Effects of ozone stress on leaf-level photosynthesis in soybean (Glycine max)

Glycine max were exposed in nine the open-top chambers to three levels of ozone (O-3) concentration (ambient, approximately 45 nL.L-1 and two elevated ozone, 80+/-10 nL.L-1 and 110+/-10 nL.L-1) in four different growing stages (branching, flowering, podding and filling). In order to study the effect of different ozone concentration on photosynthesis parameters, the emphasis of this research was on photosynthetic pigment contents, parameters of photosynthetic gas exchange, Hill reaction activity and Ca2+/Mg2+-ATPase activity in soybean leaves. This paper reveals its response process and degree of photosynthesis in soybean leaves under different elevated O-3, and it could establish the foundation for the study of plants adaptability mechanism under elevated O-3 on the molecular level. The results showed that elevated O-3 concentration accelerated peroxidation damage, and plants could not tolerate O-3-induced injure, thus reducing photosynthesis by stomatal closure because of O-3 exposure in soybean leaves. And O-3 stress caused an acceleration of caducity that might be in part responsible for the reduction of photosynthesis.