes ϕ(Eo) and ϕ(Po). This study demonstrates that the ecological adaptive regulation strategies of P. heteroclada in the riparian zone are intrinsic driving factors affecting their stoichiometric characteristics, including changes in the absorption and transport of minerals caused by root aeration structure and energy metabolism. Moreover, carbon production and allocation may be caused by the stable photosynthetic mechanism and source-sink relationship of leaves. Through the synergistic regulation of different organs realizing their roles and functions, P. heteroclada developed ecological stoichiometry characteristics adapted to the riparian zone.
... Cynodon dactylon and Ass. Cyperus rotundus, accompanied by some annual plant communities that are associated with water level fluctuations (Wang et al., 2014;Chen et al., 2020). Substrate types in this area vary based on elevation and were mainly silty in the flatter areas and loamy on slopes. ...
Seasonal water level fluctuation is a typical characteristic of reservoirs created by dams on rivers. Due to their important roles in connecting ecological processes between riparian zones and adjacent uplands or waterbodies, ground-dwelling arthropods are essential components for maintaining riparian ecosystem health. However, the dynamic characteristics and response mechanisms of ground-dwelling arthropod assemblages to seasonal water level fluctuations have not been clearly established. We investigated ground-dwelling arthropods before and after summer floods (along with the influence of planned winter impoundment) in the drawdown zone of the Three Gorges Reservoir. Redundancy analysis and examination of interspecific associations were conducted to explore driving mechanisms for variations in these arthropod assemblages. Our results demonstrated that: i. floods are dominant mediating factors for variations in ground-dwelling arthropod assemblages in riparian zones; ii. species composition and abundances of ground-dwelling arthropod assemblages were in a state of dynamic change under the influence of floods; iii. Interplay of habitat modifications and interspecific associations influenced the composition as well as the distribution of ground-dwelling arthropods. We suggest that ground-dwelling arthropods are sensitive indicators for riparian ecosystem health and are valuable for evaluating work on the conservation and management of riparian zones.
... However, it also poses a significant impact on the ecosystem, land surface processes, and social economy in the reservoir area. In particular, the ecological degradation in the riparian zone has attracted widespread attention, and many studies have been conducted to explore the impacts of the TGR on landscape patterns (Wu et al. 2017, Chen et al. 2018, variations of vegetation distribution, and diversity (Hu et al. 2018, Zhu et al. 2019, as well as the spatial-temporal characteristics of the plant-soil system (Ye et al. 2020, Liu et al. 2021. Though these studies have elucidated the changes in the eco-hydrological environment since the reservoir impoundment, the dynamic characteristics and maintaining mechanism of the plant community function derived from the hydrological regime in the riparian zone of the reservoir are still unclear. ...
The plant is an important component of the riparian ecosystem, which could reflect both the environmental and functional characteristics of the riparian zone. Studies on species composition, diversity, community structure, distribution pattern, and adaptation strategies of plant communities in the riparian zone of the Three Gorges Reservoir (TGR) will help to explore the maintaining mechanism of the plant communities’ ecological function under severe water-level fluctuation. The paper reviewed the plant community characteristics, functional traits as well as their eco-physiological responses and environmental adaptations in this special ecological zone. Based on this, future research orientations in this field were also prospected, which may focus on the maintenance mechanism of the plant community, suitable plants selection and their adaptation mechanism, the relationship between plant functional traits and ecosystem functions, plant niche in the riparian zone, and the connectivity of riparian zone to the surrounding environment. The results can promote the correlational research on plant communities in the riparian zone and deepen the understanding of ecosystem services the riparian ecotone provides.
... This result indicated that the distance from the reservoir may also play a role in influencing how plant functional features respond to hydrological regimes. Different distances may result in changes in topography, flow velocity, and soil properties, all of which affect vegetation development and consequently have a substantial impact on vegetation functional traits (Ye et al., 2020). There were differences in photosynthetic rate and leaf dry weight in different geographical situations mainly due to temperature differences and light intensity (Wright et al., 2017). ...
A unique riparian ecosystem has been created as a result of anti-seasonal flooding after reservoir operations, which notably influences the distribution patterns of plant communities and their functional characteristics in the riparian zone. Plant functional traits which reflect the physiological and ecological processes of plants in particular ecosystems are crucial for indicating the variations in the ecosystem structure and function. To better understand the adaptation strategies of plants to hydrological changes and provide a scientific basis for the selection of species in the re-vegetation of the newly formed ecosystems, 14 leaf functional traits and leaf economics spectrum (LES) of 19 dominant plants under different hydrological conditions were investigated in the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). The results showed that anti-seasonal flooding has significant effects on the leaf functional traits of plants (P < 0.05). The net photosynthetic rate of annual plants was significantly higher than that of perennial plants (P < 0.05), and there was a significant correlation between leaf phenotypic and photosynthetic traits (P < 0.05). Canonical correspondence analysis showed that soil water content and available phosphorus were the main factors affecting the leaf function of dominant species, indicating that hydrologic factors were still important environmental factors affecting leaf functional traits of dominant species in the WLFZ. And annuals from the WLFZ have characteristics of thick leaves, high photosynthetic rate, short lifespan, and high nutrient concentrations, which make them close to the fast investment-return end of LES. On the contrary, perennials are close to the slow investment-return end of LES. The high productivity investment of annuals is better than the high defense investment of perennials for adapting to the special habitats in the WLFZ. These results indicated that different functional plants in the WLFZ of the TGR under different hydrological regimes can adopt different strategies by weighing the associations and trade-offs between their economic traits.
... As sustainable energy production and a low-carbon means for economic development, the development of cascade hydropower is an important pattern to tap the hydropower potential of the rich river systems in southwest China (Wang et al., 2011;Li et al., 2018;Niu et al., 2018;Yue et al., 2021). Recent studies have enhanced the understanding of the impacts of hydropower reservoirs focused on the atmosphere, aquatic, and riparian ecosystems (Wang et al., 2017;Song et al., 2019;Ye et al., 2020;Chen et al., 2021;Nsabimana et al., 2021;Reynolds and Aldridge, 2021). Hydropower reservoirs are now considered an integral part of the terrestrial ecosystem (Miranda et al., 2008;Arif et al., 2021;Hoppenreijs et al., 2022). ...
The construction of giant reservoirs can affect the hydroclimatic cycles and related soil nutrient recycling. The current understanding of variations in soil nutrients driven by reservoir impoundment is limited because soil often reacts slowly to changes and the impoundment effects can be masked by various factors, making detection difficult. The soils in the hot-dry valleys suffer from a savanna-like hot and dry climate, making it an ideal area for studying the effect of reservoir impoundment on the soil. Here we collected 138 soil samples in April and November along the cascading reservoirs located in the hot-dry valleys of China, including Xiangjiaba, Xiluodu, Baihetan, and Wudongde reservoirs. Results showed that (1) the reservoir impoundment does alter the soil nutrients. The contribution of the impoundment to the variation of soil nutrients was 3.82% in April and 6.44% in November. (2) Compared to April, a relatively dry and cold November is preferred for revealing the reservoir impact on soil nutrients in the hot-dry valleys. (3) Available nitrogen and available phosphorus, followed by soil organic matter, are potential sensitive indicators that can be used to reflect the reservoir impoundment effects. Additionally, pH may be a potential indicator, particularly in the head reservoir area. It is important to note that the effect of reservoir impoundment on soil nutrients is easily masked. This study encourages dam operating agencies, policymakers, and researchers to regard reservoirs as integral parts of the forcings that modify soil nutrients and is an essential step in gaining an insight into the impact of hydropower development on surrounding terrestrial ecosystem services related to soil nutrients.
... Additionally, plant growth can reduce the sediment TN concentrations by absorbing mineral N leading to reduced N concentrations in the floodplain sediments (Ye et al., 2012;Esley-Quirk et al., 2019). Therefore, the net changes in sediment TN in the floodplain wetlands are complex and are determined by flooding conditions, sediment deposition, and plant growth (Ye et al., 2019b). Our results also indicate that the TN content in floodwater and the ID could explain the variance in sediment Δ TN post-flooding, which is consistent with the observations recorded in previous studies (Perez et al., 2000;VanZomeren et al., 2012). ...
Changes in flood regimes, floodwater quality, and macrophyte types may affect sediment characteristics post-flooding. However, few studies have attempted to unravel their complex influences in floodplain wetlands. From 2011 to 2020, the physical and chemical properties of surface layer sediment pre- and post-flooding was investigated through field surveys in the Dongting Lake wetland. Results indicated that the pre-flooding soil total phosphorus (TP) and total nitrogen (TN) exhibited an increasing trend during 2011-2020. Soil TP increased post-flooding relative to that pre-flooding. The changes in TN, sediment organic matter (SOM), sediment moisture content (SMC), and sediment bulk density (SBD) fluctuated over the years. The best-fitting multi-regression model demonstrated that the changes in sediment variables post-flooding showed a parabolic trajectory along the inundation duration (ID), except for SMC. Changes in soil properties post-flooding were negatively correlated with ID for sediment with a low IDs (<148 days). Meanwhile, changes in soil properties post flooding were positively correlated with ID for sediment with a high IDs (>193 days). Changes in SBD and SOM post-flooding were positively influenced by the TP content in the floodwater. These findings indicate that changes in the flooding regime, and water quality generated by anthropogenic disturbances such as the Three Gorges Dam significantly affect sediment properties, and subsequently influence the ecological functions of the Dongting Lake wetland.
