The aim of this study was to verify photosynthetic performance and photoinhibition occurrence in three "cerrado" species in the dry and rainy seasons. In both seasons, potential quantum yield of photosystem II (Fv/Fm), at miday, after one hour of dark adaptation, was lower than 0.8 in all species, which characterizes photinhibition. In spite of stomatal conductance reductions and lower values of effective quantum yield (D F/F`m), and apparent rates of photosynthetic electron transport (ETR) during dry season, all species showed values of photosynthetic light saturation similar to those during rainy season, approximantely 1500 mmol.m-2.s-1. At this level of light, the relative excessive photon flux increased from 60%, at rainy season, to 80% at dry season in all studied species. The maximum apparent ETR (ETRmax) in rainy season was similar for E. dysenterica and C. adamantium, 200 mmol.m-2.s-1, and 170 mmol.m-2.s-1 for A. crassifolia, but decreased to approximately 100 mmol.m-2.s-1 at drought period for all of three species. The data suggested that the reduction on gas exchange at the dry season was accompanied by reduction on photosystem II activity, with an increase in photoinhibition .
Photosynthesis; photoinhibition; "cerrado" plants
