The oxygen isotopic signature of soil- and plant-derived sulphate is controlled by fertilizer type and water source.

The oxygen isotope signature of sulphate (δ O ) is increasingly used to study nutritional fluxes and sulphur transformation processes in a variety of natural environments. However, mechanisms controlling the δ O signature in soil-plant systems are largely unknown. The objective of this study was to determine key factors, which affect δ O values in soil and plants. The impact of an O-water isotopic gradient and different types of fertilizers was investigated in a soil incubation study and a radish (Raphanus sativus L.) greenhouse growth experiment. Water provided 31-64% of oxygen atoms in soil sulphate formed via mineralization of organic residues (green and chicken manures) while 49% of oxygen atoms were derived from water during oxidation of elemental sulphur. In contrast, δ O values of synthetic fertilizer were not affected by soil water. Correlations between soil and plant δ O values were controlled by water δ O values and fertilizer treatments. Additionally, plant δ S data showed that the sulphate isotopic composition of plants is a function of S assimilation. This study documents the potential of using compound-specific isotope ratio analysis for investigating and tracing fertilization strategies in agricultural and environmental studies.