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The article discusses the impacts of climate change and human activities on the ecosystem structure and functioning with emphasis on quantifying the magnitude and carbon (C) distribution pools and C sequestration in China. Information on how species diversity, species traits and nitrogen (N) and phosphorus (P) stoichiometry mediate ecosystem C pool is offered. The background and scientific significance of the research project is also tackled.

Temperate- and high-latitude forests have been shown to contribute a carbon sink in the Northern Hemisphere, but fewer studies have addressed the carbon balance of the subtropical forests. In the present study, we integrated eddy covariance observations established in the 1990s and 2000s to show that East Asian monsoon subtropical forests between 20°N and 40°N represent an average net ecosystem productivity (NEP) of 362 ± 39 g C m-2 yr-1 (mean ± 1 SE). This average forest NEP value is higher than that of Asian tropical and temperate forests and is also higher than that of forests at the same latitudes in Europe- Africa and North America. East Asian monsoon subtropical forests have comparable NEP to that of subtropical forests of the southeastern United States and intensively managed Western European forests. The total NEP of East Asian monsoon subtropical forests was estimated to be 0.72 ± 0.08 Pg C yr-1, which accounts for 8% of the global forest NEP. This result indicates that the role of subtropical forests in the current global carbon cycle cannot be ignored and that the regional distributions of the Northern Hemisphere's terrestrial carbon sinks are needed to be reevaluated. The young stand ages and high nitrogen deposition, coupled with sufficient and synchronous water and heat availability, may be the primary reasons for the high NEP of this region, and further studies are needed to quantify the contribution of each underlying factor. [ABSTRACT FROM AUTHOR]

The regional determining factors underlying inter- and intra-site variation of 15N natural abundance in foliage, O horizon and mineral soil were investigated in eastern China.15N natural abundance values for these forest ecosystems were in the middle of the range of values previously found for global forest ecosystems. In contrast to commonly reported global patterns, temperate forest ecosystems were significantly more15N-enriched than tropical forest ecosystems, and foliage δ15N was negatively correlated with increasing mean annual temperature and net soil Nmineralisation in eastern China. TightNcycling in forest ecosystems and the use of atmospheric N deposition by trees might underlie the δ15N distribution patterns in eastern China. The existence of mycorrhizal fungi and root distribution profiles in the soil may also influence the15N natural abundance patterns in forest ecosystems of eastern China. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition, an important component in the global N cycle, has increased sharply in recent decades in China. Here, we constructed national-scale inorganic N wet deposition (Ndep) patterns in China based on data from 280 observational sites and analysed the effects of anthropogenic sources and precipitation on Ndep. Our results showed that the mean Ndep over China increased approximately 25%, from 11.11 kg ha-1 a-1 in the 1990s to 13.87 in the 2000s. Ndep was highest over southern China and exhibited a decreasing gradient from southern to western and northern China. The decadal difference in Ndep between the 1990s and 2000s was primarily caused by increases in energy consumption and N fertiliser use. Our findings conformed that anthropogenic activities were the main reason for the Ndep increase and provide a scientific background for studies on ecological effects of N deposition in China [ABSTRACT FROM AUTHOR]

Protecting groundwater from nitrogen contamination is an important public-health concern and a major national environmental issue in China. In this study, we monitored water quality in 29 wells from 2009 to 2010 in a village in Shanghai city, whick belong to typical rural-urban continuum in China. The total N and NO3-N exhibited seasonal changes, and there were large fluctuations in NH4-N in residential areas, but without significant seasonal patterns. NO2-N in the water was not stable, but was present at high levels. Total N and NO3-N were significantly lower in residential areas than in agricultural areas. The groundwater quality in most wells belonged to Class III and IV in the Chinese water standard, which defines water that is unsuitable for human consumption. Our health risk assessments showed that NO3-N posed the greatest carcinogenic risk, with risk values ranging from 19×10-3 to 80×10-3, which accounted for more than 90% of the total risk in the study area. [ABSTRACT FROM AUTHOR]

