Fisiologia de florestas plantadas no Brasil: efeitos climáticos e genéticos

Abstract

Photosynthesis and stomatal conductance are essential processes in the functioning of ecosystems. Photosynthesis is the key process in the carbon cycle, and this exchange of carbon and water exchange by the plant is regulated by the stomata, a process that is responsible for balancing the photosynthetic uptake of CO2 against the need to control the loss of water from the leaves. These processes influence the water use efficiency of plants, growth, the distribution of vegetation in the ecosystem and the productivity of forests. Understanding how these physiological processes are influenced by environmental and genetic factors provides information to improve the simulation of forest productivity and also to understand how plants will behave in future climate change scenarios. Within this context, this work aims to model the photosynthetic capacity and stomatal conductance of eucalypt and pine forests in Brazil in two articles. In the first article, we used the model by Farquhar et al., (1980) to obtain the parameters Vcmax, Jmax and Jmax/Vcmax, and we analyzed the influence of age, growth temperature, this is, at the average temperature of the daily average 10 and 30 days before the photosynthetic measurement, and precipitation variables, and climatic groups on these parameters for the two functional groups (pine and eucalypt). Our results show that the photosynthetic capacity of forests presents a difference between the functional groups, the variables growth temperature and precipitation at 10 and 30 days before data collection influenced photosynthetic parameters, suggesting acclimatization of foliar photosynthesis. Age os stand influenced photosynthetic capacity throughout the rotation. Older forests have higher Jmax. There were no differences between the subtropical and tropical climate groups, demonstrating an adaptation of the genotypes to the environmental conditions of Brazil. The second article investigates the performance of three stomatal conductance models (BB, BBL and USO) to identify the best model, in addition to to analyze how stomatal conductance and water use efficiency vary between functional groups and between eucalypt genotypes in Brazilian forest plantations. Our results revealed that the BBL and USO models performed better in the Brazilian forestry data. The species of the pine group had the highest stomatal conductance response parameter (g1) and, consequently, the lowest efficiency in water use when compared to the genotypes of the eucalypt group. Within the eucalypt group, the genotypes of showed differences in stomatal responses, indicating that in addition to the genotype characteristics, local climatic conditions may also have influenced the variation in g1. We found in these two articles photosynthetic parameters Vcmax, Jmax, Jmax/Vcmax and stomatal response parameter (g1) modeled by the three gs models, most used in global vegetation models and process-based models for various eucalyptus and pine genotypes. Our study will expand the physiological parameters database for planted forests in Brazil, making it possible to use them in global vegetation modeling studies.