Avaliação de isótopos estáveis nos anéis de crescimento de árvores do gênero Cedrela da Floresta Amazônica e da Caatinga

Abstract

There is growing concern about the conservation of Neotropical Forests in face of the current climate changes. Nevertheless, the lack of studies limits the understanding of the behaviour of trees during past events and their predicted resilience towards future climatic variations. In this context, we evaluate the stable carbon isotope record of cellulose from tree-rings of Cedrela from the Amazon Forest and the Caatinga, aiming to identify intra-annual patterns, climatic signals and possible tree strategies associated with precipitation and temperature. For the cellulose extraction, we used dated cross sections from previously developed chronologies of Cedrela odorata from "FLOTA do Paru" and Cedrela fissilis from a fragment of Seasonally Dry Tropical Forest (STDF). In order to cover different stages of radial growth, each growth ring was sectioned in three equal parts (1st, 2nd and 3rd parts) between 1970 and 1995 for subsequent determination of carbon isotope discrimination (∆13C). Our results for C. odorata from Amazon showed an increasing pattern of intra-annual ∆13C and climatic signals of the current season only. The correlation was negative between ∆13C from 1st part of the ring and

temperature and positive between ∆13C from 3rd part and precipitation. Thus, in this non- restrictive environment, trees probably start radial growth at same season of the phenophases,

using carbon from reserves and then continue the development with photoassimilates of the current season. For C. fissilis from STDF, our findings do not indicate an intra-annual ∆13C pattern and showed signals of precipitation from previous wet and dry seasons on ∆13C, both at the beginning and end of the ring (1st and 3rd part). These results suggest that trees predominantly use the carbon assimilated in the previous year for the current radial development of the stem, with precipitation being the main growth driver in seasonally dry environment.