Seasonal contribution of C3 and C4 species to ecosystem respiration and photosynthesis estimated from isotopic measurements of atmospheric CO2 at a grassland in Japan.

摘要

Measurements of t p#pdC in atmospheric CO and plant samples were made in 2003, along with CO flux measurements, at a grassland site in Tsukuba in central Japan. The objective of the study was to obtain estimates of relative seasonal contributions of C and C plants to the net CO flux over a C/C grassland area influenced by the Asian monsoon. C contribution to the ecosystem respiration (f R) increased from June to September, and then became constant at 63-67% through October and November. The seasonal variation in f R reflected the biomass composition of C and C plants at the measurement site. The seasonal C contribution to photosynthesis (f P) was significantly different from its contribution to f R in May (8%) while it showed similar values to f R after June. The seasonal variations in f R and f P reflect the biomass composition ratio. Such seasonal transition from C to C of relative contribution to the carbon flux is similar to that observed in humid prairie ecosystems, while it is different from that in dry prairie ecosystems where the contribution of C plants is lower and the seasonal maximum of the C-plant contribution occurs earlier compared to the humid prairie ecosystems.