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Responses of aboveground and belowground net primary productivity to sand burial and enhanced precipitation in a semi‐arid desertified steppe

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Abstract

Sand burial and precipitation drive plant community structure and functions in (semi‐)arid desertified areas, while net primary productivity (NPP) is one of the most important indicators of plant community function. However, how NPP responds to sand burial in combination with changed precipitation regimes is still unclear. We conducted a field experiment with simultaneous sand burial and enhanced precipitation treatments to test the responses of both aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP) in a semi‐arid desertified steppe in North China. The results showed that sand burial significantly affected the community ANPP but had no significant effects on the community BNPP. Sand burial increased the ANPP of rhizome grass and decreased the ANPP of perennial herbs, bunchgrass and annual herbs, with no significant effects on legume herbs, while enhanced precipitation did not significantly affect the community ANPP and BNPP or the ANPP of all five plant functional types (PFTs). Sand burial combined with enhanced precipitation mediated the vertical allocation of BNPP in the community. There are multiple significant relationships between the ANPP of different PFTs and the BNPP among the different soil layers. These findings will be conducive to understanding the consequences of grassland desertification under the background of climate change, with corresponding implications for grassland management and vegetation restoration in (semi‐)arid desertified areas. This article is protected by copyright. All rights reserved.

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Sand burial and precipitation play important roles in vegetation of inland deserts and desertified areas, and both are under strong influence of climate and land-use change. Sand deposition and precipitation both vary greatly in space and time, and different plant species, with diverse adaptations, occupy different niches along spatial gradients in the combination of sand and water availability dynamics. We hypothesized that species specificity in spatial and temporal niche occupation along such gradients is a mechanism for their co-existence and, thereby, a driver and stabilizer of biodiversity in dry, sandy areas.
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The relationship between abovegound net primary production (ANPP) and water use varies significantly among ecosystem types. For both hot deserts and shortgrass prairie-cold deserts which are water limited, ANPP is linearly related to annual water use above minimum amount of water, estimated at 38 and 170 mm, respectively, needed annually to sustain each system. Once the minimum water too sustain ANPP is reached, ANPP increases an estimated 0.38 g and 1.09 g per 1000 g of additional water in the hot desert and the shortgrass prairie-cold desert. In forest systems not water stressed, ANPP was not related to water use. For grasslands representing a gradient from water stressed toward not water stressed, ANPP correspondingly declined per unit of water used. Classically evaluating water-use efficiency as annual ANPP divided by annual evapotranspiration, forests are the most efficient, 0.9 to 1.8 g ANPP/1000 g water, followed by shortgrass prairie, 0.2 to 0.7, then hot deserts, 0.1 to 0.3.
Article
(1) During the summers of 1980 and 1981 part of an established population of Ammophila breviligulata growing along the Lake Huron shoreline was subjected to varying levels of artificial burial by sand. (2) As the burial depth was increased the number of emerging shoots as well as the above-ground biomass per unit area decreased. The dry weight per shoot increased with increasing burial depth only during 1980. (3) The plants emerged from a maximum depth of about 100--120 cm of sand. This emergence was primarily by elongation of stem internodes. However, there was an increase in the number of nodes on shoots emerging from ⩽ 60 cm of sand. Stem elongation brought the apical meristem to about 6--15 cm below the sand surface. Then the leaves grew upwards until they emerged from the sand surface. (4) After emergence, the longest shoots were equally high regardless of depth of burial.
Article
There has long been controversy on which environmental factor is the predominant determinant of community zonation on sand dunes. It is demonstrated here that, on a dune system in southern New Zealand, several environmental factors that could limit growth all vary along the sea-to-inland sand dune zonation: soil moisture, soil nutrients, wind exposure, sand burial, salt spray and soil salinity. Correlation of the responses of 30 species to experimental stress (burial, darkness, rooting-medium salinity and salt spray) with the zonation of the species in the field indicates that, in the four dune systems studied, sand burial and salt are both important, with salt generally being the more important. However, the relative importance of the factors differs between sites.
Article
The Chihuahuan desert of New Mexico, USA, has changed in historical times from semiarid grassland to desert shrublands dominated by Larrea tridentata and Prosopis glandulosa. Similar displacement of perennial grasslands by shrubs typifies desertification in many regions. Such structural vegetation change could alter average values of net primary productivity, as well as spatial and temporal patterns of production. We investigated patterns of aboveground plant biomass and net primary production in five ecosystem types of the Jornada Basin Long-Term Ecological Research (LTER) site. Comparisons of shrub-dominated desertified systems and remnant grass-dominated systems allowed us to test the prediction that shrublands are more heterogeneous spatially, but less variable over time, than grasslands.