Quantification of the spatiotemporal pattern of soil respiration (Rs) at the regional scale can provide a theoretical basis and fundamental data for accurate evaluation of the global carbon budget. This study summarizes the Rs data measured in China from 1995 to 2004. Based on the data, a new region-scale geostatistical model of soil respiration (GSMSR) was developed by modifying a global scale statistical model. The GSMSR model, which is driven by monthly air temperature, monthly precipitation, and soil organic carbon (SOC) density, can capture 64% of the spatiotemporal variability of soil Rs. We evaluated the spatiotemporal pattern of Rs in China using the GSMSR model. The estimated results demonstrate that the annual Rs in China ranged from 3.77 to 4.00 Pg C yr-1 between 1995 and 2004, with an average value of 3.84 ± 0.07 Pg C yr-1, contributing 3.92%-4.87% to the global soil CO2 emission. Annual Rs rate of evergreen broadleaved forest ecosystem was 698 ± 11 g C m-2 yr-1, significantly higher than that of grassland (439 ± 7 g C m-2 yr-1) and cropland (555 ± 12 g C m-2 yr-1). The contributions of grassland, cropland, and forestland ecosystems to the total Rs in China were 48.38 ± 0.35%, 22.19 ± 0.18%, and 20.84 ± 0.13%, respectively. [ABSTRACT FROM AUTHOR]

• Carbon (C) and water cycles of terrestrial ecosystems are two coupled ecological processes controlled partly by stomatal behavior. Water-use efficiency (WUE) reflects the coupling relationship to some extent. At stand and ecosystem levels, the variability of WUE results from the trade-off between water loss and C gain in the process of plant photosynthetic C assimilation. • Continuous observations of C, water, and energy fluxes were made at three selected forest sites of ChinaFLUX with eddy covariance systems from 2003 to 2005. WUE at different temporal scales were defined and calculated with different C and water flux components. • Variations in WUE were found among three sites. Average annual WUE was 9.43 mg CO2 g−1 H2O at Changbaishan temperate broad-leaved Korean pine mixed forest, 9.27 mg CO2 g−1 H2O at Qianyanzhou subtropical coniferous plantation, and 6.90 mg CO2 g−1 H2O at Dinghushan subtropical evergreen broad-leaved forest. It was also found that temperate and subtropical forest ecosystems had different relationships between gross primary productivity (GPP) and evapotranspiration (ET). • Variations in WUE indicated the difference in the coupling between C and water cycles. The asynchronous response of GPP and ET to climatic variables determined the coupling and decoupling between C and water cycles for the two regional forest ecosystems. [ABSTRACT FROM AUTHOR]

Black soils in Northeast China are characteristic of high soil organic carbon (SOC) density and were strongly influenced by human activities. Therefore, any change in SOC pool of these soils would not only impact the regional and global carbon cycle, but also affect the release and immobilization of nutrients. In this study, we reviewed the research progress on SOC storage, budget, variation, and fertility under different scenarios. The results showed that the organic carbon storage of black soils was 646.2 TgC and the most potential sequestration was 2887.8 g m−2. According to the SOC budget, the net carbon emission of black soils was 1.3 TgC year−1 under present soil management system. The simulation of CENTURY model showed that future climate change and elevated CO2 concentration, especially the increase of precipitation, would increase SOC content. Furthermore, fertilization and cropping sequence obviously influenced SOC content, composition, and allocation among different soil particles. Long-term input of organic materials such as manure and straw renewed original SOC, improved soil structure and increased SOC accumulation. Besides, soil erosion preferred to transport soil particles with low density and fine size, decreased recalcitrant SOC fractions at erosion sites and increased activities of soil microorganism at deposition sites. After natural grasslands were converted into croplands, obvious variation of soil chemical nutrients, physical structure, and microbial activities had taken place in surface and subsurface soils, and represented a degrading trend to a certain degree. Our studies suggested that adopting optimal management such as conservation tillage in black soil region is an important approach to sequester atmospheric CO2 and to slow greenhouse effects. [ABSTRACT FROM AUTHOR]

