Physiological adjustments of an invasive tree species to extreme hydrological events in a tropical seasonal wetland

摘要

Plants in seasonal wetlands are subject to large hydrological fluctuations and the physiological trade-offs that occur during these variations are still poorly understood. Within the Brazilian Pantanal, the largest tropical seasonal wetland in the world, the abundance of Vochysia divergens Pohl (Vochysiaceae) has been increasing and it forms mono-specific stands. The physiological performance of V. divergens trees to withstand seasonal variations in flooding and drought was evaluated to understand how the hydrological regime affects the species habitat and encourages new areas to be occupied. Individuals were evaluated for changes in their physiological parameters by means of CO2 response curves, chlorophyll fluorescence, photosynthetic pigment and nitrogen (N) concentrations. Drought conditions caused reductions of 82, 64 and 80% of the maximum rate of CO2-saturated photosynthesis (A(max m)), electron transport (J(max m)), and carboxylation (V-cmax m) per unit leaf mass, an increase in leaf fluorescence (F-0: 27%) and non-photochemical quenching (Phi(NPQ): 18%), and a decrease in photochemical quantum yield of photosystem II (Phi(PSII in): 29%). The dry season also caused a significant reduction in leaf photosynthetic pigments and an increase in leaf N concentration, but most of the N was allocated away from carboxylation and electron transport proteins and toward leaf structure. Our data indicate that dry season drought caused a significant decline in biochemical properties associated with leaf gas exchange and an increase in allocation to leaf structure. The ability to rapidly shift to high photosynthesis as soon as water levels rise in the wet season may be critical for the growth and expansion of this species in the Pantanal.