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The terrestrial carbon (C) cycle plays an important role in global climate change, but the vegetation and environmental drivers of C fluxes are poorly understood. We established a global dataset with 1194 available data across site-years including gross primary productivity (GPP), ecosystem respiration (ER), net ecosystem productivity (NEP), and relevant environmental factors to investigate the variability in GPP, ER and NEP, as well as their covariability with climate and vegetation drivers. The results indicated that both GPP and ER increased exponentially with the increase in mean annual temperature (MAT) for all biomes. Besides MAT, annual precipitation (AP) had a strong correlation with GPP (or ER) for non-wetland biomes. Maximum leaf area index (LAI) was an important factor determining C fluxes for all biomes. The variations in both GPP and ER were also associated with variations in vegetation characteristics. The model including MAT, AP and LAI explained 53% of the annual GPP variations and 48% of the annual ER variations across all biomes. The model based on MAT and LAI explained 91% of the annual GPP variations and 92.9% of the annual ER variations for the wetland sites. The effects of LAI on GPP, ER or NEP highlighted that canopy-level measurement is critical for accurately estimating ecosystem-atmosphere exchange of carbon dioxide. The present study suggests a significance of the combined effects of climate and vegetation (e.g., LAI) drivers on C fluxes and shows that climate and LAI might influence C flux components differently in different climate regions. [ABSTRACT FROM AUTHOR]

Terrestrial carbon cycling is one of the hotspots in global change issues. In this paper, we presented the rationale for determination of net exchange of CO2 between terrestrial and the atmosphere (NEE) and the methods for measuring several relevant components. Three key processes for determination of NEE were addressed, including the separation of shoot autotrophic respiration from total CO2 emissions of the ecosystem, the partition of root respiration from soil CO2 efflux, and the quantification of rhizodeposition C from NPP. With an understanding of the processes involved in the CO2 exchange between terrestrial and the atmosphere, we estimated NEE of rice ecosystem in Nanjing based on field measurements of CO2 emissions and several relevant biotic components as well as abiotic factors. The field measurements of CO2 emissions were made over the rice-growing seasons in 2001 and 2002 with the static opaque chamber method. Calculations indicated that the seasonal pattern of NEE is comparable for two seasons. Either net carbon emission or fractional carbon fixation occurred during 3 weeks after rice transplanting and thereafter net carbon fixation appeared with an increasing trend as rice growing. Higher net carbon fixation occurred in the rice developmental period from elongating to heading. A decline trend in the fixation was documented after rice heading. The mean daily NEE was -6.06 gC .m-2M 2001 season and -7.95 -2 . gC . m -2in 2002 season, respectively. These values were comparable to the results obtained by Campbell et al. who made field measurements with the Bowen ratio-energy balance technique in irrigated rice, Texas USA. Moreover, the mean daily NEE in this study was also comparable to the values obtained from a Japanese rice paddy with the eddy covariance method under the similar water regime, either drainage course or waterlogged. It is concluded that NEE determined by the static opaque chamber method is comparable and in agreement with those measured by Bowen ratio energy balance and eddy covariance methods. [ABSTRACT FROM AUTHOR]

Soil respiration ( Rs) is one of the key processes that underline our understanding of carbon cycle in terrestrial ecosystems. Great uncertainty remains in the previous global Rs estimates with a difference of 70 Pg C a −1 between the highest and lowest estimates. Thus, the present study aimed to estimate the global annual Rs and investigate the interannual and spatial variability in global annual Rs using a semi-mechanistic, empirically-based model which included climatic factors (temperature and precipitation) and topsoil (0–20 cm) organic carbon storage. About 657 published studies of annual Rs from 147 measurement sites were included in this meta-analysis. The global data sets from 1970 to 2008 on climate, surface air temperature, and soil properties were collected. The Monte Carlo method was used to propagate the simulation errors to global Rs. The results indicated that the mean annual global Rs was 94.4 Pg C a −1, increasing at roughly 0.04 Pg C a −1 (∼0.04% a −1) from 1970 to 2008. The Rs rate increased from colder, drier and less soil carbon-rich regions to warmer, moister and more carbon-rich regions. Highest Rs rates appeared in the tropical forest, while the lowest ones were in polar and desert regions. The annual Rs correlated directly with global temperature anomalies, suggesting that the interannual variability in temperature was responsible for the interannual variations in predicted global Rs. The global Rs increased from high-latitude zones to low-latitude zones. Further studies are recommended to explore the relationship between soil respiration and vegetation characters. [ABSTRACT FROM AUTHOR]