The soil microbiome plays an important role in wetland ecosystem services and functions. However, the impact of soil hydrological conditions on wetland microorganisms is not well understood. This study investigated the effects of wetted state (WS); wetting–drying state (WDS); and dried state (DS) on the diversity of soil bacteria, fungi, and archaea. The Shannon index of bacterial diversity was not significantly different in various flooding conditions (p > 0.05), however, fungal diversity and archaeal communities were significantly different in different flooding conditions (p < 0.05). Significant differences were found in the beta diversity of bacterial, fungal, and archaeal communities (p < 0.05). Additionally, the composition of bacteria, fungi, and archaea varied. Bacteria were predominantly composed of Proteobacteria and Actinobacteria, fungi mainly consisted of Ascomycota and Mucoromycota, and archaea were primarily represented by Crenarchaeota and Euryarchaeota. Bacteria exhibited correlations with vegetation coverage, fungi with plant diversity, and archaea with aboveground vegetation biomass. The pH influenced bacterial and archaeal communities, while soil bulk density, moisture, soil carbon, soil nitrogen, and plant community diversity impacted fungal communities. This study provides a scientific basis for understanding the effects of different hydrological conditions on microbial communities in the Huihe Nature Reserve; highlighting their relationship with vegetation and soil properties, and offers insights for the ecological protection of the Huihe wetland.
Mangroves and wetlands are critical intermediary ecosystems between terrestrial and marine environments. These ecosystems offer a wide range of invaluable ecological and economic services. However, under the influence of natural and anthropogenic threats, mangroves and wetlands face rapid degradation. Microbes and microbiomes are integral components of a mangrove, playing key roles in the stability of the ecosystem. The present chapter compiles a comprehensive review of the classification and the role of microorganisms in the sustainability of mangrove and wetland ecosystems. The chapter discusses the most critical features of microbial groups, including archaea, bacteria, algae, and fungi in mangroves and wetlands. Bacterial groups under discussion consist of sulfur-related bacteria, nitrogen-related bacteria, phosphate-solubilizing bacteria, and photosynthetic bacteria. A separate section is dedicated to periphytic communities encompassing a microhabitat involving various prokaryotic and eukaryotic microorganisms. Moreover, biochemical transformations brought about by wetlands' microbial groups are explained. In addition, the following chapter emphasizes the degree of complexity in microbial interactions and draws attention to how alterations to these interactions ultimately impact ecosystems' health status. Furthermore, the role of wetland microorganisms in processes, such as detoxification, bioremediation, methanogenesis, carbon sequestration, nutrient cycling and transformations, and primary production is articulated.
Riparian taxa are subject to dynamic, intense, flood‐related stressors, and have evolved traits to persist in this environment. Climate change‐induced intensification of flood regimes pose a threat to these ecosystems, and little is understood about their resilience to this intensification. Following two consecutive major floods (the first flood record‐breaking) along the subtropical coast of eastern Australia in March 2022, we used methods based on persistence (resprouting, seedling recruitment), and floristic structure (height, DBH) and assemblage, to assess the resilience of an old growth riparian rainforest to severe flooding in the 12‐month post‐flooding window. Smallerwoody plants (stems <10 m tall, <30 cm DBH) were the most impacted and were significantly impacted by flooding. Native species richness and plant density (plants/m ⁻² ) significantly decreased between before and 3 months post‐flooding, after which they continued to significantly increase to surpass pre‐flood values. Overall, ~35% of taxa exhibited resprouting, ~28% of taxa exhibited seedling recruitment, and ~11% exhibited both resprouting and recruitment. An additional ~21% native taxa were introduced to the site via seedling recruitment, along with 65 invasive species. Model‐based multivariate analysis showed flooding significantly altered community floristics ( p = 0.026) at 3 months. At 12 months post‐flooding the community was recovering, becoming more floristically similar to its pre‐flood composition. The riparian rainforest exhibited high resilience to intense flooding. Impact, persistence, and resilience varied amongplots, and the community took 12 months to move into recovery. We found that persistence, and floristic structure and composition weighted against impact were effective measures of ecosystem resilience. In the absence of further consecutive events, mature‐phase riparian rainforests are likely to be structurally and floristically resilient to climate change‐induced amplification of flood regimes. Further studies should build on this framework to include invasive weed species impacts, for a more accurate assessment of impacts.
为了探究三峡水库消落带植被的分布规律及其对库区生态环境和渔业的潜在贡献, 对秭归、云阳和忠县库区共计30个典型消落带断面的植物群落结构特征、植物营养成分、断面坡度及土壤理化特性进行了调查分析。结果表明, (1)共发现54科、61属、209种植物, 其中狗牙根(Cynodon dactylon)和苍耳(Xanthium sibiricum)为主要优势种, 平均盖度分别为29.73%和26.87%; 随着水位高程逐渐降低, 狗牙根、喜旱莲子草(Alternanthera philoxeroides)和茼麻(Abutilon theophrasti)的盖度逐渐增加, 苍耳、草木犀(Melilotus officinalis)和狼粑草(Bidens tripartite)的盖度逐渐降低, 而葎草(Humulus scandens)、狗尾草(Setaria viridis)和酸模叶蓼(Polygonum lapathifolium)的盖度先增加后降低; 植被的分布还受到断面坡度的影响, 狗牙根的盖度与坡度呈显著负相关(P<0.001), 而苍耳的盖度则随着坡度呈现先增后降的显著单峰形态分布(P<0.001)。较高的土壤含水率促进了以狗牙根为主的共优势群落的形成, 而随着土壤含水率降低, 植被类型逐渐演替成以苍耳为主的共优势群落; (2)低水位高程(150—160 m)消落带地表土壤呈现明显的磷吸收趋势, 而高水位(160—175 m)表
层土壤则呈现明显的磷释放趋势, 这与样地的植被类型和土壤微生物群落结构特征密切相关; (3)三峡水库消
落带狗牙根和苍耳的地面鲜重总量为2.51×108和2.48×108 kg, 它们的鲜重总量和蛋白质含量均远高于其他植物, 对库区渔产潜力贡献分别为1.25×108和1.24×108 kg。综上, 三峡库区消落带植被的主要优势种为狗牙根和苍耳, 植被的分布主要受到水位高程、断面坡度和土壤含水率的影响。消落带植被在库区陆源磷营养截留、水体磷营养调控和鱼产力贡献方面具有较高的生态服务功能价值。研究可为评估水库消落带的生态渔业功能及研发水库消落带的植被修复技术提供重要参考。
Soil carbon dynamics are closely related to pedologic properties and highly variable among different soil types, however, it is not clear if the effects of soil types on carbon storage can be erased by a continuous environmental stress. Periodic flooding, the dominant environmental stress on natural riparian habitats, greatly regulates the biogeochemical cycles of carbon. To reveal how flooding stress affects carbon storage within different soils, here, we have examined soil types’ effects on carbon storage along a flooding gradient in the riparian zones of the Three Gorges Reservoir. The two-way ANOVA analysis was applied to measure the effects of soil type, flooding stress, and their interactions on aggregate proportion, organic carbon fraction, carbon concentration, and content in aggregates and bulk soils. The partial least squares path model was used to uncover the potential mechanisms of flooding stress affecting carbon storage for different soils. The results presented that the topsoil of the riparian zone of the Three Gorges Reservoir holds exceeding 3.95 Tg of carbon. Anthrosols, Luvisols, and Regosols stored 351.02, 275.50, 1349.50 Gg C, respectively. Flooding stress was found to positively affect C content for Anthrosols and Regosols with total effect sizes of 0.52 and 0.59, respectively. However, flooding stress had a negative impact on C content in Luvisols. In addition, the effect sizes of soil types on C content were alleviated by the strong flooding stress, and the effect size at the control and weak stress levels were higher than that at strong and intermediate stress levels. The original heterogeneousness of soil physical properties within different soils was homogenized by the extreme flooding stress, which can be indicated by aggregate proportion and particulate organic carbon.
