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As the Third Pole of the world, the Tibetan Plateau provides a typical alpine grassland environment for soil bacteria with its unique frigid and arid climate. Owing to clear changes in spatial moisture and increased grazing intensity, moisture and livestock grazing have become key factors influencing the microbial communities. Accordingly, we investigated the diversity and composition of soil bacteria in a selected alpine grassland within the dual gradients of moisture and grazing using high-throughput sequencing. Our results showed that grazing changed the soil bacterial diversity and composition, whereas moisture only influenced the relative abundance of the segmental community at the small spatial scale. Species richness was found to be increased by moderate grazing compared with that by high or low-grazing intensity. The relative abundance of dominant species and β-diversity of soil bacteria both showed differences with heavy, moderate, and low grazing. Some dominant bacteria were altered with the moisture content. However, there were no significant differences according to the moisture gradient in terms of the overall bacterial β diversity and composition. These results might be taken account into the small spatial scale as well as the compensation of grazing to moisture on this scale. This work provides new insights into the soil bacterial response to moisture gradients and grazing intensity in alpine steppe habitat. [ABSTRACT FROM AUTHOR]

Plant growth plays an important role in regulating soil C and N as well as water regimes and can therefore influence soil biochemical or geochemical processes. A sub-model was built in DNDC (DeNitrification-DeComposition) to simulate crop growth; since its development, it has often been modified and adapted to suit specific purposes, crops and circumstances. Here, we review the chronological history of various versions of the DNDC plant growth sub-models and present the results of a literature search regarding the application of the DNDC model to various crops in agriculture. We found that food, oil and sugar crops were the primary research focus and accounted for 67.5%, 12.5% and 6.3% of all DNDC crop-based studies, respectively. We also summarize the research achievements published in recent years, and conclude that the DNDC plant growth sub-model could be successfully used to assist in predicting trace gas emissions and soil carbon and nitrogen dynamics after modifying some of the parameters obtained from relevant literature to suit local cultivars. The objective of this study is to provide DNDC users with an understanding of the model mechanisms related to field and horticultural crops, with suggestions for modelling different crops and outlining further model applications and modifications. [ABSTRACT FROM AUTHOR]

Furrow irrigation, which can be combined with fertilisation by dissolving solid fertilisers in irrigation water, is the most common practice in vineyards in the Ningxia Hui Autonomous Region, and drip irrigation and fertigation have been employed in some areas. These irrigation methods and their corresponding fertilisation schemes may affect nitrous oxide (N 2 O) emissions from the soil. Therefore, it is important to use a model to simulate differences in N 2 O emissions and identify farmland management methods that limit N 2 O emissions. During the July–August 2012 and July–September 2013 growing seasons, the denitrification and decomposition (DNDC) model was tested against experimental N 2 O emissions data from vineyards in Yuquanying, Yongning, Yinchuan, Ningxia. After model validation, the simulated differences in emissions between furrow irrigation and drip irrigation were 9.86 ± 0.845 and 0.966 ± 0.464 kg ha −1 a −1 in 2012 and 2013, respectively. Thus, the emissions were reduced by approximately 72.5% and 52.4% in 2012 and 2013. In the regional simulation, the Global Warming Potential (GWP) of the annual N 2 O emission reductions reached 27,749,760 ± 5,489,160 kg CO 2 -equivalents after the vineyards in the Ningxia Autonomous Region were converted from furrow irrigation to drip irrigation. In conclusion, the DNDC model, which proved to be a powerful tool for addressing the efficacy of alternative management practices in vineyards, revealed that N 2 O emissions can be reduced by adopting drip irrigation systems rather than traditional furrow irrigation systems. [ABSTRACT FROM AUTHOR]

Abstract: A study was carried out to examine the effect of dynamic photosynthetically active photon flux density (PPFD) on photoinhibition and energy use in three herbaceous species, prostrate Saussurea superba, erect-leaved S. katochaete, and half-erect-leaved Gentiana straminea, from the Qinghai—Tibet Plateau. Chlorophyll fluorescence response was measured under each of three sets of high–low PPFD combinations: 1700–0, 1400–300, and 1200–500μmolm−2 s−1, illuminating in four dynamic frequencies: 1, 5, 15, and 60 cycles per 2h. The total light exposure time was 2h and the integrated PPFD was the same in all treatments. The highest frequency of PPFD fluctuation resulted in the lowest photochemical activity, the highest level of non-photochemical quenching, and the greatest decrease of F v/F m (maximal photochemical efficiency of PSII). The 5 and 15 cycles per 2h treatments resulted in higher photochemical activity than the 1 cycle per 2h treatment. The 1700–0 PPFD combination led to the lowest photochemical activity and more serious photoinhibition in all species. S. superba usually exhibited the highest photochemical activity and CO2 uptake rate, the lowest reduction of F v/F m, and the smallest fraction of energy in thermal dissipation. With similar fractions of thermal dissipation, S. katochaete had relatively less photoinhibition than G. straminea owing to effective F 0 quenching. The results suggest that high frequency of fluctuating PPFD generally results in photoinhibition, which is more serious under periods of irradiation with high light intensity. [Copyright &y& Elsevier]