Biodiversity is essential for maintaining the terrestrial ecosystem multifunctionality (EMF). Recent studies have revealed that the variations in terrestrial ecosystem functions are captured by three key axes: the maximum productivity, water use efficiency, and carbon use efficiency of the ecosystem. However, the role of biodiversity in supporting these three key axes has not yet been explored. In this study, we combined the (i) data collected from more than 840 vegetation plots across a large climatic gradient in China using standard protocols, (ii) data on plant traits and phylogenetic information for more than 2,500 plant species, and (iii) soil nutrient data measured in each plot. These data were used to systematically assess the contribution of environmental factors, species richness, functional and phylogenetic diversity, and community-weighted mean (CWM) and ecosystem traits (i.e., traits intensity normalized per unit land area) to EMF via hierarchical partitioning and Bayesian structural equation modeling. Multiple biodiversity attributes accounted for 70% of the influence of all the variables on EMF, and ecosystems with high functional diversity had high resource use efficiency. Our study is the first to systematically explore the role of different biodiversity attributes, including species richness, phylogenetic and functional diversity, and CWM and ecosystem traits, in the key axes of ecosystem functions. Our findings underscore that biodiversity conservation is critical for sustaining EMF and ultimately ensuring human well-being. [ABSTRACT FROM AUTHOR]

The article offers the author's insights on the concept of a carbon (C) healthy threshold in the ecosystem, which is important for the fight against climate change and making suitable climate policies. The authors explain the impact of climate change on forest growth, since the growth of plants depends of the ecosystem's health and C availability. They discuss several conditions to recognize the ecosystem's healthy threshold. They suggest the need for the designing of proper forest strategies by having the knowledge C cycle in forests.

Atmospheric nitrogen (N) deposition is composed of both inorganic nitrogen (IN) and organic nitrogen (ON), and these sources of N may exhibit different impacts on ecosystems. However, our understanding of the impacts of N deposition is largely based on experimental gradients of INs or more rarely ONs. Thus, the effects of N deposition on ecosystem productivity and biodiversity may be biased. We explored the differential impacts of N addition with different IN:ON ratios (0:10, 3:7, 5:5, 7:3, and 10:0) on aboveground net primary productivity (ANPP) of plant community and plant diversity in a typical temperate grassland with a long-term N addition experiment. Soil pH, litter biomass, soil IN concentration, and light penetration were measured to examine the potential mechanisms underlying species loss with N addition. Our results showed that N addition significantly increased plant community ANPP by 68.33%–105.50% and reduced species richness by 16.20%–37.99%. The IN:ON ratios showed no significant effects on plant community ANPP. However, IN-induced species richness loss was about 2.34 times of ON-induced richness loss. Soil pH was positively related to species richness, and they exhibited very similar response patterns to IN:ON ratios. It implies that soil acidification accounts for the different magnitudes of species loss with IN and ON additions. Overall, our study suggests that it might be reasonable to evaluate the effects of N deposition on plant community ANPP with either IN or ON addition. However, the evaluation of N deposition on biodiversity might be overestimated if only IN is added or underestimated if only ON is added. [ABSTRACT FROM AUTHOR]

Forests play a vital role in global carbon (C) cycling. Accordingly, afforestation engineering programs that promote increased terrestrial C stocks are an important means to help gradually decrease atmospheric CO2 emissions. China, however, had increased its afforested area bordering hydroclimatic zones to 275.71 million hm² between 1949 and 2010. Ecosystem water use efficiency (EWUE) and plant water use efficiency (PWUE) provide data on ecosystem sensitivity to water availability across rainfall regimes. The water consumption cost of C sequestration (WCCC) is also an important parameter that gauges the cost of C sequestration under afforestation. However, abrupt changes in EWUE and PWUE (threshold values of 1.5 and 3.6 gC kg-1 H2O, respectively) have been measured within the 400-500mm precipitation climatic isoline boundary situated between semi-humid and arid zones. The threshold value of the corresponding WCCC was 1.0 kg H2O gC-1. Forest ecosystems in China typically generate high EWUE and PWUE values (2.80±0.77 and 4.25±1.02 gC kg-1 H2O, respectively) but low WCCC values (0.52±0.42 kg H2Og-1C), providing proof that afforestation is the best choice in increasing terrestrial C stocks. However, China's major afforestation engineering programs have concentrated efforts toward low EWUE and PWUE and high WCCC in the western region of the 400-500mm precipitation isoline boundary, belonging to the arid and semiarid zones, which introduced potential environmental risks. Therefore, policies related to large-scale C sequestration initiatives under afforestation must first fully consider the statuses of WCCC and WUE. [ABSTRACT FROM AUTHOR]

