Chinese Grasslands Research Articles

Deterministic processes dominate soil methanotrophic community assembly in grassland soils

The biogeographical distribution of methanotrophic communities and the mechanisms driving methanotrophic community assembly in grassland soils are largely unknown. In this study, the assembly mechanisms of methanotrophic communities and the niche preferences of specific methanotrophic taxa were investigated in three Chinese grassland regions, including the Inner Mongolian Plateau (IMP), the Xinjiang Autonomous Region (XAR) and the Tibetan Plateau (TP) across 1500, 1000 and 1000 km, respectively. We analyzed the relative importance of deterministic and stochastic processes on methanotrophic community assembly and assessed how assembly is affected by environmental and spatial factors. The results revealed the presence of various methanotrophic taxa in the different grassland regions. Deterministic processes were dominant in the methanotrophic community assembly, and heterogeneous selection had a greater contribution in shifting the methanotrophic community than did homogeneous selection, dispersal limitations, homogenizing dispersal and drift. Moreover, key environmental factors shaping the methanotrophic communities were scale-dependent and varied among the three regions. The primary variables identified as shaping methanotrophic communities were the aridity index, total nitrogen, and mean annual temperature in the IMP, XAR and TP grasslands at regional scales, whereas pH was the primary variable when considering all of the regions together. In general, the soil methanotrophic community assembly was primarily influenced by deterministic processes and responded in a predictable manner to major environmental factors at a regional scale.

Changes in productivity and carbon storage of grasslands in China under future global warming scenarios of 1.5°C and 2°C

Abstract Aims The impacts of future global warming of 1.5°C and 2°C on the productivity and carbon (C) storage of grasslands in China are not clear yet, although grasslands in China support ~45 million agricultural populations and more than 238 million livestock populations, and are sensitive to global warming. Methods This study used a process-based terrestrial ecosystem model named ORCHIDEE to simulate C cycle of alpine meadows and temperate grasslands in China. This model was driven by high-resolution (0.5° × 0.5°) climate of global specific warming levels (SWL) of 1.5°C and 2°C (warmer than pre-industrial level), which is downscaled by EC-EARTH3-HR v3.1 with sea surface temperature and sea-ice concentration as boundary conditions from IPSL-CM5-LR (low spatial resolution, 2.5° × 1.5°) Earth system model (ESM). Important Findings Compared with baseline (1971–2005), the mean annual air temperature over Chinese grasslands increased by 2.5°C and 3.7°C under SWL1.5 and SWL2, respectively. The increase in temperature in the alpine meadow was higher than that in the temperate grassland under both SWL1.5 and SWL2. Precipitation was also shown an increasing trend under SWL2 over most of the Chinese grasslands. Strong increases in gross primary productivity (GPP) were simulated in the Chinese grasslands, and the mean annual GPP (GPPMA) increased by 19.32% and 43.62% under SWL1.5 and SWL2, respectively. The C storage increased by 0.64 Pg C and 1.37 Pg C under SWL1.5 and SWL2 for 50 years simulations. The GPPMA was 0.670.390.88 (0.82) (model meanminmax (this study)), 0.850.451.24 (0.97) and 0.940.611.30 (1.17) Pg C year−1 under baseline, SWL1.5 and SWL2 modeled by four CMIP5 ESMs (phase 5 of the Coupled Model Inter-comparison Project Earth System Models). In contrast, the mean annual net biome productivity was −18.55−40.374.47 (−3.61),18.65−2.0364.03 (10.29) and 24.158.3838.77 (24.93) Tg C year−1 under baseline, SWL1.5 and SWL2 modeled by the four CMIP5 ESMs. Our results indicated that the Chinese grasslands would have higher productivity than the baseline and can mitigate climate change through increased C sequestration under future global warming of 1.5°C and 2°C with the increase of precipitation and the global increase of atmospheric CO2 concentration.

