Leaf photosynthetic acclimation of Echinochloa crusgalli grown in rice field to free-air CO2 enrichment (FACE)]

A comparative study was made between the leaves of Echinochloa crusgalli grown at 580 (FACE) and 380 (control, ambient air) mumol CO2 mol-1 air by observation of net photosynthetic rates (Pn) and the contents of soluble protein and the key enzyme of photosynthetic carbon assimilation, Rubisco. When measured at the ambient air CO2 concentration (380 mumol.mol-1), Pn were significantly lower in leaves grown under FACE conditions than that in those leaves grown in the ambient air. This indicates that photosynthetic acclimation to high CO2 occurs in the leaves grown under FACE conditions. Also, the stomatal conductance (Gs) and intercellular CO2 concentration (Ci) were decreased significantly in the leaves grown under FACE. The content of total soluble protein was much lower in the leaves grown under FACE conditions than that the in the control, and the content of Rubisco was also decreased in the FACE leaves, but the difference was not significant. From these results it is deduced that the photosynthetic acclimation to high CO2 in Echinochloa crusgalli leaves grown under FACE conditions is mainly related to the partial closure of stomata and the decrease in soluble protein containing some enzymes.