Intra-annual variability of the water use efficiency of trees from a Seasonal Dry Forest in response to climate extremes

Abstract

Tropical forests are a fundamental part of the global climate system, playing important roles in rainfall patterns and the global carbon cycle. This role is sensitive to the increase in atmospheric CO2 and global warming, factors that can result in high water-use efficiency (WUE) of the trees. A widespread increase in WUE of forests in a warmer world with high concentrations of atmospheric CO2 would have serious consequences for the hydrological cycle at various scales, with implications for biodiversity, environmental services and socio-economic sectors. Despite this, there is currently little information on how is the physiological response of tropical trees to the increase in CO2 affects their WUE.In this work we seek to understand how tropical trees can respond to short-term climatic variations in a warmer world with high concentrations of CO2. We will take advantage of an unusual scenario existing in the Cavernas do Peruaçu National Park (PNCP) region, where the surface temperature has increased above the global average. Therefore, this location presents itself as a natural experiment, which the variation of the WUE in the response to the seasonal climate must be analogous to the physiological response of the trees in a warmer world. We will assess the WUE of trees in response to exceptionally seasonal local climate variation using isotopic carbon 13 (d13C) ratio analysis on the tree wood cellulose on a sub-annual scale.d13C analyzes are useful for this purpose because cellulose d13C is related to isotopic fractionation resulting from variations in the WUE and also to the metabolism of the use of carbon stocks stored in wood. This type of analysis has already been widely used for this purpose, including in carbon fertilization experiments (FACE), but until now it has never been used in a tropical context like that found in the PNCP. Therefore, this study will bring new and relevant information to the theme, which will assist in the understanding of future climate scenarios and in predictions based on climate models. In parallel to this study, intra and inter-annual analyses of carbon and oxygen isotopes are being carried out in the same location by associated projects that together will bring a complete picture of the functioning of the local forest in a warmer world with high concentrations of CO2 atmospheric.