Effects and relationships of grazing intensity on multiple ecosystem services in the Inner Mongolian steppe

Grassland ecosystems are one of the most important terrestrial ecosystems in the world, producing essential both goods and ecosystem services (ES) for human beings. The Inner Mongolian steppe is a major grassland ecosystem in Northern China, covering 13.5% of the northern Chinese grassland area, and playing important ecological roles for the adjacent region of the capital Beijing-Tianjin-Hebei. Quantification of grassland ES under the different utilization patterns is vital for the maintenance of multiple ES and mitigation against ES loss in this region. We made a manipulative experiment with four grazing intensities (grazing exclusion, GE; light grazing intensity, LG; medium grazing intensity, MG; heavy grazing intensity, HG). We then quantified the intensities of eight different grassland ES (1. herbage intake, HT; 2. biodiversity conservation, BI; 3. soil nutrient retention, SN; 4 soil carbon stocks SC; 5. soil erosion prevention, SEP; 6. soil water storage, SWC; 7. potential nutrient recycling, PNC; 8. carbon sequestration from atmosphere. CS) and total ES via a series of field measurements. Pearson coefficients and trade-offs index were used to access the above ES relationships and degree of trade-offs between ES. Grazing intensities significantly (p < 0.05) affected the grassland intensities of ‘regulating’, ‘culture’ and ‘provisioning’ services, but the ‘supporting’ services. We found three types of relationships (trade-offs, synergy or neutral) have been found in this study. Trade-offs occurred between ‘provisioning’ and ‘regulating’ services. Although GE management presented significantly higher intensity of total ES (0.64) than LG (0.52), LG management significantly weakened the trade-offs between ‘provisioning’ and ‘regulating’ services (Trade-offs index 0.22) in comparison with GE (Trade-offs index 11.02). Our study suggests, therefore, that LG is the most suitable grassland utilization practice in the Inner Mongolian steppe.

Climate and soil parameters are more important than denitrifier abundances in controlling potential denitrification rates in Chinese grassland soils

Denitrification is an important process that influences nitrogen (N) loss and the production of greenhouse gas in grassland soils. However, the relative contributions of abiotic and biotic factors to soil denitrification potential at the regional and sub-regional scales in grassland ecosystems remain elusive. In this study, soil samples were collected from 21 sites at three steppes of China, including the Inner Mongolia Plateau (IMP), the Xinjiang Autonomous Region (XAR) and the Tibetan Plateau (TP) grasslands. Results showed that the key factors controlling the denitrification potential were regional and scale-dependent. At the sub-regional scales, soil pH, aridity index (AI) and total organic carbon (TOC) explained the highest variances on denitrification potential in the IMP, XAR and TP steppe, respectively. At the regional scale, the mean annual precipitation (MAP) was the most important environmental driver for the denitrification potential. Partial least squares (PLS) path modeling revealed that the MAP might regulate denitrification potential directly and indirectly by its effects on the plant and soil properties. Overall, these results help to improve our understandings on the prediction of the denitrification potential under global changes and revealed that the denitrification potential at various scales could be regulated by the multiple interactions of abiotic and biotic factors.

Illumina Sequencing Revealed Soil Microbial Communities in a Chinese Alpine Grassland

Soil microbial community is the main driving force for nutrient cycles and energy transformations in the alpine grassland. A limited number of studies have investigated the soil microbial diversity in alpine grassland and its influencing factors. Here, we present the first description of microbial communities inhabiting the soil from the Bayinbuluke alpine grassland, which lies in the middle of the southern slope of the Tianshan Mountains in Xinjiang, China using Illumina amplicon sequencing. In total, we obtained 432,820 high quality sequences. The results showed that the Shannon index ranged from 4.631 to 6.578, and extremely diverse soil microbial communities with 41 phyla, or groups, were spread out among the 16 soil samples. The communities were dominated by Thaumarchaeota (20.2 ± 15.5%) in the soil of the alpine grassland. The other five most abundant phyla were Chloroflexi (18.1 ± 9.2%), Acidobacteria (13.2 ± 7.5%), Planctomycetes (10.4 ± 3.4%), Proteobacteria (10.2 ± 8.1%), and Actinobacteria (9.4 ± 4.3%). Additionally, the Candidatus Nitrososphaera, Roseiflexus, Blastocatella. Pirellula, Thiobacillus, Sphingomonas, Rubrobacter were the dominant genus among the 16 soil samples. Statistical analyses showed significant spatial variations in the soil microbial community at our field sites, and total organic carbon was the factor most highly correlated with the soil microbial community variance.

