Fósforo restringe respostas alométricas, mas não fisiológicas, de plântulas de Inga edulis Mart. sob crescimento em CO2 elevado

Abstract

The Amazon rainforest is the largest continuous tropical forest in the world. It plays an important role in the carbon (C) cycle, by assimilating CO2 through photosynthesis, fixing it in plant biomass and working then as a terrestrial C sink. As [CO2] rises, it brings potential consequences to plant metabolism and growth. Studies in temperate regions, where soil nitrogen (N) availability is low, showed stimulation of photosynthesis and growth in plants exposed to elevated [CO2] (eCO2), which is known as CO2 fertilization. In the Amazon basin, due to variation in soil age and weathering processes, phosphorus availability (P) is distributed in an west-east gradient. In regions with lower P concentrations (east), such as Central Amazon, its limitation has the potential to restrict CO2 fertilization, affecting physiological and growth responses to eCO2. In that context, we investigated the responses of physiological variables (Net CO2 assimilation, Photorespiration, Light and dark leaf respiration), linked to the primary carbon metabolism, and allometric variables (whole-plant and crown height and diameter, total leaf area, leaf thickness and relative growth rate) of seedlings of Inga edulis Mart. Our results showed that eCO2 had an effect on carbon metabolism whereas high-P supply affected mostly aboveground growth and development (allometric variables), which indicates that P may have a differential impact on the responses of plants growing under eCO2, depending on the nature of the processes. In that case, if other species in the region present similar responses to eCO2, it could indicate major implications to C sink activity in the future.