Spatial hydrological alterations seem to influence the variability of soil-bound magnetic particles and heavy metals in water reservoir riparian wetlands (RW). To date, applying geochemical analysis with magnetic techniques to assess heavy metal pollution is rarely practiced in RW soils. We studied the magnetic properties and heavy metals, including Cu, Cr, and Zn, of topsoils in RW and the upland regions (UR, as control) in the Three Gorges Reservoir, China. Potentially elevated low-frequency mass magnetic susceptibility (χLF), anhysteretic remanent magnetization susceptibility (χARM), isothermal remanent magnetism, and heavy metals Cu, Cr, and Zn were found in RW. The grain size of the magnetic minerals was coarser in RW than that in UR. The pollution load index (PLI) of the studied samples was 1.18 ± 0.12 and 1.04 ± 0.21 in RW and UR, respectively. PLI and concentrations of Cu, Cr, and Zn were positively correlated with χLF, χARM, and the isothermal remanent magnetism in RW, whereas no clear linkages were observed between PLI and the isothermal remanent magnetism in UR. This finding reveals that hydrological alterations increased the magnetic enhancement and heavy metal enrichment in RW. We find that magnetic proxies of soils could trace the concentration of selected anthropogenic heavy metals and their pollution level in RW.
Polycyclic aromatic hydrocarbons (PAHs) pose a great threat to human health and ecological system safety. The interception of nitrogen is common found in the riparian zone. However, there is no evidence on how nitrogen addition affects the anaerobic degradation of PAHs in soil of the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) in Yangtze River, China. Here, we investigated the PAHs degradation rate, the variation of key functional genes and microbial communities after nitrogen addition in soil that experienced a flooding period of water-level-fluctuation. The results revealed that the ∑16PAHs were decreased 16.19 %-36.65 % and more 3-5-rings PAHs were biodegraded with nitrogen addition in WLFZ. The most genes involved in PAHs-anaerobic degradation and denitrification were up-regulated by nitrate addition, and phyla Firmicutes, Actinobacteria and Proteobacteria were more advantages in nitrogen addition groups. The Tax4Fun based genome function analysis revealed that the microbial activity of PAHs-degradation increased with nitrate addition. The co-occurrence network analysis indicated that nitrogen addition accelerated the metabolism of nitrogen and PAHs. It is the first time to provide the direct experimental evidences that nitrogen transformation in the WLFZ soil promotes anaerobic PAHs degradation. This work is of importance to understand the effect of nitrogen intercepted in the WLFZ soil of TGR in Yangtze River, China.
Sand is a crucial and limited resource. It is available easily. It has multifarious properties catering to many industries like construction, glass, and electroplating, as their raw material. The sand mining activity has started and increased exponentially in the past few decades. Especially in developing countries like China and India, the impact of sand mining has become extremely visible. The purpose of this study is to review the causes and impacts of sand mining on the riverine ecosystem. Through review, it was found that sand mining processes destroy sediment flow and create an imbalance in the sediment deposition formed by years of erosion and sedimentation of the riverine system. Excessive sand mining led to riverbed alteration, affecting the course of the river and causing bank erosion. Deepening of the rivers and river mouths leads to saline water. It also leads to loss of river ecosystem and services. Sand mining activities were found prominent near river body closer to construction site. This practice was found more active in the developing countries. Furthermore, illegal mining activities are rooted deeply in many regions of the world. The excavated pit has been known to cause drowning effect in the river leading to death of natives, narrowing of river width, and bank erosion. Earlier, the monitoring and assessment of sand mining activities were difficult but the use of geographical information systems (GIS) and remote sensing techniques has given a unique advantage. The satellite data, obtained from MODIS, LANDSAT, Google Earth Engine, etc., are processed using GIS tools and various topographical features such as land, water, vegetation, can easily be studied. The use of unmanned automatic vehicles (UAV's), spectral indices (Normalized Difference Water Index, Normalized Difference Vegetation Index, etc.), LULC, etc. was found to be effective in assessing the sand mining activities in the 35 river bodies. To remediate the situation, use of other materials such as M‐sand, quarry stone dust, and 36 crushing rocks were suggested. The study revealed that there is an immediate need for monitoring the sand mining activities and taking strict actions to conserve our environment.
Active revegetation (AR) and natural regeneration (NR) are two restoration approaches widely used to rehabilitate degraded riparian ecosystems, which are subjected to frequent hydrological fluctuations owing to climate change and human activities. Nevertheless, the impacts of restoration approaches and hydrological changes on the key processes of carbon and nitrogen cycling, particularly in degraded riparian ecosystems, remain unclear. In this study, we conducted hydrological experiments, which began in 2016, at three flooding zones (extreme flooding zone, severe flooding zone, and moderate flooding zone) of AR and NR areas in the Three Gorges Reservoir to investigate the effects of restoration approach and hydrological changes on soil properties, vegetation diversity, microbial characteristics, denitrification rates, and greenhouse gas fluxes. The results showed that compared with NR, AR did not change vegetation diversity, microbial diversity, and soil denitrification rates, but decreased soil ammonium and total carbon contents. The vegetation coverage of each flooding zone was more than 90%, and vegetation diversity was relatively high in the moderate flooding zone. Moreover, the maximum denitrification rates and CO2 fluxes were observed in the extreme flooding zone along with a high soil nutrient content. Additionally, the effect of flooding zone superseded the impacts of restoration approaches since AR could only significantly increase the CO2 flux (p < 0.05). Overall, this study elucidates the impacts of restoration approaches and hydrological changes on C and N cycling, and aids in developing restoration strategies for degraded riparian ecosystems.
Distylium chinense is an evergreen dominant shrub with strong adaptability under heterogeneous habitats, including natural riparian zone (NRZ), anti-seasonal water level fluctuation zone (ASWLFZ), and no water level fluctuation zone (NWLFZ) in the Three Gorges Reservoir Region (TGRR) in China. In order to understand the photosynthetic ecological adaptability and habitat adaptation strategies of D. chinense under heterogeneous habitats, its photosynthesis and chlorophyll fluorescence parameters were investigated. The results showed that photosynthetic characteristics were significantly different among heterogeneous habitats (p<0.05). The PSII potential activity and PSII maximum photochemical efficiency (Fv/Fm) of D. chinense in the ASWLFZ were the highest among heterogeneous habitats. Non-photochemical quenching coefficient (qN) in the NWLFZ was higher than that in the NRZ and ASWLFZ (p<0.05). Stepwise regression analysis showed that water use efficiency and stomatal conductance were correlated with specific leaf area (SLA), leaf area and leaf dry weight. Regression curve fitting and canonical correspondence analysis revealed that light intensity, soil water content, air humidity and temperature were the main factors affecting photosynthetic characteristics and leaf functional traits. Our results evidenced that D. chinense adapted to the high water content and low light intensity environments, especially in the valley waterfall habitats, by increasing stomatal conductance and net photosynthetic rate, reducing SLA and maintaining moderate qN and Fv/Fm with adopting a profligate water use pattern to improve photosynthetic productivity. Therefore, D. chinense has a wide photosynthetic acclimation to different environments, which provided baseline information for the conservation and ecological restoration in the newly formed hydro-fluctuation zone and other similar degenerative riparian ecosystem.
After decades of anti-seasonal water fluctuation in the Three Gorges Reservoir (TGR), a distinctive riparian zone had been formed and played critical roles on soil biogeochemistry cycling, substance exchange and soil microbial functions. However, the effect of land use on terrestrial ecological processes and soil microbial community assembly in riparian zone was still imprecise. This study focused on the relationship of soil properties and microbial communities in paddy and dryland soils of a typical riparian zone in the TGR. The results indicated a higher level of accumulation of total organic carbon (TOC) in paddy soil (14.88–20.29 g kg⁻¹) than that in dryland soil (7.59–16.20 g kg⁻¹). The riparian soil was slightly polluted by cadmium and phthalate acid esters with an average concentration of 0.19 mg kg⁻¹ and 6.45 mg kg⁻¹, which may be from agricultural sources, posing a potential health risk. Based on 16S rRNA sequencing analysis, there was a higher microbial diversity in paddy soils than dryland soils, and Acidobacteriaceae and Anaerolineaceae represented the dominant taxa in dryland and paddy soils, respectively. Furthermore, the results of redundancy analysis and structural equation modeling showed that land use driven change in soil organic carbon affected the fate of soil pollutants, and constructed soil microbial communities in the riparian zone of TGR. Null model revealed that homogeneous selection explained about 76.36% and 53.33% microbial community assembly, followed by dispersal limitation (14.54% and 37.50%) in dryland and paddy soil. In consequence, a strong effect of environmental filtering was observed on arable soil microbial community structure with different land use in the riparian zone of TGR, and TOC was the key regulator.
Continuous monocropping degrades soil physicochemical properties, leads to the accumulation of toxic compounds and changes soil microbial community composition. Pre-flooding the soil is a promising strategy to improve its productivity; however, little is known about the underlying mechanisms. Here, strawberry (Fragaria × ananassa) pot experiments were conducted with soil that had been used for continuous monocropping. The treatments were pre-flooding alone, with rice straw added and with rice straw plus a biofertilizer (mainly contained Bacillus velezensis) amendment, and the impacts of the treatments on soil physicochemical properties, bacterial diversity and composition and the integrated plant–soil–microbe responses were tracked. The strawberry biomass significantly increased after pre-flooding treatments. Pre-flooding increased the soil pH and the available P and K concentrations, while it decreased soil electrical conductivity. The bacterial diversity and abundance significantly increased after pre-flooding treatments. A Mantel test showed that soil pH and salinity were the two most important factors in shaping bacterial composition, but they exerted opposite effects. The increased strawberry biomass after pre-flooding was significantly correlated with bacterial composition and soil salinity in long-term continuous strawberry monocropping systems.