Article
w Experimental climate manipulations provide the opportunity to link predicted changes in climate to the process of community assembly. We studied plant community assembly of a recently harvested forest exposed to three years of experimental 28 degrees C warming and 20% increased precipitation. By the end of the experiment, trees were the only functional group that shifted composition in response to warming and precipitation treatments (p=0.03), while the composition of the grass, forbs, and shrub/small tree/vine functional groups were unresponsive. Individual species within groups were associated with specific treatments, but did not result in a predictable community composition shift. Temporal dynamics of functional group cover were more sensitive to treatment effects than single, static measures of plant community responses such as biomass. Both static and dynamic plant analyses revealed interactive effects of warming and increased precipitation on cover and biomass of grass and all plants together (grass cover p=0.01, grass biomass p 0.02, total cover p=0.01, total biomass p=0.05). Short forb cover was negatively affected by increased precipitation throughout our experiment (p=0.03). Grass, tree, and shrub/small tree/vine functional groups showed independent year effects on cover that can be attributed to successional development of the forest community (all p = 0.01). Random forest modeling indicated that cover of other plant functional groups and static plot-level variables such as plot location and components of soil texture were often the most important predictors of cover for a given functional group, while temperature and moisture availability measures were the least important. Importance of predictors of functional group cover varied greatly among random forest models from different treatments, suggesting that diverse environmental factors constrain functional group cover and may provide resilience of community assembly to climate change.
Article
Understanding drivers of aboveground net primary production (ANPP) has long been a goal of ecology. Decades of investigation have shown total annual precipitation to be an important determinant of ANPP within and across eco-systems. Recently a few studies at individual sites have shown precipitation during specific seasons of the year can more effectively predict ANPP. Here we determined whether seasonal or total precipitation better predicted ANPP across a range of terrestrial ecosystems, from deserts to forests, using long-term data from 36 plant communities. We also deter-mined whether ANPP responses were dependent on ecosystem type or plant functional group. We found that seasonal precipitation generally explained ANPP better than total precipitation. Precipitation in multiple parts of the growing season often correlated with ANPP, but rarely interacted with each other. Surprisingly, the amount of variation explained by seasonal precipitation was not correlated with ecosystem type or plant functional group. Overall, examining seasonal precipitation can significantly improve ANPP predictions across a broad range of ecosystems and plant types, with impli-cations for understanding current and future ANPP variation. Further work examining precipitation timing relative to species phenology may further improve our ability to predict ANPP, especially in response to climate change.
Article
Salix cheilophila Schneid. is a naturally occurring Salix species in Mu Us Sandy Land, Inner Mongolia, China. We focused on the morphological adaptability of S. cheilophila to sand dune burial. For morphological measurements, 32 S. cheilophila seedlings were removed from a community which was in the process of being buried by a shifting sand dune. Each seedling collected included the entire root system. We measured the number, length, and biomass of the adventitious roots, primary lateral roots, and taproot, and compared the morphological characteristics of the root system, including adventitious roots, for seedlings buried to various levels in the sand. The growth range of adventitious roots increased as the length of the buried portion of the main shoot increased. In addition, the total dry weight of all current-year shoots tended to increase gradually with increasing total dry weight of the adventitious roots. These results suggest that S. cheilophila tends to make use of the sedimentary sand layer that accompanies shifting sand dunes. However, there was no correlation between biomass or number of adventitious roots and the length of the buried part of the main shoot. Thus, S. cheilophila does not grow adventitious roots proportional to the buried part. These morphological characteristics of the root system, including the adventitious roots, may indicate that S. cheilophila has poor morphological adaptability to sand dune burial.
Article
Aboveground net primary production (ANPP) in grassland ecosystems is positively related to mean annual precipitation (MAP). However, at any given level of precipitation, other factors may effect ANPP. Our objective was to determine the importance of temperature and soil texture in explaining ANPP in the Great Plains of the United States. We constructed a spatial database of ANPP, climate, and soil texture for the region using a geographic information system. Holding MAP constant at 5-cm intervals, we related ANPP to mean annual temperature (MAT), and soil sand and clay contents. Our findings indicate that MAT and soil texture are important variables for explaining patterns of ANPP, after accounting for the variability explained by MAP. There is a negative relationship between temperature and ANPP when MAP is held constant; this has important climate-change implications. Results revealed an MAP crossover point for the inverse texture effect at ~80 cm of rainfall, much higher than previously reported. The consequences of this are substantial for grasslands throughout the globe, where precipitation ranges between 25 and 100 cm.