Methane emissions in grazing systems in grassland regions of China: A synthesis

The effects of grazing on methane (CH4) budgets are important for understanding the balance of greenhouse gas emissions and removals in grassland ecosystems. However, the CH4 budgets of grazing systems, that is simultaneously considering CH4 uptake by grassland soils and emissions from ruminant enteric fermentation, livestock folds and animal feces, are poorly investigated, particularly for Chinese grasslands, and thus, remained unclear currently. Here, a synthesis of 43 individual studies was carried out to assess the grazing season/annual CH4 budgets and their responses to grazing in grassland ecosystems of China. The results showed that heavy grazing (HG) significantly decreased, while light grazing (LG) and moderate grazing (MG) had no significant effects soil CH4 uptake, as compared to un-grazing sites. Grazing has shifted Chinese grasslands from a sink to source for atmospheric CH4, and the grazing season/annual CH4 budgets increased with increasing grazing intensity, while the offset of CH4 uptake by grassland soils to total CH4 emissions from sheep, sheepfolds and feces were exponentially decreased with increasing grazing intensity. Moreover, the herbage biomass (HBM), organic matter intake (OMI) and live weight gain (LWG) were decreased while CH4 emission intensities (i.e., CH4 emission per HBM, OMI, and LWG) were linearly increased with increasing grazing intensity. Our results demonstrate that mediating grazing intensity, e.g., from HG to LG, could yield the optimal balance between maintaining productive grasslands and meanwhile mitigating CH4 emissions. This study could help for building strategies with implications for grassland management in China with similar CH4 emission problems.

Patterns of soil respiration and its temperature sensitivity in grassland ecosystems across China

Abstract. Soil respiration (Rs), a key process in the terrestrial carbon cycle, is very sensitive to climate change. In this study, we synthesized 54 measurements of annual Rs and 171 estimates of Q10 value (the temperature sensitivity of soil respiration) in grasslands across China. We quantitatively analyzed their spatial patterns and controlling factors in five grassland types, including temperate typical steppe, temperate meadow steppe, temperate desert steppe, alpine grassland, and warm, tropical grassland. Results showed that the mean (±SE) annual Rs was 582.0±57.9 g C m−2 yr−1 across Chinese grasslands. Annual Rs significantly differed among grassland types, and was positively correlated with mean annual temperature, mean annual precipitation, soil temperature, soil moisture, soil organic carbon content, and aboveground biomass, but negatively correlated with soil pH (p&lt;0.05). Among these factors, mean annual precipitation was the primary factor controlling the variation of annual Rs among grassland types. Based on the overall data across Chinese grasslands, the Q10 values ranged from 1.03 to 8.13, with a mean (±SE) of 2.60±0.08. Moreover, the Q10 values varied largely within and among grassland types and soil temperature measurement depths. Among grassland types, the highest Q10 derived by soil temperature at a depth of 5 cm occurred in alpine grasslands. In addition, the seasonal variation of soil respiration in Chinese grasslands generally cannot be explained well by soil temperature using the van't Hoff equation. Overall, our findings suggest that the combined factors of soil temperature and moisture would better predict soil respiration in arid and semi-arid regions, highlight the importance of precipitation in controlling soil respiration in grasslands, and imply that alpine grasslands in China might release more carbon dioxide to the atmosphere under climate warming.

The effects of changes in water and nitrogen availability on alien plant invasion into a stand of a native grassland species.

Plant invasions are a major component of global change, but they may be affected by other global change components. Here we used a mesocosm-pot experiment to test whether high water availability, nitrogen (N) enrichment and their interaction promote performance of three invasive alien plants (Lepidium virginicum, Lolium perenne and Medicago sativa) when competing with a native Chinese grassland species (Agropyron cristatum). Single plants of the three invasive and the one native species were grown in the center of pots with a matrix of the native A. cristatum under low, intermediate or high water availability and low or high N availability. The invasive species L. virginicum and M. sativa grew larger, and produced a higher biomass relative to competitors than the native species A. cristatum did. Increasing water availability promoted biomass production of all species, but water availability did not change the biomass of the central plants relative to that of the competitors. Nitrogen addition also increased biomass production of all species, and it increased the biomass of the central plants more so than that of the competitors. The positive effect of N addition on the biomass of the central plants relative to that of the competitors increased with increasing water availability. However, compared to central plants of the native species, the positive effect of N addition on the relative biomass of L. virginicum decreased when water availability increased. These interactions indicate that future changes in water availability and N enrichment may affect the invasion success of different alien species differently.