• · The production areas of crops under RCPs slightly shift northward in future China. • · The crop yield changes under RCPs remain stable or increase in future China. • · This is caused by the combined effect of changed climatic variables on crop yields. • · The crop yield changes are mainly driven by temperature and CO 2 factors. Maize, rice, and wheat are the major staple food crops in China and are crucial components of national food security and economic development. The cultivation and production of these crops are expected to be affected by climate change and elevated atmospheric carbon dioxide (CO 2) concentration, and have drawn considerable public attention. The objective of this experiment was to understand the impact of future climate change (including increased temperature and changed precipitation patterns) and elevated CO 2 concentration on variations of crop yields in their suitable planting areas. We conducted a spatial grid-based analysis of maize, rice, and wheat yields using projections of future climate generated by a multi-model ensemble of global climate models for three representative concentration pathway scenarios (RCP2.6, RCP4.5, and RCP8.5) in suitable planting areas in China for the 2030s (2021–2040) and the 2050s (2041–2060). Suitable areas for the planting of maize, rice, and wheat under the high-emission scenarios migrated slightly northward over time. Yield of all three crops would be expected to remain stable or to slightly increase across China in the future. A possible reason for this result may be because the positive effects of increased precipitation and CO 2 offset the negative effect of increased temperature on crop yields, resulting in a much more appropriate growth environment and increased biomass accumulation and crop yield. In addition, this study also indicated that changes in crop yields were mainly driven by temperature and CO 2 factors. The potential effects of climate change and elevated CO 2 concentration on migration of planting areas and yield fluctuations for crops should be given greater attention in the future. [ABSTRACT FROM AUTHOR]

Aboveground biomass (AGB) of shrubs and low-statured trees constitutes a substantial portion of the total carbon pool in temperate forest ecosystems, contributing much to local biodiversity, altering tree-regeneration growth rates, and determining above- and belowground food webs. Accurate quantification of AGB at the shrub layer is crucial for ecological modeling and still remains a challenge. Several methods for estimating understory biomass, including inventory and remote sensing-based methods, need to be evaluated against measured datasets. In this study, we acquired 158 individual terrestrial laser scans (TLS) across 45 sites in the Yanshan Mountains and generated metrics including leaf area and stem volume from TLS data using voxel- and non-voxel-based approaches in both leaf-on and leaf-off scenarios. Allometric equations were applied using field-measured parameters as an inventory approach. The results indicated that allometric equations using crown area and height yielded results with higher accuracy than other inventory approach parameters (R2 and RMSE ranging from 0.47 to 0.91 and 12.38 to 38.11 g, respectively). The voxel-based approach using TLS data provided results with R2 and RMSE ranging from 0.86 to 0.96 and 6.43 to 21.03 g. Additionally, the non-voxel-based approach provided similar or slightly better results compared to the voxel-based approach (R2 and RMSE ranging from 0.93 to 0.96 and 4.23 to 11.27 g, respectively) while avoiding the complexity of selecting the optimal voxel size that arises during voxelization. [ABSTRACT FROM AUTHOR]

Background and aims: Interactive effect of warming and precipitation addition on litter decomposition is still scarce. Moreover, nonlinear response of its temperature sensitivity to warming is not demonstrated due to lack of warming gradient experiment in situ. Methods: we performed a warming gradient experiment (0, ~0.25–0.5, ~1, ~2, and ~4 °C, respectively) using infrared heaters and a precipitation addition treatment in a fully-factorial design for 2-years on the Tibetan Plateau. The responses of mass loss of litter components (i.e. organic matter (OM), soluble cell content (SCC), lignin, cellulose (Ce), hemi-cellulose (Hce), total organic carbon (OC)) and nutrients (total nitrogen (TN) and total phosphorus (TP)) to warming and precipitation addition were determined over 2-years. Results: We found that warming significantly increased annual mass losses of all litter components in both treatment years. Precipitation addition significantly increased annual mass losses of OM, SCC, OC, TN and TP only in the first year due to drought. There were no interactive effects between warming and precipitation addition on litter component decomposition in the semi-arid alpine region. Temperature sensitivities were lowest when soil temperature increased by a mean of about 2.3 °C. There was an inverse relationship between the temperature sensitivity of organic matter decomposition and quality of litter carbon compounds. Conclusions: Our results suggest that soil temperature effects may override soil moisture effects on litter decomposition in the alpine region, and the nonlinear temperature sensitivity of litter decomposition should be estimated using warming gradients. Lower quality of litter carbon compounds had higher temperature sensitivity of organic matter decomposition. [ABSTRACT FROM AUTHOR]

