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Forest net primary productivity (NPP), representing the biomass carbon gain from the atmosphere, varies significantly with forest age. Reliable forest NPP-age relationships are essential for forest carbon cycle modelling and prediction. These relationships can be derived from forest inventory or field survey data, but it is unclear which model is the most effective for simulating forest NPP variation with age. Here, we aim to establish NPP-age relationships for China’s forests based on 3121 field survey samples. Five models, including the Semi-Empirical Mathematical (SEM) function, the Second- Degree Polynomial (SDP) function, the Logarithmic (L) function, the Michaelis-Menten (M) function, and the Γ function, were compared against field data. Results of the comparison showed that the SEM and the Γ function performed much better than the other three models. SEM also outperformed the Γ function in tracking forest NPP-age curves at old ages and therefore is regarded as the best NPP-age model. The finalized forest NPP-age curves for five forest types in six regions of China can facilitate forest carbon modelling and future carbon projections in China and may also be useful for other regions. [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]

Plant functional traits have increasingly been studied as determinants of ecosystem properties, especially for soil biogeochemical processes. While the relationships between biological community structures and ecological functions are a central issue in ecological theory, these relationships remain poorly understood at the large scale. We selected nine forests along the North-South Transect of Eastern China (NSTEC) to determine how plant functional traits influence the latitudinal pattern of soil microbial functions, and how soil microbial communities and functions are linked at the regional scale. We found that there was considerable variation in the profiles of different substrate use along the NSTEC. Soil microorganisms from temperate forests mainly metabolized high-energy substrates, while those from subtropical forests used all the substrates equally. The soil silt content and plant functional traits together shaped the biogeographical pattern of the soil microbial substrate use. Soil organic matter decomposition rates were significantly higher in temperate forests than in subtropical and tropical forests, which was consistent with the pattern of soil microbial biomass carbon concentrations. Soil organic matter decomposition rates were also significantly and negatively related to soil dissolved organic carbon concentrations, and carboxylic acid, polymer, and miscellaneous substrates. The soil microbial community structures and functions were significantly correlated along the NSTEC. Soil carbohydrate and polymer substrate use were mainly related to soil G+ bacterial and actinomycetes biomass, while the use of amine and miscellaneous substrates were related to soil G- bacteria, fungal biomass, and the F/B ratio. The contributions of different groups of microbial biomass to the production of soil enzyme activities differed. The relationship between soil microbial community structure and functions supported that there was functional dissimilarity. [ABSTRACT FROM AUTHOR]

Ecosystem carbon allocation can indicate ecosystem carbon cycling visually through its quantification within different carbon pools and carbon exchange. Using the ecological inventory and eddy covariance measurement applied to both a mature temperate mixed forest in Changbai Mountain (CBM) and a mature subtropical evergreen forest in Dinghu Mountain (DHM), we partitioned the ecosystem carbon pool and carbon exchange into different components, determined the allocation and analyzed relationships within those components. Generally, the total carbon stock of CBM was slightly higher than that of DHM due to a higher carbon stock in the arbor layer at CBM. It was interesting that the proportions of carbon stock in vegetation, soil and litter were similar for the two mature forests. The ratio of vegetation carbon pool to soil carbon stock was 1.5 at CBM and 1.3 at DHM. However, more carbon was allocated to the trunk and root from the vegetation carbon pool at CBM, while more carbon was allocated to foliage and branches at DHM. Moreover, 77% of soil carbon storage was limited to the surface soil layer (0-20 cm), while there was still plentiful carbon stored in the deeper soil layers at DHM. The root/shoot ratios were 0.30 and 0.25 for CBM and DHM, respectively. The rates of net ecosystem productivity (NPP) to gross ecosystem productivity (GPP) were 0.76 and 0.58, and the ratios of ecosystem respiration (Re) to GPP were 0.98 and 0.87 for CBM and DHM, respectively. The net ecosystem carbon exchange/productivity (NEP) was 0.24 t C ha–1 yr–1 for CBM and 3.38 t C ha–1 yr–1 for DHM. Due to the common seasonal and inter-annual variations of ecosystem carbon exchange resulting from the influence of environmental factors, it was necessary to use the long record dataset to evaluate the ecosystem sink capacity. [ABSTRACT FROM AUTHOR]

The article provides information on the Chinese Ecosystem Research Network (CERN), which is considered as the longest-lived ecological network in China that facilitates research on the country's ecosystems. Topics discussed include the founding and organization of the CERN, missions and achievements of the CERN, and motivation and future orientation of the CERN.

