Overnight rainfall inducing rapid changes in photosynthetic behaviour in a cerrado woody species during a dry spell amidst the rainy season

Abstract

We examined the effects of a short rainfall during a dry spell amidst the rainy season on CO₂ and H₂O gas exchange and chlorophyll a fluorescence in leaves of Miconia albicans (Sw.) Tr. (Melastomataceae), a common shrub of the Brazilian cerrado. A strong midday depression of gas exchange was observed at the end of the dry spell. Nevertheless, during the day after a rainfall, net CO₂ uptake (J_CO2), stomatal conductance to water vapour (g_s), transpiration rates (J_H2O) and the actual photosystem II (PSII) efficiency (ΔF/F´_m) increased, whereas the fraction of light absorbed in the PSII antennae that is dissipated directly within the antennae (1 – F´_v/F´_m) and the degree of PSII closure (1 – q_P) decreased. Although CO₂ and H₂O gas exchange were very sensitive to the rain-free event in the wet season, the occurrence of a small rainfall was enough to elicit rapid changes in g_s, J_H2O and J_CO2. We hypothesise that the strong effect of the dry spell during the wet season on gas exchange may be due to the highest leaf area available for transpiration at this time and a lower hydraulic limit for catastrophic embolism to occur.