Article

Afforestation drives soil carbon and nitrogen changes in China: Soil C-N dynamics following afforestation

Authors:
  • Northwest A&F University; CAS
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Abstract

Afforestation has been proposed as an effective method of carbon (C) sequestration; however, the magnitude and direction of soil C and nitrogen (N) dynamics following afforestation are not well understood. This study was designed to examine soil C and N dynamics following afforestation and to determine how various factors affect soil organic C (SOC) and total N (TN) after land-use conversions through the compilation and analysis of published data from 61 individual studies (512 observations at 61 sites in China). This analysis showed that for different previous land uses, post-afforestation SOC, TN, and C/N ratio varied in diverse temporal patterns. The relationship of soil C-N coupling was related to land use prior to afforestation and forest age. At 0-100cm soil depths, SOC and TN increased at rates about 0·23 and 0·03gkg-1y-1, respectively, and the C/N ratio was about 0·19y-1. SOC and TN were significantly affected by tree species, forest age, and soil depth. SOC, TN, and C/N were negatively correlated with soil bulk density (p<0·01) and pH (p>0·05) but positively correlated with soil total phosphorus (p<0·01), soil moisture (p<0·01) and soil microbial biomass C (p<0·01) and N (p<0·01). Additionally, SOC and TN were higher for the mid-level humidity index in China and were also determined by precipitation, temperature, and forest age. These results highlight the importance of previous land use, tree species, soil depth, and forest age in determining soil C and N changes in a range of environments and land-use transitions.

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... However, scientists have only recently focused on the dynamics of the soil C pool after afforestation. The variation in the soil N stock is poorly understood (Bárcena et al., 2014;Gou et al., 2019), and the existing data on C-N interactions is mainly derived from short-term CO 2 enrichment experiments Deng and Shangguan, 2017), which are often not long enough to quantify the variation in N stocks in ecosystems (Deng and Shangguan, 2017). The overlooking of the soil N pool might hamper the accurate estimation of the soil C sequestration potential of afforestation and its contributions to global C and N cycling (Raheb et al., 2017). ...
... However, scientists have only recently focused on the dynamics of the soil C pool after afforestation. The variation in the soil N stock is poorly understood (Bárcena et al., 2014;Gou et al., 2019), and the existing data on C-N interactions is mainly derived from short-term CO 2 enrichment experiments Deng and Shangguan, 2017), which are often not long enough to quantify the variation in N stocks in ecosystems (Deng and Shangguan, 2017). The overlooking of the soil N pool might hamper the accurate estimation of the soil C sequestration potential of afforestation and its contributions to global C and N cycling (Raheb et al., 2017). ...
... Additionally, the retention of fine windblown particles in afforested sites due to the reduced wind speed and the disrupted large turbulent eddies by the shrub canopy could deliver extra C and N to the ecosystem (Wasson and Nanninga, 1986;Li et al., 2006;Zhao and Wang, 2019). The capture of fine materials by shrublands improves soil physicochemical properties, which favors the growth of herbaceous plants and eventually enhances ecosystem productivity and SOM inputs (Deng and Shangguan, 2017). ...
Article
Afforestation, as a key measure to curb land degradation and to drive the changes in soil C and N stocks and cycles, has been increasingly implemented in drylands worldwide. However, the long-term effects of this restoration practice on C accumulation in soil are still uncertain, especially because C-N interactions are poorly understood, which constrains the accurate assessment of potential soil C sequestration. In this study, we investigated the soil organic C (SOC) and soil total N (STN) storage in artificial shrublands in chronosequences in the Tengger Desert to address the hypothesis that afforestation with xerophytic shrubs significantly enhanced SOC and STN stocks in desert regions and that SOC and STN stocks would be positively correlated during the restoration processes. Our results showed that afforestation significantly enhanced SOC and STN accumulation. The SOC and STN stocks in 17-, 52- and 60-year-old artificial shrublands were 1.22, 2.67, 2.80 and 1.21, 2.33, 2.47 times greater than those in mobile sand dunes, respectively, with increased rates of 5.61 g C m⁻² yr⁻¹, 14.25 g C m⁻² yr⁻¹ and 13.30 g C m⁻² yr⁻¹ and 1.27 g N m⁻² yr⁻¹, 2.61 g N m⁻² yr⁻¹ and 2.50 g N m⁻² yr⁻¹, respectively. The significant enhancement of SOC and STN stocks primarily occurred in the upper 0–20 cm soil layer. SOC stocks were positively correlated with STN stocks and the C:N ratio, and the regression slopes increased with vegetation age, indicating a coupling relationship between SOC and STN stocks. Additionally, this finding suggests that the increase in STN stocks was slower than that of SOC during restoration, leading to an asynchrony in N supply and the demand and subsequent N limitations on SOC accumulation. It would take approximately 139 and 177 years to fully recover SOC and STN stocks in the 100 cm soil profile, respectively, in mobile sand dunes through afforestation with xerophytic shrubs in the Tengger Desert, which implied that afforestation-induced soil quality improvements were a long-term process and that soil conservation was a key issue in water-limited ecosystems; therefore, optimized management strategies are urgently needed.
... Vegetation restoration is considered to be a potentially useful strategy for controlling soil erosion and improving soil quality in arid and semiarid ecosystems [5][6][7]. The conversion of farmland to forests or grasslands has been shown to increase SOC by increasing C derived from new vegetation, thus simultaneously decreasing C loss from decomposition and erosion [8,9]. Thus, afforestation and revegetation have been proposed as effective methods for reducing atmospheric CO 2 due to C sequestration in soils. ...
... Soil physical-chemical properties have been extensively used to evaluate SOC; however, these properties usually change slowly, and thoroughly reflecting soil changes through these properties is impossible; thus, the selection of indicators that appropriately reflect the overall change in SOC is important. Previous studies have mainly focused on SOC dynamics during vegetation restoration [5], the effects of land use change and SOC [10,11], and C-N relations [9], as well as the effects of aspect-vegetation complexes on the decomposition of SOC [12]. Moreover, many studies have focused on the effects of soil microbes [13], soil enzyme activities [14,15], soil nutrients [16], soil aggregates and SOC fractions [17,18], Int. ...
... Usually, different vegetation types provide different surface residues and root distributions [33], leading to varied soil N content. For example, the patterns of soil N dynamics differed greatly among different tree species used in afforestation and depended on the transfer of soil organic matter (SOM) into soil via the roots of ground vegetation and litter decomposition [9]. Soils with different vegetation undergo different litter decomposition processes and rates, meaning that the release of N and P in soil differs [34]. ...
Article
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Vegetation restoration is considered a potentially useful strategy for controlling soil erosion and improving soil organic carbon (SOC) in arid and semiarid ecosystems. However, there is still debate regarding which vegetation restoration type is the best choice. In this study, four vegetation restoration types (i.e., grasslands, shrubs, forests and mixed forests) converted from sloping farmlands were selected to explore the SOC variation among the four types and to investigate which soil factors had the greatest effect on SOC. The results showed while the magnitude of effect differed between vegetation restoration type, all studied systems significantly increased SOC and labile organic carbon contents (p < 0.01), soil nutrients such as total nitrogen (TN) (p < 0.01), available nitrogen (AN) (p < 0.01), total phosphorus (TP) (p < 0.05) and available phosphorus (AP) (p < 0.05), soil enzyme activities such as phosphatase (p < 0.01), soil microbial biomass carbon (MBC) (p < 0.05), and basal respiration (BR) (p < 0.05), but had significant negative correlationswith polyphenol oxidase (p < 0.05). However, the effects of vegetation restoration of farmland converted to natural grasslands, shrubs, forests and mixed forests varied. Among the types studied, the mixed forests had the largest overall positive effects on SOC overall, followed by the natural grasslands. Soil nutrients such as N and P and soil microbial activities were the main factors that affected SOC after vegetation restoration. Mixed forests such as Robinia pseudoacacia and Caragana korshinskii are the best choice for farmland conversion on the central of the Loess Plateau.
... Soil organic carbon (SOC) content is recognized as the primary parameter of soil quality. SOC, soil total N (TN), soil total P (TP), soil total K (TK), and pH are critical for carbon pool, soil fertility, and land recovery Deng & Shangguan 2017;Qiu et al. 2018). The influences of reforestation on soil physiochemical parameters have been studied for decades, and the conclusions are inconsistent due to different influential elements such as history of land use, soil types, tree species, and forest age (Guo & Gifford 2002;Laganiere et al. 2010;Deng & Shangguan 2017). ...
... SOC, soil total N (TN), soil total P (TP), soil total K (TK), and pH are critical for carbon pool, soil fertility, and land recovery Deng & Shangguan 2017;Qiu et al. 2018). The influences of reforestation on soil physiochemical parameters have been studied for decades, and the conclusions are inconsistent due to different influential elements such as history of land use, soil types, tree species, and forest age (Guo & Gifford 2002;Laganiere et al. 2010;Deng & Shangguan 2017). A global meta-analysis revealed that soil C, N, and available P stocks increased since forestation (Li et al. 2012a), but it had no coherent effect on total P . ...
... The addition from plant inputs, atmospheric and symbiotic nitrogen fixation, might be the reason behind the increase of SOC and TN after restoration. Our findings of increase of SOC and TN after restoration are in agreement with most of the previous studies (Paul et al. 2002;Li et al. 2012b;Deng & Shangguan 2017) but differed from a meta-analysis where no significant increase of TN was found after afforestation (Li et al. 2012b). Many factors have been found to affect SOC and TN dynamics following afforestation, including former land use, climate, soil property, tree species planted, fertilizer application, and N 2 fixation (Paul et al. 2002). ...
Article
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Afforestation has been an important approach to mitigate land deterioration and biodiversity reduction. Soil microbes play a crucial role while interacting with plants and mediation of ecosystem functions, there are increasing interests in understanding the responses of soil microbial communities under long‐term forest restoration. Here we examined the effects of four forests (Acacia species (AM), Eucalyptus species (EE), mixed coniferous species (MC), mixed native species (NS)) after 35‐year restoration on soil environmental factors and soil microbial communities. Combining with previous data of soil physicochemical property in four plantations (1986‐2015), our results suggested that afforestation significantly increased soil organic carbon (SOC) and total N while decreased soil pH. Among the four forest types, there were significant differences for total N and total K but not for pH, soil organic C and total P. Bacterial species richness and phylogenetic diversity in Acacia forest significantly declined than those of other forests, but those of fungal communities were remarkably higher in the Acacia forest. Both the bacterial and fungal communities’ structure of each forest were strongly related to soil TK and TP. Besides, TK and SOC were primary edaphic properties that respectively affected the distribution pattern of bacterial and fungal communities in four forests. Network structures in Acacia forest and mixed coniferous forest compared with Eucalyptus forest and NS were more complex and closely linked, hence more resistant to extrinsic interference. Our results demonstrate that reforestation altered soil properties and microbial communities during long‐term restoration, which may provide insight into ecological restoration practices and biodiversity maintenance. This article is protected by copyright. All rights reserved.
... Our results suggested the bulk soil C-acquiring (BG and CHB) and N-acquiring enzymes (NAG and LAP) showed an increasing trend with stand age, peaking in the 59-yr plantation. The reason for this phenomenon was that the input of more litter from the older plantation provided a richer substrate for microbial metabolism and decomposition (Deng and Shangguan, 2017;Deng et al., 2018), and higher soil moisture enhanced microbial activity, thereby producing more C-and N-acquiring enzymes (Cui et al., 2021a(Cui et al., , 2021b. Differently, the fluctuating changes of EEAs in the rhizosphere soil suggested that rhizosphere metabolism had an impact on the synthesis of extracellular enzymes. ...
... However, changes in microbial metabolic C-limitation were also the result of the combined effects of plants, soil, and microorganisms . Compared with mobile dunes, long-term plant carbon input improves the soil C pool and nutrient content, which provides protection for microbial colonization and growth (Deng et al., 2017). Microorganisms produce extracellular enzymes to catalyze the mineralization of SOC and convert nutrients from organic to inorganic forms (Demisie et al., 2014). ...
Article
The resource acquisition strategy of soil microorganisms can be reflected by soil extracellular enzyme activity (EEA). However, there are few reports on the application of extracellular enzyme stoichiometry (EES) method to study the difference in microbial metabolic nutrient limitation between rhizosphere and bulk soil. Here, we choose the rhizosphere and bulk soils of Pinus sylvestris var. mongolica (P. sylvestris) plantations with five stand ages in the Mu Us sandy land, and analyzed the variation and differences of microbial metabolic limitation between rhizosphere and bulk soils with stand age by EES method. The results showed that the microbial metabolic C-limitation in the rhizosphere and bulk soil gradually increased with stand age. Almost all the vector angles were less than 45°, which indicated that the soil microbial metabolism was relatively limited by N rather than P. Furthermore, the microbial C- and N-limitation in rhizosphere soils were generally stronger than bulk soils. Soil physical properties (59.73%) explained most of the variations in soil EES based on the variation-partitioning analysis, followed by total nutrients (43.00%). The partial least squares path model suggested that the main driving factor for the variation of soil microbial metabolic C-limitation in the rhizosphere and bulk soils was physical properties, while the microbial N-limitation was for total nutrients. In general, the study emphasized the application of EES methods to assess the dynamic equilibrium between soil microbial resource acquisition and nutrient availability in desert ecosystems. These insights provide guidance for formulating afforestation strategies, such as nutrient management of sandy plantations.
