Effects of land-use types on soil organic carbon stocks: a case study across an altitudinal gradient within a farm-pastoral area on the eastern Qinghai-Tibetan Plateau, China

A crucial region for China’s ‘Grain-for-Green Policy’ is located within a traditional farmpastoral area, between 2000 to 3000 m above sea level, on the eastern Qinghai-Tibetan Plateau. However, the responses of soil organic carbon (SOC) to different land-use patterns in this region are unclear. Here, we determined the SOC (0–20 cm) content of grasslands and forests that are being converted from farmlands, as well as in abandoned arable land and arable land in this region. The factors influencing the reclaimed lands were analyzed along altitudes from 2030 to 3132 m. Our results showed that SOC content was higher for grassland and abandoned arable land than forest and arable land. The SOC content increased with the increase in altitude for total land-use patterns. Further, the grassland and abandoned arable land had higher SOC content than the forest with almost parallel trends along the increase in altitude. However, the proportion of regulated factors of altitude and species richness varied among forest, grassland, and abandoned arable land. Our results indicated that the land-use pattern of returning farmland to grassland and abandoned arable land was more effective in terms of the SOC storage in the superficial layer in this altitude range in the Qinghai-Tibetan Plateau, thereby being beneficial to optimizing land management in this region.