Sensitivity of photosynthesis and carbon sink in tropical rainforests to projected atmospheric CO_2 and climate change

摘要

Terrestrial ecosystems currently take up as much as one third of anthropogenic CO_2 emitted annually to the earth’s atmosphere (Schimel 1995). CO_2 fertilization (i.e. the stimulation in photosynthesis and plant growth by elevated atmospheric CO_2concentration), forest re-growth, nitrogen deposition and climate change are believed to contribute to this C sink (Field 2001). CO_2 fertilization is of particular interest as it could provide a negative feedback on the growth rate of the atmospheric CO_2 concentration. Recent field measurements and model simulations indicate that a significant fraction of the terrestrial sink (approximately 1 Gt C yr~(-1)) may be attributed to CO_2 fertilization occurring in tropical rainforests (Malhi and Grace 1998). However it is crucial to understand the dynamic properties of this C sink before assuming that CO_2 fertilization in tropical rainforests will play a significant role in offsetting future anthropogenic CO_2 emissions. Previous evaluations of C sink dynamics have been limited mostly to model simulations (Tian et al. 1999; Kicklighter et al. 1999, Chamber et al. 2001), and have not been linked with experiments at appropriate spatial scales. Here we present results from an empirical evaluation of photosynthesis and carbon sink sensitivity to projected CO_2 and climate change, based on measurements in a large-scale rainforest mesocosm.