F. E. P. Fernandes

Ecophysiology of deciduous plants grown at different densities in the semiarid region of Brazil

Physiological differences in the Cordia oncocalyx tree growing at different densities in two distinct areas were investigated. An agrosilvopastoral system (AGP) and a secondary forest (SF) were studied. Under both types of land-use, C. oncocalyx presented a relative frequency of approximately 50%, and absolute densities of 670 and 80 individuals per hectare, respectively. Net photosynthesis (A), stomatal conductance (gs), and transpiration (E) were measured, and the SPAD index was recorded in sun leaves from the canopy and shade leaves from the lower canopy, in both the wet and dry seasons. We quantified the dry biomass of leaves and fruit on a per-tree basis at the end of the wet season. Net photosynthesis was higher in shaded leaves in the AGP in the wet season, reaching an average of 4.8 μmol m-2 s-1 against 3.2 μmol m-2 s-1 under SF. As trees began to shed their leaves at the beginning of the dry season and more radiation reached the shaded leaves, there was an increase in SF for A, depending on the intensity of light reaching the leaves. In the sun leaves, gas exchange was similar for the land-use systems during the wet season, but stronger in AGP than under SF during the dry season. This happened when the leaves in AGP retained more relative water content during a period of low gravimetric levels of the soil water. The lower tree density in AGP promoted a higher SPAD index and dry biomass in both the sun and shaded leaves, and allowed greater A, E and gs rates in the sun leaves at the beginning of the dry period.