Processes controlling the stable isotope compositions of Li, B, Mg and Ca in plants, soils and waters: A review

Li, B, Mg and Ca isotopes became of increasing interest during the last decade due to their potential for better constraining the carbon cycle and nutrient cycling. At the soil-water-plant scale, Li and B isotopes are powerful tools for the understanding of processes leading to clay mineral formation in soils. Ca and Mg isotopes allow, for their part, to identify plant-mineral interactions and recycling by vegetation. At the scale of monolithological silicate watersheds, Li and B isotope fractionations are mainly controlled by the degree of mineral leaching and the amount of clay mineral formation. Ca and Mg isotope signatures in soil and waters vary seasonally, depending on the vegetation growth cycle and rain events. In mixed-lithology basins, B and Li isotopes are controlled by alteration rates of silicate minerals and the residence time of waters within the watershed. Ca and Mg isotope ratios of river waters appear to be also lithology-controlled.