Aggregates play crucial roles in protecting soil carbon (C) and nitrogen (N) loss since aggregates could mediate the effect of environmental factors on the C and N accumulation. As ecotone habitats, reservoir riparian zones undergo disturbances from both land use and dam-regulated flooding, which could pose threats to aggregate stability. Yet, we know little about the effects of the flooding intensity and land use on the dynamics of soil C and N, as well as the mediating role of soil aggregates. In this study, along a flooding gradient, firstly we examined the effects of seven land-use types (corn, rice paddy, and vegetable lands; Chinese fir, willow, and mulberry restored lands; and grassland) on soil C and N accumulation; secondly, we identified the size distribution and stability of aggregates in mediating the effect of riparian land uses under periodic flooding regimes. We found that the C and N concentrations in soil aggregate fractions were all significantly impacted by land-use types, and aggregate-size distribution showed tight links with both land-use types and C and N contents. Conservative farmlands contained a higher proportion of macro-aggregates which stores significantly higher C and N concentrations than micro-aggregates. Notably, higher aggregate stability was also found in conservative farmland. We concluded that, in the riparian ecotone, conservative farming promotes C and N accumulation via stabilizing aggregate fractions, and suggested the conservative practices could be acceptable for soil conservation considering the scarcity of land resources in the ambient mountainous regions.
Understanding how microorganisms respond to environmental disturbance is one of the key focuses in microbial ecology. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are responsible for ammonia oxidation which is a crucial step in the nitrogen cycle. Although the physiology, distribution, and activity of AOA and AOB in soil have been extensively investigated, their recovery from a natural disturbance remains largely unknown. To assess the recovery capacities, including resistance and resilience, of AOA and AOB, soil samples were taken from a reservoir riparian zone which experienced periodically water flooding. The samples were classified into three groups (flooding, recovery, and control) for a high-throughput sequencing and quantitative PCR analysis. We used a relative quantitative index of both the resistance (RS) and resilience (RL) to assess the variation of gene abundance, alpha-diversity, and community composition. The AOA generally demonstrated a better recovery capability after the flooding disturbance compared to AOB. In particular, AOA were more resilient after the flooding disturbance. Taxa within the AOA and AOB showed different RS and RL values, with the most abundant taxa showing in general the highest RS indices. Soil NH4⁺ and Fe²⁺/Fe³⁺ were the main variables controlling the key taxa of AOA and AOB and probably influenced the resistance and resilience properties of AOA and AOB communities. The distinct mechanisms of AOA and AOB in maintaining community stability against the flooding disturbance might be linked to the different life-history strategies: the AOA community was more likely to represent r-strategists in contrast to the AOB community following a K-life strategy. Our results indicated that the AOA may play a vital role in ammonia oxidation in a fluctuating habitat and contribute to the stability of riparian ecosystem.
Background
Species recovery after disturbances depends on the strength and duration of disturbance, on the species traits and on the biotic interactions with other species. In order to understand these complex relationships, it is essential to understand mechanistically the transient dynamics of interacting species during and after disturbances. We combined microcosm experiments with simulation modelling and studied the transient recovery dynamics of a simple microbial food web under pulse and press disturbances and under different predator couplings to an alternative resource. ResultsOur results reveal that although the disturbances affected predator and prey populations by the same mortality, predator populations suffered for a longer time. The resulting diminished predation stress caused a temporary phase of high prey population sizes (i.e. prey release) during and even after disturbances. Increasing duration and strength of disturbances significantly slowed down the recovery time of the predator prolonging the phase of prey release. However, the additional coupling of the predator to an alternative resource allowed the predator to recover faster after the disturbances thus shortening the phase of prey release. Conclusions
Our findings are not limited to the studied system and can be used to understand the dynamic response and recovery potential of many natural predator–prey or host–pathogen systems. They can be applied, for instance, in epidemiological and conservational contexts to regulate prey release or to avoid extinction risk of the top trophic levels under different types of disturbances.
We studied bank vegetation between the spring high-water level and the summer low-water level along two rivers in northern Sweden. The hypothesis that natural and ruderal species would show different downstream patterns of species richness was tested by sampling species composition and environmental variables along 200 m long stretches of riverbank 10 km apart. Natural species richness was highest in the midreaches of both rivers, whereas ruderal species showed a significant, monotonic increase downstream. There are no obvious mechanisms producing the quadratic pattern of natural species richness. The downstream increase in ruderal species suggests a founder effect depending on larger artificial disturbances near the coast, but alternative explanations are also given. Total species richness did not exhibit any interpretable downstream patterns. The only factors significantly correlated with total species richness along both rivers were substrate heterogeneity and substrate fineness. Total species richness increased with substrate heterogeneity and was at maximum at intermediate levels of substrate fineness. This suggests that co-occurrence of natural and ruderal species is most likely where substrate types are numerous and dominant substrate particle size intermediate.
In a disturbed alpine ecosystem on the Beartooth Plateau, Montana, diaspores of species with varying morphology were sown over soils of five different particle sizes and later collected from three depths. Regardless of diaspore morphology, the total number of diaspores trapped increased with increasing particle size until a threshold soil particle size was reached above which no more diaspores were trapped. At small particle sizes (0.5-1.0 and 1.0-2.0 mm) small diaspores and diaspores with adhesive seed coats were trapped, but most large diaspores moved horizontally across the surface and were not trapped. Most diaspores trapped were at the 0-1cm depth at small particle sizes. At large particle sizes (2.0-4.0, 4.0-8.0, and 8.0-16.0 mm) high numbers of large diaspores were trapped, and more diaspores moved vertically through the soil column. In small particle size soils small diaspores reached greater depths than large diaspores. Diaspores with adhesive seed coats responded more like large diaspores in terms of vertical movement. Diaspore length and eccentricity (length/width) were highly correlated with entrapment at small particle sizes and appeared to have the greatest effect on horizontal movement. -from Authors
With the completion of the Three Gorges project, native vegetation in the water level fluctuation zone between the elevations of 145 m to175 m disappeared due to the inundation with a hydrological regime with flooding in winter instead of summer, a reversal of the natural one. We conducted a field experiment in the riparian ecosystem in the Three Gorges Reservoir to study nitrogen (N) dynamics under short-term revegetation and flooding during the period from 2008 to 2009. Soil chemical and physical characteristics, net mineralization potential rate (NMPR), net nitrification potential rate (NNPR), and denitrification potential rate (DPR) were determined in the laboratory. These results showed a significant decrease in inorganic N (NH4+-N and NO3−-N) following the short-term revegetation and flooding, which was probably related to the interactions between surface flow, flooding, plant N uptake, and N transformation. Plants in conjunction with flooding increased the NMPR and NNPR, and increased the DPR only at the beginning of the revegetation and then decreased DPR after the flooding by regulating the concentration of soil organic carbon (SOC) and C:N ratios in soil, and decreasing the soil bulk density. Vegetation types affected N dynamics by changing SOC, soil N availability, and C:N ratios. The inorganic N, NMPR, and NNPR were higher in shrub soil than those in herb and tree soils due to higher SOC, whereas the DPR in tree soils was lower compared to shrub and herb soils because of lower C:N ratios together with the lower SOC. These results imply that soil inorganic N declined following the revegetation and flooding, and the revegetation in the riparian zone could potentially improve water quality.
Transitional wetlands occur along an estuarine salinity continuum bracketed by salt and nontidal freshwater wetlands. Long-term disturbances, such as sea level rise, may shift physical characteristics and hydrologic features of estuarine systems leading to transitional wetland habitat alterations, with unknown affects to associated biological communities. To begin to assess the ecological significance of a change in transitional wetland character, physicochemical parameters, and fish and invertebrate communities were surveyed seasonally in two extensive meso-oligohaline marshes, currently undergoing changes due to sea level rise. Faunal communities were similar between marshes, and included economically important species and forage fish. Temporal shifts in communities occurred seasonally and annually with high variability in species abundance among years. Drastic annual variability in salinity regimes due to extremes in precipitation occurred during the survey period driving shifts in biotic community composition.
Wetlands in the Mesopotamian Plain in southern Iraq were extensively drained in the 1990s. Re-flooding of drained areas commenced in 2003, and included parts of the Central marsh between the Euphrates and Tigris Rivers. New vegetation in the re-flooded areas of the Central marsh was studied in 2006. Most of the wetland plant species and communities widely distributed prior to drainage have reappeared, but there were some species and communities that did not re-establish. Aboveground plant biomass is recovering in some communities, but in most of the new communities, biomass and diversity were low. Post-flooding sites were characterized by higher concentrations of chloride and bicarbonates in surface water and higher percent organic matter in sediment than those prior to drainage. Comparisons among the three study sites in the re-flooded areas and those between pre-drainage and post-flooding sites suggests that differences in water quality, including more saline conditions in the re-flooded wetlands, might be hindering the biomass recovery. The water source being limited to only the Euphrates River, a much more subdued seasonal fluctuation in the quantity of water input and output, and inputs of contaminated waters appear to be responsible for the delay in vegetation recovery in the Central marsh.
