Grassland conversion along a climate gradient in northwest China: Implications for soil carbon and nutrients

Abstract

AbstractSoil organic carbon (SOC) stocks and nutrient availability are key indicators of soil quality, and both can be influenced by land‐use change. However, it is still unclear whether the impact of land‐use change on SOC and nutrient stocks differs between ecoregions. Grasslands near the northeast border of the Qinghai‐Tibetan Plateau (QTP) occur across several ecoregions that have recently been subjected to substantial land‐use change. Based on long‐term land‐use history, we conducted a field investigation comparing soil C and nutrient stocks between natural grassland (NGL) and three types of converted grassland (agricultural grassland, AGL; farmland, FL; and abandoned farmland, AFL) in three ecoregions along a climate gradient: alpine meadow, temperate steppe and temperate desert. Compared with NGL, soil C stocks in converted grasslands were 22%–30% lower in the alpine meadow, but 60–82% higher in the temperate steppe and 6%–76% higher in the temperate desert. Converted grasslands also contained higher stocks of available nitrogen and phosphorus than NGL in the temperate steppe and desert. Soils (0–40 cm) in NGL contained 14.8 ± 0.1 kg C m−2 in alpine meadow, 6.7 ± 0.6 kg C m−2 in temperate steppe and 1.7 ± 0.3 kg C m−2 in temperate desert. Together, our results indicate that the responses of soil C and nutrients to grassland conversion differed between ecoregions. Thus, to optimize soil C sequestration rates and overall soil quality, we suggest that land‐use policies in this area should take into account local environmental conditions.