Tropical rain forests play important roles in global carbon cycling and balance. An accurate estimation of forest carbon sink strength is important for a better understanding of global carbon cycling. The Xishuangbanna tropical seasonal rain forest, located on the northern edge of the Indian-Malaysia tropical rain forest zone, is considered surprising for its persistence under relatively cold and dry conditions.

　　  XTBG established an eddy covariance system mounted on a 70-m meteorological tower in Xishuangbanna in 2002. Based on eddy covariance data and corresponding eco-physiological data, Prof. Zhang Yiping and his research team investigated the ecosystem carbon balance and its environmental controlling mechanisms.

　  The main results were:

　   1) The studied ecosystem was a carbon sink as determined by both eddy covariance (1.19 Mg C ha–1 yr–1) and biometric methods (3.59 Mg C ha–1 yr–1);

　  2) Biometric and eddy covariance based net ecosystem production did not converge during the investigation period;

　 3) The large biomass increment, caused by the rapid annual growth rate of large trees, accounted for most of the large ecosystem carbon sink according to the biometric method;

　 4) High leaf respiration in relation to carbon allocation and therefore a low ecosystem carbon use efficiency (0.34) were observed.

　  　  The research observation has been published online in Journal of Geophysical Research-Atmospheres by the American Geophysical Union ( doi: 10.1029/2009JD012913).