Midday depression in savanna trees: coordinated adjustments in photochemical efficiency, photorespiration, CO2 assimilation and water use efficiency.

摘要: High irradiances, high air temperatures and low relative humidities characterize the seasonal savannas of central Brazil, locally known as cerrados. In present study, we investigated implications to photoprotection diurnal adjustments in photochemical non-photochemical processes five cerrado woody species that differed photosynthetic capacity duration extension midday depression photosynthesis. We also evaluated contribution photorespiration minimize danger photoinhibition potential carbon costs operation this mechanism response changes irradiance levels. Notwithstanding large differences patterns photosynthesis stomatal conductance, four out showed a tight common linear relationship between net CO2 assimilation rates transpiration over range environmental conditions prevailed during typical sunny days at end rainy season. Large reversible decreases efficiency were compensated by proportional increases related photoprotection, irrespective prevailing levels degree stomata closure. Light curves used evaluate photorespiratory production electron flow A percentage was drive light-saturated leaves. conclusion, an efficient control quenching partition assimilative non-assimilative alleviated photoinhibition. However, results suggest losses gain because could impose strong limitations on leaf balance species.