Zn isotope fractionation in laterites from Yunnan province, southwest China: Implications for the Zn cycles and its environmental impacts in (sub-) tropics.

The weathering and development of laterites can influence trace element cycling in (sub-) tropics. Zinc (Zn) is a ubiquitous trace metal that involves both abiotic and biotic processes in soils. To explore Zn behavior in laterites, Zn cycling in (sub-) tropics, and the environmental impacts, Zn isotope systematics were presented for two laterite profiles from Yunnan province, southwest China. The laterite samples exhibit the δZn of 0.02 ‰-0.56 ‰, indicating a light shift of Zn isotope ratios (ΔZn = -0.47 ‰-0.07 ‰) relative to bulk parent granite. This observation is attributed to the preferential preservation of light Zn isotopes on the surface of secondary Fe oxides. As a result, laterites are likely to control the instantaneous riverine δZn in (sub-) tropical regions heavier than unweathered rocks. The isotopic signature of different vegetation covered soils show that shrub-covered soils are stronger leached (average τ = -0.61) and have a smaller ΔZn (=-0.15 ‰), relative to forest-covered soils (=-0.20 ‰). Due to the strong loss of Zn (average τ = -0.61 to -0.12) and large amounts of low-bioavailable Zn preserved in oxides, the micronutrient supplies for plant growth are difficult to maintain and need more fertilization. This study is helpful for a better understanding of global Zn cycling and the management of micronutrients in (sub-) tropical soil-plant systems.