Nutrient concentrations of 17- year-old Pinus taeda annual tree-rings analyzed by X-ray fluorescence microanalysis

Tree-rings are sensitive indicators of soil chemical changes. X-ray fluorescence microanalysis (μ-XRF) can reveal the elemental distribution pattern along these rings. However, reports on quantitative μ-XRF methods targeted to wood analysis are scarce. This study aimed to analyze iron (Fe), manganese (Mn), calcium (Ca), potassium (K), sulfur (S) and phosphorus (P) in annual tree-rings of wood cores cut from 24 trees of 17 year-old Pinus taeda planted in soil amended with six doses of composted pulp-mill sludge (CPMS). The nutrient concentrations were accessed using calibration curves built with spiked P. taeda wood pellets. Calcium and Mn content decreased from the pith to bark direction; K and S decreased from the pith up to 3rd tree-ring and, then, increased to the bark. Iron and P slight decreased from the pith up to the 13–14th tree-ring. Calcium, K and S presented strong and positive correlation with the rainier and hotter season (r > 0.4, p < 0.05). The CPMS increased the Ca, K, Fe and S and decreased Mn and P concentration in P. taeda wood in the 2nd–5th years. Furthermore, the P. taeda annual tree-ring molar ratios of Ca/Mn and K/Ca were good indicators of soil-pH and wood cambium activity. The μ-XRF methodology, as non-destructive method of nutrient concentration analysis in tree-rings, revealed potential uses in monitoring soil fertilizer treatments.