... Shrub is more extensively used for desertification restoration than herb and tree, because shrub has more positive interspecific interaction and lower inter-species competition cost, as well as the better ability of improving the microclimate and soil fertility (Gómez-Aparicio, 2009;Yoshihara et al., 2010). The recovery of vegetation and soil physicochemical properties is very critical for evaluating ecological restoration projects, and has a meaningful impact on future grassland management (Deng and Shangguan, 2017;Hu et al., 2018). SWC, soil organic matter (SOM), N, P (phosphorus), K (potassium), macro-and micro-nutrients are more abundant at understory than at interspace in many shrub-dominated ecosystems (Bochet et al., 1999;Navarro-Cano et al., 2014;Navarro-Cano et al., 2015). ...
... Many experiments had shown that the establishment of shrubs could improve the soil nutrient status around the shrubs (Mcclaran et al., 2008;Deng and Shangguan, 2017;Hu et al., 2018), which was confirmed in our experiment. The litter from shrub was generally deposited around the shrub, where the soil nutrients were locally enriched by the microbial litter decomposition (Brantley and Young, 2008;Buckeridge et al., 2010). ...
Article
Salix cupularis is a common shrub for ecological restoration of the desertified alpine meadow on the Tibetan Plateau. However, the effect of S. cupularis on spatial heterogeneity of soil resources (i.e., resource islands effect) has not been systematically evaluated, and the influence of shrub patches on the rehabilitation of understory herbs has also been unknown. In this study, we randomly selected S. cupularis individuals in the early restoration stage of desertified alpine meadow, where the three native forages (Elymus nutans, Elymus sibiricus and Festuca sinensis) were sown at different microsites around S. cupularis to explore the effects of S. cupularis on soil resources and emergence rates of the native forages. The results showed that S. cupularis significantly increased SWC (soil water content), C (carbon) and N (nitrogen) nutrients (p < 0.01) and enzyme activities (p < 0.05) under canopy compared with the bare land, and the improvement performed better in the topsoil (0–5 cm) than in the subtop-soil (5–15 cm). Moreover, the soil properties were affected significantly by microsites around S. cupularis, resulting in regular changes of SWC, nutrients and enzyme activities in different microsites (Shrub center > Middle of canopy radius > Bare land). In addition, there are significant regression relationships between emergence rates and enriching soil water, C and N nutrients, so the emergence rates of native forages under canopy may be improved significantly with the enriched soil resources, especially for E. nutans. As a result, S. cupularis is a suitable pioneer shrub for the vegetation restoration of desertified alpine meadow on the Tibetan Plateau, because it could not only shape the enrichment of soil resources under canopy, but also facilitate emergence of companion forages in the process of vegetation restoration.
... Further, these temporal recovery dynamics can vary between climate zones, ecosystems, soil layers and levels of initial soil C (Shi et al. 2013, Deng et al. 2014, Shi et al. 2016, Deng and Shangguan 2017, Ren et al. 2017a). However, it remains unknown what are the restoration patterns of belowground EMF and which functions are key in determining EMF recovery following cropland conversion across China. ...
... As restoration time extended up to 100 years, soil EMF was steadily increased, implying that chronic restored ecosystems are able to attain a greater overall functioning on soil C, N and P cycling (Ren et al. 2017b). This time-dependent restoration in EMF was greater in moist than dry environments (Fig. 4), which is supported by former restoration studies revealing the positive effect of precipitation on the restoration of soil nutrient cycling processes (Deng et al. 2014, Deng andShangguan 2017). However, a decrease in EMF restoration with increasing initial SOC means less recovery room for EMF at those sites with higher initial SOC. ...
Article
Full-text available
Ecological restoration is essential to reverse land degradation worldwide. Most studies have assessed the restoration of ecosystem functions individually, as opposed to a holistic view. Here we developed a network‐based ecosystem multifunctionality (EMF) framework to identify key functions in evaluating EMF restoration. Through synthesizing 293 restoration studies (2900 observations) following cropland abandonment, we found that individual soil functions played different roles in determining the restoration of belowground EMF. Soil carbon, total nitrogen and phosphatase were key functions to predict the recovery of belowground EMF. On average, abandoned cropland recovered about 19% of EMF during 18 years. The restoration of EMF became larger with longer recovery time and higher humidity index, but lower with increasing soil depth and initial soil carbon. Overall, this study presents a network‐based EMF framework, effectively helping to evaluate the success of ecosystem restoration and identify the key functions.
... Conversely, changes in soil nutrient storage and stoichiometry will affect ecosystem functions and processes. A clear evaluation of soil nutrients in ecological restoration areas is essential for understanding the ecological consequences of mixed afforestation and may have meaningful implications for long-term nutrient availability and the sustainable management of plantations [8]. ...
... It can be seen that a reasonable mixing mode can effectively improve the soil nutrient status. However, the current research on the effect of mixed afforestation mainly focuses on the changes in nutrient content [8]. In terms of soil nutrient availability, nutrient cycling, and balance mechanisms, understanding of the impacts on SOC, TN, and TP storages and their ecological stoichiometric characteristics also need to be strengthened. ...
Article
Full-text available
Mixed-species tree plantations have additional ecological benefits over single-species tree plantations, such as habitat restoration and increasing biodiversity. However, changes in the soil carbon, nitrogen, and phosphorus storages and stoichiometry after mixed afforestation with the N-fixing tree species under the “Grain for Green Project” in the Loess Plateau of China are not well understood. Typical restoration types, including the mixed plantations of Pinus tabuliformis with Hippophae rhamnoides (HrPt) and Robinia pseudoacacia with H. rhamnoides (HrRp), as well as the pure forests of P. tabuliformis (Pt) and R. pseudoacacia (Rp), were chosen to examine changes in the storages and stoichiometry of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in 0–100 cm soil layers. The results showed that compared with the corresponding pure forest, HrRp significantly increased the SOC content in the 0–20 cm soil layer and the SOC storage in the 0–100 cm layer, while HrPt significantly increased the SOC content in the 0–10 cm layer, but there was no significant difference for SOC storage in the 0–100 cm layer between Pt and HrPt. Similarly, HrRp significantly increased the TN content in the 0–10 cm layer and the TN storage in the 0–100 cm layer, but there was no significant difference in TN storage between Pt and HrPt. Furthermore, HrRp significantly increased the TP content in the 0–100 cm layer and TP storage was higher than that of Rp, while there were no significant differences in TP content and storage between Pt and HrPt. In the 0–10 cm soil layer, HrRp significantly reduced C:N and increased N:P, but HrPt significantly increased C:P. In addition, compared with the pure forest, the soil physical and chemical properties had a stronger control effect on the soil storages and stoichiometric ratios in the mixed forests. In summary, compared with P. tabuliformis, the introduction of N-fixing tree species into the R. pseudoacacia forest was more conducive to the accumulation of SOC, TN, and TP reserves and the improvement of the N and P utilization efficiency. These results have important implications for the restoration of degraded vegetation and scientific management of mixed plantations on the Loess Plateau and can provide basic data for the assessment of soil quality at the regional scale.
... Aggregate-associated organic carbon can respond quickly to land-use changes and can usually indicate changes in nutrients and structure of soils (Nie et al., 2014). Generally, afforestation changes the fractions of soil aggregates, with an increase in the coarse fraction and a decrease in the fine fraction, and drives the accumulation of soil C, mainly in macroaggregates (Qiu et al., 2015;Zhang et al., 2020), due to less disturbance, more organic matter inputs, and lower decomposition compared to other land uses (e.g., farmland) (Deng and Shangguan, 2017;Rahman et al., 2017;Zhang et al., 2018). The majority of soil OC is concentrated within aggregates, which can physically protect microbial decomposition and mineralization (Liu et al., 2020;Von Lutzow and Kogel-Knabner, 2009). ...
... However, the effects of long-term afforestation on OC mineralization in aggregates have not been well examined (Feng et al., 2018), which is critical for understanding OC sequestration and dynamics in forest soil. Moreover, it has been reported that OC in bulk soils and aggregates is sequestered during the beginning stage of afforestation and then becomes stable after several decades of afforestation (Deng and Shangguan, 2017;Zhang et al., 2018). Whether soil OC mineralization changes with afforestation age, however, is not yet clear (Rahman et al., 2017). ...
Article
The conversion of land use from agricultural land to forests is considered an effective measure of mitigating atmospheric CO2, but the impacts of long-term afforestation on soil organic carbon mineralization (Cm) and its temperature sensitivity (Q10) remain uncertain. In this study, we aimed to investigate the effects of different afforestation ages on OC contents and Cm and Q10 in bulk soils and aggregates. Soils were collected from 0–10 cm and 10–20 cm depths in afforested woodlands after 10, 20, 30 and 40 yrs of establishment of Robinia pseudoacacia on abandoned farmlands on the Loess Plateau, China. Cm and Q10 were measured in an 83-day incubation experiment at 25 °C and 15 °C. The results showed that long-term afforestation accelerated soil OC accumulation but decreased its Cm and Q10 in bulk soils and aggregates, and the effects were greater at the 0–10 cm soil depth. Macroaggregates contributed most of the OC content (62%), but microaggregates and silt + clay contributed most of the OC mineralized (40% and 36%) in the bulk soils. The increased OC content and decreased Cm in aggregates suggested an increase in the sequestration of OC in fine soil particles. The temperature sensitivity of OC mineralization increased with increasing particle size, with a higher Q10 value for macroaggregates (1.81 ± 0.44) than for microaggregates (1.42 ± 0.35) and silt + clay (1.31 ± 0.14). Our results indicated that long-term afforestation would be conducive to the accumulation of OC and would decrease the release of CO2 from soils under future climate warming scenarios. The findings highlighted the OC dynamics in abandoned farmland were more sensitive to the temperature changes than those in forests, and the stability of OC in aggregates increased as the aggregate size decreased. This study contributed to bridging current knowledge gapes about the process underlying the observed OC budget and its response to warming scenarios in rehabilitated ecosystems.
... Whether afforestation can increase the SOC storage and its stability to environmental variations is controversial. The stability of SOC to temperature and humidity has been one of the major research topics owing to their direct relations to land-use change and global climate change (Deng and Shangguan, 2017). Until now, respiratory efflux of SOC decomposition and its sensitivity to temperature and humidity are not fully understood by the well-designed experiment in shelterbelt farmland afforestation, which are essential for understanding the ecological significance in forest ecosystems in comparison with others (Hao et al., 2017;Jiang et al., 2017;Luyssaert et al., 2008). ...
Article
Shelterbelt farmland afforestation has been well-reported in its wind-break and climate regulation function, but less is on underground-soil organic carbon (SOC) sequestration and environmental stability. In this paper, we collected 180 soil samples from soil depths of 1 m (0–20, 20–40, 40–60, 60–80, 80–100 cm) in the farmland and neighbor shelterbelts in Songnen Plain, northeastern China. The sample plots covered six regions in the study area. SOC concentration and respiration decomposition rate, Q10 (temperature sensitivity), Hs (humidity sensitivity) were determined in the laboratory cultivation. Soil properties (N, P, K, electrical conductivity-EC, pH) and geographic-climate factors (multiple-year mean annual temperature and precipitation, MAT&MAP; temperature and precipitation during sampling month, MT &MP) were used to reveal the underlying reason for the changes in soil carbon sequestration. The results showed no significant difference in SOC respirational decomposition rate between farmland and shelterbelt forests but a 15.8% higher SOC concentration in shelterbelt forests (p < 0.05). The poplar shelterbelts reduced the Q10 value by 15.4% (p < 0.05), with deeper soils a more significant reduction in Q10. With soil moisture increases, both shelterbelt forests and farmland showed an obvious respiration pattern of first-increasing-then-decreasing. No significant Hs (linear gradients) differences were found in farmland and shelterbelt forests. Partitioning of the RDA ordination-based variation showed that SOC stability (Hs and Q10) of farmland was more affected by geo-climate. In contrast, the SOC stability of shelterbelt forests was greatly influenced by soil properties. Our findings manifest that the above-mentioned SOC changes can improve shelterbelt forest carbon sequestration function by prolonging the SOC lifespan in soil by at least 7% and SOC concentration by >15%. This should be included in the future to assess the underground soil carbon impact of Three-North shelterbelts in China and provide data supports for the estimation of similar forest stands in other parts of the world.
