LAUSR

Abstract Serpentine soils contain high levels of geogenic Cr and Ni, which may pose potential risks to the environment due to the increase of bioavailability of the metals during soil weathering. This study determined the lability of Cr and Ni by sequential selective extraction (SSE) and illustrated its relationships to mineral composition and physicochemical properties of serpentine soils for eight pedons along a climate gradient including temperate, subtropical, and tropical regions in Austria, Japan, Taiwan, and Indonesia. Although the mineral origin of Cr was different from that of Ni, Cr significantly accompanied Ni in various climates. Geochemical Cr and Ni fractions (by SSE) followed the order: residual (F4) > Fe/Mn oxide (F2) > organic matter (F3) > acid soluble (F1). Soil properties associated with changes in climate/weathering state, including pH, organic carbon, exchangeable Ca/Mg, and dithionite-citrate-bicarbonate extractable Fe, correlated with all fractions of Cr and Ni. Individual and the sum of all labile pools (∑F1–F3) of Ni were much higher than those of Cr in all pedons. Cr and Ni associated with Fe/Mn oxides (F2) was higher in the tropical soils than in the temperate soils, while Cr and Ni associated with organic matter (F3) was higher in the temperate soils than in the tropical soils along this gradient. Our results demonstrate that Cr and Ni are gradually transformed into labile pools in the soils as chemical weathering progresses from temperate to tropical climate.