Effects of elevated CO2 and warming on physiology of two contrasting tropical forage species

Abstract

Strong evidences indicate that the atmospheric CO2 is rising and it will reach high levels until the end of this century, even if the CO2 emissions from humans stabilize on the current levels. The ecological consequence of this event has a deep relationship with the plant physiology, once that elevated CO2 and warming influences directly the dynamics of fundamental processes, as photosynthesis. Recent works about this topic have been shown that the C3 and C4 plants respond differently to global climate changes, given the physiological and biochemical peculiarities of each photosynthesis type. Some frequent responses of the plants grown under elevated CO2 have been largely spread: the increase in net photosynthesis - higher in C3 than in C4 -, the decrease in stomatal conductance and its physiological correlations, as the increase in transpiration and water use efficiency. Among the methods used to study the effects of elevated CO2 on plant physiology, FACE (Free Air CO2 Enrichment) systems have been shown as the most efficient, once that they are able to maintain plants under elevated CO2 without causing relevant environmental disturbance. In view of the considerable gap about the climate changes consequences on tropical plants, besides the lack of Brazilian works using FACE system, we propose here to study the physiological and growth responses of a C3 plant, Stylosanthes guianensis (Faboideae, Fabaceae), and a C4 plant, Panicum maximum (Poaceae), grown in consortium in a miniFACE system, under increased CO2 (600 ppm) and warming (plus 2°C). Through the evaluation of chlorophyll a fluorescence, gas exchanges, water status and biomass yield, we aim to detect which are the separated and combined effects of elevated CO2 and warming, besides testing the hypotheses that C3 plants have higher responsiveness to elevated CO2 than C4 plants and that the interaction between elevated CO2 and warming influence significantly the physiological responses. This project is linked to the thematic project n° 08/58075-8 "MiniFACE climate-change impact experiment to analyze the effects of elevated CO2 and warming on photosynthesis, gene expression, biochemistry, growth, nutrient dynamics and yield of two contrasting tropical forage species", coordinated by professor Carlos Alberto Martinez y Huaman. (AU)