Farmers’ adaptability to the policy of ecological protection in China—A case study in Yanchi County, China

Due to long-term human activities, grassland ecosystems have been severely damaged. To protect grassland ecosystems, the prohibited grazing policy (PGP), a grassland ecological protection policy, was instituted for Chinese grasslands in 2002. However, it is unknown whether farmers have effectively adapted to the PGP. The adaptability of farmers to this policy has directly influenced the effective implementation of the policy and the sustainable development of the ecosystem. Previous research on adaptability has not focused on the adaptation to political change. This article uses a case study in Northwest China to investigate the adaptability of farmers to the policy. First, we study the restoration status of ecosystems. In addition, this paper studies the perceptions regarding farmers’ adaptability to the policy and explores the adaptation strategies of different types of farmers. Finally, this paper discusses the main factors that influence farmers’ choice of adaptation strategies. The implementation of the PGP has achieved remarkable ecological benefits. Farmers of different types had different adaptation perceptions, and their choices of adaptation strategies also varied. In addition to the farmers’ perception of the policy, the main factors that influenced farmers’ adaptation strategies also included livelihood capital.

Annual N2O emissions from conventionally grazed typical alpine grass meadows in the eastern Qinghai–Tibetan Plateau

Annual nitrous oxide (N2O) emissions from high-altitude alpine meadow grasslands have not been effectively characterized because of the scarcity of whole-year measurements. The authors performed a year-round measurement of N2O fluxes from three conventionally grazed alpine meadows that represent the typical meadow landscape in the eastern Qinghai–Tibetan Plateau (QTP). The results showed that annual N2O emissions averaged 0.123±0.053 (2SD, i.e., the double standard deviation indicating the 95% confidence interval) kgNha−1yr−1 across the three meadow sites. N2O flux pulses during the spring freezing-thawing period (FTP) were observed at only one site, indicating a large spatial variability in association with soil moisture differences. Approximately 34–57% (mean: 46%) of the annual N2O emissions occurred in the non-growing season, highlighting the substantial importance of accurate flux observations during this period. The simultaneous observations showed conservative, marginal nitric oxide (NO) fluxes of 0.058±0.032 (2SD) kgNha−1yr−1. The N2O fluxes across the three field sites correlated negatively with the soil nitrate concentrations during the entire year-round period (P<0.05). Furthermore, a significant joint regulatory effect of topsoil temperature and moisture on the N2O and NO fluxes was observed during the relatively warm periods. Based on the results of the present and previous studies, a simple extrapolation roughly estimated the annual total N2O emission from Chinese grasslands to be 73±15 (2SD) GgNyr−1 (1Gg=109g). A linear dependence of the annual N2O fluxes on the aboveground net primary productivity (ANPP) was also found. This result may provide a simple approach for estimating the N2O emission inventories of frigid alpine or temperate grasslands that are ungrazed either in the summer or year round. However, further confirmation of this relationship with a wider ANPP range is still needed in the future studies.

Large‐Scale Distribution of Molecular Components in Chinese Grassland Soils: The Influence of Input and Decomposition Processes

AbstractChinese grasslands hold a third of the national soil organic carbon (OC) stocks but remain poorly investigated in terms of soil molecular components and their distribution patterns. Such information is important for understanding mechanisms governing grassland soil OC dynamics and its response to global changes. Here employing solvent‐extractable compounds as a group of widely used biomarkers, we present a large‐scale study on the distribution of different soil OC components (including plant‐ and microbial‐derived carbohydrates and aliphatic and cyclic lipids) in the surface soils of Chinese grasslands, spanning from temperate grasslands in the arid/semiarid regions to alpine grasslands on the Qinghai‐Tibetan Plateau. We show that alpine grassland soils are more enriched with carbohydrates and plant‐derived compounds relative to the temperate counterparts due to temperature‐inhibited decomposition. While plant belowground biomass plays a key role in explaining the spatial variation of compounds in the alpine grasslands, climatic variables do in the temperate region. In particular, aliphatic lipids accumulate with increasing mean annual temperature in the temperate grasslands due to a preferential decay of labile soil OC, whereas they decrease in the alpine grasslands owing to dilution by an enhanced plant input of nonlipid components. Collectively, these results demonstrate different mechanisms governing the distribution of solvent‐extractable compounds in grassland soils, with climate‐mediated decomposition processes dominating in the temperate grasslands and plant inputs being more important in the alpine region. In the context of climate change, alterations to soil OC input and decomposition processes may have varied impacts on soil carbon cycling in these two regions.