Abstract Maize, rice, wheat and soybean—the major staple food crops in China—have a crucial role in national food security and economic development. Predictions of changes in the requirements for irrigation water in food crop production under climate change may provide scientific support for the optimum allocation of water resources and measures to mitigate climate change. We conducted a spatial grid-based analysis using projections of future climate generated by a bias-correction and spatial disaggregation multi-model ensemble for three representative concentration pathway scenarios (RCP2.6, RCP4.5 and RCP8.5) adopted by the fifth phase of the Coupled Model Intercomparison Project. We investigated the effects of climate change associated with increasing temperature, changed precipitation and increased concentrations of atmospheric carbon dioxide (CO 2) on the irrigation water requirements of maize, rice, wheat and soybean in China at the end of the 21st century (2081–2100). Our results indicate that the irrigation water requirements of maize and wheat are driven by temperature and especially by CO 2 concentrations in the northwest interior area as a result of the low rainfall and high rates of evaporation; the irrigation water requirement of soybean is influenced by a combined effect of temperature, precipitation and CO 2 concentration, whereas the irrigation water requirement for rice is dominated by precipitation alone in the southern coastal region, which has high rainfall. The irrigation water requirements of crops decrease mainly as a result of the beneficial effects of CO 2 on plant growth in China. The regions requiring vast amounts of irrigation water as a result of climate change are mainly concentrated in northwestern China. The effects of climate change affect the requirement for irrigation water, especially under high-emission scenarios, and should be studied further to design appropriate adaptation strategies for the management of agricultural water to maintain the sustainable development of agriculture. Graphical abstract Irrigation water requirements with temperature-only (T-only), precipitation-only (P-only) and carbon dioxide-only (CO 2 -only) for (a) maize, (b) rice, (c) soybean and (d) wheat under the representative concentration pathway scenario RCP8.5 in China in the 2010s (2006–2020), 2030s (2021–2040), 2050s (2041–2060), 2070s (2061–2080), and 2090s (2081–2100). Unlabelled Image Highlights • We predict the changes in irrigation water requirement for four crops in China. • The irrigation water requirements for crops are dominated by various climatic factors. • The irrigation water requirements under RCP8.5 reduce mainly by the CO 2 effect. • Northwestern China always requires vast amounts of irrigation water for crops. [ABSTRACT FROM AUTHOR]

Abstract A Standardized Precipitation Evapotranspiration Index (SPEI) model, which uses the FAO-56 Penman–Monteith equation to calculate potential evapotranspiration, has been developed and is considered appropriate for drought monitoring and assessment. However, the correlation of SPEI to total water storage (TWS) across multiple timescales, derived from future climate scenarios, is still unclear for China. In this study, the correlation of SPEI on different timescales (1-, 3-, 6-, 12-, 24- and 48-month) to TWS projected by a global climate model [the Community Climate System Model, version 4 (CCSM4)] under two representative concentration pathway scenarios (RCP2.6 and RCP8.5) for the period 2021–2100 in China is analyzed. The results show that, in general, SPEI is highly correlated with CCSM TWS in most of China (especially in eastern China) at the 12-month timescale, and is therefore regarded as an adequate indicator for representing situations of water resources and evaluating hydrological droughts. At the 12-month timescale, the correlations of SPEI to CCSM TWS vary across different river basins; and the variations in the pattern of correlations are greater due to faster warming and greater precipitation under RCP8.5. It is hoped that this article will provide guidance on the use of SPEI for detecting the impacts of future climate change on drought severity in China. Highlights • SPEI is highly correlated with CCSM TWS on 12-month timescale in general. • Good fitting effects mainly show in eastern river basins in China. • The variation of correlation patterns is greater under RCP8.5 than that under RCP2.6 • SPEI gives a good indication of hydrological variability in China's future. [ABSTRACT FROM AUTHOR]

Predictions of changes in the distribution of areas suitable for the cultivation of rice and maize in China under future climate change scenarios may provide scientific support for the optimization of crop production and measures to mitigate climate change. We conducted a spatial grid-based analysis using projections of future climate generated by the National Center for Atmospheric Research Community Climate System Model version 4 for two representative concentration pathway scenarios (RCP2.6 and RCP8.5), adopted by the fifth phase of the Coupled Model Intercomparison Project to study the areas suitable for the cultivation of rice and maize in China. We investigated the migration of the centers of gravity of the cultivation areas based on climatic and hydrological factors from 2021 to 2100. The results indicated that, under RCP2.6, the areas suitable for the cultivation of rice were located throughout China, except for on the Qinghai–Tibetan Plateau, while the areas suitable for the cultivation of maize were located in northern, southwestern, central, eastern, parts of northeastern and some northern parts of western China. The distributions of both crops under RCP2.6 showed little change over time. In contrast, the areas suitable for the cultivation of rice and maize under RCP8.5 shifted northward and expanded from northwestern to northern China, as a result of greater warming in northern China and the faster warming trend under RCP8.5. This scenario would require much stronger climate mitigation policies to maintain the stable development of agriculture and to slow down the future migration of crop cultivation areas in China. The distribution of areas suitable for the cultivation of rice and maize should be studied further to design appropriate adaptation strategies for dealing with future climate change. [ABSTRACT FROM AUTHOR]

Understanding the differentiation of soil bacterial communities under precipitation and temperature gradients is crucial for assessing the impacts of environmental filters on ecosystem structure and function. Here we investigated spatial variations of bacterial communities along a precipitation and temperature transect in the eastern Inner Mongolia steppe, China. The aims are to understand the biogeographic pattern and key drivers shaping soil bacterial communities along the transect. Our results showed that the soil bacterial community along the 451-km transect exhibited the distance-decay relationship, decreasing in community similarity with geographic distance. Obvious changes in the bacterial community structure occurred at an annual precipitation from 215 to 261 mm, which was close to the boundary between arid and semi-arid systems. The relative abundances of Proteobacteria, Bacteroidetes, and Acidobacteria increased with precipitation, while those of Actinobacteria, Chloroflexi, and Gemmatimonadetes decreased. Environmental filtering was observed to be the key in shaping bacterial biogeographic patterns, and climate conditions exert indirect effects on soil bacterial communities mainly through direct effects on soil properties. Soil pH and plant coverage were important to soil bacterial communities in both arid and semi-arid steppes. Our findings provided insights for understanding the linkages among geographic distance, environmental filters, and soil bacterial communities in Eurasian steppe ecosystems. [ABSTRACT FROM AUTHOR]

