Controls on the distribution of the soil organic matter in mountain permafrost regions on the north Qinghai-Tibet Plateau

Abstract. It has been known a large amount of soil organic carbon (SOC) have been accumulated over thousands of years and stored at considerable depths in permafrost regions, which could extent down tens of meters. Although the vegetation plays an important role in the distribution of SOC in upper 1 or 2 m soils, little is known about the determines of the organic carbon pools below these depths. We hypothesized that the SOM distribution and its chemical characteristics for different depths were determined by vegetation types and soil texture in mountain permafrost. To test the hypothesis, ten boreholes which were about 20 m depth under alpine swamp meadow (ASM), alpine meadow (AM) and alpine steppe (AS) were drilled in the permafrost regions on the northern Qinghai Tibetan Plateau. The results showed that the SOC stocks were highest over ASM, and lowest over AS for different depths. The soil textures were mainly silt loam over ASM, while varied with sandy loam, silt loam, and sand in AM. All the soils with higher fine-fractions have higher SOC contents than that in coarse soils. Meanwhile, the C / N ratios and carbon isotopes suggested that the SOC pools accompanied with fine-fractions soils under swamp meadow are more decomposable than those of coarse soils. Our results suggest and both the SOC stocks distribution and the chemical nature of organic matter are determined by the soil texture and vegetation types, and this rule is applicable for SOC distribution for the 20 m depth in mountain permafrost regions.