... Already 62 million hectares of current forests have been plantations until 2008, occurring for the largest percentage of the world's afforestation, according to the seventh national forest resource inventory report (2004)(2005)(2006)(2007)(2008) (Deng and Shangguan, 2017;Li et al., 2018c). The growth of newly planted forests could make further greening more significant. ...
Article
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Quantifying the drivers of terrestrial vegetation dynamics is critical for monitoring ecosystem carbon sequestration and bioenergy production. Large scale vegetation dynamics can be observed using the Leaf Area Index (LAI) derived from satellite data as a measure of “greenness”. Previous studies have quantified the effects of climate change and carbon dioxide fertilization on vegetation greenness. In contrast, the specific roles of land-use-related drivers (LURDs) on vegetation greenness have not been characterized. Here, we combined the Interior-Point Method-optimized ecosystem model and the Bayesian model averaging statistical method to disentangle the roles of LURDs on vegetation greenness in China from 2000 to 2014. Results showed a significant increase in growing season LAI (greening) over 35% of the land area of China, whereas less than 6% of it exhibited a significantly decreasing trend (browning). The overall impact of LURDs on vegetation greenness over the whole country was comparatively low. However, the local effects of LURDs on the greenness trends of some specified areas were considerable due to afforestation and urbanization. Southern Coastal China had the greatest area fractions (35.82% of its corresponding area) of the LURDs effects on greening, following by Southwest China. It was because of these economic regions with great afforestation programs. Afforestation effects could explain 27% of the observed greening trends in the forest area. In contrast, the browning impact caused by urbanization was approximately three times of the greening effects of both climate change and carbon dioxide fertilization on the urban area. And they made the urban area had a 50% decrease in LAI. The effects of residual LURDs only accounted for less than 8% of the corresponding observed greenness changes. Such divergent roles would be valuable for understanding changes in local ecosystem functions and services under global environmental changes.
... Our results con rm that afforestation with pine, carried out to consolidate mountain slopes and reduce erosion phenomena, induced profound changes in the soil characteristics and C sequestration rate, which was in accordance with previous research results (Ono et al. 2011;Deng et al. 2017). In fact, in the investigated Mediterranean area, pine forests signi cantly increased the amount of soil OM and the soil C and N pools compared to shrublands. ...
Article
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Plant cover and microclimatic conditions can profoundly alter the balance between productivity and decay, with relevant effects on soil carbon (C) and nitrogen (N) pools. Despite their importance, the combined effects of plant cover and microclimatic conditions on soil C and N pools have been poorly assessed, especially in the Mediterranean environment. Therefore, the aims of the present study were to assess how, in Mediterranean areas, C and N pools differ between afforested pine forests and natural shrublands and to highlight the different impacts of plant cover on C and N sequestration at low and high elevations Along a forest floor-mineral soil continuum, plant cover and elevation effects were evaluated through measurements of C and N pools and water-soluble fractions, molecular characterization by ¹³C and ¹H NMR, and microbial and fungal amounts and activities. Our data show that C accumulated more in afforested pine forest soils than in shrubland soils, especially at low elevations. In pine forests, the higher content of aromatic and O alkyl compounds in the upper organic layers and the abundance of aromatic and carboxylic components in the soluble fraction suggest a greater stability of soil organic matter than in shrublands. Additionally, the high concentration of N in the upper organic layer and its reduction in the fermentative layer stimulate soil C accumulation mainly in pine forests at low elevations. The abundant organic mass at high elevations in pine forests improves microbial growth, whereas the greater recalcitrance of organic residues at low elevations in pine forests leads to a decrease in the bacterial component compared with the fungal component. In conclusion, the plant cover effect appears to be strongly conditioned by elevation, and afforestation with pine at low elevations could favour long-term soil C storage.
... 3-North Shelter Forest Project), which have produced actively ecological and environmental benefits (Deng et al. 2014;Bryan et al. 2018;Chu et al. 2019). These projects have significantly increased the vegetation coverage and primary productivity of ecosystems in northwest and north China and improved soil physical-chemical properties , enriched the soil carbon pool (Deng et al. 2014;Deng and Shangguan 2017;Chu et al. 2019) and changed the biogeochemical cycles of C, N and P and their stoichiometric characteristics (Hu et al. 2018;Zhang et al. 2020b). The Mu Us Desert is a typical restoration area in northwest China where herbaceous plants, such as A. ordosica, were randomly established with aircraft seeding. ...
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PurposeVegetation restoration is an effective measure for improving the function of soil ecosystems and promoting the biogeochemical cycling of carbon (C), total nitrogen (TN) and total phosphorus (TP). Here, we aimed to quantify the fine-scale (pedon scale) spatial distribution of soil C, N, P and soil physical–chemical properties in the Mu Us Desert ecosystems.Methods We systematically evaluated the effects of A. ordosica on fine-scale (pedon scale) spatial distribution of C, TN, TP, soil-available nutrients, and liable organic carbon (LOC) and their stoichiometric characteristics in the semiarid Mu Us Desert in the 0–100-cm soil profiles at various distances from the plant.Results and discussionThe results demonstrated that soil organic carbon (SOC), TN and LOC were decreased with increasing distance from the plant and soil depth. SOC stocks at 20 cm were 16.98% higher than those at 120 cm from the plant. SOC stocks at 20, 60 and 120 cm from the plant were increased by 71.62%, 58.14% and 46.72% compared with shifting sandy land (Sland), respectively. Microbial biomass carbon (MBC) and readily oxidised organic carbon (ROOC) were significantly affected by different soil layers and distances and their interaction (p < 0.05), whereas dissolved organic carbon (DOC) was affected by the soil layers. TN and soil-available nutrients in the surface layer and at closer distances to the plant were higher than those in the sublayer and Sland. The ratio of C:N:P was generally decreased with different distances from the plant and different soil layers. The ratios of soil C:N, C:P and N:P were significantly different at different soil layers, whereas the ratios of soil C:P and N:P were significantly different at different distances from the plant (p < 0.05). Soil C:P ratio was positively correlated with soil C:N and N:P ratios (p < 0.001). N and P contents in leaves were higher than those in roots, branches and litter, but C contents in leaves were lower than those in other plant tissues and litter (p < 0.01). N:P ratio in leaves (13.94) showed that there was a shortage of N and P in the Mu Us Desert ecosystems.Conclusions We concluded that A. ordosica could enhance the accumulation of SOC, LOC and N on a fine scale and improve mineral-nutrient availability in semiarid deserts and, as a result, the function of soil ecosystems could be improved. Moreover, the limitation of N and P can be alleviated by adding additional N and P.
... The vegetation impacted by human activities had a degradation trend from 1990 to 2001 and an increase after 2001, with 93% of this improved trend being linked to human activity [48]. Increasing vegetation cover not only increases soil organic carbon and total nitrogen, but also enhances ecosystem services, lessens soil erosion, and modifies regional climate [49,50]. This is supported by the improvement in climatic conditions from 2002 to 2013 [48] and the decreased trend of drought area at multiple time scales (Figures 3b and 4). ...
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Long-term drought variation provides a scientific foundation for water resource planning and drought mitigation. However, the spatiotemporal variation characteristics of drought in northeast China (NEC) are unclear. We conducted a comprehensive assessment of drought status and trends based on the Standardized Precipitation Evapotranspiration Index (SPEI) in NEC from 1990 until 2018. The findings show that: (1) the drying trend peaked in 2001, and then exhibited a miti-gation tendency before drying again after 2013. The implementation of ecological restoration projects is primarily responsible for drought mitigation. (2) The areas with wetting and drying trends in the future would cover 86% and 17% of NEC, respectively. (3) There is a time lag between improved vegetation and the trend shift from dry to wet. (4) Spring and winter revealed wet trends within 71% and 84% of NEC, respectively, showing high sensitivity and resilience to drought, while 92-93% of NEC displayed dry tendencies during the summer and autumn seasons. The drought-affected area was the highest in summer and lowest in autumn. (5) The interannual drought severity was highest in May and June. (6) The highest drought impacts and trends occur within shrub and grass and sparsely vegetated land, as well as middle-temperate semiarid regions (M-semiarid). (7) The warmer the temperature zone, the more sensitive it is towards drought under the same hydrological conditions, showing a high drought-affected area. The drier the land, the higher the drought-affected area within the same temperature zone, with pronounced drought trends during the spring and summer seasons. Our findings highlight the need for the government to more explicitly develop drought mitigation strategies in accordance with NEC's spatiotemporal drought variations and specifically the need to concentrate on droughts in M-semiarid regions occurring in summer, particularly in May and June.
... Land use change can adversely affect ecosystems and the ecosystem services which they provide. These include carbon sequestration, soil quality, water regulation, and climate regulation (Defries, Foley, and Asner 2004;Laganiere, Angers, and Pare 2010;Sauer et al. 2012;Deng, Wang, and Li et al. 2014;Deng and Shangguan 2016). Global climate regulation is perhaps the most important ecosystem service, including sequestration or emission of greenhouse gases (Perrings et al. 2011). ...
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Complex and diverse land use and land cover patterns play a significant role in global carbon regulation. Southern China accounts for over 65% of China’s total carbon sink. But in Xishuangbanna (in Southern China), rubber plantations (Hevea brasiliensis) are expanding rapidly. Therefore, there is an urgent need to understand and monitor land use change, land use cover and how spatial variation affects carbon storage capacity. This is vital for the formation and implementation of better land use management practices. We studied land use and land cover changes over a 22-year period; addressing how these changes have affected the carbon storage capacity of a diverse landscape in Southern China. We used remote sensing methods to quantify changes in land cover of different types between 1988 and 2010. We used the Integrated Valuation of Ecosystem Services and Tradeoffs model to calculate changes in carbon storage across the landscapes of Xishuangbanna. Our analysis showed that between 1988 and 2010, the rate of deforestation accelerated to 203.2 km2 y−1. Approximately 23% of natural forests were lost during this period. Conversion of natural forest to rubber plantations was responsible for 78% of this deforestation. Rubber plantations expanded at a rate of 153.4 km2 y−1. Changes to land cover drove a temporal reduction in carbon storage across the whole landscape of 0.223 Tg C/km2. Local stakeholders have strong economic interest in converting land to more profitable crops and plantations. Government efforts will be required to control land use conversion through new policies and incentives to retain natural forest cover. Assessment of specific potential land use change will be required in order to avoid promoting the conversion of high carbon storage land uses to low carbon storage land uses.
... China's Loess Plateau, with an area of 6.24 × 10 5 km 2 , experiences severe soil erosion and land degradation (Chen et al., 2007). The Chinese government implemented an ecological afforestation project, converting cropland to woodland to rehabilitate degraded land (Deng and Shangguan, 2017). A variety of leguminous trees were planted in cropland at different times (Qiu et al., 2010), providing an ideal experimental platform for examining how agricultural land-use change affects soil OC and N cycling at different spatial and temporal scales. ...
Article
Afforestation on abandoned cropland has great potential to increase soil organic carbon (OC) and nitrogen (N). Identifying the effect of afforestation on mineralization of OC and N as well as their temperature sensitivity at large spatial and temporal scales is essential to understand soil OC and N dynamics. In this study, we measured mineralization of soil OC and N at standard temperatures (15 and 25 °C) by laboratory incubation, and calculated their temperature sensitivity (Q10). Soil samples were collected from cropland (0 years, selected as a control) and adjacent woodlands with different afforestation age (10, 20 and 30 years) at five sites from north to south on China’s Loess Plateau. The objectives were to understand how long-term afforestation affects OC and N mineralization and their Q10 and whether such effects depend on afforestation age and soil texture. The results showed that afforestation increased OC and N mineralization, but this effect was not affected by afforestation age (10–30 years). The Q10 of OC and N mineralization increased in the first 10 years of afforestation but decreased in the late stage. Furthermore, the increases of OC and N mineralization by afforestation were higher at sites with fine-textured soils than those at sites with coarse-textured soils. However, the Q10 increased at sites with a relatively high sand content but decreased or remained unchanged at sites with a relatively high clay content. The changes in OC and N mineralization and their Q10 were related to soil OC and N contents, pH and clay content. Overall, we concluded that long-term afforestation would contribute to the stability of soil OC and N in afforested ecosystems. Soil texture is an important factor controlling OC and N mineralization and their Q10, and should be considered when predicting soil OC and N dynamics in response to temperature change in different landscapes.
... Relative to the cropland, SOCD and POCD significantly increased under both managed and natural vegetation restoration after approximately 15 years of cropland abandonment (Fig. 2a). The average accumulation rate of SOC following vegetation restoration in our study was relatively higher than the average value in China (Deng and Shangguan, 2017) or the world (Li et al., 2012). This result is consistent with that reported previously at the catchment scale (Hu et al., 2018b). ...
