Respiração Foliar Diurna e Noturna em Árvores da Amazônia Central

Abstract

Autotrophic respiration is quantitatively important for providing carbon and energy skeletons during plant growth and maintenance. Leaf respiration is a major component of autotrophic respiration, especially in the tropics where a major fraction of global autotrophic respiration occurs. At the same temperature, leaf respiration is lower during the day (Rlight) than during the night (Rdark) due to a light suppression of mitochondrial aerobic respiration. However, Rlight is poorly characterized in diverse tropical ecosystems, and little to no information exists on the degree of Rdark light suppression. Moreover, little is known about the relationships between Rdark and Rlight with plant functional traits, within common tree species which make up a large fraction of individuals within the Amazon Basin and how the seasonal variation in precipitation and the vertical gradient of light affects their variations. The main objective of this study was to quantify the light suppression of the Rlight and Rdark leaf in dominant species of "Terra Firme" forest in Central Amazonia and to evaluate correlations with leaf functional characteristics (i.e. leaf mass per area, macronutrient content and soluble carbohydrates) and tree growth. The study was carried out in the tropical forest reserve ZF2, managed by the National Institute for Research in the Amazon (INPA), approximately 60 km NW of Manaus, Brazil. Gas exchange data were collected from 26 individuals. Light curves were performed with the following levels of photosynthetically active radiation (PAR) (100, 90, 80, 70, 60, 50, 40, 30, 20, 15, 10, 5 and 0 µmol m-2 s-1), to obtain Rdark and Rlight estimate by the Kok method. After the gas exchange measurements, the leaves were taken to the laboratory for analysis of the functional leaf characteristics. It was observed that the respiratory rates did not differ according to seasonality, but according to the degree of crown exposition. In addition, Rlight is strongly correlated with Rdark, also a weak relationship with nitrogen content and medium correlation with leaf mass area (LMA) and phosphorus content. The rate of suppression had an inverse variation with the degree of crown exposure, being lower in the upper canopy trees. These results reiterate the need to differentiate the understanding of the biochemical and physiological functions of leaf respiration in the different vertical gradient of the forest, considering the degree of crown exposure in tropical ecosystems, allowing for better representation in the Models of the Earth System, considering the light suppression of the leaf respiration.