Soil salinization causes the degradation of soil structure, which seriously affects the global agricultural production. Currently, planting halophytes to improve saline soil has been widely used. However, most of the experiments were short-term, and the effect of long-term continuous cropping of halophytes on soil is still uncertain. This study aimed to investigate the multi-year effect of continuous cropping of euhalophyte Suaeda salsa on soil physicochemical properties. The space-for-time substitution approach was used to compare changes in soil physicochemical indicators under 3-year, 5-year, and 7-year continuous cropping periods of Suaeda salsa under drip irrigation, with bareland(0-year) serving as the control. In the 0–20 cm soil layer, the soil moisture content increased from 10.76% to 11.72–14.92%; in the 0–40 cm soil layer, the average bulk density decreased from 1.61 g cm−3 to 1.45–1.46 g cm−3 (P < 0.05), the average total porosity increased from 40.54% to 45.63–46.82% (P < 0.05), the average content of soil water-stable macroaggregates rose from 2.38% to 3.07–7.42%, and the average clay particle content declined from 20.88% to 16.63–18.63%; in the 0–60 cm soil layer, the average total salt content decreased from 48.11 g kg−1 to 12.43–22.01 g kg−1, and the average soil organic matter(SOM) content decreased from 8.73 g kg−1 to 7.40–8.15 g kg−1; in the 0–100 cm soil layer, the average pH value increased from 7.33 to 7.38–7.75, and the average content of Ca2+, Mg2+, Na+, K+, SO 4 2-, and Cl- all decreased, whereas the average HCO 3 - content increased from 0.16 g kg−1 to 0.25–0.29 g kg−1. After 7 years of continuous cropping, the mean weight diameter (MWD) of 0–40 cm soil layer increased by 19.01%, the sodium adsorption ratio (SAR) of 0–40 cm soil layer decreased by 53.57% (P < 0.05), and the soil hydro-chemical type of 0–100 cm soil layer changed from Cl--Na+·Ca2+ to Cl-·SO 4 2--Na+·Ca2+. The salt accumulation in the aboveground part of Suaeda salsa accounted for only 1.85–4.36% of the annual desalination quantity in the 0–100 cm soil layer. The continuous cropping of Suaeda salsa improved the soil structure and promoted salt leaching, which was the main mechanism of soil salt reduction. The results showed continuous cropping of Suaeda salsa under drip irrigation in arid regions is an effective method to improve saline soil, providing a theoretical reference for long-term continuous cropping of halophytes to improve saline soil in arid regions. • Effects of different planting years of Suaeda salsa on soil quality under drip irrigation were investigated. • Continuous cropping of Suaeda salsa can significantly improve soil structure. • Continuous cropping of Suaeda salsa can sustainedly reduce the average salt content of 0–100 cm soil profile. • Mechanism of saline soil improvement by halophytes under drip irrigation was analyzed. • Continuous cropping of Suaeda salsa will cause SOM reduction and soil alkalization in the early stage. [ABSTRACT FROM AUTHOR]

Changes in ecological processes over time in ambient treatments are often larger than the responses to manipulative treatments in climate change experiments. However, the impacts of human‐driven environmental changes on the stability of natural grasslands have been typically assessed by comparing differences between manipulative plots and reference plots. Little is known about whether or how ambient climate regulates the effects of manipulative treatments and their underlying mechanisms. We collected two datasets, one a 36‐year long‐term observational dataset from 1983 to 2018, and the other a 10‐year manipulative asymmetric warming and grazing experiment using infrared heaters with moderate grazing from 2006 to 2015 in an alpine meadow on the Tibetan Plateau. The 36‐year observational dataset shows that there was a nonlinear response of community stability to ambient temperature with a positive relationship between them due to an increase in ambient temperature in the first 25 years and then a decrease in ambient temperature thereafter. Warming and grazing decreased community stability with experiment duration through an increase in legume cover and a decrease in species asynchrony, which was due to the decreasing background temperature through time during the 10‐year experiment period. Moreover, the temperature sensitivity of community stability was higher under the ambient treatment than under the manipulative treatments. Therefore, our results suggested that ambient climate may control the directional trend of community stability while manipulative treatments may determine the temperature sensitivity of the response of community stability to climate relative to the ambient treatment. Our study emphasizes the importance of the context dependency of the response of community stability to human‐driven environmental changes. [ABSTRACT FROM AUTHOR]