An understanding of the factors controlling plant community composition will allow improved prediction of the responses of plant communities to natural and anthropogenic environmental change. Using monitoring data from 1980 to 2009, we quantified the changes in community composition in Leymus chinensis and Stipa grandis dominated grasslands in Inner Mongolia under long-term grazing-exclusion and free-grazing conditions, respectively. We demonstrated that the practice of long-term grazing exclusion has significant effects on the heterogeneity, the dominant species, and the community composition in the two grasslands. The community composition of L. chinensis and S. grandis grasslands exhibited directional changes with time under long-term grazing exclusion. Under free grazing, the L. chinensis community changed directionally with time, but the pattern of change was stochastic in the S. grandis community. We attributed the divergent responses to long-term grazing exclusion in the S. grandis and L. chinensis grasslands to litter accumulation and changes in the microenvironment after grazing exclusion, which collectively altered the growth and regeneration of the dominant species. The changes in the grazed grasslands were primarily determined by the selective feeding of sheep during longterm heavy grazing. Overall, the responses of the community composition of the Inner Mongolian grasslands to long-term grazing exclusion and heavy grazing were divergent, and depended primarily on the grassland type. Our findings provide new insights into the role of grazing in the maintenance of community structure and function and therefore have important implications for grassland management. [ABSTRACT FROM AUTHOR]

Emissions of nitrous oxide (N2O) from the soil following simulated nitrogen (N) deposition in a disturbed (pine), a rehabilitated (pine and broadleaf mixed) and a mature (monsoon evergreen broadleaf) tropical forest in southern China were studied. The following hypotheses were tested: (1) addition of N will increase soil N2O emission in tropical forests; and (2) any observed increase will be more pronounced in the mature forest than in the disturbed or rehabilitated forest due to the relatively high initial soil N concentration in the mature forest. The experiment was designed with four N treatment levels (three replicates; 0, 50, 100, 150 kg N ha−1 year−1 for C (Control), LN (Low-N), MN (Medium-N), and HN (High-N) treatment, respectively) in the mature forest, but only three levels in the disturbed and rehabilitated forests (C, LN and MN). Between October 2005 to September 2006, soil N2O flux was measured using static chamber and gas chromatography methodology. Nitrogen had been applied previously to the plots since July 2003 and continued during soil N2O flux measurement period. The annual mean rates of soil N2O emission in the C plots were 24.1 ± 1.5, 26.2 ± 1.4, and 29.3 ± 1.6 μg N2O–N m−2 h−1 in the disturbed, rehabilitated and mature forest, respectively. There was a significant increase in soil N2O emission following N additions in the mature forest (38%, 41%, and 58% when compared to the C plots for the LN, MN, and HN plots, respectively). In the disturbed forest a significant increase (35%) was observed in the MN plots, but not in the LN plots. The rehabilitated forest showed no significant response to N additions. Increases in soil N2O emission occurred primarily in the cool-dry season (November, December and January). Our results suggest that the response of soil N2O emission to N deposition in tropical forests in southern China may vary depending on the soil N status and land-use history of the forest. [ABSTRACT FROM AUTHOR]

The article presents the results of a study of the role of warming in homogenizing temperature sensitivity of terrestrial ecosystem respiration (Re) or Q10. Topics discussed include the use of Re and meteorological data from the FLUXNET sites, tendency of Q10 to decline in increasing temperature due to ecosystem thermal acclimation, and the use of correlation analysis (COR) and partial COR (PCOR) between Re and climate factors to determine the factors driving seasonal Re.