Article
Vegetation restoration has been proposed as an effective strategy for increasing soil organic carbon (SOC) sequestration. However, the responses of SOC to managed and natural vegetation restoration strategies at a large scale are poorly understood due to the varying SOC components and changing climatic conditions. Here, we measured bulk SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MOC) after 15 years of vegetation restoration along an elevation gradient with a corresponding temperature gradient in the calcareous soils of karst region, Southwest China. We compared managed plantation forest and naturally recovered shrubland vegetation restoration strategies, using cropland and mature forest as references. Overall, we found that the SOC and POC densities in both plantation forest and shrubland were significantly higher than in the cropland but lower than in the mature forest. There were no significant differences in the SOC pool between the plantation forest and shrubland. Furthermore, the relative changes in the SOC and POC densities increased with increasing mean annual temperature in the plantation forest and shrubland. Our results showed that both vegetation restoration strategies, characterized by higher soil microbial abundance and exchangeable Ca concentration, were beneficial to POC but not MOC accumulation, and sufficiently compensated SOC decomposition at lower elevation with higher MAT. Our results highlight the potential of both vegetation restoration strategies for promoting SOC accumulation in warmer karst regions and emphasize the necessity to understand soil carbon stabilization mechanisms in calcareous soils.
... Afforestation is a restoration technique that aims to recover degraded ecosystems by increasing vegetation cover and biodiversity. Ultimately, this will positively impact the restored area's ecosystem functions and services (e.g., Deng and Shangguan, 2017; P.J. Yu et al., 2018;Z.Q. Yu et al., 2018). ...
Article
Long-term afforestation has important implications on soil properties and quality in semi-arid areas. A large-scale afforestation project has been carried out in the Loess Plateau in the last 20 years. This work aims to study the afforestation (Robinia pseudoacacia, Caragana korshinskii and natural grassland recover 10, 20, 30, and 40 years after) impacts on soil properties and quality. The results showed that coverage and root biomass (RB) was the highest 30 years after the restoration in Robinia pseudoacacia and Caragana korshinskii treatments, while the highest 40 years post-restoration in natural grasslands. Sand content and BD showed the highest values 10 years post afforestation in all study areas. Clay, Silt, mean weight diameter (MWD), and geometric mean diameter (GMD) in Robinia pseudoacacia, Caragana korshinskii had the highest values 30 years after the afforestation, while in natural grasslands, this was observed 40 years after. In Robinia pseudoacacia, Caragana korshinskii treatments, soil moisture content (SMC) reached the highest levels 30 years post afforestation at 20-40 and 40-60 cm. Regarding natural grasslands, SMC had the highest values 40 years post-afforestation. Sand content and BD increased with soil depth, while the opposite was identified in RB, clay, silt, MWD, GMD and SMC. In Robinia pseudoacacia and Caragana korshinskii treatments, soil organic matter, total nitrogen, available nitrogen, total phosphorous, and available phosphorus had the highest levels 40 years post-restoration at 0-20 cm, while at 20-40 and 40-60 cm, the highest concentrations were identified 30 years after. In all the treatments, the soil quality index (SQI) was the highest 40 years post-restoration. The values of SQI were always higher in natural grasslands than in Robinia pseudoacacia and Caragana korshinskii treatments. Overall, natural recovery (natural grasslands) is more efficient than afforestation (Robinia pseudoacacia and Caragana korshinskii treatments) in soil quality.
... Where the effects of afforestation on soil carbon have been investigated, the results have been variable, with a range of studies finding an increase, decrease or no effect of afforestation on soil carbon (Ashwood et al., 2019;Burton et al., 2018;Deng et al., 2014;Li et al., 2017;Mayer et al., 2020;Smal et al., 2019;Whitehead, 2011). Generally, there is an initial decrease in soil organic carbon immediately following afforestation due to soil disturbance, with a gradual increase in the subsequent years and decades back to pre-disturbance levels and (sometimes) beyond (Deng et al., 2014;Deng and Shangguan, 2017;Vanguelova et al., 2019). The magnitude and duration of these different stages varies and is dependent on factors such as ground preparation practices, soil type, forest type and forest management, but is an important consideration if tree planting aims to mitigate climate change (Mayer et al., 2020). ...
Article
Extensive afforestation is currently being widely promoted as a key nature-based solution for climate change mitigation. Fundamental to this strategy is the sequestration of carbon into long-term stable storage, either in wood products or the soil. However, the long-term effects of tree planting on soil carbon, or other soil properties, has rarely been examined. Importantly, afforestation can take many different forms, with differing effects on soil properties. Here, we evaluate how the historical afforestation of sandy heathland adopting a range of management options – including different combinations of conifers and broadleaves in monocultures and mixtures – have affected soil pH, total carbon and nitrogen concentrations, the C:N ratio, and carbon and nitrogen stocks almost a century later. We analyse these properties at a range of soil depths through the organic (litter, F and grass layers) and upper mineral (0–5 cm, 5–10 cm and 10–20 cm depth) soil layers. In comparison to the historical heathland sites, afforestation decreased soil pH, most dramatically under conifers, and increased the C:N ratio. However, there was overall little difference in carbon and nitrogen concentrations between alternative management options. While the total carbon and nitrogen concentrations were much higher in the organic layers of the forest options compared to the open sites, this did not translate into differences in the mineral layers. Furthermore, although we found some evidence of the transferral of carbon and nitrogen into the uppermost soil mineral layers, this was minimal in comparison to the concentrations of the organic layers. The soils at our study site are low quality and sandy, and are therefore unfavourable for incorporating organic matter, but it is still notable how little was incorporated after nearly a century of afforestation. Given the current emphasis on tree planting as a means to tackle climate change, these results demonstrate the fundamental importance of the appropriate consideration of both the afforestation management option and underlying soil type.
... layers under different treatments, which suggests that N is the main limiting element in these reclaimed soils (Qu et al., 2014;Xu et al., 2019). The stoichiometric ratio of soil C:N:P is a significant factor affecting soil microbial composition and plays an important role in soil-plant interactions and soil nutrient limitation (Garcia-Franco et al., 2015;Deng and Shangguan, 2017). For example, compared with microorganisms fed with higher C:N ratio supplements, those provided with lower C:N ratio supplements had higher growth efficiency and lower respirational carbon release, which resulted in more carbon being converted into biomass . ...
Article
Reclamation of coastal land is increasingly being used as a means of raising agricultural productivity and improving food security in China. Applications of organic and inorganic supplements on reclaimed soils can significantly adjust a range of soil properties, C, N, P content and stoichiometry, and extracellular enzyme activities. However, the linkages between soil C꞉N꞉P stoichiometry and extracellular enzyme activities following reclamation of coastal saline soil remain largely unclear. In this experimental study, treatments included control (CK), chicken manure (OM), polyacrylamide plus chicken manure (PAM+OM), straw mulching plus chicken manure (SM+OM), buried straw plus chicken manure (BS+OM), and bio-organic manure plus chicken manure (BM+OM) were conducted to explore the linkages between soil physicochemical characteristics in reclaimed soils under different treatments and to evaluate their impact on oat yield. Soils under all reclamation treatments exhibited higher moisture content and, with the exception of SM+OM, lower soil pH compared to the control. The reclamation treatments also significantly decreased soil bulk density (BD) and soil salt content (SSC), and increased soil organic carbon (SOC), total nitrogen (TN) and organic phosphorus (OP). Our study of soil C꞉N꞉P stoichiometry revealed that newly reclaimed soils in the study area are N limited. Additionally, soil invertase (INV), urease (URE) and alkaline phosphatase (ALP) activity under different reclamation treatments were significantly enhanced compared with CK in surface soil, while soil catalase (CAT) activity was observed to be much higher in BM+OM than in other treatments. Mean oat yields for each of the treatments were ranked as follows: BM + OM > SM + OM > PAM + OM > BS + OM > OM > CK treatment. Our results also indicate that TN (12.1% and 12.4%) was the main factor affecting URE and ALP, whereas BD (13.5%) and pH (8.5) were key factors affecting INV and CAT activity, respectively.
... pH, temperature, water content, texture, C:N ratio, microbial biomass, and other available nutrients are significantly affected by afforestation (Deng et al., 2016;Lauber et al., 2013;Li et al., 2012). The main purpose of rehabilitation works is to enrich the soil with nutrients (Deng & Shangguan, 2017) and thus provide favorable conditions for plant development (Agegnehu et al., 2017). ...
... Our results con rm that afforestation with pine, carried out to consolidate mountain slopes and reduce erosion phenomena, induced profound changes in the soil characteristics and C sequestration rate, which was in accordance with previous research results (Ono et al. 2011;Deng et al. 2017). In fact, in the investigated Mediterranean area, pine forests signi cantly increased the amount of soil OM and the soil C and N pools compared to shrublands. ...
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Aims Plant cover and microclimatic conditions can profoundly alter the balance between productivity and decay, with relevant effects on soil C and N pools. In this contest, the aim of the present study was to assess how, in Mediterranean areas, soil properties and C and N sequestration differs between afforested pine forests and natural shrublands in different microclimatic conditions at low and high elevations. Methods The study was performed along the soil profile distinguishing between the organic layers, fermentation and humic layers, and surface mineral soils. The comparison between plant covers and elevations were carried out for C and N pools and soluble fractions, molecular characterization by solid state ¹³C NMR of organic layers and by ¹HNMR of soil soluble fractions, potential mineralization rates and microbial and fungal amounts. Results Our data confirm that coniferous tree species sequester C faster than shrubs and herbaceous species especially at low elevation under favourable microclimatic conditions. Soil C and N pools reflect changes in the chemical composition of the upper organic layers and of soil soluble organic matter. In pine forests, the higher concentration of N in the upper organic layer speeds up the N loss in the fermentative layer and stimulates humus formation and C accumulation at low elevations. Conclusions Plant cover and microclimatic conditions drive the C sequestration rate and the soil organic matter stability. Chemical changes highlighted by nuclear magnetic resonance spectroscopy can clarify patterns of decay processes and help to make predictions in a climate change scenario.
... Over time, SOM input increases with stand productivity [75]. Deng and Shangguang [76] highlight the importance of tree species, soil depth, and forest age on soil C and N content. ...
Article
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Post-mining areas require reclamation. The main aim of reclamation is to restore the soil as a basic element of the terrestrial ecosystem. This paper presents the results of an evaluation of the enzymatic activity of soils formed on an afforested heap from an opencast sulphur mine. Six research sites were selected on the overburden heap of the Piaseczno sulphur mine, afforested 50 years ago. They differed in the type of soil in the subsoil and in the species composition of the stand. The activity of dehydrogenases, phosphatases, urease, total organic carbon, and total nitrogen was determined and statistical analysis of the obtained results showed that the activity of the evaluated enzymes in the soils formed in the reclaimed areas was significantly dependent on the type of substrate and the species composition of the plants. The activity of the evaluated enzymes was significantly positively correlated with the content of total nitrogen and the C/N ratio, and the activity of phosphatases and urease with the total organic carbon content. Within soils developed on the same texture, the influence of stand species was revealed. In soils formed on clay, the soils under the beech stand and under the birch stand were characterized by higher activity of enzymes. The soil developing under the stands of European larch and red oak was characterized by higher enzymatic activity on weakly clayey sands. On loose sands, the activity of dehydrogenases and urease was significantly higher under acacia robinia than under hornbeam.
... Mao et al. (2019) [22] also confirmed that better protection and restoration of the natural ecosystems were achieved in the western part of the NEC including substantial enhancement of sandstorm prevention, habitat provision, and grain production. Enhancing vegetation cover not only increases soil organic carbon and total nitrogen, but also improves ecosystem services, reduces soil and water erosion, and improves regional climate [54,55]. Our results proved that the improvement of vegetation under the influence of human activities was accompanied by the overall improvement of climatic conditions and soil moisture conditions in NEC, as evidenced by PRE, and SPEI-12 experienced an increasing trend from 2001 to 2013, while PET showed an opposite trend (Figure 2). ...