Aims: The effect of cropping regime on nitrogen (N) uptake in two coexisting plant grass species (Avena sativa and Agropyron cristatum) was investigated. Methods: The two grass species were cultivated by monocropping or intercropping. 15N-labeling was used to examine N uptake of NH4+ versus NO3− at 0–5 cm and 5–15 cm soil depths. Results: The aboveground and total biomass of intercropped A. sativa was 1.3 times greater than monocropped A. sativa. The biomass of A. cristatum did not change between cropping systems. In the 0–5 cm soil layer, uptake of NO3− by A. sativa was 0.5 times less in the intercropped system than in the monocropped system, whereas uptake of NO3− by A. cristatum was 2.0 times more in the intercropped system. In the 5–15 cm depth, intercropping did not change N uptake by A. sativa but decreased NO3− uptake to 0.6 times by A. cristatum. Conclusions: Complementarity in N uptake between A. sativa and A. cristatum in the upper 0–5 cm soil layer is conducive to biomass accumulation. Intercropped A. sativa and A. cristatum does not compete strongly for soil resources and can alter their N uptake patterns to optimize biomass production. [ABSTRACT FROM AUTHOR]

Rejection and infection are 2 major complications affecting the health and survival of patients receiving an allograft organ transplantation. We describe a diagnostic assay that simultaneously monitors for rejection and infection in recipients of kidney transplant by sequencing of cell-free DNA (cfDNA) in plasma. By using cfDNA in plasma, we established a noninvasive method that simultaneously monitors rejection and infection in patients with a history of organ transplant. A total of 6200 single-nucleotide polymorphisms were captured by liquid hybridization and sequenced by next-generation sequencing. The donor-derived cfDNA (ddcfDNA) level was calculated based on maximum likelihood estimation, without relying on the donor's genotype. We also analyzed the nonhuman cfDNA to test for infections in the patients' plasma. Artificial ddcfDNA levels quantified by a donor-dependent and donor-independent algorithm were significantly correlated, with the multivariate coefficient of determination, or R 2 value, of 0.999. This technique was applied on 30 patients (32 samples) after kidney transplantation, and a significant difference was observed on the ddcfdNA levels between nonrejection and rejection. Furthermore, 1 BK virus infection and 1 cytomegalovirus infection were revealed by this method, and the enrichment efficiency of the viral sequences was 114 and 489 times, respectively, which are consistent with clinical results. This method can be used to simultaneously monitor for acute rejection as well as a broad spectrum of infections for patients of allograft organ transplant because it provides comprehensive information for clinicians to optimize immunosuppression therapy. • This study explores a novel method to simultaneously monitor rejection and infection in patients with a history of transplant. • A maximum likelihood estimation–based algorithm is used to quantify the donor-derived cell-free DNA without the donor's genotype. • The donor-derived cell-free DNA levels in patients with rejection were significantly higher than those without rejection. • Pathogenic microorganisms can be identified by using both on-target and off-target reads. [ABSTRACT FROM AUTHOR]

Highlights • PDSI is highly correlated with the variations of P and ET 0 on 12-month timescale. • PDSI is more sensitive to P on national scales, except the northeastern China. • PDSI is preferred to recommend to estimate long-term drought in China. Abstract The self-calibrating Palmer Drought Severity Index (sc_PDSI) is developed within the frame of the PDSI model, but is considered to be more appropriate for global drought monitoring. The sc_PDSI can automatically calibrate itself at any location using dynamically computed values and can calculate evapotranspiration using the FAO-56 Penman–Monteith (P–M) equation. However, the correlation of the sc_PDSI(P–M) with some factors that drive drought, such as precipitation (P) and the reference evapotranspiration (ET 0), is still unclear in China. With the aim of solving this issue, we analyzed the correlation of the detrended sc_PDSI(P–M) with the detrended P and ET 0 on different timescales (one, three, six and 12 months) in China for the period 1951–2015. The results show that both the P and ET 0 are highly correlated with the sc_PDSI(P–M) on a 12-month timescale. On this timescale, the sc_PDSI(P–M) is more sensitive to P than to ET 0 on the national scale, except for northeastern China. Thus the sc_PDSI(P–M) may effectively fit the long-term variations in these drivers of drought, especially P. These results provide guidance on the use of the sc_PDSI(P–M) to detect the impacts of climate change on drought severity under the climatic conditions found in China. [ABSTRACT FROM AUTHOR]

Background: Natural and managed soils have been identified as the largest sources of atmospheric nitrous oxide (N2O). However, the quantification of N2O emissions from soils under natural vegetation in China and their possible responses to changing climate and atmospheric nitrogen deposition remains uncertain. In particular, information regarding N2O emissions from Chinese shrublands is lacking.Method: This study used 28 sets of N2O field measurements in China to validate a process-based dynamic nitrogen cycle model (DyN-LPJ), which was then used to investigate the N2O fluxes from soils under natural vegetation in China from 1970 to 2009.Results: N2O emissions from Chinese forests, grasslands, and shrublands in the 2000s were estimated to be 0.10 ± 0.06 Tg N yr.−1, 0.09 ± 0.09, Tg N yr.−1 and 0.14 ± 0.07 Tg N yr.−1, respectively. Monthly N2O fluxes were linearly correlated with precipitation, and exponentially (Q10 = 3) with air temperature. The total N2O fluxes from natural terrestrial ecosystems in China increased from 0.28 ± 0.03 Tg N yr.−1 in the 1970s to 0.46 ± 0.03 Tg N yr.−1 in the 2000s. Warming and atmospheric nitrogen deposition accounted for 37% (or 0.07 ± 0.03 Tg N) and 63% (0.11 ± 0.01 Tg N) of this increase respectively.Conclusions: Our results indicate that when compared to grassland ecosystems, N2O emissions from forest and shrubland ecosystems contain larger uncertainties due to either their uncertain areal extent or their emission rates. Long-term and continuous field measurements should be conducted to obtain more representative data in order to better constrain shrubland N2O emissions. [ABSTRACT FROM AUTHOR]

