Isótopos estáveis de carbono em anéis de crescimento como proxies climáticos em floresta tropical sazonalmente seca

Abstract

Isotopic dendrochronology, which links the study of growth rings to the analysis of stable isotopes, is a tool with potential for reconstructing and correlating environmental and climatic conditions. During the seasons of the year in which rainy and dry periods occur, the stomata found in tree leaves regulate gas exchange, allowing the entry of carbon dioxide (CO₂) necessary for photosynthesis, a process that can be limited in dry conditions due to the partial closure of stomata to prevent excessive water loss. During this process, the plant incorporates more ¹³C (heavy) in dry periods and more ¹²C in rainy periods. Thus, the δC values in wood reflect the environmental and physiological conditions existing at the time of growth ring formation. For tree species from seasonal tropical regions, this approach allows the investigation of physiological responses to hydrological and thermal variations over time. Given the scenario of climate change, understanding how these trees respond to water stress is important for the conservation and management of these ecosystems. Therefore, this study aims to develop a delta C (δC) chronology from annual growth ring series of *Cedrela fissilis* Vell., from the northern region of Minas Gerais state, near the Cavernas do Peruaçú National Park, to investigate the relationships between isotopic variations and climatic variables, as well as the physiological strategies of the species in a seasonally dry tropical forest environment. αcellulose was extracted from each growth ring of six previously dated trees, and subsequently isotopic analysis was performed using isotope ratio mass spectrometry (IRMS) coupled to an elemental analyzer (EA-IRMS). In parallel, historical climatic data from the region were obtained and compiled: precipitation, air temperature, Palmer drought index, and vapor pressure deficit. The data were subjected to δC-Climate Correlation and Principal Component Analysis (PCA) to investigate patterns among isotopic, physiological, and climatic variables. As a result, an intra-annual pattern of ¹³C was identified, although the individual Δ¹³C series showed low synchronism in their absolute values, a high interannual coherence was observed after the application of the first difference, indicating synchronized responses to year-on-year variations in precipitation, showing that water availability acts as the main driving factor of the isotopic composition of the wood. The results also indicate that the carbon ass variations in precipitation, showing that water availability acts as the main driving factor of the isotopic composition of the wood. The results also indicate that the carbon assimilated in the year prior to the current growth, strongly conditioned by rainfall, constitutes the main source for wood formation.