Synchrotron-based X-ray microscopy for assessing elements distribution and speciation in mangrove tree-rings

Micro-X-ray fluorescence (μ-XRF) spectroscopy has been used for dendrochemistry as a high spatial resolution, multi-elemental and non-destructive technique. Furthermore, micro-X-ray absorption near edge structure (μ-XANES) spectroscopy has a potential application in environmental studies by adding speciation information under in-situ conditions. Both, μ-XRF and μ-XANES, techniques were used to assess the inter-ring and intra-ring chemical content variations of Avicennia schaueria mangrove tree from Southeastern Brazil. Ca, Cl, K, P, and S were the major chemical elements distributed in almost all tree-rings. Ca was the most abundant element and showed a decreasing trend from heartwood to sapwood tree-rings. Calcium also showed a characteristic distribution pattern along the growth layer, acting as a chemical marker of growth layers. Ca chemical species were distinct in sapwood (calcium oxalate and carbonate-rich) and heartwood tree-rings (calcium sulfate-rich), showing different physiological Ca roles on tree performance. The synchrotron radiation-based techniques at micrometer scale provided information on the distribution and speciation of chemical elements within and between tree-rings. We also present a µ-XANES procedure for data collection and processing for dendrochemical studies. Altogether, we opened opportunities for further studies aiming to understand which environmental or physiological variables are responsible for tree-ring chemical speciation and distribution changes in tree species.