Sustainable management of Chinese grasslands—issues and knowledge

Sustainable management of Chinese grasslands—issues and knowledge

Foliar carbon, nitrogen, and phosphorus stoichiometry in a grassland ecosystem along the Chinese Grassland Transect

Carbon (C), nitrogen (N), and phosphorus (P) are the basic nutrient elements required for plant growth and function. Ecological stoichiometry provides an important method for the determination of plant nutrient utilization and the environmental adaptation strategies of plants. Studying the stoichiometry of C, N and P is crucial to the understanding of nutrient cycling and ecosystem stabilization mechanisms. Most studies so far have focused only on N and P stoichiometry for plant leaves and ignored the stoichiometry characteristics among C, N, and P. As a major element of plant dry matter, C, along with critical nutrient elements (N and P) could regulate and influence the consumption and fixation of organic matter in ecosystems. Therefore, it is necessary to study the ecological stoichiometry of C, N, and P in plants. Here, C, N and P concentrations and their ratios were measured for 329 foliar samples collected at 132 sites along the 4500km-long Chinese Grassland Transect (CGT) that traverses the Inner Mongolian and Qinghai-Tibet Plateaus. The content of C, N, and P of plant leaves in grassland ranged from 257.40 to 590.77mg/g, 4.49 to 45.85mg/g, and 0.20 to 3.40mg/g, with an average of 463.76mg/g, 19.94mg/g, 1.31mg/g, respectively. The coefficient of variation (CV) of P was highest (0.47) while the CV values of C and N were 0.09 and 0.34, respectively. N and P were positively correlated (R2=0.491, P<0.0001), in agreement with previous studies, while no significant correlation was found between C and P or between C and N. The ranges for C/N, N/P, and C/P were 10.93–93.67 (with an average of 26.86 and a CV value of 0.46) for C/N, 1.68–53.00 (with an average of 16.59 and a CV value of 0.39) for N/P, and 61.49–1995.24 (with an average of 436.77 and a CV value of 0.59) for C/P, respectively. The mass ratio of C:N:P in grassland plant was 440:17:1, and the atom ratio was 1136:43:1. C/N and C/P, C/N and N/P were positively correlated (R2=0.509, P<0.0001; R2=0.410, P<0.0001, respectively), while C/N and N/P were not significantly correlated. C concentrations of grassland plant in the Chinese Grassland Transect were close to those at the global scale, but lower than that in forests in China. N and P concentrations in grassland plant were lower than those in global terrestrial plants, while N concentrations were much higher but P concentrations were much lower than those in forest plants. C/N and C/P were relatively higher, reflecting the higher vegetative utilization efficiency of grassland vegetation. The CV of P was much higher and the N/P in this study was higher than 16, which indicated that grassland plants in China are more restricted by P elements. Our results could help to understand the relationship between C, N, and P stoichiometry in grassland plants and provide basic data for related ecological models.

Scale-dependent key drivers controlling methane oxidation potential in Chinese grassland soils

