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Understanding the dynamics and underlying mechanism of carbon exchange between terrestrial ecosystems and the atmosphere is one of the key issues in global change research. In this study, we quantified the carbon fluxes in different terrestrial ecosystems in China, and analyzed their spatial variation and environmental drivers based on the long-term observation data of China FLUX sites and the published data from other flux sites in China. The results indicate that gross ecosystem productivity ( GEP), ecosystem respiration ( ER), and net ecosystem productivity ( NEP) of terrestrial ecosystems in China showed a significantly latitudinal pattern, declining linearly with the increase of latitude. However, GEP, ER, and NEP did not present a clear longitudinal pattern. The carbon sink functional areas of terrestrial ecosystems in China were mainly located in the subtropical and temperate forests, coastal wetlands in eastern China, the temperate meadow steppe in the northeast China, and the alpine meadow in eastern edge of Qinghai-Tibetan Plateau. The forest ecosystems had stronger carbon sink than grassland ecosystems. The spatial patterns of GEP and ER in China were mainly determined by mean annual precipitation ( MAP) and mean annual temperature ( MAT), whereas the spatial variation in NEP was largely explained by MAT. The combined effects of MAT and MAP explained 79%, 62%, and 66% of the spatial variations in GEP, ER, and NEP, respectively. The GEP, ER, and NEP in different ecosystems in China exhibited 'positive coupling correlation' in their spatial patterns. Both ER and NEP were significantly correlated with GEP, with 68% of the per-unit GEP contributed to ER and 29% to NEP. MAT and MAP affected the spatial patterns of ER and NEP mainly by their direct effects on the spatial pattern of GEP. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the ‘ensemble block’ time average procedure and the Ogive function are applied to three ChinaFLUX sites to determine the low-frequency contribution to eddy fluxes. It is found that both methods give similar results. They show that 30min flux-averaging periods are sufficient to capture all flux scales over a wheat field, but 60min or longer is necessary over forests. Our results show that the optimal averaging period is a site-specific parameter. According to this analysis, for some ChinaFLUX sites at least, an averaging period that captures the low-frequency transport may improve the energy balance problem. [Copyright &y& Elsevier]

Abstract: Variation in temperature accounts for most of the seasonal fluctuation of terrestrial ecosystem respiration. However, other factors, such as soil moisture, also influence ecosystem respiration. In this study, continuous measurement of carbon dioxide exchange was made over a subtropical Pinus plantation of southeastern China using the eddy covariance (EC) technique. The effect of soil water content on ecosystem respiration and its sensitivity to temperature (Q 10) were examined during the unusual dry summer of 2003. The results indicate that soil water content significantly affected the dynamics of respiration rate and its relationship with temperature in the drought-stressed ecosystem. The effect of soil water content on the Q 10 value of ecosystem respiration is described best by a quadratic function, instead of the commonly used multiplicative model. The regression model analysis revealed that ecosystem respiration was more sensitive to soil water content than is estimated by the multiplicative model. The multiplicative model led to an overestimation of response of the respiration to warming under the dry soil condition. Sensitivity of the ecosystem respiration to temperature was found to vary with air temperature and soil water content. This, to a considerable extent, precludes accurate estimates of the seasonal dynamics of ecosystem respiration. [Copyright &y& Elsevier]

Abstract: Understanding the spatial variation of temperature sensitivity (i.e. Q 10) of soil respiration (R s) and its controlling factors, is critical to improve the precision of carbon budget estimations at regional scales. In this study, data from 2–3 continuous years of R s measurements over 15 ecosystems of ChinaFLUX were summarized to analyze the response of R s to soil temperature. Moreover, we improved our dataset by collecting previously published Q 10 values from 34 ecosystems in China. The ecosystems studied were located in the main climatic zones of China, spanning from alpine via temperate to tropical. Spatial variations of Q 10 and its controlling factors were analyzed. The results showed that soil temperature at a 5 cm depth satisfactorily explained the seasonal variations in R s of the 15 ChinaFLUX ecosystems (R 2 varying from 0.37 to 0.83). Based on the overall data, the Q 10 values of R s in China ranged from 1.28 to 4.75. The spatial variations in Q 10 were primarily determined by soil temperature during measurement periods, soil organic carbon (SOC) content, and ecosystem type. Ecosystems in colder regions and with higher SOC content had relatively higher Q 10 values. Moreover, ecosystems of different vegetation types showed different Q 10 values. A temperature- and SOC-dependent function for Q 10 is suggested, which could be a valuable reference for improving the regional-scale models of R s and ecosystem carbon cycles. [Copyright &y& Elsevier]