Spatial variability and major controlling factors of CO2 sink strength in Asian terrestrial ecosystems:: evidence from eddy covariance data

Asian terrestrial ecosystems cover an extensive area characterized by a large variety in climates and ecosystem properties. The observations of ecosystem CO2 flux in this area are increasing both in duration and spatial density, but no synthesis has yet been conducted. We surveyed CO2 flux observation data obtained by eddy covariance methods at 49 sites in terrestrial Asia. The measurements at most sites (44 of 49) began after 2000. The net ecosystem uptake of CO2 (NEE) varied greatly among sites and years and averaged -132.6 +/- 73.7, -250.1 +/- 206.1, and -180.1 +/- 361.7 g C m(-2) yr(-1), in boreal, temperate, and tropical Asia, respectively, and the coefficient of variation among sites increased from boreal to tropical Asia. The site-averaged annual NEE was correlated linearly with the mean annual temperature (T-air) and also correlated logarithmically with the precipitation. Multiple regression analysis and stepwise analysis indicated that photosynthetic active radiation (PAR) and T-air were the most significant predictors of the annual NEE. The study results suggest that Asian terrestrial ecosystems are currently significant net CO2 sinks and that the sink strength is largely controlled by temperature, moisture, and light conditions.