Methane (CH4) oxidation plays a critical role in mitigating global warming. However, the key environmental drivers shaping CH4 oxidation rate at regional and sub-regional scales in grassland ecosystems remain poorly understood. In this study, we collected soils from 21 sites at the regional scale across three steppes of China, including grasslands in Inner Mongolia Plateau (IMP), Xinjiang Autonomous Region (XAR) and Tibetan Plateau (TP). Potential CH4 oxidation rate was measured, and the compositions and abundances of methanotrophs were analyzed by quantitative PCR (qPCR) and Miseq sequencing technique. The factors controlling CH4 oxidation potential at regional and sub-regional scales were evaluated by means of partial least squares path modeling (PLS-PM) and multiple regression on distance matrices (MRM). The results showed that the compositions and abundances of methanotrophs varied at different sub-regions. Type I methanotrophs were predominant in soils from the Inner Mongolia steppe and Xinjiang Autonomous Region, whereas pxmA methanotrophs mainly distributed in the Tibetan alpine steppe soil. Measured environmental variables explained the variations of CH4 oxidation potential well at both regional and sub-regional scales in these Chinese grassland ecosystems. However, the contributions of different variables to CH4 oxidation potential were scale-dependent. At the regional scale, total nitrogen (TN) was the environmental variable that best explained the potential CH4 oxidation rate, and its influence might be mainly associated with its effects on plant growth and methanotrophic community traits. At sub-regional scales, the main controlling variables were total organic carbon (TOC) and soil texture in Inner Mongolia steppe, aridity index (AI) and mean annual temperature (MAT) in Xinjiang Autonomous Region, and TN in Tibetan alpine steppe. These results further suggested that the impacts of environmental variables on CH4 oxidation rate were realized either through their effects on methanotrophic communities, and/or by affecting soil properties in the grassland ecosystems.

Grassland restoration in northern China is far from complete: evidence from carbon variation in the last three decades

AbstractEcosystem restoration requires considering both above‐ground biomass (AGB) and soils, and the latter is even more essential due to the importance and restoration difficulty of soil organic matter (SOM). Remote sensing studies have shown that AGB has recovered in the grasslands of northern China, but the recovery of soil organic carbon (SOC) or SOM is still unclear. Here, based on the published data between the 1980s and 2014, we used the variation in carbon (C) density observed in the vegetation and soils of four regions across northern China as integrative indicator to explore grassland restoration. Overall, northern Chinese grasslands were a weak carbon source (−14 Tg C), although C density in AGB and below‐ground biomass increased on average by 0.019 and 0.224 kg C/m2, respectively, during the period considered in the present study. Unexpectedly, SOC density in the 0–20 cm soil layer decreased by 0.193 kg C/m2 on average, and all regions registered a decrease in SOC, although values differed among them. Our findings were consistent with previous evaluations using remote sensing and with the idea that vegetation in northern China has been restored. However, SOC has not been restored, and given its importance for sustaining nutrient supply and water conservation, as well as the high difficulty of SOC restoration, grassland restoration in northern China is still far from being achieved.

Relationships between below-ground biomass and foliar N:P stoichiometry along climatic and altitudinal gradients of the Chinese grassland transect

N and P concentrations and their ratios were determined for 132 foliar and 120 below-ground biomass (BGB) samples obtained at 132 sites along the 4500 km Chinese Grassland Transect (CGT) across the Inner Mongolian and Qinghai–Tibet Plateaus. Patterns of foliar and BGB N, P and their ratio (N/P) at the community level were related to altitude, temperature, and precipitation gradients. Also, patterns of relative N and P foliar and BGB concentrations were determined (NF/B, foliar N/BGB N; PF/B, foliar P/BGB P). The relationship between foliar N concentrations and mean annual temperature (MAT) was negative, agreeing with the Temperature-Plant Physiological hypothesis, whereas BGB N decreased with decreasing MAT, supporting the Biogeochemical hypothesis. Patterns of BGB N varying with altitude, MAP and MAT differed from the patterns for leaf N, which may indicate differences in nutrient allocation and utilization by leaves and BGB. NF/B and PF/B may reflect trade-offs by plants for N and P in leaves and BGB. For the entire CGT, NF/B and PF/B increased as altitude increased. NF/B was positively related with MAP but negatively related with MAT, while PF/B showed no correlations with MAP and MAT. Results suggest that ecological stoichiometry at the community level is similar to that at the species level. Strategies of nutrient utilization by leaves and BGB are indicated to be different, and abiotic environmental conditions could influence the stoichiometric characteristics and nutrient allocation to leaves and BGB.

