Analysis of the impact of extreme events on isotopic fractionation of urban trees

Abstract

Cities are especially vulnerable to climate extremes because of the reduced vegetation cover, and the common heat islands and impermeable surfaces. The 2014-2015 drought is a recent example of extreme drought that caused one of the largest water shortages in São Paulo's history. Such extreme weather events may lead to different responses of tree species, some of which are more resilient to the urban environment and thus have a greater prospect of providing long-term ecosystem services. The deployment of these services are intrinsically linked to physiological processes and growth of the trees. Thus it is important to assess the resilience of a tree species to the urban environment and their role in ecosystem services such as carbon sink. This project aims to analyze at the intra-annual stable isotopes of oxygen and carbon in the tree rings corresponding to the years 2010 to 2016 to estimate the effects of the 2014-2015 drought on estimated assimilation and stomatal conductance of trees. These effects of drought will be compared between tolerant and intolerant species, and between individuals growing in a fragment of urban Atlantic Rainforest (Parque Estadual Fontes do Ipiranga) and a recreational park formed by few forest patches (Parque do Ibirapuera). We will sample tree species from the Meliaceae, Apocynaceae and Fabaceae families. Thin sections of the wood samples will be obtained using circular saws, which will then be subjected to cellulose extraction. The cellulose samples from each tree ring will be divided into 10 parts, weighed and encapsulated to be analyzed in the mass spectrometer. The following parameters will be estimated: discrimination value, ratio between CO2 concentrations in the mesophyll of leaves and atmosphere, and intrinsic efficiency in water use. Thus, this study will provide insights into the behave of trees facing climate extremes in São Paulo to support public policies of urban afforestation in the city of São Paulo - SP. (AU)