Tropical forest loss and degradation are proceeding at unprecedented rates, eroding biological diversity and prospects for sustainable economic development of agricultural and forest resources. There is increasing evidence that forest plantations can play a key role in harmonising long-term forest ecosystem rehabilitation or restoration goals with near-term socio-economic development objectives. Recent studies have shown that plantations can facilitate or "catalyse," forest succession and biodiversity enrichment in their understories on sites where persistent ecological barriers to succession would otherwise preclude recolonisation by native forest species. These studies suggest that the catalytic effect of plantations is due to changes in understorey microclimatic conditions, increased vegetation structural complexity, and development of litter and humus layers that occur during the early years of plantation growth. These changes lead to increased seed inputs from neighbouring native forests by seed dispersing wildlife attracted to the plantations, suppression of grasses or other light-demanding species that normally prevent tree seed germination or seedling survival, and improved light, temperature and moisture conditions for seedling growth. Wildlife, particularly birds and bats, are critical "allies" in the restoration process, responsible for seed dispersal for the overwhelming majority of tree, shrub and liana species present in moist tropical forests. Understanding the habitat preferences and behaviour of these restoration facilitators, including their relationship to vegetation structure and composition, can help us to better design restoration treatments (including tree species selection) that will lead to rapid increases in floristic diversity and overall improvements in the value of these forests as wildlife habitat. In this paper, the results of recent studies conducted since 1995 in several countries in Latin America, Africa and the Asia-Pacific region on the phenomenon of plantation-catalysed native forest restoration will be summarised and their potential application in wildlife conservation programmes discussed.
Correlative studies have shown a ‘hump-backed’ relation between the vegetation N:P ratio and plant species diversity with the highest diversity at balanced N:P ratios (between 10 and 14). We tested the hypothesis that adding growth-limiting nutrients to mesotrophic grasslands that were in shortage of either N (N:P ratio<10) or P (N:P ratio>14) would lead to an increase of plant diversity. Thereto, we studied the effects of long-term (11 yr) experimentally increased N and/or P supply on soil nutrient pools, vegetation nutrient dynamics and biodiversity in a riverine grassland in the Netherlands with a low soil N:P ratio (N shortage) and a peat grassland with a high soil N:P ratio (P shortage), respectively. Eleven years of nutrient addition hardly had any effects on the total stocks of C, N and P in the soils of both sites, due to the large size of the soil nutrient pools already present and to the management at both sites (annual hay-making and -removal). However, in the riverine grassland the treatments increased the cycling of the small pool of labile N and P compounds resulting in large increases in annual fluxes of especially N. In the unfertilised controls, species establishments balanced more or less species losses during an 11 year period, thus leading to a dynamic equilibrium of the species pool. However, contrary to our hypothesis, addition of the growth-limiting nutrient led at both sites to a reduction of species diversity even when total biomass remained below critical levels. Species diversity and species evenness were strongly determined by N mineralisation and to a lesser extent by total soil N and extractable P, respectively. Total aboveground biomass of the vegetation was determined by total soil N.
Current methods of wetland assessment rely on the use of ecological indicators such as vegetation and amphibians, but often
lack an in-depth analysis of soil parameters. The objective of this study was to determine whether the Ohio Rapid Assessment
Method (ORAM) can be used to predict soil quality in forested wetlands. Soil cores were taken from six wetlands ranging in
ORAM scores. The soil samples were analyzed for key soil parameters (aggregate stability, bulk density, organic matter, C,
N, S, P, microbial biomass, and enzyme activity). Some of these soil parameters (i.e., microbial biomass, soil C, N and S,
bulk density, soil moisture) were correlated with the ORAM scores, while others (i.e., P, pH, aggregate stability) showed
no correlation. Enzyme activity was correlated with the ORAM score for one of the four sampling events. When analyzed together
by a principal component analysis, the soil parameters did not separate the wetland sites along a gradient of ORAM scores.
Our results indicate that the ORAM reflects some of the key soil quality conditions, but not all. We further discuss whether
some of the soil parameters we selected are appropriate indicators of the quality of wetland soils.
We critically review recent literature on carbon storage and fluxes within natural and constructed freshwater wetlands, and
specifically address concerns of readers working in applied science and engineering. Our purpose is to review and assess the
distribution and conversion of carbon in the water environment, particularly within wetland systems. A key aim is to assess
if wetlands are carbon sinks or sources. Carbon sequestration and fluxes in natural and constructed wetlands located around
the world has been assessed. All facets of carbon (solid and gaseous forms) have been covered. We draw conclusions based on
these studies. Findings indicate that wetlands can be both sources and sinks of carbon, depending on their age, operation,
and the environmental boundary conditions such as location and climate. Suggestions for further research needs in the area
of carbon storage in wetland sediments are outlined to facilitate the understanding of the processes of carbon storage and
removal and also the factors that influence them.
Herbaceous species comprise most of the floristic diversity in semi-arid region riparian zones, yet little is known about
their response to river flooding. We compared cover, richness, and distribution of six functional groups of herbaceous plants
after a large fall flood (pre-vs. post-flood year comparison) and after small monsoon floods and rains (dry vs. wet season
contrast), and compared richness across a longitudinal (upstream-downstream) gradient of flood intensity. Herbaceous cover
and richness increased significantly (p≤0.05, ANOVA) from the pre-flood to post-flood year and from the dry to wet season.
Overall, the post-flood increases in richness and cover were related to the combined effects of disturbance (as indicated
by strong increases of annual plants) and increased water availability (as indicated by response patterns of hydric perennials
and other functional groups). All annuals showed strong increases in richness and cover in the year following the large fall
flood, with hydric annuals increasing in richness by 43%, mesic annuals by 52%, and xeric annuals by 75%. Hydric perennials
had a small net increase in richness following the large flood, reflecting a positive response to increased flow permanence,
countered by low richness at sites with very high flood intensity (total stream power). Mesic and xeric perennials did not
change significantly in richness from the pre- to post-flood year. However, across the spatial flood intensity gradient, the
richness response pattern of the annuals and perennials alike peaked at intermediate levels of disturbance. In response to
seasonal rains and moderate flooding, hydric perennials did not change in abundance, reflecting their primary association
with shallow ground water and perennial stream base flows, but mesic perennials increased in cover and xeric perennials increased
in both cover and richness. All three annual groups increased in cover and richness and in distribution across the flood plain
following the summer monsoon floods and rains: hydric annuals had peak cover in inundated zones, suggesting positive response
to river flooding, while xeric annuals peaked in cover above inundation zones, suggesting positive response to icreased rainfall;
mesic annuals had intermediate patterns. During the dry season, in contrast, annuals had low richness and cover and were restricted
to low elevation fluvial surfaces adjacent to the stream channel and/or underlain by shallow ground water. Overall, both disturbance
and increased moisture conditions caused by floods, as well as moisture from seasonal rains, contribute to increased richness
and cover of herbaceous plants within the flood plain of the San Pedro River.
The effects of flooding on rhizospheric organic acid concentrations of three abundant flooding tolerant plant species (Alternanthera philoxeroides Mart., Arundinella anomala Steud., Salix variegata Franch.) from the water fluctuation zone of the Three Gorges Reservoir (TGR, Yangtze River) were investigated. Soil solution samples of eight low molecular weight organic acids were obtained from rhizotrons using micro suction cups during 3 weeks of waterlogging, after 6 weeks flooding and after a 1 week recovery. To estimate the contribution of water temperature and microbial community, plants in sterile glass bead substrate and original Yangtze sediment were submerged in laboratory at +10A degrees, +20A degrees and +30A degrees C. Waterlogged plants did seldom express a significantly different pattern of rhizospheric organic acid (OA) composition compared to control plants. Flooding caused no burst of organic acid concentration in soil solution: All species express a silencing strategy. Average OA levels were higher in A. anomala rhizosphere than in the other two species, but increased again after resurfacing in all species. Temperature had a stronger influence in sediment than in sterile setup. In contrast to field measurements, succinate, malate and citrate were detected in the sterile setup. Microbial contribution appeared to have great influence on increasing OA occurrence.
