Seasonal patterns of leaf-level photosynthetic gas exchange in an eastern Amazonian rain forest. (Special Issue: Ecosystem dynamics of Amazonian and Andean forests.)

摘要

Background: Global changes are challenging the equilibrium in the Amazon. Understanding how that biome responds to seasonality in water availability is essential to build scenarios of ecosystem functioning in the near future. Aims: Our aim was to test for seasonal variations in leaf traits related to primary productivity. Methods: Chemical composition, mass to area ratio and photosynthetic response curves to light and CO₂ and of stomatal conductance (g_s) to leaf-to-air water pressure deficit ( nu ) were determined from leaves of Amazonian trees and lianas. Results: Weak responses of g_s to nu suggested limited stomatal control over transpiration. Dry season stomatal limitation of photosynthesis was not a common feature as only one individual studied (out of 14) exhibited concomitant decreases in light saturated photosynthetic rate (A_Sat) and g_s (measured during A_Sat) associated with the dry season. Furthermore, 75% of the individuals evaluated did not show decreased photosynthetic capacity (V_cmax) during the dry season, suggesting limited seasonal leaf acclimation. Grouped analyses indicated that most parameters evaluated remained constant across seasons. The exceptions were leaf nitrogen and its isotopic signature, and the integrated stomatal sensitivity to light, CO₂ and nu . Conclusions: These findings reinforce the notion that the dry season in eastern Amazonia is not associated with significant limitations in leaf-level photosynthesis.