The assumption of a linear relationship between temperature and phenophases may be misleading. Furthermore, a lack of understanding of the changes in temperature sensitivity of phenophases to changes in temperature strongly limits our ability to predict phenological change in response to climate change. We investigated the timing of seven phenophases of six alpine plant species to test the hypothesis of nonlinear responses in their temperature sensitivities to warming and cooling, using a reciprocal transplant experiment along a 3200-3800 m mountain slope gradient. Our results supported our hypothesis and showed that there were different thresholds in temperature sensitivity of phenophases to warming and cooling. Moreover, linear temperature sensitivity models significantly underestimated advances and delays of phenophases within the thresholds of temperature change. The nonlinear temperature sensitivity of phenophases is best explained by plastic and adaptive responses of phenophases to temperature change gradients. Therefore, our results suggest that the thresholds of temperature sensitivity for different species should be determined and that nonlinear models of temperature sensitivity may be essential to predict accurately phenological responses to climate change. [ABSTRACT FROM AUTHOR]

Aims: A lacking of understanding about cooling effects on methane (CH) fluxes and potential asymmetrical responses to warming and cooling causes uncertainty about climate change effects on the atmospheric CH concentration. We investigated CH fluxes in an alpine meadow on the Tibetan Plateau in response to climate warming and cooling. Methods: A 2-year reciprocal translocation experiment was implemented to simulate climate warming (i.e. downward translocation) and cooling (i.e. upward translocation) along an elevation gradient with four different vegetation types (at 3200, 3400, 3600 and 3800 m elevation) during the growing season (May to October) in 2008 and 2009. Results: Although the effects of warming and cooling varied depending on vegetation type, elevation and timescale (i.e., daily and seasonally), warming increased average seasonal CH uptake by 60 %, while cooling reduced it by 19 % across all vegetation types, based on a 1.3-5.1 °C difference in soil temperature at 20 cm depth. Soil temperature over the range of 4-10 °C explained 11-25 % of the variation in average seasonal CH fluxes, while there was no relationship with soil moisture over the range of 13-39 % and soil NH-N and NON content. Methane uptake was more sensitive to warming than to cooling. Conclusions: Because of warming and cooling spells in the alpine region, warming effects on CH uptake would be over-estimated by 64 % if cooling effects on it are not considered. Our findings suggest that asymmetrical responses of CH fluxes to warming and cooling should be taken into account when evaluating the effects of climate change on CH uptake in the alpine meadow on the Tibetan plateau. [ABSTRACT FROM AUTHOR]

Information about the potential effects of climate change, especially cooling, on ecosystem respiration (Re) in alpine meadows is scarce. We determined the effects of warming and cooling on Re on the Tibetan Plateau using a 2-year reciprocal translocation experiment with 4 different vegetation types (3 alpine meadows and 1 alpine shrub differentiated by plant community composition) along an elevation gradient from 3200 to 3800 m (with vegetation types E2, E4, E6 and E8 at 3200, 3600, 3800 and 3800 m, respectively) during the growing seasons in 2008 and 2009. Mean growing seasonal Re decreased by 13.6, 30.3 and 40.7% per 200 m rise in elevation (cooling) for vegetation types E2, E4 and E6, but increased by 1.3, 35.9 and 58.8% per 200 m decrease in elevation (warming) for vegetation types E4, E6 and E8, respectively. Soil temperature explained 49.3–64.0% of daily Re variation and aboveground biomass explained 21.5–61.6% of average Re variation of the growing season for all vegetation types, but the effect of soil moisture on Re was small over 2-year. The values of Re temperature sensitivity increased with an increase in elevation for both warming (3.3, 24.3 and 53.5% °C −1 for vegetation types E4, E6 and E8) and cooling (8.0, 19.1 and 24.4% °C −1 for vegetation types E2, E4 and E6), suggesting that alpine meadow at higher elevation was more sensitive to both warming and cooling. Based on the values of Re temperature sensitivity for all pooled vegetation types (25.4, 5.6 and 19.6% °C −1 for warming, cooling and pooled warming and cooling), it could be over-estimated by 23% for warming alone compared with pooled warming and cooling. Therefore, asymmetrical responses of Re to warming and cooling should be taken into account when we evaluate the effect of temperature change on Re using models in the future. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding the effect of grazing season on net ecosystem CO exchange (NEE) and its components is crucial to predict the feedback of grazing management to climate change. Methods: We estimated NEE, gross primary productivity (GPP) and ecosystem respiration (Re) under different seasonal grazing practices (i.e. no-grazing (NG), warm season grazing (WG) and cold season grazing (CG)) by sheep during the growing seasons from 2008 to 2012 on the Tibetan Plateau. Results: Our results show that the impacts of seasonal grazing on daily GPP, Re and NEE in the alpine meadow ecosystem varied with sampling date and year. Compared with NG and CG, WG significantly reduced average seasonal NEE by 22.7 %, because grazing impact was exacerbated by drought in July in 2010. Soil temperature only explained 19-31 % of the variation in daily GPP, Re and NEE for all grazing treatments. The interannual variabilities of GPP, Re and NEE were mainly determined by root biomass and/or average soil temperature during the growing season. Conclusions: Our results suggest that although WG may decrease sequestration of CO under continuous drought conditions after grazing, it would have little impact on CO sequestration during the growing season under conditions of future warming with greater rainfall in alpine meadows on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Organic nitrogen (N) uptake by plants has been recognized as a significant component of terrestrial N cycle. Several studies indicated that plants have the ability to switch their preference between inorganic and organic forms of N in diverse environments; however, research on plant community response in organic nitrogen uptake to warming and grazing is scarce. Here, we demonstrated that organic N uptake by an alpine plant community decreased under warming with 13C-15N-enriched glycine addition method. After 6 years of treatment, warming decreased plant organic N uptake by 37% as compared to control treatment. Under the condition of grazing, warming reduced plant organic N uptake by 44%. Grazing alone significantly increased organic N absorption by 15%, whereas under warming condition grazing did not affect organic N uptake by the Kobresia humilis community on Tibetan Plateau. Besides, soil NO3-N content explained more than 70% of the variability observed in glycine uptake, and C:N ratio in soil dissolved organic matter remarkably increased under warming treatment. These results suggested warming promoted soil microbial activity and dissolved organic N mineralization. Grazing stimulated organic N uptake by plants, which counteracted the effect of warming. [ABSTRACT FROM AUTHOR]

