Comparative analysis of water relations in C3 and C4 forage species subjected to higher CO2 and warming in TROP-T-FACE system

Abstract

The intensification of use of fossil fuels and land use change has been reported as the major source of the unprecedented increasing of atmospheric CO2 concentration. Until 1750, the concentration of this Greenhouse Gas (GHG) was approximately 280 ppm and now exceeds 400 ppm, with an increase rate higher than 2 ppm per year. Following this trend is expected an average concentration of 800 to 1000 ppm by the end of the century. The increase of CO2 in the atmosphere and other GHGs will lead to increased average global temperature by 2°C in the most optimistic scenario of the IPCC. The impact of climate change will influence the energy balance of ecosystems, mainly by modifying the physiology of cultivated plants, forests and pastures, also influencing human activities such as agriculture and livestock. Brazil is one of the largest producers and exporters of milk and beef in the world that use pastures as the major food source for cattle. Thus, studies assessing the physiological and water relations behavior of forage species used as food for livestock become essential, since water is one of the factors limiting agricultural production. In this context, the present study aims to evaluate the independent and combined effects of high temperature (+ 2°C) and high concentration of CO2 (600 ppm) on parameters related to water relations of two tropical forage species, Panicum maximum Jacq. (C4) and Stylosantes capitata Vogel (C3). Evaluations will be performed under field conditions using the TROP-T-FACE system in operation on the campus of USP in Ribeirão Preto. In this system, the atmosphere is enriched with a CO2 injection system and the warming is induced by infrared radiation. The water potential, leaf water content relative, stomatal conductance, carbon exchange rate, leaf temperature, transpiration rate, transpiration efficiency, intrinsic efficiency of water use, stomatal sensitivity to vapor pressure deficit and the diameter (equatorial and polar) and the distribution and density of stomata, will be assessed. The hypothesis that elevated CO2 reduces the stomatal conductance and consequently the transpiration rate and that reduction of transpiration will increase the canopy temperature, with sinergistics interaction between CO2 and temperature, will be assessed. This research proposal is linked to the thematic project 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 (process 2008/58075-8) in progress at USP/RP. (AU)