In the last 10 years the Sri Lankan government has changed its policy regarding its remaining rain forest from one that promoted commercial exploitation to one of conservation. The growing importance of uplands as catchments for water production, biodiversity conservation and other downstream services has been recognized by the Sri Lankan government. It is therefore timely that we review 15 years of research investigating rain forest dynamics of southwest Sri Lanka with the objective of using this knowledge for forest restoration. We provide six common principles for understanding the integrity of rain forest dynamics in southwest Sri Lanka. The principles are: (i) disturbances provide the simultaneous initiation and/or release of a new forest stand; (ii) that disturbances are generally non-lethal to the groundstory vegetation; (iii) disturbances are variable in severity, type and extent across rain forest topography; (iv) guild diversity (habitat diversity) is dependent upon “advance regeneration”; (v) tree canopy stratification is based on both “static” and “dynamic” processes; and (vi) canopy dominant late-successional tree species are site specialists restricted to particular topographic positions of the rain forest. These principles are applied to determine effects of two rain forest degradation processes that have been characterized as chronic (continuous detrimental impacts) and acute (one-time detrimental impacts). Restoration pathways are suggested that range from: (i) the simple prevention of disturbance to promote release of rain forest succession; (ii) site-specific enrichment planting protocols for canopy trees; (iii) sequential amelioration of arrested fern and grasslands by use of plantation analogs of old field pine to facilitate secondary succession of rain forest, and plantings of late-seral rain forest tree species; and (iv) establishment and release of successionally compatible mixed-species plantations. We summarize with a synthesis of the restoration techniques proposed for reforestation using native vegetation on cleared conservation areas and parks, and for the stabilization of eroded upland watersheds. We conclude with a comparative analysis with restoration work done in other tropical forest regions.
The effects of fumigation on organic C extractable by 0.5 M K2SO4 were examined in a contrasting range of soils. EC (the difference between organic C extracted by 0.5 M K2SO4 from fumigated and non-fumigated soil) was about 70% of FC (the flush of CO2-C caused by fumigation during a 10 day incubation), meaned for ten soils. There was a close relationship between microbial biomass C, measured by fumigation-incubation (from the relationship Biomass C = FC/0.45) and EC given by the equation: Biomass C = (2.64 ± 0.060) EC that accounted for 99.2% of the variance in the data. This relationship held over a wide range of soil pH (3.9–8.0).ATP and microbial biomass N concentrations were measured in four of the soils. The ratios were very similar in the four soils, suggesting that both ATP and the organic C rendered decomposable by CHCl3 came from the soil microbial biomass. The C:N ratio of the biomass in a strongly acid (pH 4.2) soil was greater (9.4) than in the three less-acid soils (mean C:N ratio 5.1).We propose that the organic C rendered extractable to 0.5 m K2SO4 after a 24 h CHCl3-fumigation (EC) comes from the cells of the microbial biomass and can be used to estimate soil microbial biomass C in both neutral and acid soils.
The water level fluctuation zone (WLFZ) in the Three Gorges Reservoir is located in the intersection of terrestrial and aquatic ecosystems, and assessing heavy metal pollution in the drown zone is critical for ecological remediation and water conservation. In this study, soils were collected in June and September 2009 in natural recovery area and revegetation area of the WLFZ, and geochemical approaches including geoaccumulation index (I
geo) and factor analysis and soil microbial community structure were applied to assess the spatial variability and evaluate the influence of revegetation on metals in the WLFZ. Geochemical approaches demonstrated the moderate pollutant of Cd, the slight pollutant of Hg, and four types of pollutant sources including industrial and domestic wastewater, natural rock weathering, traffic exhaust, and crustal materials in the WLFZ. Our results also demonstrated significantly lower concentrations for elements of As, Cd, Pb, Zn, and Mn in the revegetation area. Moreover, soil microbial community structure failed to monitor the heavy metal pollution in such a relatively clean area. Our results suggest that revegetation plays an important role in controlling heavy metal pollution in the WLFZ of the Three Gorges Reservoir, China.
The biogeochemical and stoichiometric signature of vegetation fire may influence post-fire ecosystem characteristics and the evolution of plant ‘fire traits’. Phosphorus (P), a potentially limiting nutrient in many fire-prone environments, might be particularly important in this context; however, the effects of fire on P cycling often vary widely. We conducted a global-scale meta-analysis using data from 174 soil studies and 39 litter studies, and found that fire led to significantly higher concentrations of soil mineral P as well as significantly lower soil and litter carbon:P and nitrogen:P ratios. These results demonstrate that fire has a P-rich signature in the soil–plant system that varies with vegetation type. Further, they suggest that burning can ease P limitation and decouple the biogeochemical cycling of P, carbon and nitrogen. These effects resemble a transient reversion to an earlier stage of ecosystem development, and likely underpin at least some of fire's impacts on ecosystems and organisms.
The operating scheme of the Three Gorges Reservoir results in a summer drought in the water-level fluctuation zone during which plants grow vigorously. In the winter inundation season, soaking plants may decompose and release nutrients resulting in water quality deterioration. This study quantifies the contributions of the underwater decomposition of nine dominant plant species in the water-level fluctuation zone to nutrient release. The in-situ litterbag technique was used to study for soaking decomposition over 200 days. All soaking plant species decomposed rapidly at an average rate of 1.99 ± 0.33% d− 1 in the early stage of soaking (0 to 30 days) and at an average rate of only 0.07 ± 0.04% d− 1 in the later stage (30 to 200 days). After 200 days of soaking, the nine plant species released an average of 312.40 ± 39.97 g kg− 1 organic carbon, 6.71 ± 4.29 g kg− 1 of nitrogen and 2.25 ± 1.25 g kg− 1 of phosphorus. A positive relationship was found between soaking plant decomposition rates and initial C/N ratios of 25 to 50, and a negative relationship where the C/N ratios were between 50 and 100. The amounts of total nitrogen or total phosphorus released were significantly negatively correlated with the initial C/N or C/P ratios of the plants. Among the studied plant species, Xanthium sibiricum Patr ex Widder showed high level of nutrient release via soaking decomposition. In contrast, Cynodon dactylon (Linn.) Pers. and Polygonum hydropiper exhibited low levels of nutrient release and are recommended as suitable species for the ecological restoration of the water-level fluctuation zone. Our results demonstrate that after 200 days of soaking plant decomposition, the loadings of total organic carbon, nitrogen, and phosphorus in the water-level fluctuation zone of the Three Gorges Reservoir were 2942.1, 81.1, and 24.7 kg ha− 1, respectively and therefore could potentially damage the aquatic environment of the reservoir.
This study was conducted to understand the patterns of plant species richness in the Three Gorges Reservoir after 5 years after 175 m submergence. We hypothesized that hygrophyte and xerophyte species would show different species richness patterns, which was tested by collecting species composition and environmental variable data in 50 m long and 5 m wide transects in the drawdown zone from 145 m to 180 m. Xerophyte species richness ( XSR ) was highest in the middle of the drawdown zone, whereas hygrophyte species showed a continuous downward trend from 145 m to 180 m. Correlation analyses showed that the flooding period was significantly negatively correlated with the total species richness ( TSR ), XSR , and hygrophyte species richness ( HSR ). The TSR and XSR showed a significant positive correlation with soil type and a significant negative correlation with available K. HSR was significantly correlated with soil type and negatively correlated with ammonium N.
Natural flow regimes are important for sustaining riverine vegetation. The regulation of river flows to provide water for agriculture often results in changes to flow timing. This study assesses the impact of altered seasonal flow patterns on riverine flora.
Within temperate Australia, we surveyed the vegetation of five lowland rivers, three of which have large dams that alter their seasonal flow patterns; the other two are unregulated. From four to six sites were selected on each river, and these were classified into three levels of regulation based on the extent to which the timing of their seasonal flow patterns were altered. Sites were surveyed in winter and the following summer. Permanent quadrats were also established at a number of the surveyed sites and resurveyed every 3 months.
Of the 267 plant taxa identified, 145 were exotic (non-native). More exotic taxa and fewer native taxa were associated with increasing level of seasonal flow inversion (regulation). In particular, greater numbers of short-lived exotic terrestrial taxa and fewer native woody taxa were associated with increasing level of regulation. Some exotic woody species (e.g. willows) were more common in the unregulated rivers and may have life-history traits favoured by the natural seasonal flow patterns of study area. Multivariate analyses showed that level of regulation had a significant effect on the overall composition of the riverine vegetation.
Our results provide support for the hypotheses that flow regulation adversely affects native species diversity and increases the vulnerability of riparian zones to invasion by exotic species; however, these effects are dependent on plant species' life-history strategies. Our study highlights the importance of natural seasonal flow patterns for sustaining native riverine plant communities. Flow management aimed at maintaining or restoring ecological values should consider seasonal flow patterns. Winter/spring flow peaks may be particularly important for the recruitment of native riverine plants, especially trees and shrubs, and reducing the extent of exotic annuals and grasses. Copyright
Pulsing storms and prolonged rainfall events have been associated to floods, soil erosion and nutrient fluxes in many European river catchments. This motivated us to develop a parsimonious approach to model the climate forcing on sediment yields in a mountainous Austrian–German river catchment. The hydro-climatologic forcing was interpreted by the novel RAMSES (RAinfall Model for SEdiment yield Simulation) approach to estimate the annual sediment yields. We used annual data on suspended-solid yields at the gauge Füssen, monitored from 1924 to 2003, and monthly rainfall data. The dataset was split into the period 1924–1969 for calibration and the period 1970–2003 for validation. The quality of sediment yield data was critically examined, and a few outlying years were identified and removed from further analyses. These outliers revealed that our model underestimates exceptionally high sediment yields in years of severe flood events. For all other years, the RAMSES performed well against the calibration set, with a correlation coefficient (r) equal to 0.83 and a Nash–Sutcliffe Index (NSI) of 0.69. The lower performance in the validation period (r = 0.61, NSI = 0.36) has to be partly attributed to discontinuities in the monitoring strategy. For the calibration dataset, monthly precipitations proved nonetheless to be better predictors for annual sediment yields than annual values. These first results lay the foundation for reconstructing intra- to inter-decadal variability of sediment yields in river catchments where detailed precipitation records are not available as well as for the reconstruction of historical sediment yields.