Solar radiation, especially photosynthetically active radiation (PAR), is the main energy source of plant photosynthesis; and the diffuse component can enhance canopy light use efficiency, thus increasing ecosystem productivity. In order to predict the terrestrial ecosystem productivity precisely, we not only need global radiation and PAR as driving variables, but also need to treat diffuse radiation and diffuse PAR explicitly in ecosystem models. Therefore, we generated a series of radiation datasets, including global radiation, diffuse radiation, PAR, and diffuse PAR of China from 1981 to 2010, based on the observations of China Meteorology Administration (CMA) and Chinese Ecosystem Research Network (CERN). The dataset should be useful for the analysis of the spatio-temporal variations of solar radiation in China and the impact of diffuse radiation on terrestrial ecosystem productivity based on ecosystem models. [ABSTRACT FROM AUTHOR]

Whether and how seasonality of environmental variables impacts the spatial variability of soil fungal communities remain poorly understood. We assessed soil fungal diversity and community composition of five Chinese zonal forests along a latitudinal gradient spanning 23°N to 42°N in three seasons to address these questions. We found that soil fungal diversity increased linearly or parabolically with latitude. The seasonal variations in fungal diversity were more distinguishable in three temperate deciduous forests than in two subtropical evergreen forests. Soil fungal diversity was mainly correlated with edaphic factors such as pH and nutrient contents. Both latitude and its interactions with season also imposed significant impacts on soil fungal community composition (FCC), but the effects of latitude were stronger than those of season. Vegetational properties such as plant diversity and forest age were the dominant factors affecting FCC in the subtropical evergreen forests while edaphic properties were the dominant ones in the temperate deciduous forests. Our results indicate that latitudinal variation patterns of soil fungal diversity and FCC may differ among seasons. The stronger effect of latitude relative to that of season suggests a more important influence by the spatial than temporal heterogeneity in shaping soil fungal communities across zonal forests. [ABSTRACT FROM AUTHOR]

The modeling and partitioning of regional evapotranspiration (ET) are key issues in global hydrological and ecological research. We incorporated a stomatal conductance model and a light-use efficiency-based gross primary productivity (GPP) model into the Shuttleworth-Wallace model to develop a simplified carbon-water coupling model, SWH, for estimating ET using meteorological and remote sensing data. To enable regional application of the SWH model, we optimized key parameters with measurements from global eddy covariance (EC) tower sites. In addition, we estimated soil water content with the principle of the bucket system. The model prediction of ET agreed well with the estimates obtained with the EC measurements, with an average R² of 0.77 and a root mean square error of 0.72 mm·day-1. The model performance was generally better for woody ecosystems than herbaceous ecosystems. Finally, the spatial patterns of ET and relevant model outputs (i.e., GPP, water-use efficiency and the ratio of soil water evaporation to ET) in China with the model simulations were assessed. [ABSTRACT FROM AUTHOR]

Water use efficiency (WUE) is a useful indicator to illustrate the interaction of carbon and water cycles in terrestrial ecosystems. MODIS gross primary production (GPP) and evapotranspiration (ET) products have been used to analyze the spatial and temporal patterns of WUE and their relationships with environmental factors at regional and global scales. Although MODIS GPP and ET products have been evaluated using eddy covariance flux measurements, the accuracy of WUE estimated from MODIS products has not been well quantified. In this paper, we evaluated WUE estimated from MODIS GPP and ET products against eddy covariance measurements of GPP and ET during 2003-2008 at eight sites of the Chinese flux observation and research network (ChinaFLUX) and conducted sensitivity analysis to investigate the possible key contributors to the bias of MODIS products. Results show that MODIS products underestimate eight-day water use efficiency in four forest ecosystems and one cropland ecosystem with the bias from -0.36-2.28 g.C.kg-1 H2O, while overestimating it in three grassland ecosystems with the bias from 0.26-1.11 g.C.kg-1 H2O. Mean annual WUE was underestimated by 14%-54% at four forest sites, 45% at one cropland site and 7% at an alpine grassland site, but overestimated by 66% and 9% at a temperate grassland site and an alpine meadow site, respectively. The underestimation of WUE by MODIS data results from underestimated GPP and overestimated ET at four forest sites, while MODIS WUE values are significantly overvalued mainly due to underestimated ET in the three grassland ecosystems. The maximum light use efficiency and fraction of photosynthetically-active radiation (FPAR) were the two most sensitive factors to the estimation of WUE derived from the MODIS GPP and ET algorithms. The error in meteorological data partly caused the overestimation of ET and accordingly underestimation in WUE in subtropical and tropical forests. The bias of MODIS-produced WUE was also derived from the uncertainties in eddy flux data due to gap-filling processes and unbalanced surface energy issue. Their contributions to the uncertainty in estimated WUE at both eight-day and annual scales still need to be further quantified. [ABSTRACT FROM AUTHOR]