Increasing temperature reduces the coupling between available nitrogen and phosphorus in soils of Chinese grasslands

Changes in climatic conditions along geographical gradients greatly affect soil nutrient cycling processes. Yet how climate regimes such as changes in temperature influence soil nitrogen (N) and phosphorus (P) concentrations and their stoichiometry is not well understood. This study investigated the spatial pattern and variability of soil N and P availability as well as their coupling relationships at two soil layers (0–10 and 10–20 cm) along a 4000-km climate transect in two grassland biomes of China, the Inner Mongolian temperate grasslands and the Tibetan alpine grasslands. Our results found that in both grasslands, from cold to warm sites the amounts of soil total N, total P and available P all decreased. By contrast, the amount of available N was positively related to mean annual temperature in the Tibetan grasslands. Meanwhile, with increasing temperature ratio of available N to P significantly increased but the linear relationship between them was considerably reduced. Thus, increasing temperature may not only induce a stoichiometric shift but also loose the coupling between available N and P. This N-P decoupling under warmer conditions was more evident in the Tibetan alpine grasslands where P limitation might become more widespread relative to N as temperatures continue to rise.

Ecosystem response more than climate variability drives the inter-annual variability of carbon fluxes in three Chinese grasslands

The inter-annual variability (IAV) of net ecosystem productivity (NEP) may be caused by both climatic factors and ecosystem responses. In this study, we used eddy covariance (EC) measurements over three typical grasslands in China to investigate the dynamics of NEP and its two components − gross primary productivity (GPP) and ecosystem respiration (Re) and their driving forces. We found that climatic factors and ecosystem response simultaneously influence the IAV of ecosystem carbon fluxes, with a dominant effect arising from an ecosystem response. On a daily scale, carbon fluxes were driven primarily by climatic factors, but effects from an ecosystem response strengthened when the period of analysis was extended. On an annual scale, ecosystem responses weakened the effects of climatic variability on ecosystem carbon fluxes for the three grasslands. This negative feedback demonstrated that ecosystem acclimatization to climate variability can constrain the IAV of carbon fluxes induced by such variability.

An economic analysis of photovoltaic water pumping irrigation systems

ABSTRACTIrrigation using the photovoltaic water pumping (PVWP) systems represents a sustainable and attractive solution, which can combat Chinese grassland desertification and promote a sustainable development of the agricultural sector. This paper investigates the economics of PVWP systems taking into consideration the effects of the key components on the initial capital cost (ICC), life cycle cost (LCC), and revenues. Sensitivity analyses are conducted regarding the crop yield and price, cost of photovoltaic modules, and system components included in the ICC. Results show that the cost of the PVWP system is the most sensitive parameter affecting the ICC under the assumptions made, especially the cost of the PV modules; whereas, the crop production and price affect the net present value (NPV) and payback period (PBP) clearly. The PVWP has surplus power output when the crop water demand is low or it is non-irrigation season. The potential benefit from selling the surplus electricity is also discussed. In addition, the indirect benefits of carbon sequestration and CO2 emission reduction by applying PVWP systems are addressed in this paper.

Carbon storage in Chinese grassland ecosystems: Influence of different integrative methods.

The accurate estimate of grassland carbon (C) is affected by many factors at the large scale. Here, we used six methods (three spatial interpolation methods and three grassland classification methods) to estimate C storage of Chinese grasslands based on published data from 2004 to 2014, and assessed the uncertainty resulting from different integrative methods. The uncertainty (coefficient of variation, CV, %) of grassland C storage was approximately 4.8% for the six methods tested, which was mainly determined by soil C storage. C density and C storage to the soil layer depth of 100 cm were estimated to be 8.46 ± 0.41 kg C m−2 and 30.98 ± 1.25 Pg C, respectively. Ecosystem C storage was composed of 0.23 ± 0.01 (0.7%) above-ground biomass, 1.38 ± 0.14 (4.5%) below-ground biomass, and 29.37 ± 1.2 (94.8%) Pg C in the 0–100 cm soil layer. Carbon storage calculated by the grassland classification methods (18 grassland types) was closer to the mean value than those calculated by the spatial interpolation methods. Differences in integrative methods may partially explain the high uncertainty in C storage estimates in different studies. This first evaluation demonstrates the importance of multi-methodological approaches to accurately estimate C storage in large-scale terrestrial ecosystems.