Plants in the water level fluctuation zone of the Three Gorges Reservoir Region disappeared due to winter-flooding and prolonged inundation. Revegetation (plantation and natural recovery) have been promoted to restore and protect the riparian ecosystem in recent years. Revegetation may affect soil qualities and have broad important implications both for ecological services and soil recovery. In this study, we investigated soil properties including soil pH values, bulk density, soil organic matter (SOM), soil nutrients and heavy metals, soil microbial community structure, microbial biomass, and soil quality index under plantation and natural recovery in the Three Gorges Reservoir Region. Most soil properties showed significant temporal and spatial variations in both the plantation and natural recovery areas. Higher contents of SOM and NO3-N were found in plantation area, while higher contents of soil pH values, bulk density, and total potassium were observed in the natural recovery area. However, there were no significant differences in plant richness and diversity and soil microbial community structure between the two restoration approaches. A soil quality index derived from SOM, bulk density, Zn, Cd, and Hg indicated that natural recovery areas with larger herbaceous coverage had more effective capacity for soil restoration.
Boltonia decurrens (Torrey and Gray) Wood (Asteraceae), a perennial species confined primarily to a 400-km stretch of the Illinois River floodplain, is threatened with extinction due to the destruction of its natural habitat. Construction of a system of levees along the Illinois River has altered flood patterns during the last 100 years, converting wet prairies and natural marshes into cropland. Remaining shore habitats have been modified by altered flooding regimes. The flood of 1993 exceeded 100-year records on the Mississippi River, but was much less severe on the Illinois River. A gradient of flood severity on the Illinois River, from the area of confluence with the Mississippi River to a site 267.5 km upriver, provided an opportunity to study the effects of flooding on the vegetation at three B. decurrens sites which experienced different flood regimes. A comparison of pre- and post-flood data (1991 and 1994) revealed that the flood altered site vegetation. Species richness declined in all three study areas by an average of 34% and species diversity declined at two sites (11% and 37%). Populations of B. decurrens increased in size at all three locations (5-, 10- and 400-fold) following the flood, with the greatest increase occurring at the two sites which had the most severe flooding. The results suggest that the removal of competing species by flood waters may be an important factor in maintaining populations of B. decurrens in the floodplain. © 1998 John Wiley & Sons, Ltd.
Changes in land use and vegetation cover affect various soil properties, including the soil organic carbon (SOC) pool and the transfer of atmospheric CO2 to terrestrial landscapes. In natural or quasi-natural conditions a reduction in biomass increases the risk of erosion, and can reduce the stored soil organic matter content. This can cause (i) consolidation of low levels of organic carbon stored in the soil; (ii) reduction in the levels of organic carbon because of the onset of erosion processes; and (iii) differing rates of recovery of the soil in response to environmental factors including precipitation, which is a principal agent of indirect recharge of soil organic matter.Few comparable studies have analyzed the reduction of SOC because of erosion, and assessed how this contributes to the loss of soil as vegetation cover decreases. This is particularly the case in semiarid Mediterranean environments, where erosion is one of the main causes of soil degradation.This study presents the results of an experiment carried out along a pluviometric gradient from humid to semiarid Mediterranean conditions, in southern Spain. The study involved two soil depths at five field sites having similar lithology, slope and aspect, but differ in vegetation cover and composition related to their location along the gradient. We used soil cation exchange capacity (CEC) as an indicator of soil degradation.The results showed that: a) SOC decreased with decreasing rainfall; b) SOC is greater at the soil surface than at depth; c) CEC is a good indicator of the degradation of soil surface formations, as it is directly related to the SOC storage capacity; and d) the so-called “Mediterranean mountain” landscape, with sparse and mixed vegetation composed of scrubland and woodland species, is a good organic carbon sink with direct implications in relation to climate change.
The biodiversity of microbial communities has important implications for the stability and functioning of ecosystem processes. Yet, very little is known about the environmental factors that define the microbial niche and how this influences the composition and activity of microbial communities. In this study, we derived niche parameters from physiological response curves that quantified microbial respiration for a diverse collection of soil bacteria and fungi along a soil moisture gradient. On average, soil microorganisms had relatively dry optima (0.3 MPa) and were capable of respiring under low water potentials (-2.0 MPa). Within their limits of activity, microorganisms exhibited a wide range of responses, suggesting that some taxa may be able to coexist by partitioning the moisture niche axis. For example, we identified dry-adapted generalists that tolerated a broad range of water potentials, along with wet-adapted specialists with metabolism restricted to less-negative water potentials. These contrasting ecological strategies had a phylogenetic signal at a coarse taxonomic level (phylum), suggesting that the moisture niche of soil microorganisms is highly conserved. In addition, variation in microbial responses along the moisture gradient was linked to the distribution of several functional traits. In particular, strains that were capable of producing biofilms had drier moisture optima and wider niche breadths. However, biofilm production appeared to come at a cost that was reflected in a prolonged lag time prior to exponential growth, suggesting that there is a trade-off associated with traits that allow microorganisms to contend with moisture stress. Together, we have identified functional groups of microorganisms that will help predict the structure and functioning of microbial communities under contrasting soil moisture regimes.
Enhanced development of gas-spaces beyond that due to the partial cell separation normally found in ground parenchymas and their derivatives creates tissue commonly termed “aerenchyma”. Aerenchyma can substantially reduce internal impedance to transport of oxygen, nitrogen and various metabolically generated gases such as carbon dioxide and ethylene, especially between roots and shoots. Such transport lessens the risk of asphyxiation under soil flooding or more complete plant submergence, and promotes radial oxygen loss from roots leading to oxidative detoxification of the rhizo-sphere. Aerenchyma can also increase methane loss from waterlogged sediments via plants to the atmosphere. This review of the formation and functioning of aerenchyma particularly emphasises research findings since 1992 and highlights prospects for the future. Regarding formation, attention is drawn to how little is known of the regulation and processes that create schizogenous aerenchyma with its complex cell arrangements and differential cell to cell adhesion. More progress has been made in understanding lysigenous aerenchyma development. The review highlights recent work on the processes that sense oxygen deficiency and ethylene signals, subsequent transduction processes which initiate cell death, and steps in protoplast and wall degeneration that create the intercellular voids. Similarities between the programmed cell death and its causes in animals and the predictable patterns of cell death that create lysigenous aerenchyma are explored. Recent findings concerning function are addressed in terms of the diffusion aeration of roots, rhizosphere oxygenation and sediment biogeochemistry, photosynthesis and ventilation, pressurised gas-flows and greenhouse gas emissions and aspects of ventilation related to secondary thickening.
Severe soil and water loss has led to widespread land degradation of the Loess Plateau, China. During the past two decades, significant efforts have been made to revegetate degraded soil in the region. However, a better understanding of the ability of plants to promote soil microbial processes is important for successful revegetation. The current study was conducted at the Dunshan watershed on the Loess Plateau, with the aim of evaluating the effect of different vegetation types on the microbial properties of rhizosphere soil. Six vegetation types were evaluated: two natural grassland (Artemisia capillaries and Heteropappus altaicus), two artificial (i.e. planted by humans) grassland (Astragalus adsurgens and Panicum virgatum) and two artificial shrubland (Caragana korshinskii and Hippophae rhamnoides) species; an area without vegetation cover was used as a control. The results indicated that the highest values of soil organic C, total nitrogen (TN), microbial biomass carbon (MBC), MBN, saccharase, urease, catalase and peroxidase were recorded for H. altaicus and A. capillaries; of basal respiration (BR), the MBN: TN ratio, alkaline phosphatase and polyphenol oxidase for A. adsurgens; and of the BR: MBC ratio for P. virgatum. A rhizosphere soil microbial index (RSMI) was obtained using principal component analysis, and metabolic quotient (BR/MBC), BR, urease, water-soluble C and cellulase were found to be most important for assessing rhizosphere soil quality. All revegetated soil showed higher RSMI compared with control soil, with soil under natural grassland species (H. altaicus and A. capillaries) recording the highest value. It was concluded that plant species under arid climatic conditions have different effects on the microbial properties of rhizosphere soil owing to their different root exudates and plant debris. In addition, natural grasslands are most effective for revegetation of the Loess Plateau.
