Assimilação de carbono, eficiência no uso da água, condutâncias estomática e do mesofilo, transporte de elétrons em árvores de dossel de Dinizia excelsa Ducke (Fabaceae, Mimosoideae)

Abstract

This work aimed to evaluate leaf chamber leakage and to determine leaf gas exchange at two positions (upper and lower branches) within the canopy of six angelim trees, Dinizia excelsa. Data collection was carried out at Distrito Agropecuário da Suframa (ZF-3) during the second semester of 2010, in adult, emergent trees (diameter at breast height, DAP > 1m). The electron transport rate and carboxylation velocity of Rubisco were 81.6 to 107.8 μmol m-2 s-1 and 31.8 to 38.2 μmol m-2 s-1, respectively. Regarding photosynthetic parameters, leaves in upper and lower branches were statistically similar, what suggests light homogeneity within Dinizia excelsa‟s canopy. Maximum carboxylation velocity of Rubisco (at ambient [CO2]) and maximum electron transport rate (at high [CO2]) were the most important limitations to photosynthesis in both environments. There was a close correlation between Amax and gs and gm, what indicates that stomatal and mesophyll resistance influence photosynthesis. Leaf characteristics in upper and lower branches were largely similar, only diverging in leaf thickness and chlorophyll relative value (SPAD values measured in the field). Other leaf traits, like maximum quantum photochemical efficiency (Fv/Fm), specific leaf area (SLA) and absolute chlorophyll content were statistically identical. Although leaf chamber leakage was not significant, it should be recommended to take into consideration eventual gas leaking during photosynthetic measurements.