Carbon isotopic composition of leaf wax n-alkanes in mangrove plants along a latitudinal gradient in Brazil

Abstract The carbon isotopic composition (δ13C) of selected specific biomarkers provides important information on the relationship between plant species and the environment in which they developed. Here we present baseline data of δ13C values of individual n-alkanes (δ13Cn-alkanes) from leaf waxes of mangrove species – Avicennia spp., Rhizophora mangle and Laguncularia racemosa – typical of mangrove forests collected from equatorial to sub-tropical regions in Brazil. The objective was to evaluate the influence of tree physiology, local hydrology and climatic factors upon the molecular and isotopic signature of the leaf wax n-alkanes. Total n-alkanes concentration, average chain length (ACL25-35) and carbon preference index (CPI24-36) are higher for Avicennia spp. contrasting with the lower values found for R. mangle and L. racemosa. This seems to derive from the physiological characteristics of each species with respect to the intrinsic water use efficiency under the specific tidal flooding regime of mangrove forests. For Avicennia spp. inverse correlations between δ13Cn-alkanes values (δ13C27, δ13C29, δ13C31, δ13C33 and δ13CWA) and mean annual precipitation suggests plant response to local environmental conditions. For R. mangle species, relationships between ACL25-35 and mean annual potential evapotranspiration, and between CPI24-36 and mean annual temperature were observed. These results indicate that δ13Cn-alkanes values in Avicennia spp. as well as ACL25-35 and CPI24-36 in R. mangle may be useful in tracing environmental changes and, as long as preservation of reliable record in sediments is verified, may also be applied in the reconstruction of past environmental conditions. The different molecular and isotopic footprints of the mangrove species presented here have potential in future interpretations of n-alkanes as biomarkers in biogeochemical studies in mangrove-dominated coastal regions.