Apparent carboxylation efficiency and relative stomatal and mesophyll limitations of photosynthesis in an evergreen cerrado species during water stress.

摘要

Miconia albicans, a common evergreen cerrado species, was studied in the garden of the Botany Department in Sao Carlos Federal University, Sao Paulo, Brazil, under field conditions. Leaf gas exchange and pre-dawn leaf water potential ( Psi pd) were determined during wet and dry seasons. The potential photosynthetic capacity (PNpmax) and the apparent carboxylation efficiency ( epsilon ) dropped in the dry season to 28.0 and 0.7%, respectively, of the maximum values in the wet season. The relative mesophyll (Lm) and stomatal (Ls) limitations of photosynthesis increased, respectively, from 24 and 44% in the wet season to 79 and 57% at the peak of the dry season when mean Psi pd reached -5.2 MPa. After first rains, the PNpmax, epsilon and Lm recovered reaching the wet season values, but Ls was maintained high (63%). The shallow root system growing on stonemason limited by lateral concrete wall to a depth of 0.33 m explained why extreme Psi pd occurred. Thus, M. albicans is able to quickly overcome the strains imposed by severe water stress..