Article
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Vegetation in Northeast China (NEC) has faced dual challenges posed by climate change and human activities. However, the factors dominating vegetation development and their contri- bution remain unclear. In this study, we conducted a comprehensive evaluation of the response of vegetation in different land cover types, climate regions, and time scales to water availability from 1990 to 2018 based on the relationship between normalized difference vegetation index (NDVI) and the standardized precipitation evapotranspiration index (SPEI). The effects of human activities and climate change on vegetation development were quantitatively evaluated using the residual analysis method. We found that the area percentage with positive correlation between NDVI and SPEI increased with time scales. NDVI of grass, sparse vegetation, rain-fed crop, and built-up land as well as sub-humid and semi-arid areas (drylands) correlated positively with SPEI, and the correlations increased with time scales. The negatively correlated area was concentrated in humid areas or areas covered by forests and shrubs. Vegetation water surplus in humid areas weakens with warming, and vegetation water constraints in drylands enhance. Moreover, potential evapotranspiration had an overall negative effect on vegetation, and precipitation was a controlling factor for vegetation development in semi-arid areas. A total of 53% of the total area in NEC showed a trend of improve- ment, which is mainly attributed to human activities (93%), especially through the implementation of ecological restoration projects in NEC. The relative role of human activities and climate change in vegetation degradation areas were 56% and 44%, respectively. Our findings highlight that the government should more explicitly consider the spatiotemporal heterogeneity of the influence of human activities and water availability on vegetation under changing climate and improve the resilience of regional water resources. The relative proportions and roles map of climate change and human activities in vegetation change areas provide a basis for government to formulate local-based management policies.
... Their distributions have been shown to vary with soil aggregate size [9], and they are closely related to SAS [10,11]. Vegetation restoration has proven effective in improving SOC and TN content of soils while also improving SAS [12,13]. Zhang et al. found that while SAS was quite low in bare fallow land, revegetation could augment SOC and TN, thus also playing a positive role in enhancing SAS [14]. ...
Article
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Rational land use can enhance soil nutrient sequestration and control erosion, but the mechanisms of the ecological restoration of soil-aggregate-associated carbon and nitrogen are still not well understood. A large-scale ecological restoration program was launched in the Loess Plateau during the 1990s. The ecological restoration programs involved converting slope farmland to woodland, grassland, shrub land, and terrace. We studied their effects in relation to cultivated land as control on soil aggregate structure and stability and their associated organic carbon and total nitrogen contents to 60 cm soil depth in the Loess Plateau. Our results indicate that the restoration practices reduced soil aggregate fragmentation, increased soil structure stability, and transformed micro-aggregates into small and large aggregates. Comparing with the soil aggregate >0.25 mm in cultivated land, the amount in woodland, grassland, shrub land and terrace increased by 71%, 66%, 46%, and 35%, respectively, which improved soil health overall. The mean weight diameter of aggregate indicates that soil aggregate stability (SAS) increased and soil hydraulic erosion resistance improved. In conclusion, ecological restoration directly or indirectly affected SAS through the influence of soil organic carbon and total nitrogen in different soil layers. Results of this study provide a scientific reference for understanding stabilization of soil aggregate and regional restoration.
... Results of the present study showed that the C:P and N:P ratios of the forest were significantly negatively affected by soil depth (Figures 4E-4F) but no change was observed in C:N ratios (Liu et al., 2017). The same findings were reported by (Deng et al., 2013) in the loess plateau of China that C:N ratios remained unchanged, therefore it is important to conduct further research on C:N ratios to enhance the understanding of soil stoichiometry in forest development (Deng and Shangguan, 2017). Usually, the C:N ratio is negatively associated with the rate of soil organic matter decomposition and a lower C/N ratio led to a quicker mineralization process, and it is often constant (10:1) estimating global soil carbon storage (Stevenson and Cole, 1999). ...
Article
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Liupan Mountains are an important region in China in the context of forest cover and vegetation due to huge afforestation and plantation practices, which brought changes in soil physio-chemical properties, soil stocks, and soil stoichiometries are rarely been understood. The study aims to explore the distribution of soil nutrients at 1-m soil depth in the plantation forest region. The soil samples at five depth increments (0-20, 20-40, 40-60, 60-80, and 80-100 cm) were collected and analyzed for different soil physio-chemical characteristics. The results showed a significant variation in soil bulk density (BD), soil porosity, pH, cation exchange capacity (CEC), and electric conductivity (EC) values. More soil BD (1.41 g cm-3) and pH (6.97) were noticed in the deep soil layer (80-100 cm), while the highest values of porosity (60.6%), EC (0.09 mS cm-1), and CEC (32.9 c mol kg-1) were reflected in the uppermost soil layer (0-20 cm). Similarly, the highest contents of soil organic carbon (SOC), total phosphorus (TP), available phosphorus (AP), total nitrogen (TN), and available potassium (AK) were calculated in the surface soil layer (0-20 cm). With increasing soil depth increment a decreasing trend in the SOC and other nutrient concentration were found, whereas the soil total potassium (TK) produced a negative correlation with soil layer depth. The entire results produced the distribution of SOCs and TNs (stocks) at various soil depths in forestland patterns were 0→20cm > 20→40cm > 40→60cm ≥ 60→80cm ≥ 80→100 cm. Furthermore, the stoichiometric ratios of C, N, and P, the C/P, and N/P ratios showed maximum values (66.49 and 5.46) in 0-20 cm and lowest values (23.78 and 1.91) in 80-100 cm soil layer depth. Though the C/N ratio was statistically similar across the whole soil profile (0-100 cm). These results highlighted that the soil depth increments might largely be attributed to fluctuations in soil physio-chemical properties, soil stocks, and soil stoichiometries. Further study is needed to draw more conclusions on nutrient dynamics, soil stocks, and soil stoichiometry in these forests. Resumo As montanhas de Liupan são uma região importante na China no contexto de cobertura florestal e vegetação devido às enormes práticas de florestamento e plantação, que trouxeram mudanças nas propriedades físico-químicas do solo, e estoques e estequiometrias do solo raramente são compreendidos. O estudo visa explorar a distribuição de nutrientes do solo a 1 m de profundidade do solo na região da floresta plantada. As amostras de solo em cinco incrementos de profundidade (0-20, 20-40, 40-60, 60-80 e 80-100 cm) foram coletadas e analisadas para diferentes características físico-químicas do solo. Os resultados mostraram uma variação significativa nos valores de densidade do solo (BD), porosidade do solo, pH, capacidade de troca catiônica (CEC) e condutividade elétrica (CE). Mais DB do solo (1,41 g cm-3) e pH (6,97) do solo foram observados na camada profunda do solo (80-100 cm), enquanto os maiores valores de porosidade (60,6%), CE (0,09 mS cm-1) e CEC (32,9 c mol kg-1) foram refletidos na camada superior do solo (0-20 cm). Da mesma forma, os maiores teores de carbono orgânico do solo (SOC), fósforo total (TP), fósforo disponível (AP), nitrogênio total (TN) e potássio disponível (AK) foram Variations in soil physico-chemical properties, soil stocks, and soil stoichiometry under different soil layers, the major forest region Liupan Mountains of Northwest China Variações nas propriedades físico-químicas do solo, estoques e estequiometria do solo sob diferentes camadas de solo, a principal região florestal das montanhas Liupan do
... The relative stability index currently is roughly studied considering soil MBC as the main component of soil activated carbon (Yu et al., 2020c) and ASI as a measure of soil aggregate organic carbon stability. Soil C: N is also one important factor to assess the relevance of SOC sequestration after vegetation restoration (Deng and Shangguan, 2017), which could be combined with the WSC because it impacts soil microbial communities and enzyme activities (Yang et al., 2017). Some authors also consider particulate organic carbon (POC) because it mainly affects the balance between soil carbon input from plant residues and soil carbon loss caused by microbial decomposition . ...
Article
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Afforestation of degraded lands close to mega-urban areas such as Beijing may help to restore some of the original soil carbon stocks and hold the potential for ameliorating the rate of increase in atmospheric CO2. However, the determinants of the stability of different soil carbon pools and the utility of indices of stability remain poorly characterized near these highly anthropogenic areas. In the current study, we compared metrics of soil organic carbon (SOC) stability taking into account different soil types and plantation forest combinations (Quartisamment soil-poplar plantation–QP, Eutrochrepts soil-Chinese pine plantation–ECP, Haplustepts soils-East-Liaoning oak plantation–HEO), in an experimental sub-humid area close to a mega-urban area (Beijing, China). We evaluated the following relative stability indices sequence: respired carbon from incubations (RI) for several incubation days to respire 5% of initial SOC (D), aggregate stability index (ASI), the ratio of SOC to total nitrogen (C: N), water-soluble carbon (WSC), particulate organic carbon (POC) and microbial biomass carbon (MBC). We examined the indices by three repeated measurements on soil samples from four soil layers (0–40 cm) in three soil-forest types in a forest area close to the peri-urban area of Beijing. Our results showed that there are inconsistencies among the six SOC stability indexes. The contribution rates of different indexes to the SOC in three plantations were different, for QP the highest contributor is WSC (54.73%), and for ECP and HEO the highest contributor is RI, contribution rates are 34.85% and 36.382%, respectively. Respired carbon from incubations registered the largest contribution rate to SOC (69.79%), and the correlation between RI and soil physical and chemical properties was the highest. We conclude that a combination of indices and knowledge of soil and vegetation types are needed for assessing SOC stability in restoration and reforestation projects close to mega-urban areas.
... In addition, Chytrý et al. (2007) reported that climatic factors regulate pH variation at a regional level. Therefore, the high SOM content in this study may considerably influence soil nutrients and physical properties (Bruun et al. 2013;Deng and Shangguan 2017). ...
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... The inconsistent response was mainly due to the production of organic acids during the decomposition processes of SOM [40]. Furthermore, the negative correlation between pH and total N was consistent with previous studies [41,42]. In fact, soil pH could affect SOM and total N by regulating microbial activities [43]. ...
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... Afforestation on cropland (CL) has been recognized as an important measure to enhance soil aggregate stability and sequestrate soil organic carbon (SOC) in fragile ecosystems (Wei et al., 2012;Qiu et al., 2015;Hu et al., 2018;Hu and Lan, 2019). As a consequence, afforestation is important to mitigate climate change (Deng et al., 2014), regulate ecosystem restoration (Deng and Shangguan, 2017), and prevent land degradation (Lan, 2020) in terrestrial ecosystems. Numerous studies have explored the effects of afforestation on changes in SOC and its fractions (Pang et al., 2019;Lan, 2020;Zhang et al., 2020) as well as their interaction with soil aggregate fractions and stability (Wei et al., 2012;Qiu et al., 2015;Liu et al., 2020a;Xiao et al., 2021). ...
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... Mao et al. (2019) [22] also confirmed that better protection and restoration of the natural ecosystems were achieved in the western part of the NEC including substantial enhancement of sandstorm prevention, habitat provision, and grain production. Enhancing vegetation cover not only increases soil organic carbon and total nitrogen, but also improves ecosystem services, reduces soil and water erosion, and improves regional climate [54,55]. Our results proved that the improvement of vegetation under the influence of human activities was accompanied by the overall improvement of climatic conditions and soil moisture conditions in NEC, as evidenced by PRE, and SPEI-12 experienced an increasing trend from 2001 to 2013, while PET showed an opposite trend (Figure 2). ...
... With the development of China's policy, Chinese agricultural systems and agronomic management practices have had dramatic changes in the past decades (Deng and Shangguan, 2017). As a result, the SOC stock in the surface soil (0-20 cm) of croplands has increased in most regions. ...
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Soil organic carbon (SOC) was studied across a gradient of 400–550 ppm CO2 in calcareous contaminated semi-arid areas. An experiment was performed under natural and artificial vegetation cover of Atriplex canescens (Pursh) Nutt. SOC and vegetation cover were investigated every 2 years from 2012 to 2018. Findings disclosed that there was a polynomial relation between SOC and CO2 concentration. The SOC change rate had the highest positive relationship with CO2 concentration in the uppermost 20 cm of soil: R2 = 0.96 and 0.47 in plantation and control areas, respectively. Moreover, plant life forms had a significant effect on the SOC in CO2 contaminated areas (P < 0.01). The highest correlation (R2 = 0.93–0.99) was observed between SOC rate changes and perennial cover percentage at a depth of 0–20 and 20–40 cm, respectively, through the time.
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A series of complex organic fractions with different physical and chemical properties make up soil organic carbon (SOC), which plays a vital role in climate change and the global carbon cycle. Different SOC fractions have different stability and respond differently to vegetation succession. This research was carried out to assess the impacts of vegetation succession on SOC dynamics in the Qingmuguan karst valley area, southwest China. Soil samples were collected from four typical vegetation succession stages, including farmland, grassland, shrubland, and forest. The total SOC content and four oxidizable SOC fractions were measured. Results showed that the total SOC content and storage under farmland were highest, followed by forest and shrubland, and the grassland had the lowest total SOC content and storage. The SOC sequestration potential under different vegetation types in the study area was grassland (26.32 Mg C ha⁻¹) > shrubland (9.64 Mg C ha⁻¹). All SOC content, storage, and fractions showed a decrease with the increase of soil depth over the 0–50 cm in the study area. The four SOC fractions under forest at topsoil (0–10 cm) were higher than that under the other vegetation types. Compared with the other land uses, the farmland had the highest stable oxidizable SOC fractions (F3 and F4) at the 10–50-cm depth, while the shrubland had the highest active oxidizable SOC fractions (F1 and F2). In terms of the lability index of SOC, shrubland was the largest, followed by grassland and forest, and farmland was the smallest. These results provide essential information about SOC fractions and stability changes resulting from changes of vegetation types in a karst valley area of southwest China. It also supplements our understanding of soil carbon sequestration in vegetation succession.
