Soil organic carbon stocks in the Yunnan Plateau, southwest China: spatial variations and environmental controls

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Greater increases in temperature are expected in high mountain regions than the global average making mountain soils a potentially vulnerable component of the global carbon cycle. Little is known about the spatial distribution and environmental factors controlling soil carbon in mountainous regions. This study analyzed the spatial patterns of soil organic carbon (SOC) density in mountainous regions and evaluated the impact of various environmental factors on SOC density. This study focused on Yunnan Province, a typical high-elevation, mountainous region in southwest China. A soil database was constructed based on 684 soil profiles documenting 12 environmental factors. Significant differences in SOC density among the upper and subsoil layers were found. Forestland and grassland SOC density were significantly higher than that of cropland. The widely distributed forestland in Yunnan Province had a higher SOC storage capacity than non-forested areas. The forests of the northwestern mountainous region had higher SOC densities than those of the agricultural areas of the southeastern plateau region. Environmental factors affected SOC density more strongly in forestland than grassland and cropland, and those factors were better correlated to the 0–20 cm layer of soils than the 20–100 cm layer. Elevation is the major controlling factor controlling SOC density for the three land uses. Correlating topography to SOC density proved difficult. SOC densities were highest when annual temperatures ranged from 0–2 °C. SOC density decreased with increased precipitation up to 800 mm per year and then remained constant. The SOC density increased with elevation up to 4,000 m then decreased. The results indicate that both the local land use development plans and regional climatic change scenarios may result in a decrease in SOC storage in this region and increase the CO2 flux into the atmosphere. In consideration of the high sensitivity of the regional response to global warming, effective ecological compensation mechanisms and active forest protection should be undertaken in this region.