Increased understanding of the response of soil methane (CH) uptake in alpine meadow ecosystems to warming and grazing could reduce uncertainty in estimates of the soil-atmospheric CH budget. To determine the effects of warming and grazing on soil CH uptake at different timescales (that is, daily, monthly, seasonal, and annual), we conducted a controlled warming and grazing experiment [that is, no warming with no grazing (NWNG), no warming with grazing (NWG), warming with no grazing (WNG), and warming with grazing (WG)] in an alpine meadow on the Tibetan plateau from 2006 to 2009. Soil CH uptake was mainly affected by warming and sample date and their interaction. Warming treatment regardless of grazing significantly increased seasonal average CH uptake by 31-39% during the growing season (from May to September) and by 162% during the non-growing season (from October to April next year) in 2007-2008, whereas only WNG increased seasonal average CH uptake by 87-138% compared with NWNG during the non-growing seasons in 2006-2007 and 2008-2009. Warming in WNG and WG increased annual CH uptake by 50-87% compared with NWNG or NWG. Moreover, warming regardless of grazing and warming with grazing (compared with NWNG) significantly increased the contribution to annual uptake of CH uptake during the non-growing season in 2007-2008 and 2008-2009. However, moderate grazing did not significantly influence soil CH uptake, although grazing with warming decreased CH uptake by 43% during the growing season in 2006. Soil moisture explained 16-25% of the CH variation during the growing season, but there was no significant relationship between soil CH uptake and soil moisture during the non-growing season. Our results suggest that more attention should be paid to the stimulating effect of warming on soil CH uptake during the non-growing season due to its greater response to warming and different stimulating mechanisms compared to responses during the growing season in the alpine meadow. [ABSTRACT FROM AUTHOR]

Stable carbon isotope composition ( δ13C) usually shows a negative relationship with precipitation at a large scale. We hypothesized that sampling method affects foliar δ13C and its response pattern to precipitation. We selected 11 sites along a precipitation gradient in Inner Mongolia and collected leaves of Leymus chinensis with five or six replications repeatedly in each site from 2009 to 2011. Additionally, we collected leaves of L. chinensis separately from two types of grassland (grazed and fenced) in 2011. Foliar δ13C values of all samples were measured. We compared the patterns that foliar δ13C to precipitation among different years or different sample sizes, the differences of foliar δ13C between grazed and fenced grassland. Whether actual annual precipitation ( AAP) or mean annual precipitation ( MAP), it was strongly correlated with foliar δ13C every year. Significant difference was found between the slopes of foliar δ13C to AAP and MAP every year, among the slopes of foliar δ13C to AAP from 2009 to 2011. The more samples used at each site the lower and convergent P-values of the linear regression test between foliar δ13C and precipitation. Furthermore, there was significant lower foliar δ13C value in presence of grazed type than fenced type grassland. These findings provide evidence that there is significant effect of sampling method to foliar δ13C and its response pattern to precipitation of L. chinensis. Our results have valuable implications in methodology for future field sampling studies. [ABSTRACT FROM AUTHOR]

Abstract: Grasslands cover about 40% of China''s land area. This paper synthesizes 133 papers from China on the impacts of land use conversion and improved management practices on soil organic carbon (SOC) in China''s grasslands. The synthesis finds that overgrazing and conversion of freely grazed grassland to cropland lead to an annual average decline of 2.3–2.8% in SOC, and have caused a loss of 30–35% of total grassland SOC in China. Improved management practices may reverse the loss of SOC. Exclosure of degraded grassland from grazing and conversion of cropland to abandoned fields (i.e. natural restoration) increased carbon content by 34% and 62% on average. Carbon sequestration rates were greatest during the first 30yr after treatments began and tended to be greatest in the top 10cm of soil. Carbon sequestration potential was negatively related to initial carbon and nitrogen concentrations in soils. Exclosure from grazing and the conversion of cropland to abandoned fields resulted in average carbon sequestration rates of 130.4gCm−2 yr−1 for 0–40cm soil and 128.0gCm−2 yr−1 for 0–30cm soil, representing annual average increases of 5.4–6.3%. Based on our results, achievement of the national objective to exclude grazing livestock from 150 million ha of China''s grasslands and to establish 30 million ha of cultivated pasture by 2020 would sequester over 0.24PgCyr−1, which is equivalent to about 16% of fossil fuel CO2 emissions in China in 2006. [Copyright &y& Elsevier]