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The study determined the distribution of organic carbon (OC), cation exchange capacity (CEC) and total nitrogen (TN) associated with soil aggregates across land-use types in Ile-Ife, Nigeria. Six agricultural land-use types were considered which were undisturbed secondary forest, continuously cropped land, paddock, oil palm, cocoa and teak plantations at the Teaching and Research Farm, Obafemi Awolowo University, Ile-Ife, Nigeria. Soils samples were randomly collected from each land use at 0-15 and 15-30cm soil depths in three replicates. The samples were segregated into four aggregate classes; <63µm, 63-250µm, 250µm-1mm and 1-2mm respectively. The following analyses were carried out on the whole soil: particle size distribution, soil pH, CEC, OC and TN while CEC, OC and TN were carried out on different soil aggregate fractions. Data obtained were subjected to analysis of variance using SAS software and means were separated using Duncan’s Multiple Range Test at p ≤0.05. Results showed that OC, TN and CEC were more associated with smaller sized soil aggregates (<250µm) across all the land-use types, except under oil palm plantation, which had most of its SOC associated with 1-2mm sized soil aggregate. In the whole soil, continuously cultivated land had the least OC and TN while secondary forest surprisingly had the least CEC. The study revealed that aggregate size <250µm contributes the most to soil nutrient available. Therefore, conservative land-use practices (such as conservative tillage, mulching, manuring etc.) that protect the loss of soil micro-aggregates (<250µm) especially to erosion should be adopted for sustainable land-use.
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Soil erosion poses a major threat to the sustainability and stability of global terrestrial ecosystems. Mixed forests have more advantages in restoring degraded land and enhancing soil fertility than monocultures, but their influence on soil erosion remains uncertain. Therefore, we presented a meta-analysis consisting of 261 paired observations of mixed forests and the corresponding monocultures from 65 studies to evaluate the effect of tree diversity on soil erosion in China. The results showed that compared with monocultures, mixed forests significantly reduced the annual runoff and sediment yield by 17.4% and 23.6%, respectively. Tree-shrub mixtures showed more efficiency in reducing runoff (24.2%) and sediment yield (32.1%) than tree-tree mixtures. However, the positive effect of mixed forests on soil erosion control was significant > 20 years after stand establishment. Mixed forests showed the highest capacity to control soil erosion at slope angles of 16°-25° (runoff: 27.7%; sediment yield: 37.7%). In terms of soil textures, mixed forests performed better with respect to soil erosion control on sandy soils (runoff: 21.4%; sediment yield: 30.1%), whereas significant differences were not observed between different stand types on clayey soils. In addition, in the dry areas (humidity index (HI) < 30), mixed forests conferred the greatest benefits in reducing runoff and sediment yield (25.8% and 33.0%, respectively). Our results indicate that increasing tree species richness is a suitable approach to controlling soil erosion in China. This research provides a scientific basis for the management and sustainable development of forest ecosystems in the future.
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Afforestation made great contributions to ecological benefits across China. Robinia pseudoacacia is widely used in the Grain-for-Green Program. The responses of soil organic carbon (SOC) and soil total nitrogen (STN) to afforestation with R. pseudoacacia on cropland depend on plantation attributes, climatic factors, topographic features, and edaphic variables, thus making a synthesis of these studies necessary for understanding the magnitude and direction of SOC and STN to afforestation and the associated regulating factors. A meta-analysis was employed by compiling data of 1202 paired observations from 94 peer-reviewed publications to depict potential mechanisms of change in SOC and STN stocks following afforestation with R. pseudoacacia on cropland. Afforestation with R. pseudoacacia on cropland, on average, significantly and positively increased SOC and STN stocks. The changes in SOC and STN stocks increased with plantation age and altitude, but decreased with mean annual temperature, slope gradients, soil depth, soil clay content, initial SOC content and initial STN content. Greater accumulation rates of SOC and STN stocks after afforestation were detected in middle canopy density (0.6–0.8) and middle mean annual precipitation (450–550 mm). Among four kinds of biotic and abiotic factors, plantation attributes made greatest contributes to the variance in the response size of SOC and STN stocks. In particular, plantation age was the most essential variable on the response size of SOC and STN stocks. These results indicated that SOC and STN stocks following afforestation with R. pseudoacacia on cropland could be enhanced through plantation management practices.
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Soil erosion has a significant influence on nutrient redistribution and deposition. However, the effect of soil erosion on nutrient deposition remains unclear in karst areas such as southwest China, which represents an ecologically fragile zone experiencing severe soil erosion. The objective of this study was to investigate the characteristics of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) deposition in a karst watershed of southwest China over the past 60 years and evaluate the relationship between soil erosion and nutrient deposition. The peak-cluster depressions in southwest China are typical for the geomorphological type, which is an ideal place to determine the sediment chronology, and the estimation of sediment and nutrient deposition rates. The ¹³⁷Cs, ²¹⁰Pbex, particle size distribution, and nutrients of 194 soil samples in three sediment cores retrieved from a karst depression were investigated to evaluate the effect of soil erosion on nutrient deposition. Results showed that there was a significant negative correlation between nutrient concentrations and clay content (P < 0.001). Generally, compared with ¹³⁷Cs, ²¹⁰Pbex had a higher correlation with SOC and TN. In an undisturbed sediment profile, Pb/Cs can reflect nutrient dynamics better than a single nuclide. The nutrient deposition rates increased before 1953, reached its maximum in 1954–1956, and then dropped rapidly from 1957 to 2015. The sediment deposition rates were negatively correlated with nutrient concentrations (P < 0.01), but had a positive influence on nutrient deposition rates (P < 0.01). This implied that the temporal variation in nutrient deposition rates over the past 60 years was dominated by soil erosion rather than nutrient concentrations. This study provides a new insight to explore the historical nutrient deposition rates in a peak-cluster karst depression, and may help effectively control soil erosion and sustainable development of agro-ecosystems.
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Vegetation restoration plays an important role in enhancing soil organic carbon (SOC) sequestration. However, there are diverse types of vegetation restoration with different SOC sequestration rates. Understanding the dynamic of SOC at topsoil (0–20 cm) and potential problems of the different types (i.e., woodlands, shrub lands, artificial grasslands, orchards, and abandoned lands) are important for future sustainable development. We surveyed 73 peer-reviewed studies conducted on the Chinese Loess Plateau from 2000 to 2019. The relative change in SOC stock under shrub lands, woodlands, and abandoned lands performed significantly and positively related to restoration time (P < 0.001). The rate was highest for shrub lands (0.55 ± 0.45 t ha⁻¹ yr⁻¹) compared to that of other restoration types. The Robinia pseudoacacia, a typical N-fixers, sequestrate more SOC (3.84% yr⁻¹) than other tree species (1.18% yr⁻¹). Orchards and artificial grasslands, however, were based on the relatively weak relations between restoration age and SOC stock with the low efficiency of SOC stock change (19.0 ± 32.1% and 20.2 ± 35.2% respectively overall time). The restoration age, initial SOC stock, and temperature significantly influenced the relative change in SOC stock (P < 0.001). In addition, the shrub lands remained inert to the temperature and precipitation (P > 0.05), indicating its wide adaptability on the Loess Plateau. We conclude that restoration types and environmental factors control SOC dynamic, and must be considered for the vegetation restoration types.
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The Himalayan ecosystem has global significance for supporting unique and rich ecological and socio-cultural diversity as well as a range of ecosystem services important for the very survival of human beings. However, constant anthropogenic pressure, unsustainable developmental practices and climate change led to the transformation of irrational land-use practices that have seriously compromised the ecosystem productivity and livelihood of the mountain communities. Considering the above, integrated land use planning, effective land use policy and legislation is a key element to address unsustainable land-use practices in the Himalayan ecosystem. Realising the increasing trend of degradation of natural resources and associated livelihood challenges for rural communities, a comprehensive scientific framework was developed for improving the functionality of marginal degraded land. A total of twelve tree species used for a variety of purposes prioritised by local communities based on ecological, social and economic value were selected for plantation on marginal degraded land belonging to the village community. Significant improvement in survival rate, growth, and circumference of planted tree species was observed across the sites after ten years of the plantation. The plantation activities enhanced the net productivity of degraded landscape while increasing characteristics of soil leading to increment in water percolation, improve soil moisture and decreased runoff. Total biomass accumulated by tree species planted in three selected sites within the period significantly contributed to carbon sequestration thus reducing the adverse impact of changing climate. The provisioning services in the form of fuel, fodder, and grasses obtained from developed landscapes reduced the drudgery and workload of marginal communities. The study advocates interdisciplinary knowledge production, enrich social learning among stakeholders, improved understanding of current and future challenges associated with land-use practices and relevant policy implications for sustainable land management in the region.
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Afforestation is helpful to improve soil functions and increase soil organic carbon (SOC) sequestration in semiarid deserts. However, the fine-scale (around a single plant) spatial distribution of SOC and its liable organic carbon (LOC) fractions after afforestation in semiarid deserts are poorly understood. Pinus sylvestris and Salix psammophila afforested on shifting sandy land (Sland) were selected to quantify fine-scale (at 20, 80, 150 and 240 cm away from the trees) spatial distribution of SOC and its LOC fractions in the southeast edge of Mu Us Desert, China. The results showed that the afforested S. psammophila and P. sylvestris significantly increased SOC, total nitrogen, dissolved organic carbon, microbial biomass carbon and readily oxidized organic carbon (ROOC). At 20 cm distance, SOC storage of P. sylvestris was 27.21% higher than S. psammophila in 0–100 cm soil layers, and SOC storage of S. psammophila at 80 and 150 cm distances was 5.50% and 5.66% higher than P. sylvestris, respectively. Compared with Sland, SOC storage under S. psammophila and P. sylvestris significantly increased by 94.90%, 39.50%, 27.10% and 18.50% at 20, 80, 150 and 240 cm distance, respectively. ROOC accounted for 14.09% and 18.93% of SOC under S. psammophila and P. sylvestris, respectively. Our results suggest that afforestation can promote SOC accumulation at different distances from the plants, and that P. sylvestris allocates more organic matter to the closer soil compared with S. psammophila (<80 cm from the tree).
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Thinning is a common forest management practice. However, its impact on soil organic carbon (SOC) stocks is still unknown. Therefore, we conducted a meta-analysis of 270 measurements from 77 articles to evaluate the effect of forest thinning on SOC stocks in mineral soil (0–30 cm) across planted forests in China. The results showed that, compared to reference (non-thinned) plantations, thinning significantly increased SOC stocks in planted forests by 7.2%. Among different thinning intensities, moderate thinning (35–55% of thinning intensity) increased SOC stocks in planted forests (+16.1%) more than other levels of thinning intensity. However, the positive effect of thinning on SOC stock was significant > 5 years after harvesting. In the humidity-restricted areas (humidity index (HI) < 30), the increase in SOC stocks after thinning was significantly higher than that of other areas. In addition, thinning increased the sensitivity (i.e. slope value) of soil total nitrogen (TN) stocks changes to SOC stocks. Therefore, we conclude that forest thinning strategy is potentially a viable silvicultural measure to increase SOC fixation in planted forests. Our results provide a reference for the formulation and implementation of future forest management strategies.
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Despite hundreds of field studies and at least a dozen literature reviews, there is still considerable disagreement about the direction and magnitude of changes in soil C stocks with land use change. This paper reviews the literature on the effects of land use conversions on soil C stocks, based on a synthesis of 103 recent publications, including 160 sites in 29 countries, with the aims of determining the factors responsible for soil C sequestration and quantifying changes in soil C stocks from seven land use conversions. The results show that as an overall average across all land use change examined, land use conversions have significantly reduced soil C stocks (0.39 Mg ha yr ). Soil C stocks significantly increased after conversions from farmland to grassland (0.30 Mg ha yr ) and forest to grassland (0.68 Mg ha yr ), but significantly declined after conversion from grassland to farmland (0.89 Mg ha yr ), forest to farmland (1.74 Mg ha yr ), and forest to forest (0.63 Mg ha yr ). And after conversion from farmland to forest and grassland to forest, soil C stocks did not change significantly. Globally, soil C sequestration showed a significant negative correlation with initial soil C stocks ( <0.05), and the effects of climatic factors (mean annual temperature and mean annual precipitation) on soil C sequestration varied between the land use conversion types. Also, the relationships between soil C sequestration and age since land use conversion varied in different land use change types. Generally, where the land use changes decreased soil C, the reverse process usually increased soil C stocks and vice versa. Soil C sequestration dynamics were not determined by age since land use conversion at the global level when all land use change types were combined.