The U.S.-China EcoPartnership for Environmental Sustainability (USCEES), one of 30 EcoPartnerships, was established within the U.S.-China Strategic Economic Dialogue framework in May 2011 by a joint agreement between the U.S. Department of State and China's National Development and Reform Commission. The USCEES has the goal of fostering bi-national research innovation, communication, and entrepreneurship to address the interconnected challenges of environmental, social, and economic sustainability. Research and education programs within the USCEES are focused on understanding current and past degradation of natural resources, investigating the drivers, impacts, and mitigation of global climate change, and assessing options for sustainable use of natural resources. Although both the U.S. and China have embraced a future based on science, technology, and innovation, our bi-national framework acknowledges that these two nations have vastly different cultural, political, and demographic legacies that could pose distinct challenges to uniform solutions or mandated collaborative networks. The peer-to-peer connections that drive the research component of the USCEES program are promoted and initiated from the ground up; they are based on the voluntary participation of scientists and engineers who are fascinated by the intellectual challenge of solving complex problems of inherent interest to them. Herein, we present highlights of USCEES activities that describe our efforts to discover, incubate, and nurture U.S.-China research collaborations to meet our collective goals. We discuss our pilot programs that are designed to highlight university facilities, resources, and technologies for tech transfer and licensing with an environmental solutions-oriented direction. Additionally, programs to promote cross-EcoPartnership collaborations are discussed. [ABSTRACT FROM AUTHOR]

Climate change inevitably leads to changes in hydrothermal circulation. However, thermal-hydrologic exchanging caused by land cover change has also undergone ineligible changes. Therefore, studying the comprehensive effects of climate and land cover changes on land surface water and heat exchanges enables us to well understand the formation mechanism of regional climate and predict climate change with fewer uncertainties. This study investigated the land surface thermal-hydrologic exchange across southern China for the next 40 years using a land surface model (ecosystem-atmosphere simulation scheme (EASS)). Our findings are summarized as follows. (i) Spatiotemporal variation patterns of sensible heat flux (H) and evapotranspiration (ET) under the land cover scenarios (A2a or B2a) and climate change scenario (A1B) are unanimous. (ii) Both H and ET take on a single peak pattern, and the peak occurs in June or July. (iii) Based on the regional interannual variability analysis, H displays a downward trend (10%) and ET presents an increasing trend (15%). (iv)The annual average H and ET would, respectively, increase and decrease by about 10% when woodland converts to the cultivated land. Through this study, we recognize that land surface water and heat exchanges are affected greatly by the future climate change as well as land cover change. [ABSTRACT FROM AUTHOR]

Due to the heterogeneity and complexity of terrestrial ecosystems of East Asia, a better understanding of relationships between climate change and net primary productivity (NPP) distribution is important to predict future carbon dynamics. The objective of this study is to analyze the temporal-spatial patterns of NPP in East Asia (10°S - 55°N, 60 - 155°E) from 1982 to 2006 using the process-based Boreal Ecosystem Productivity Simulator (BEPS) model. Prior to the regional simulation, the annual simulated NPP was validated using field observed NPP demonstrating the ability of BEPS to simulate NPP in different ecosystems of East Asia. Simulated NPP exhibited a southeast-northwest decreasing distribution, above 1000 g Cm-2 yr-1 in most areas of Southeast Asia and below 50 g Cm-2 yr-1 in northwestern China. The annual total of simulated NPP was 11.27 Pg C yr-1 (˜18.78% of the global total) averaged over 25 years from 1982 to 2006. Total NPP increased by 7.33%, mainly in the northwestern part of the study area. The change of NPP was determined by precipitation in northern and southwestern regions, vapor pressure deficit and precipitation in North and Northeast Plains of China, radiation in South China, and temperature on the Tibetan Plateau. Climate was the main factor regulating the NPP trends in the interior and northern parts of the study area while the change in leaf area index was the factor dominating the trends of NPP in the eastern part of the study area. [ABSTRACT FROM AUTHOR]