Abstract: We used an eddy covariance technique to measure evapotranspiration and carbon flux over two very different growing seasons for a typical steppe on the Inner Mongolia Plateau, China. The rainfall during the 2004 growing season (344.7mm) was close to the annual average (350.43mm). In contrast, precipitation during the 2005 growing season was significantly lower than average (only 126mm). The wet 2004 growing season had a higher peak evapotranspiration (4mmday−1) than did the dry 2005 growing season (3.3mmday−1). In 2004, latent heat flux was mainly a consumption resource for net radiation, accounting for ∼46% of net radiation. However, sensible heat flux dominated the energy budget over the whole growing season in 2005, accounting for 60% of net radiation. The evaporative rate (LE/R n) dropped by a factor of four from the non-soil stress to soil water limiting conditions. Maximum half-hourly CO2 uptake was −0.68mgm−2 s−1 and maximum ecosystem exchange was 4.3gCO2 m−2 day−1 in 2004. The 2005 drought growing stage had a maximum CO2 exchange value of only −0.22mgm−2 s−1 and a continuous positive integrated-daily CO2 flux over the entire growing season, i.e. the ecosystem became a net carbon source. Soil respiration was temperature dependent when the soil was under non-limiting soil moisture conditions, but this response declined with soil water stress. Water availability and a high vapor pressure deficit severely limited carbon fixing of this ecosystem; thus, during the growing season, the capacity to fix CO2 was closely related to both timing and frequency of rainfall events. [Copyright &y& Elsevier]

Abstract: In this study, we conducted eddy covariance (EC) measurements of water vapor exchange over a typical steppe in a semi-arid area of the Inner Mongolia Plateau, China. Measurement sites were located within a 25-year-old enclosure with a relatively low leaf area index (∼1.5m2 m−2) and dominated by Leymus chinensis. Energy balance closure was (H +LE)=17.09+0.69×(Rn− G) (W/m2; r 2 =0.95, n =6596). Precipitation during the two growing seasons of the study period was similar to the long-term average. The peak evapotranspiration in 2004 was 4mmd−1, and 3.5mmd−1 in 2003. The maximum latent heat flux was higher than the sensible heat flux, and the sensible heat flux dominated the energy budget at midday during the entire growing season in 2003; latent heat flux was the main consumption component for net radiation during the 2004 growing season. During periods of frozen soil in 2003 and 2004, the sensible heat flux was the primary consumption component for net radiation. The soil heat flux component was similar in 2003 and 2004. The decoupling coefficient (between 0.5 and 0.1) indicates that evapotranspiration was strongly controlled by saturation water vapor pressure deficit (VPD) in this grassland. The results of this research suggest that energy exchange and evapotranspiration were controlled by the phenology of the vegetation and soil water content. In addition, the amount and frequency of rainfall significantly affect energy exchange and evapotranspiration upon the Inner Mongolia plateau. [Copyright &y& Elsevier]

• Warming did not alter annual total ecosystem CO 2 exchange (annual NEE). • Summer grazing decreased a net carbon sink, but winter grazing increased it. • Interactions between warming and grazing on NEE varied with year and grazing season. • Rotational grazing between summer and winter seasons caused neutral climate feedback. In natural grasslands, effects of warming on net ecosystem CO 2 exchange (NEE) may interact with grazing. Yet, the effects of these two main drivers of terrestrial carbon cycling are typically studied in isolation, limiting our understanding of how NEE would be affected under different global change scenarios. Here, we report results of a warming experiment using infrared heaters combined with summer and winter grazing for 7-years in a Tibetan alpine grassland. We found that regardless of warming summer grazing decreased soil carbon sink (i.e., increased annual mean net biome productivity (NBP) indicated by a negative value of NBP), and warming also reduced soil carbon sink under no-grazing only during 3-years of summer grazing. However, warming and grazing did not change soil carbon sink during 4-years of winter grazing. Interactive effects between warming and grazing on annual NBP varied with year and grazing season. Overall, both warming and grazing did not alter annual mean NBP under 7-years of the rotational grazing system in summer and winter grasslands because of offsetting effects on annual mean gross primary productivity and ecosystem respiration. Annual mean soil temperature explained 58% of the variation of annual mean NBP during summer grazing, whereas seasonal mean soil moisture explained 48 and 44% of its variation during winter grazing and the two season grazing system, respectively. Together, our results suggest that rotational grazing between summer and winter alpine grasslands would result in net neutral climate feedback based on the response of annual NBP under future warming. The two season grazing system not only supports animal production but also realizes balance in the soil carbon budget under future warming. [ABSTRACT FROM AUTHOR]