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Land degradation resulting from improper land use and management is a major cause of declined productivity in the arid environment. The objectives of this study were to examine the effects of a sequence of land use changes, soil conservation measures, and the time since their implementation on the degradation of selected soil properties. The climate for the selected 105 km2 watershed varies from semi-arid sub-tropical to Mediterranean sub-humid. Land use changes were detected using aerial photographs acquired in 1953, 1978, and 2008. A total of 218 samples were collected from 40 sites in three different rainfall zones to represent different land use changes and variable lengths of time since the construction of stone walls. Analyses of variance were used to test the differences between the sequences of land use changes (interchangeable sequences of forest, orchards, field crops, and range), the time since the implementation of soil conservation measures, rainfall on the thickness of the A-horizon, soil organic carbon content, and texture. Soil organic carbon reacts actively with different combinations and sequences of land use changes. The time since stone walls were constructed showed significant impacts on soil organic carbon and the thickness of the surface horizon. The effects of changing the land use and whether the changes were associated with the construction of stone walls varied according to the annual rainfall. The changes in soil properties could be used as indicators of land degradation and to assess the impact of soil conservation programs. The results help in understanding the effects of land use changes on land degradation processes and carbon sequestration potential and in formulating sound soil conservation plans.
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In many estuarine areas around the world, the safety of human societies depends on the functioning of embankments (dikes) that provide protection against river floods and storm tides. Vegetation on land-side slopes protects these embankments from erosion by heavy rains or overtopping waves. We carried out a field experiment to investigate the effect of plant species diversity on soil loss through erosion on a simulated dike. The experiment included four diversity treatments (1, 2, 4, and 8 species). In the third year of the experiment, we measured net annual soil loss by measuring erosion losses every 2 weeks. We show that loss of plant species diversity reduces erosion resistance on these slopes: net annual soil loss increased twofold when diversity declines fourfold. The different plant species had strongly diverging effects on soil erosion, both in the single-species and in the multi-species plots. Analysis of the dynamics of the individual species revealed that the main mechanism explaining the strong effects of plant species diversity on soil erosion is the compensation or insurance effect, that is, the capacity of diverse communities to supply species to take over the functions of species that went extinct as a consequence of fluctuating environmental conditions. We conclude that the protection and restoration of diverse plant communities on embankments and other vegetated slopes are essential to minimize soil erosion, and can contribute to greater safety in the most densely populated areas of the world.
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Global biosphere models vary greatly in their projections of future changes of global soil organic carbon (SOC) stocks and aggregated global SOC masses in response to climate change. We estimated the certainty (likelihood) and quantity of increases and decreases on a half-degree grid. We assessed the effect of changes in controlling factors, including net primary productivity (NPP), litter quality, soil acidity, water saturation, depth of permafrost, land use, temperature, and aridity associated with probabilities (Bayesian network) on an embedded, temporally discrete, three-pool decomposition model. In principle, controlling factors were discretized into classes, where each class was associated with a probability and linked to an output variable. This creates a network of links that are ultimately linked to a set of equations for carbon (C) input and output to and from soil C pools. The probability-weighted results show that, globally, climate effects on NPP had the strongest impact on SOC stocks and the certainty of change after 75 years. Actual land use had the greatest effect locally because the assumed certainty of land use change per unit area was small. The probability-weighted contribution of climate to decomposition was greatest in the humid tropics because of greater absolute effects on decomposition fractions at higher temperatures. In contrast, climate effects on decomposition fractions were small in cold regions. Differences in decomposition rates between contemporary and future climate were greatest in arid subtropical regions because of projected strong increases in precipitation. Warming in boreal and arctic regions increased NPP, balancing or outweighing potential losses from thawing of permafrost. Across contrasting NPP scenarios, tropical mountain forests were identified as hotspots of future highly certain C losses. Global soil C mass will increase by 1% with a certainty of 75% if NPP increases due to carbon dioxide fertilization. At a certainty level of 75%, soil C mass will not change if CO2-induced increase of NPP is limited by nutrients.
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The holistic study of soils requires an interdisciplinary approach involving biologists, chemists, geologists, and physicists amongst others, something that has been true from the earliest days of the field. In more recent years this list has grown to include anthropologists, economists, engineers, medical professionals, military professionals, sociologists, and even artists. This approach has been strengthened and reinforced as current research continues to use experts trained in both soil science and related fields and by the wide array of issues impacting the world that require an in-depth understanding of soils. Of fundamental importance amongst these issues are biodiversity, biofuels/energy security, climate change, ecosystem services, food security, human health, land degradation, and water security, each representing a critical challenge for research. In order to establish a benchmark for the type of research we seek to publish in each issue of SOIL we have outlined the interdisciplinary nature of soil science research we are looking for. This includes a focus on the myriad ways soil science can be used to expand investigation into a more holistic and therefore richer approach to soil research. In addition, a selection of invited review papers are published in this first issue of SOIL that address the study of soils and the ways in which soil investigations are essential to other related fields. We hope that both this editorial and the papers in the first issue will serve as examples of the kinds of topics we would like to see published in SOIL and will stimulate excitement among our readers and authors to participate in this new venture.
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Restoring the native vegetation is one of the most effective ways to control soil degradation in Mediterranean areas, especially in very degraded areas. In the initial months after afforestation, vegetation cover establishment and soil quality could be better sustained if the soil was amended with an external extra source of organic matter. The goal of this study was to test the effect of various organic amendments on select soil properties (soil organic carbon (SOC), pH and EC) over a 24 month period. Four amendments were applied in an experimental set of plots: straw mulching (SM); mulch with chipped branches of Aleppo Pine (Pinus halepensis L.) (PM); sheep manure compost (SH); and sewage sludge (RU). Plots were afforested following the same spatial pattern and amendments were mixed with the soil at the rate 10 Mg ha-1. Organic amendments helped maintain SOC over the initial six months after the afforestation. However, only the SM and PM treatments had increased SOC values after 24 months. Decreases in EC were found after the addition of SM, PM and SH amendments. However, RU increased EC values 24 months after the afforestation. Variations in pH values were sufficient to establish differences among the various treatments. Furthermore, the results show that forest soils with or without organic amendments responded similarly to the seasonal changes in Mediterranean conditions.
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Planting of Pinus radiata D. Don in previously grazed pastures is a common land-use change in New Zealand. Although carbon (C) accumulates relatively rapidly in the trees, there have been no studies of the annual effect on soil C content during the early years of establishment. Here, we study soil properties under P. radiata and pasture each year over 11 years after P. radiata was planted into pasture that had been grazed by sheep. Under the growing trees, grass was gradually shaded out by the unpruned trees, and completely disappeared after 6 years; needle litterfall had then increased appreciably. By year 9, soil microbial C and nitrogen (N), and net N mineralisation, were significantly lower under pine than under pasture. Soil pH, sampled at 0–100 mm in early spring each year, decreased by ~0.3 units under pine and increased by ~0.3 units under pasture. Close to the pine stems, total C and N decreased significantly for 3 years, while ~100 kg N/ha accumulated in the trees. Soil C and N increased in subsequent years, when litterfall increased. Overall, the mineral soil under pine lost ~500 kg N/ha over 11 years, consistent with uptake by the trees. Leaching losses (estimated using lysimeters) in year 9 were 4.5 kg N/ha.year. These data indicate that ~6 Mg C/ha may have been lost from the mineral soil at this site. The difficulties associated with measuring losses of C are discussed.
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Soil physic-chemical properties differ at different depths; however, differences in afforestation-induced temporal changes at different soil depths are seldom reported. By examining 19 parameters, the temporal changes and their interactions with soil depth in a large chronosequence dataset (159 plots; 636 profiles; 2544 samples) of larch plantations were checked by multivariate analysis of covariance (MANCOVA). No linear temporal changes were found in 9 parameters (N, K, N:P, available forms of N, P, K and ratios of N: available N, P: available P and K: available K), while marked linear changes were found in the rest 10 parameters. Four of them showed divergent temporal changes between surface and deep soils. At surface soils, changing rates were 262.1 g·kg(-1)·year(-1) for SOM, 438.9 mg·g(-1)·year(-1) for C:P, 5.3 mg·g(-1)·year(-1) for C:K, and -3.23 mg·cm(-3)·year(-1) for bulk density, while contrary tendencies were found in deeper soils. These divergences resulted in much moderated or no changes in the overall 80-cm soil profile. The other six parameters showed significant temporal changes for overall 0-80-cm soil profile (P: -4.10 mg·kg(-1)·year(-1); pH: -0.0061 unit·year(-1); C:N: 167.1 mg·g(-1)·year(-1); K:P: 371.5 mg·g(-1) year(-1); N:K: -0.242 mg·g(-1)·year(-1); EC: 0.169 μS·cm(-1)·year(-1)), but without significant differences at different soil depths (P > 0.05). Our findings highlight the importance of deep soils in studying physic-chemical changes of soil properties, and the temporal changes occurred in both surface and deep soils should be fully considered for forest management and soil nutrient balance.
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The agricultural Mediterranean areas are dedicated to arable crops (AC), but in the last decades, a significant number of AC has led to a land use change (LUC) to olive grove (OG) and vineyards (V). A field study was conducted to determine the long-term effects (46 years) of LUC (AC by OG and V) and to determine soil organic carbon (SOC), total nitrogen (TN), C : N ratio and their stratification across the soil entire profile, in Montilla-Moriles denomination of origin (D.O.), in Calcic-Chromic Luvisols (LVcc/cr), an area under semiarid Mediterranean conditions. The experimental design consisted of studying the LUC on one farm between 1965 and 2011. Originally, only AC was farmed in 1965, but OG and V were farmed up to now (2011). This LUC principally affected the horizon thickness, texture, bulk density, pH, organic matter, organic carbon, total nitrogen and C : N ratio. The LUC had a negative impact in the soil, affecting the SOC and TN stocks. The conversion from AC to V and OG involved the loss of the SOC stock (52.7% and 64.9% to V and OG respectively) and the loss of the TN stock (42.6% and 38.1% to V and OG respectively). With respect to the stratification ratios (SRs), the effects were opposite; 46 years after LUC increased the SRs (in V and OG) of SOC, TN and C : N ratio.
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Forest biogeochemical cycles are shaped by effects of dominant tree species on soils, but the underlying mechanisms are not well understood. We investigated effects of temperate tree species on interactions among carbon (C), nitrogen (N), and acidity in mineral soils from an experiment with replicated monocultures of 14 tree species. To identify how trees affected these soil properties, we evaluated correlations among species-level characteristics (e.g. nutrient concentrations in leaf litter, wood, and roots), stand-level properties (e.g. nutrient fluxes through leaf litterfall, nutrient pools in stemwood), and components of soil C, N, and cation cycles. Total extractable acidity (aciditytot) was correlated positively with mineral soil C stocks (R 2 = 0.72, P < 0.001), such that a nearly two-fold increase in aciditytot was associated with a more than two-fold increase of organic C. We attribute this correlation to effects of tree species on soil acidification and subsequent mineral weathering reactions, which make hydrolyzing cations available for stabilization of soil organic matter. The effects of tree species on soil acidity were better understood by measuring multiple components of soil acidity, including pH, the abundance of hydrolyzing cations in soil solutions and on cation exchange sites, and aciditytot. Soil pH and aciditytot were correlated with proton-producing components of the soil N cycle (e.g. nitrification), which were positively correlated with species-level variability in fine root N concentrations. Soluble components of soil acidity, such as aluminum in saturated paste extracts, were more strongly related to plant traits associated with calcium cycling, including leaf and root calcium concentrations. Our results suggest conceptual models of plant impacts on soil biogeochemistry should be revised to account for underappreciated plant traits and biogeochemical processes.
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Afforestation is known as an available mitigation activity to climate change because it causes sequestration of CO2 from the atmosphere and stores it as the living biomass and the dead organic matter. However, the response of soil organic carbon (SOC) to afforestation in deep soil layers is still poorly understood. We surveyed previously published literature for changes in deep SOC (defined as at least 10 cm deeper than the 0–10 cm layer) after afforestation of croplands and grasslands (total 63 sites from 56 literature), in order to examine changes in deep SOC and quantify the relationship between SOC change rates in topsoil and subsoil. The results of the meta analysis indicated that the responses of SOC to afforestation were opposite for cropland than grassland. The SOC in soil depth layers of 0–10, 10–20, 20–40, 40–60 and 60–80 cm were reduced with afforestation of grassland but not significantly (p > 0.05), while conversion of cropland to forests (trees or shrubs) increased SOC significantly for each soil depth layer up to 60 cm depth (p < 0.05). Significant relationships of SOC change rate were found between topsoil (0–20 cm) and deeper soil layers (20–40 and 40–60 cm). The linear regression showed that SOC change rate in 0–40 cm, 0–60 cm, and 0–100 cm soil profiles was 1.33, 1.49, and 1.55 times greater, respectively than the change rates in the corresponding 0–20 cm depth profile. Partial correlation analysis revealed that stand age and initial SOC content were determinants of deep soil SOC change after afforestation of agricultural soils. This study also showed that the O horizon can play an important role in carbon sequestration after afforestation of agricultural sites. We concluded that subsoil carbon must be taken into account when evaluating of SOC change with afforestation and, therefore, recommended that the soil sampling depth for afforested soils be set to at least 60 cm in mineral soils and include the O horizon. However, due to poor study designs and lack of standardized sampling protocols in the literature, these results were high in uncertainty.