Article
Precipitation regimes are predicted to become more variable with more extreme rainfall events punctuated by longer intervening dry periods. Water-limited ecosystems are likely to be highly responsive to altered precipitation regimes. The bucket model predicts that increased precipitation variability will reduce soil moisture stress and increase primary productivity and soil respiration in aridland ecosystems. To test this hypothesis, we experimentally altered the size and frequency of precipitation events during the summer monsoon (July through September) in 2007 and 2008 in a northern Chihuahuan Desert grassland in central New Mexico, USA. Treatments included (1) ambient rain, (2) ambient rain plus one 20 mm rain event each month, and (3) ambient rain plus four 5 mm rain events each month. Throughout two monsoon seasons, we measured soil temperature, soil moisture content (y), soil respiration (R s), along with leaf-level photosynthesis (A net), predawn leaf water potential (C pd), and seasonal aboveground net primary productivity (ANPP) of the dominant C 4 grass, Bouteloua eriopoda. Treatment plots receiving a single large rainfall event each month maintained significantly higher seasonal soil y which corresponded with a significant increase in R s and ANPP of B. eriopoda when compared with plots receiving multiple small events. Because the strength of these patterns differed between years, we propose a modification of the bucket model in which both the mean and variance of soil water change as a consequence of interannual variability from 1 year to the next. Our results demonstrate that aridland ecosystems are highly sensitive to increased precipitation variability, and that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.
Article
Global nitrogen (N) enrichment and changing precipitation regimes are likely to alter plant community structure and composition, with consequent influences on biodiversity and ecosystem functioning. Responses of plant community structure and composition to N addition and increased precipitation were examined in a temperate steppe in northern China. Increased precipitation and N addition stimulated and suppressed community species richness, respectively, across 6 years (2005–2010) of the manipulative experiment. N addition and increased precipitation significantly altered plant community structure and composition at functional groups levels. The significant relationship between species richness and soil moisture (SM) suggests that plant community structure is mediated by water under changing environmental conditions. In addition, plant height played an important role in affecting the responses of plant communities to N addition, and the effects of increased precipitation on plant community were dependent on species rooting depth. Our results highlight the importance and complexity of both abiotic (SM) and biotic factors (species traits) in structuring plant community under changing environmental scenarios. These findings indicate that knowledge of species traits can contribute to mechanistic understanding and projection of vegetation dynamics in response to future environmental change.
Article
Question: Is there a critical depth of burial by sand beyond which species and communities fail to recover, and does repeated incremental burial have a greater impact than a single large deposition?Location: The machair on the calcareous sand dunes on South Uist, in the Outer Hebrides of Scotland, UK.Methods: Eight turves were collected from each of four machair sub-community types. After acclimatization in an unheated polythene tunnel, they were buried with sterilized machair shell sand, either by one single burial to 5 cm or by five applications of 1 cm of sand at approximately seven-week intervals. Species response was recorded on five occasions.Results: Within machair sub-communities, burial by sand reduced the abundance (local rooted frequency) of plants more than it reduced species richness. Intermittent burial was more damaging than a single burial event. Those species with the highest pre-burial frequencies tended to dominate recovery in the sub-community as a whole. Species occurring across all four sub-community types exhibited varying responses to community burial between the differing types. Samples from slack sub-communities had distinctly different response characteristics from those of foredunes and unploughed and three-year fallow dune grassland.Conclusions: The perennial life-form of many machair species has been evolutionarily selected for and dominates throughout the machair habitat. Account needs to be taken of competitive interaction between species in relation to burial response. The results of the investigation show that the hypotheses of Gilbertson et al. and Kent et al. on ‘machair stratification’ require refinement in that frequency of shallow burial can be as important as overall burial depth.
