CAPACIDADE FOTOSSINTÉTICA E MÉTODO “ONE-POINT” EM AMBIENTES HIDROLÓGICOS NA AMAZÔNIA CENTRAL

Abstract

Understanding how forests are responding to extreme drought and flood events in contrasting hydrological environments, and how this might affect the photosynthetic process, is of utmost importance, as these effects can lead to large-scale alterations in forest structure and composition. Therefore, this study aims to answer the following questions: are Vcmax estimates for trees in the floodplain and plateau using the "one-point" method consistent with estimates from full A-Ci curves? Is there a difference in Vcmax between the plateau and the floodplain, and how does light co-vary with these differences? Is there a difference in vein density between the floodplain and plateau? Is vein density associated with the photosynthetic capacity of floodplain and plateau species? The main operational variables for estimating maximum photosynthetic capacity are Vcmax, which describes the maximum carboxylation capacity of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and Jmax, which is the maximum electron transport rate. Vcmax is adjusted based on saturating light conditions (A) at different CO₂ concentrations in the leaf air spaces (Ci), known as the A-Ci curve. In addition to the A-Ci curve, we used the "one-point" method, which proposes the estimation of Vcmax using just one measurement, taken separately at 400 μmol CO₂ mol-1 before the start of the A-Ci curve. Vein density is one of the key anatomical-morphological parameters for photosynthetic capacity, measured by the total length of veins per unit leaf area. In response to the first question, it was shown that Vcmax estimated through the "one-point" method accurately predicts the Vcmax calculated by the traditional A-Ci curve method for both environments (p<0.001, R²=0.88). For the second question, there was no difference in Vcmax between the plateau and the floodplain, with a significant interaction between light and environment (p = 0.003, r² = 0.051). Regarding the third question, there was no difference in vein length per area (VLA) between the floodplain and plateau (p = 0.83; R² = 0.002). Finally, in response to the fourth question, there was an interaction between the hydrological environment and vein length, affecting Vcmax (p = 0.002, r² = 0.56). The study concludes that the interactions of physiological and anatomical traits demonstrate the manifestation of plant plasticity in response to the local environment.