On the ratio of intercellular to ambient CO2 (c(i)/c(a)) derived from ecosystem flux

摘要

The ratio of intercellular to ambient CO2 concentrations (c(i)/c(a)) plays a key role in ecophysiology, micromete-orology, and global climatic change. However, systematic investigation on c(i)/c(a) variation and its determinants are rare. Here, the c(i)/c(a) was derived from measuring ecosystem fluxes in an even-aged monoculture of rubber trees (Hevea brasiliensis). We tested whether c(i)/c(a) is constant across environmental gradients and if not, which dominant factors control c(i)/c(a) variations. Evidence indicates that c(i)/c(a) is not a constant. The c(i)/c(a) exhibits a clear "V"-shaped diurnal pattern and varies across the environmental gradient. Water vapor pressure deficit (D) is the dominant factor controls over the c(i)/c(a) variations. c(i)/c(a) consistently decreases with increasing D. c(i)/c(a) decreases with square root of D as predicted by the optimal stomatal model. The D-driving single-variable model could simulate c(i)/c(a) as well as that of sophisticated model. Many variables function on longer timescales than a daily cycle, such as soil water content, could improve c(i)/c(a) model prediction ability. Ecosystem flux can be effectively used to calculate c(i)/c(a) and use it to better understand various natural cycles.