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The revegetation of abandoned farmland significantly influences soil organic C (SOC) and total N (TN). However, the dynamics of both soil OC and N storage following the abandonment of farmland are not well understood. To learn more about soil C and N storages dynamics 30 years after the conversion of farmland to grassland, we measured SOC and TN content in paired grassland and farmland sites in the Zhifanggou watershed on the Loess Plateau, China. The grassland sites were established on farmland abandoned for 1, 7, 13, 20, and 30 years. Top soil OC and TN were higher in older grassland, especially in the 0-5 cm soil depths; deeper soil OC and TN was lower in younger grasslands (<20 yr), and higher in older grasslands (30 yr). Soil OC and N storage (0-100 cm) was significantly lower in the younger grasslands (<20 yr), had increased in the older grasslands (30 yr), and at 30 years SOC had increased to pre-abandonment levels. For a thirty year period following abandonment the soil C/N value remained at 10. Our results indicate that soil C and TN were significantly and positively correlated, indicating that studies on the storage of soil OC and TN needs to focus on deeper soil and not be restricted to the uppermost (0-30 cm) soil levels.
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Selected chemical, biochemical and biological properties of mineral soil (0–30 cm) were measured under a 19 year old forest stand (mixture of Pinus ponderosa and Pinus nigra) and adjacent unimproved grassland at a site in South Island, New Zealand. The effects of afforestation on soil properties were confined to the 0–10 cm layer, which reflected the distribution of fine roots (< 2 mm) in the soil profile. Concentrations of organic C, total N and P and all organic forms of P were lower under the forest stand, while concentrations of inorganic P were higher under forest compared with grassland, supporting the previously described suggestion that afforestation may promote mineralisation of soil organic matter and organic P. On the other hand, microbial biomass C and P, soil respiration and phosphatase enzyme activity were currently all lower and the metabolic quotient was higher in soil under forest compared with grassland, which is inconsistent with increased mineralisation in the forest soil. Reduced biological fertility by afforestation may be mainly attributed to changes in the quantity, quality and distribution of organic matter, and reduction in pH of the forest soil compared with the grassland soil. We hypothesize that the lower levels of C, N and organic P found in soil under forest are due to enhanced microbial and phosphatase activity during the earlier stages of forest development. Forest floor material (L and F layer) contained large amounts of C, N and P, together with high levels of microbial and phosphatase enzyme activity. Thus, the forest floor may be an important source of nutrients for plant growth and balance the apparent reduction in C, N and P in mineral soil through mineralisation and plant uptake.
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Abandonment and reforestation of agricultural lands has been a major influence on the landscape of eastern North America. Cultivation and soil amendments can dramatically alter soil nutrient pools and cycling, yet few studies have examined the longterm (>50 yr) influence of pasturing and cultivation on soil processes in the forests that develop after abandonment. Twelve forested sites at Harvard Forest in central New England were compared 90-120 yr after abandonment from agricultural use. We measured soil carbon (C), nitrogen (N), and phosphorus (P); light fraction C, N, and δ15N; microbial chloroform-N; net N mineralization and nitrification; nitrification potential; and culturable nitrifiers on sites with differing land-use history and vegetation. The sites had similar soil series and topography but were arrayed along a soil disturbance gradient from permanent woodlots (selective logging but no mineral soil disturbance) to formerly pastured sites (clearcut and grazed but no deep [>10 cm] soil disturbance) to formerly cultivated sites (cleared-with-plow horizon 15-20 cm thick). Mineral soil C (0-15 cm soil depth) was very similar among all sites, but the forest floor C was lower in the cultivated sites than in the woodlots of both stand types. Mineral soil in cultivated sites contained 800 kg P/ha and 300 kg P/ha more than woodlots, a relative increase of 39% for N and 52% for P. The cultivated soils had lower C:N and C:P ratios, largely driven by higher soil N and P. The light fraction appeared to be more sensitive to prior land use than the bulk soil organic matter. The C content and C:N ratio of light fraction were lower in cultivated soils, which suggests that input and/or turnover of organic matter pools of relatively recent origin remain altered for a century after abandonment. Similar δ15N for the light and heavy fraction organic matter pools in cultivated soils suggests that cultivation accelerates the mineralization of humus N, increasing the proportion of N available for plant uptake, resulting in a convergence of the light and heavy fractions. The N pool in the woodlot soils may have been subject to preferential losses of small amounts of 14N over a longer time period, resulting in a more pronounced divergence between the light fraction (reflecting recent plant inputs) and the mineral-associated heavy fraction (more recalcitrant). Nitrification was strongly influenced by land-use history, with highest rates in formerly cultivated sites. In contrast, soil net N mineralization and chloroform-N were more strongly influenced by present vegetation. Nitrifying bacteria were relatively abundant in all pastured and cultivated sites; however, only the cultivated hardwood sites, with lowest C:N ratios (16-18), had substantial net nitrification. Historical manure inputs may explain the more rapid soil net nitrification rates, by decreasing soil C:N ratios and thus reducing nitrate immobilization in the mineral soil of cultivated sites. Regionally, 65% of the land area was pastured, and a proportion of the nutrients obtained from grazing was transferred to the cultivated croplands, which comprise ≤15% of the land area. Pastures generally had intermediate nutrient ratios and N transformations but were often more similar to woodlots, which suggests that plowing and amendments, rather than forest clearance, have the greatest impact on soil organic matter and nutrients. The influence of land-use history on soil N and P and nitrification rates was more dramatic in hardwood sites, which indicates that characteristics of the recovering vegetation and/or changes in plant community composition associated with prior land use are important factors in the rate of recovery. Our findings lead to the surprising conclusion that 19th century agricultural practices decreased forest floor nutrient content and ratios, and increased nitrifier populations and net nitrate production for approximately a century after abandonment. Consideration of site history clearly deserves more attention in the design of field experiments, and in our understanding of patterns of element distributions and transformations in dynamic forested landscapes.
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Mixed tree-grass vegetation is important globally at ecotones between grass- lands and forests. To address uncertainties vis-a`-vis productivity and nitrogen (N) cycling in such systems we studied 20 mature oak savanna stands, ranging from 90% woody dominated to 80% herbaceous dominated, growing on comparable soils in a 32-yr-old fire frequency experiment in Minnesota, USA. Fire frequencies ranged from almost annual burning to complete fire protection. Across all stands, aboveground net primary productivity (ANPP) ranged from 2 to 12 Mg·ha 21 ·yr 21 , decreased with fire frequency (r2 5 0.59), increased with woody canopy dominance (r2 5 0.83), and increased with soil net N min- eralization rates (r2 5 0.79), which varied from 25 to 150 kg·ha 21 ·yr 21 . ANPP was positively related to total biomass (r2 5 0.95), total canopy leaf N content (r2 5 0.88), leaf area index (LAI; r2 5 0.87), annual litterfall N cycling ( r2 5 0.70), foliage N concentration (r2 5 0.62), and fine root N concentration (r2 5 0.35), all of which also increased with increasing tree canopy cover. ANPP, soil N mineralization, and estimated root turnover rates increased with woody canopy cover even for stands with similar fire frequency. ANPP and N min- eralization both decreased with fire frequency for stands having a comparable percentage of woody canopy cover. Fine root standing biomass increased with increasing grass dom- inance. However, fine root turnover rate estimated with a nitrogen budget technique de- creased proportionally more with increasing grass dominance, and hence fine root produc- tivity decreased along the same gradient. Via several direct and indirect and mutually reinforcing (feedback) effects, the com- bination of low fire frequency and high tree dominance leads to high rates of N cycling, LAI, and productivity; while the opposite, high fire frequency and high grass dominance, leads to low rates of N cycling, LAI, and productivity. Carbon and N cycling were tightly coupled across the fire frequency and vegetation type gradients.
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Interactions involving carbon (C) and nitrogen (N) likely modu- late terrestrial ecosystem responses to elevated atmospheric carbon dioxide (CO2) levels at scales from the leaf to the globe and from the second to the century. In particular, response to elevated CO2 may generally be smaller at low relative to high soil N supply and, in turn, elevated CO2 may influence soil N processes that regulate N availability to plants. Such responses could constrain the capacity of terrestrial ecosystems to acquire and store C under rising ele- vated CO2 levels. This review highlights the theory and empirical evidence behind these potential interactions. We address effects on photosynthesis, primary production, biogeochemistry, trophic in- teractions, and interactions with other resources and environmental factors, focusing as much as possible on evidence from long-term field experiments.
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Objectives This study examines the influence of tree species in relation to biomass and soil C dynamics in plantations established on former pasture land. Data on the C sink capacity of such plantations will provide valuable information for designing improved management strategies for afforestation programmes aimed at mitigating CO2 emissions. Methods The study was carried in the temperate forest of southern Europe, one of the most productive timber production systems in Europe. The study, designed to control most of the variability at regional level, involved a network of 120 paired plots (former pasture land-new plantations of different ages) established to construct three well-replicated chronosequences of the most common tree species in humid temperate systems. Results The mean rates of C sequestration (biomass and soil) estimated throughout the rotation ranged between 8.7 and 14.6 Mg C ha−1 year−1 (Eucalyptus nitens>Eucalyptus globulus>Pinus radiata), and the contribution of the soil (forest floor plus mineral soil) ranged from 8 to 18% (Eucalyptus nitens>Pinus radiata>Eucalyptus globulus). The humid temperate climate and the sandy loam texture of the soils favoured large losses of SOC from the uppermost mineral soils during the 10 year after afforestation. The higher loss of SOC in the Pinus radiata soil (26% of initial SOC) than in the Eucalyptus soil (19.45% of initial SOC) was attributed to the lower transfer of organic C to the mineral soil, as a result of the lower litter decomposition rate and the lower belowground litter input from associated vegetation. The rapid development of tree biomass favoured the subsequent C sequestration in biomass and soils. Conclusion The C sink capacity of forest plantations can be maximized by elongating the rotation length and adopting suitable management strategies for each species. This is especially important in intensive forest plantations in which the high intensity of harvesting may prevent accumulation of SOC in the long term.
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The filtering function of soil is an important ecosystem service for groundwater and surface water protection. The efficiency of soils as a filter depends on the behaviour of pollutants in the soil and the hydrological transport processes. This paper aims to identify knowledge gaps in processes influencing pollutant behaviour in soils and their potential transport to groundwater. Currently most soil-filter function research is approached from two disciplines, one originating from agronomical/environmental sciences; one from more fundamental hydrological process research. Combining insights and approaches from both disciplines through collaboration could lead to better understanding of this complex system and enhance assessments of management strategy changes, both over the long term as well as in different climatic settings.
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The replacement of native vegetation by pastures or tree plantations is increasing worldwide. Contradictory effects of these land use transitions on the direction of changes in soil organic carbon (SOC) stocks, quality, and vertical distribution have been reported, which could be explained by the characteristics of the new or prior vegetation, time since vegetation replacement, and environmental conditions. We used a series of paired-field experiments and a literature synthesis to evaluate how these factors affect SOC contents in transitions between tree- and grass-dominated (grazed) ecosystems in South America. Both our field and literature approaches showed that SOC changes (0–20 cm of depth) were independent of the initial native vegetation (forest, grassland, or savanna) but strongly dependent on the characteristics of the new vegetation (tree plantations or pastures), its age, and precipitation. Pasture establishment increased SOC contents across all our precipitation gradient and C gains were greater as pastures aged. In contrast, tree plantations increased SOC stocks in arid sites but decreased them in humid ones. However, SOC losses in humid sites were counterbalanced by the effect of plantation age, as plantations increased their SOC stocks as plantations aged. A multiple regression model including age and precipitation explained more than 50% (p < 0.01) of SOC changes observed after sowing pastures or planting trees. The only clear shift observed in the vertical distribution of SOC occurred when pastures replaced native forests, with SOC gains in the surface soil but losses at greater depths. The changes in SOC stocks occurred mainly in the silt+clay soil size fraction (MAOM), while SOC stocks in labile (POM) fraction remained relatively constant. Our results can be considered in designing strategies to increase SOC storage and soil fertility and highlight the importance of precipitation, soil depth, and age in determining SOC changes across a range of environments and land-use transitions.