Article
More than 50 years ago it was proposed that zonation of major plant species on coastal dunes was determined by salt spray. Here, we argue against this hypothesis because (i) salt concentrations rarely exceed toxic levels; (ii) high precipitation in temperate latitudes washes the salt off the plants; (iii) major salt spray events occur in late autumn and winter when plants are dormant; and (iv) zonation also occurs on lacustrine dunes. Instead, we show evidence that zonation may be caused by burial because plant distribution was correlated with sand deposition and species were eliminated when burial exceeded their limits of tolerance, thus creating zones of different plant species. We conclude that in temperate regions (i) burial by sand may be among the most important factors in zonation, while salt spray may play a secondary role; and (ii) single environmental factors cannot be the determinants of a phenomenon as complex as species zonation.
Article
Rain-fed agriculture is widespread in Inner Mongolia, northern China, where wind erosion of farmland is very common because of sandy soil and dry, windy weather. However, very little is known about the effects of wind erosion on soil physical and chemical properties in this region. A field experiment was conducted in sandy farmland, where erosional and depositional gradients were established to evaluate the effects of wind erosion and leeward sand accumulation on soil texture, nutrient content, soil water, and soil temperature. The research showed that long term wind erosion could result in significant soil coarseness, infertility and dryness. Severe erosion reduced clay by 59.6%, organic C by 71.2%, total N by 67.4%, total P by 31.4%, available N by 64.5%, available P by 38.8%, and average soil water content by 51.8%, compared with non-eroded farmland in the study region. The sand fraction (particles > 0.05 mm), pH and ground-surface temperature increased by 6.2%, 3.7%, and 2.2 °C, respectively. Accumulated sand also caused a decrease in nutrients and soil water content. Under severe sand accumulation, clay was reduced by 2.0%, organic C by 19.3%, total N by 21.7%, total P by 13.7%, available N by 52.5%, and average soil water content by 26.6%. The sand fraction, pH, available P, and ground-surface temperature increased by 0.2%, 0.9%, 5.8% and 2.8 °C, respectively.
Article
1 Relationships between above-ground net primary productivity (ANPP) of grasslands and annual precipitation are often weak at the site level, with much of the inter-annual variation in ANPP left unexplained. A potential reason for this is that the distribution of precipitation within a growing season affects productivity in addition to the total amount.2 We analysed long-term ANPP data for three southern African temperate grasslands (mean annual precipitation ranging from 538 mm to 798 mm) to determine the effects of precipitation event size, number and spacing relative to seasonal totals.3 Ungrazed, non-manipulated treatments at each site showed contrasting results despite sharing a common, dominant species. At the driest site, a model combining average event size and number of events per growing season provided a substantially better fit to the ANPP data than precipitation amount (seasonal total). At the wettest site, the interval between events was the most important precipitation variable. Precipitation distribution was not important at the intermediate site where amount was the best predictor of ANPP. A limit to the size of precipitation events efficiently utilized for ANPP was evident for the driest site only.4 At each site, experimental treatments that altered species composition and soil fertility had little effect on precipitation–ANPP relationships. The lack of consistency in the relative importance of the precipitation variables among sites suggests that local, edaphic factors modify precipitation–ANPP relationships.5 This analysis demonstrates that the distribution and size of precipitation events can affect ANPP independent of precipitation amount. As altered precipitation regimes are forecast by global climate models, the sensitivity of ecosystems to precipitation distribution should be considered when predicting responses to climate change.6 While mean values of precipitation, and other ecosystem drivers, are typically used to predict function at the level of whole ecosystems, our results show that more complex measures of environmental variability may be required to understand ecosystem function, and to increase the accuracy of predictions of ecosystem responses to global change.
Article
Many previous studies have attributed the degradation in the Mu Us Desert in China to many centuries of human activity. The present study includes analysis of proxies of human activity such as arable land area, population and livestock number, and variations of precipitation, evaporation, temperature, sand-driving wind and dust events, covering the period since 1950. It is demonstrated that desertification and vegetation rehabilitation during this period were principally related to the climatic variation, especially correlated to sand-driving winds. It also suggests that the desert evolution in the past 2000 years was controlled by climate change rather than human activity. Although human activity was significant in the desert evolution processes over the past 50 years, the impacts seems to be overestimated in previous studies. Desertification and desert evolution in the Mu Us Desert are mainly in response to climatic trends and fluctuations. Copyright © 2005 John Wiley & Sons, Ltd.
