Impact of land use/land cover change on the topsoil selenium concentration and its potential bioavailability in a karst area of southwest China.

Selenium (Se) is an essential micronutrient for human health, and its abundance and potential bioavailability in the soil are of increasing concern worldwide. To date, how total soil Se and its bioavailability would respond to human disturbance or future environmental change is not yet clear, and associated controlling factors remain incompletely understood. Here, we collected soil samples (0-15 cm) from different land use/land cover types, including active cropland, grassland, shrubland, and secondary forest, in a Se-enriched area of Guangxi, southwest China. Total Se concentration and its potential bioavailability, as estimated by phosphate extractability, were investigated. Total soil Se concentration (Se) for all samples ranged from 220 to 1820 μg kg, with an arithmetic average value of 676 ± 24 μg kg (Mean ± SE, the same below). The concentration of phosphate extractable Se (Se) varied between 1 and 257 μg kg, with an arithmetic mean value of 79 ± 5 μg kg, accounting for on average 13 ± 1% of the Se. Among the four land use/land cover types, Se and Se were generally more enriched in the secondary forest than those in the grassland and cropland. The content of soil organic carbon (SOC) was the overriding edaphic factor controlling the abundance and potential bioavailability of Se in topsoils. In addition, climatic variables such as mean annual precipitation and mean annual temperature were also key factors affecting the abundance and potential bioavailability of soil Se. Our results suggest that changes in land use/land cover types may deeply influence Se biogeochemistry likely via alterations in soil properties, particularly SOC content.