Land-use conversion controls on the mobility of Zn in paddy soils revealed by stable Zn isotopes

Abstract

Understanding Zn biogeochemical cycling is necessary for monitoring Zn supply for plants and life during land use conversion, which is critical for environmentally sustainable development. But little is known about how the conversion of paddy soil to abandoned land affects the Zn isotope signature. A comparative field observation was conducted in northeast Thailand to investigate the Zn isotope footprint of paddy soils and abandoned paddy soils (PL and NPL). Our results show that Zn (τZnint : 0.04) slightly retains on PL, but is lost from NPL (τZnint from − 0.81 to − 0.24) to the river during weathering. Compared to PL (Δ66Znparent-soil: −0.29 ‰), more 66Zn isotopes might enter the river when rice cultivation ceases in NPL (Δ66Znparent-soil from −0.26 ‰ to −0.47 ‰). Rice harvest and then root decay might result in heavy 66Zn isotopes accumulating at the topmost soil in PL (δ66Zn: 0.14 ‰) and short-term abandonment (1–2 years) in paddy soils (NPL1 δ66Zn: 0.18 ‰). The release of assimilated Zn, and then the high adsorption of Zn in the Fe-SOM-metal(loid)s ternary system positively contribute to the high [Zn] in PL, while this was not observed in NPL. Our findings provide a comprehensive insight into the Zn isotope signature in response to the conversion of land-use types, which is beneficial for understanding the terrestrial Zn geochemical cycle.