The composition and structure of vegetation within riparian buffers prior to, and immediately post-harvesting in a managed radiata pine (Pinus radiata D.Don) forest is described and compared with riparian buffers in residual adjoining native forest on the Coromandel Peninsula, New Zealand. One hundred and twenty-one species (71% native) representing life forms from grasses to trees were recorded. The highest species richness, including both native and adventive (non-native) species, was found in riparian buffers in the post-harvest and native reference sites which had 18–25 species per site. Riparian buffers in mature pine plantations contained a mix of native species that was generally similar to, and not significantly reduced in species richness, from the reference native forest. Native species comprised 82–92% of the total cover in mature pre-harvest sites (irrespective of riparian width), and 99.8% in native reference sites. Compared with native forest the principal difference was a reduction of total cover in the upper tiers (5–12 m), and some increase in cover in the lower tiers. Adventive species in post-harvest sites comprised 16–67% of the total cover and were most frequently found in riparian areas highly disturbed by recent harvesting of the pines, particularly where riparian buffers were narrow or absent. Invasion by light-demanding adventives is expected to be temporary and most species are likely to be shaded out as the new rotation of pine trees develops. Radiata pine plantations in Whangapoua Forest can provide suitable conditions for the development of riparian buffer zones that will become dominated by native species, similar in richness and structure to neighbouring native forest.
A total of 30 surface sediments samples from the estuary wetland of the Tangxi River, Chaohu Lake Basin were obtained and
tested. Enrichment factor (EF) and geoaccumulation index (I
geo) as well as multivariate statistical analysis methods including Factor Analysis (FA) and Hierarchical Cluster Analysis (HCA)
were applied for the assessment of heavy metal pollution in surface sediments. The results of EF values show that the pollution of copper (Cu) and cadmium (Cd) occurs in the estuarine sediments, and that zinc (Zn), lead
(Pb) and chrome (Cr) may originate from crustal materials or natural weathering process. The mean EF values of the five heavy metals are in the decreasing order: Cu>Cd>Zn>Pb>Cr. Based on the I
geo of target heavy metals, the surface sediments collected from the study area can be approximately categorized as unpolluted
with Zn, Pb and Cr, and moderately polluted with Cu and Cd. The degree of heavy metal pollution decreases in the order of
Cu>Cd>Zn>Pb>Cr. Three groups of pollution factors are presented from FA: Zn-TOC, Cu-Cd and Cr-Pb, which respectively accounte
for 27.22%, 25.20% and 21.05% of variance. By means of HCA, a total number of seven groups are distinguished from 30 sampling
sites. Results indicate that Cu and Cd are the prior controlled pollutants in the estuarine sediments of the Tangxi River.
In order to reduce flood risk, river management policies advise floodplain restoration and the recreation of water retention
areas. These measures may also offer opportunities for the restoration of species-rich floodplain habitats through rewetting
and the restoration of flood dynamics. The potential to enhance biodiversity in such flood restoration areas is, however,
still subject to debate. In this paper we investigate whether flooding along a small altered lowland river can contribute
to the potential and realised species richness of semi-natural meadows. We compare the seed bank and vegetation composition
of flooded and non-flooded semi-natural meadows and test the hypothesis that flooding contributes to an input of diaspores
into the meadow seed banks, thereby promoting seed density and potential species richness. Furthermore we hypothesise that,
where habitat conditions are suitable, flooding leads to a higher realised species richness. Results showed that seed densities
in flooded meadows were significantly higher than in non-flooded meadows. The seed banks of flooded meadows also contained
a higher proportion of exclusively hydrochorous species. However, the seed bank species richness, as well as the species richness
realised in the vegetation did not differ significantly between flooded and non-flooded meadows. Finally, the seed bank and
standing vegetation of flooded sites showed larger differences in species composition and Ellenberg nitrogen distribution
than non-flooded sites. From these results we conclude that, although flooding does contribute to the density and composition
of the seed bank, most imported seeds belong to only a few species. Therefore, it is unlikely that flooding substantially
enhances the potential species richness. Furthermore, even if new species are imported as seeds into the seed bank, it seems
unlikely that they would be able to establish in the standing vegetation. However, it is unclear which factors impede the
establishment of imported species in the vegetation. The implications of our findings for flood meadow restoration are discussed.
Soil is increasingly under environmental pressures that alter its capacity to fulfil essential ecosystem services. To maintain these crucial soil functions, it is important to know how soil microorganisms respond to disturbance or environmental change. Here, we summarize the recent progress in understanding the resistance and resilience (stability) of soil microbial communities and discuss the underlying mechanisms of soil biological stability together with the factors affecting it. Biological stability is not solely owing to the structure or diversity of the microbial community but is linked to a range of other vegetation and soil properties including aggregation and substrate quality. We suggest that resistance and resilience are governed by soil physico-chemical structure through its effect on microbial community composition and physiology, but that there is no general response to disturbance because stability is particular to the disturbance and soil history. Soil stability results from a combination of biotic and abiotic soil characteristics and so could provide a quantitative measure of soil health that can be translated into practice.
A new “direct extraction” method for measuring soil microbial biomass nitrogen (biomass N) is described. The new method (fumigation-extraction) is based on CHC13 fumigation, followed by immediate extraction with 0.5 M K2SO4 and measurement of total N released by CHC13 in the soil extracts. The amounts of NH4-N and total N extracted by K2SO4 immediately after fumigation increased with fumigation time up to 5 days. Total N released by CHC13 after 1 day fumigation (1 day CHC13-N) and after 5 days fumigation (5 day CHC13-N) were positively correlated with the flush of mineral N (FN) in 37 soils that had been fumigated, the fumigant removed and the soils incubated for 10 days (fumigation-incubation). The regression equations were 1 day CHC13-N = (0.79 ± 0.022) FN and 5 day CHC13-N = (1.01 ± 0.027) FN, both regressions accounting for 92% of the variance in the data.In field soils previously treated with 15N-labelled fertilizer, the amounts of labelled N, measured after fumigation-extraction, were very similar to the amounts of labelled N mineralized during fumigation-incubation; both were about 4 times as heavily labelled as the soil N as a whole. These results suggest that fumigation-extraction and fumigation-incubation both measure the same fraction of the soil organic N (probably the cytoplasmic component of the soil microbial biomass) and that measurement of the total N released by CHC13 fumigation for 24 h provides a rapid method for measuring biomass N.
Plants can change soil biology, chemistry and structure in ways that alter subsequent plant growth. This process, referred to as plant-soil feedback (PSF), has been suggested to provide mechanisms for plant diversity, succession and invasion. Here we use three meta-analytical models: a mixed model and two Bayes models, one correcting for sampling dependence and one correcting for sampling and hierarchical dependence (delta-splitting model) to test these hypotheses. All three models showed that PSFs have medium to large negative effects on plant growth, and especially grass growth, the life form for which we had the most data. This supports the hypothesis that PSFs, through negative frequency dependence, maintain plant diversity, especially in grasslands. PSFs were also large and negative for annuals and natives, but the delta-splitting model indicated that more studies are needed for these results to be conclusive. Our results support the hypotheses that PSFs encourage successional replacements and plant invasions. Most studies were performed using monocultures of grassland species in greenhouse conditions. Future research should examine PSFs in plant communities, non-grassland systems and field conditions.
The Three Gorges Project has been subject to intense debates regarding its benefits and costs. The environmental impacts of this huge project have been an important focus of these debates since the project planning stage. After the operation of the Three Gorges Dam at full capacity at the end of 2008, new environmental and ecological issues are emerging. This paper gives a brief description of the Three Gorges Project and its environmental impact assessment process, as well as major efforts to control environmental problems brought about by the project. From the long and complicated evaluation process, it is clear that there are large uncertainties and competing opinions regarding the benefits and costs, especially the ecological and environmental ones, of the project even after great research effort. Emphasis here is given to the environmental challenges including: (1) water quality control; (2) water and sediment regulation; (3) biodiversity conservation in the riparian and aquatic ecosystems; (4) environmentally friendly dam operation and regional sustainable development. Opportunities often grow out of the challenges. The Three Gorges Project provides opportunities for grand-scale experiments on the environmental, ecological, and socio-economic impacts of large dams. Local, national, and international concerted efforts and concrete actions should be directed to the mitigation and control of the negative impacts as well as securing the positive contributions of the project across scales Yes Yes
Using canonical correspondence analysis (CCA), relationships were investigated between plant species composition and flooding characteristics, heavy metal contamination and soil properties in a lowland floodplain of the Rhine River. Floodplain elevation and yearly average flooding duration turned out to be more important for explaining variation in plant species composition than soil heavy metal contamination. Nevertheless, plant species richness and diversity showed a significant decrease with the level of contamination. As single heavy metal concentrations seemed mostly too low for causing phytotoxic effects in plants, this trend is possibly explained by additive effects of multiple contaminants or by the concomitant influences of contamination and non-chemical stressors like flooding. These results suggest that impacts of soil contamination on plants in floodplains could be larger than expected from mere soil concentrations. In general, these findings emphasize the relevance of analyzing effects of toxic substances in concert with the effects of other relevant stressors.