Photosynthetic response of a wetland- and an upland-adapted tree species to seasonal variations in hydrology in the Brazilian Cerrado and Pantanal

Abstract

Savanna (Cerrado) of the Brazilian Pantanal exhibits large variations in hydrology, ranging from well drained to intermittently flooded. Climate and land use change has led to the expansion of “super-dominant” tree species in both habitats, including Vochysia divergens, which is adapted to flooding, and Curatella americana, which is adapted to upland Cerrado. There is both theoretical and practical interest in evaluating the potential net photosynthesis rate of these species to help explain their success in invading new areas with widely differing hydrological regimes. We hypothesized that these species have physical or biochemical adjustments their photosynthetic characteristics that allow them to thrive in their native and invaded environments. To test these hypotheses, we measured chloroplast CO2 concentration response curves, leaf nitrogen and phosphorus concentrations, and specific leaf area of both species over a year in the Pantanal and Cerrado. Neither species displayed a significant decline in potential net photosynthesis in their invaded habitats compared to their native habitats. The relatively constant rate of leaf gas exchange may be important for their success at invading novel habitats, however, there were statistically significant interactions between species, ecosystem, and season that were due in part to complex interactions between biophysical, biochemical, and phenological variables. The specific leaf area (SLA) for both species was higher in their invaded habitats; however, V. divergens exhibited a significant decline in stomatal conductance and an increase in intrinsic water use efficiency in the Cerrado, especially during the dry season. High physiological flexibility, and the ability to maintain a relatively constant value of A, may allow these species to cope with large seasonal variations in soil hydrology and expand into habitats with completely different hydrological conditions.