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]

Estimating and analyzing the temporal and spatial patterns of methane emissions from agriculture (MEA) will help China formulate mitigation and adaptation strategies for the nation's agricultural sector. Based on the Tier 2 method presented in the 2006 guidelines of the Intergovernmental Panel on Climate Change (IPCC) and on existing reports, this article presents a systematic estimation of MEA in China from 1990 to 2006, with a particular emphasis on trends and spatial distribution. Results from our study indicate that China's MEA rose from 16.37 Tg yr in 1990 to 19.31 Tg yr in 2006, with an average annual increase of 1.04%. Over the study period, while emissions from field burning of crop residues remained rather low, those from rice cultivation and from livestock typically decreased and increased, respectively, showing extremely opposite trends that chiefly resulted from changes in the cultivated areas for different rice seasons and changes in the populations of different animal species. Over the study period, China's high-MEA regions shifted generally northward, chiefly as a result of reduced emissions from rice cultivation in most of China's southern provinces and a substantial growth in emissions from livestock enteric fermentation in most of China's northern, northeastern, and northwestern provinces. While this article provides significant information on estimates of MEA in China, it also includes some uncertainties in terms of estimating emissions from each source category. We conclude that China's MEA will likely continue to increase in the future and recommend a demonstration study on MEA mitigation along the middle and lower reaches of the Yellow River. We further recommend enhanced data monitoring and statistical analysis, which will be essential for preparation of the national greenhouse gas (GHG) inventory. [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]

Soil erosion transports light density and fine particle soil material from hills down to low-lying land areas, which can lead to carbon loss and subsequent sequestration. In the present paper, the profile distribution of soil organic carbon (SOC) and soil 13C natural abundance (δ13C) were analyzed across five geomorphic positions, distributed along a typical rolling farmland in the Black Soil region of Northeast China. The contents of particulate organic carbon (POC) and mineral-associated organic carbon (MOC) at each geomorphic position were measured with physical fraction method. The results showed that soil erosion decreased 5.3–22.4% of SOC and increased 4.0–6.1% of δ13C of surface soils at the eroding sites. At the typical depositional sites, SOC content and δ13C value in the buried surface layer were 1.5 times and 1.1 times as much as those of the current plough layer, respectively. Soil erosion did not change the POC content, but MOC content decreased by 9.3–35.2%. At the eroding sites, the coefficient of determination between soil δ13C and MOC ( R2 = 0.52) was higher than that between soil δ13C and POC ( R2 = 0.37). Our study indicated that soil erosion decreased SOC content and increased δ13CSOC in surface layer mainly through transferring fine sized and 13C-depleted SOC fraction. Deep burial and re-aggregation of eroded materials at depositional sites were in favor of stabilization and sequestration of SOC. [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]

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]

The article discusses research which measured components of the energy budget continuously above a 300 year old temperate mixed forest in Northeastern China from January 1 to December 31 in 2003. Researchers found that the albedo showed pronounced seasonal trends and its values ranged from 0.07 to 0.20, that latent heat was the largest component of the energy budget on a yearly time scale, and was about 30% greater than sensible heat as indicated by the annual Bowen ratio beta values, and that despite the energy budget gap, the eddy covariance method should be a sound tool for measurement of turbulent fluxes, even under extremely cold conditions.

Scaling up ecosystem processes from plots to landscapes is essential for understanding landscape structure and functioning as well as for assessing ecological impacts of land use and climate change. This study illustrates an upscaling approach to studying the spatiotemporal pattern of ecosystem processes in the Changbai Mountain Nature Reserve in northeastern China by integrating simulation modeling, GIS, remote sensing data, and field-based observations. The ecosystem model incorporated processes of energy transfer, plant physiology, carbon dynamics, and water cycling. Using a direct extrapolation scheme, the patch-level ecosystem model was scaled up to quantify the landscape-level pattern of primary productivity and the carbon source-sink relationship. The simulated net primary productivity (NPP) for the entire landscape, consisting of several ecosystem types, was 0.680 kg C m-2 yr-1. The most widely distributed ecosystem type in this region was the mixed broad-leaved and Korean pine (Pinus koraiensis) forest, which had the highest NPP (1.084 kg C m-2 yr-1). The total annual NPP for all ecosystem types combined was estimated to be 1.332 Mt C yr-1. These results suggest that the Changbai Mountain landscape as a whole was a carbon sink, with a net carbon sequestration rate of about 0.884 Mt C yr-1 for the study period. The simulated NPP agreed reasonably well with available field measurements at a number of locations within the study landscape. Our study provides new insight into the relationship between landscape pattern and ecosystem processes, and useful information for improving management practices in the Changbai Mountain Nature Reserve, which is one of the most important forested landscapes in China. Several research needs are discussed to further refine the modeling approach and reduce prediction uncertainties. [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]

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]