Article
Summary • Rhizomatous clonal plants frequently colonize and stabilize dunes on sea and lake shores, and in inland deserts and desertified areas, where sand burial is common. To date, little attention has been paid to how clonal integration affects their ability to withstand sand burial. • In an inland dune Psammochloa villosa ramets were buried under 0, 20, 40 and 60 cm of sand, and the rhizomes at the edges of the 50 × 50 cm2 treatment quadrats were either severed or left connected. • With increasing burial depth the surviving ramets of P. villosa decreased markedly both in number and in size (number of leaves and above-ground biomass). In the connected quadrats, however, sand burial resulted in significantly smaller decreases than in the severed quadrats of the number, but not in size, of the surviving P. villosa ramets. • We conclude that clonal integration increased the ability of P. villosa to withstand sand burial, and that P. villosa could emerge from deep burial probably by elongating vertical structures with the help of the energy imported from the connected, unburied ramets. ©New Phytologist (2004) doi: 10.1111/j.1469-8137.2004.01073.x
Article
Understanding the store and storage potential of carbon (C) and nitrogen (N) helps us understand how ecosystems would respond to natural and anthropogenic disturbances under different management strategies. We investigated organic C and N storage in aboveground biomass, litter, roots, and soil organic matter (SOM) in eight sites that were floristically and topographically similar, but which had been subjected to different intensities of disturbance by grazing animals. The primary objective of this study was to ascertain the impact of grazing exclusion (GE) on the store and storage potential of C and N in the Leymus chinensis Tzvel. grasslands of northern China. The results revealed that the total C storage (including that stored in aboveground biomass, litter, roots, and SOM, i.e. top 100-cm soil layer) was significantly different among the eight grasslands and varied from 7.0 kg C m−2 to 15.8 kg C m−2, meanwhile, the total N storage varied from 0.6 kg N m−2 to 1.5 kg N m−2. The soil C storage decreased substantially with grassland degradation due to long-term heavy grazing. 90% C and 95% N stored in grasslands were observed in the SOM, and they were minor in other pools. The limit range of C and N storage observed in these grassland soils suggests that GE may be a valuable mechanism of sequestering C in the top meter of the soil profile.
Article
Confirms the overwhelming importance of water availability as a control on production. Lowest values of aboveground net primary production were observed in the west, highest values in the east. This spatial pattern was shifted eastward during unfavorable years, westward during favorable years. Variability in production among years was maximum in N New Mexico and SW Kansas and decreased towards the N and S. The regional pattern of production was largely accounted for by annual precipitation. Production at site level was explained by annual precipitation, soil water-holding capacity, and an interaction term. When precipitation is <370 mm/yr, sandy soils with low water-holding capacity are more productive than loamy soils with high water-holding capacity; the opposite pattern occurs when precipitation is >370 mm/yr. -from Authors
Article
Extremes of weather and climate can have devastating effects on human society and the environment. Understanding past changes in the characteristics of such events, including recent increases in the intensity of heavy precipitation events over a large part of the Northern Hemisphere land area, is critical for reliable projections of future changes. Given that atmospheric water-holding capacity is expected to increase roughly exponentially with temperature--and that atmospheric water content is increasing in accord with this theoretical expectation--it has been suggested that human-influenced global warming may be partly responsible for increases in heavy precipitation. Because of the limited availability of daily observations, however, most previous studies have examined only the potential detectability of changes in extreme precipitation through model-model comparisons. Here we show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas. These results are based on a comparison of observed and multi-model simulated changes in extreme precipitation over the latter half of the twentieth century analysed with an optimal fingerprinting technique. Changes in extreme precipitation projected by models, and thus the impacts of future changes in extreme precipitation, may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming.
Article
Ecosystems are structurally organized as food webs within which energy is transmitted between trophic levels and dissipated into the environment. Energy flow between two trophic levels is given by the amount of production at the lower level and by the proportion of production that is consumed, assimilated and respired at the higher level. Considerable evidence indicates that food-web structure varies predictably in different habitats, but much less is known about quantitative relationships among food web fluxes. Many of the energetic properties of herbivores in African game parks are associated with rainfall and, by inference, with net primary productivity. Respiratory costs per unit production at the consumer trophic level are higher for homeotherms than for heterotherms. Plant secondary chemicals affect herbivore dietary choices and the allocation of plant resources to those chemicals varies with resource availability. How these phenomena are translated into ecosystem fluxes is unknown. We present evidence that herbivore biomass, consumption and productivity are closely correlated with plant productivity, suggesting that the latter is a principal integrator and indicator of functional processes in food webs.