The boreal forests, identified as a critical "tipping element" of the Earth's climate system, play a critical role in the global carbon budget. Recent findings have suggested that terrestrial carbon sinks in northern high-latitude regions are weakening, but there has been little observational evidence to support the idea of a reduction of carbon sinks in northern terrestrial ecosystems. Here, we estimated changes in the biomass carbon sink of natural stands throughout Canada's boreal forests using data from long-term forest permanent sampling plots. We found that in recent decades, the rate of biomass change decreased significantly in western Canada (Alberta, Saskatchewan, and Manitoba), but there was no significant trend for eastern Canada (Ontario and Quebec). Our results revealed that recent climate change, and especially drought-induced water stress, is the dominant cause of the observed reduction in the biomass carbon sink, suggesting that western Canada's boreal forests may become net carbon sources if the climate change-induced droughts continue to intensify. [ABSTRACT FROM AUTHOR]

Above- and below-ground biomass values for 17 types of grassland communities in China as classified by the Chinese Grasslands Resources Survey were obtained from systematic replicated sampling at 78 sites and from published records from 146 sites. Most of the systematic samples were along a 5,000-km-long transect from Hailar, Inner Mongolia (49°15'N, 119°15'E), to Pulan, Tibet (30°15'N, 81°10'E). Above-ground biomass was separated into stem, leaf, flower and fruit, standing dead matter, and litter. Below-ground biomass was measured in 10-cm soil layers to a depth of 30 cm for herbs and to 50 cm for woody plants. Grassland type mean total biomass carbon densities ranged from 2.400 kg m-2 for swamp to 0.149 kg m-2 for alpine desert grasslands. Ratios of below- to aboveground carbon density varied widely from 0.99 for tropical tussock grassland to 52.28 for alpine meadow. Most below-ground biomass was in the 0-10 cm soil depth layer and there were large differences between grassland types in the proportions of living and dead matter and stem and leaf. Differences between grassland types in the amount and allocation of biomass showed patterns related to environments, especially aridity gradients. Comparisons of our estimates with other studies indicated that above-ground biomass, particularly forage-yield biomass, is a poor predictor of total vegetation carbon density. Our estimate for total carbon storage in the biomass of the grasslands of China was 3.32 Pg C, with 56.4% contained in the grasslands of the Tibet-Qinghai plateau and 17.9% in the northern temperate grasslands. The need for further standardized and systematic measurements of vegetation biomass to validate global carbon cycles is emphasised. [ABSTRACT FROM AUTHOR]

Thus far, grassland ecosystem research has mainly been focused on low-lying grassland areas, whereas research on high-altitude grassland areas, especially on the carbon budget of remote areas like the Qinghai-Tibetan plateau is insufficient. To address this issue, flux of CO2 were measured over an alpine shrubland ecosystem (37°36′N, 101°18′E; 325 above sea level [a. s. l.]) on the Qinghai-Tibetan Plateau, China, for 2 years (2003 and 2004) with the eddy covariance method. The vegetation is dominated by formation Potentilla fruticosa L. The soil is Mol–Cryic Cambisols. To interpret the biotic and abiotic factors that modulate CO2 flux over the course of a year we decomposed net ecosystem CO2 exchange (NEE) into its constituent components, and ecosystem respiration ( Reco). Results showed that seasonal trends of annual total biomass and NEE followed closely the change in leaf area index. Integrated NEE were −58.5 and −75.5 g C m−2, respectively, for the 2003 and 2004 years. Carbon uptake was mainly attributed from June, July, August, and September of the growing season. In July, NEE reached seasonal peaks of similar magnitude (4–5 g C m−2 day−1) each of the 2 years. Also, the integrated night-time NEE reached comparable peak values (1.5–2 g C m−2 day−1) in the 2 years of study. Despite the large difference in time between carbon uptake and release (carbon uptake time < release time), the alpine shrubland was carbon sink. This is probably because the ecosystem respiration at our site was confined significantly by low temperature and small biomass and large day/night temperature difference and usually soil moisture was not limiting factor for carbon uptake. In general, Reco was an exponential function of soil temperature, but with season-dependent values of Q10. The temperature-dependent respiration model failed immediately after rain events, when large pulses of Reco were observed. Thus, for this alpine shrubland in Qinghai-Tibetan plateau, the timing of rain events had more impact than the total amount of precipitation on ecosystem Reco and NEE. [ABSTRACT FROM AUTHOR]