Variation in basic properties and carbon sequestration capacity of an alpine sod layer along moisture and elevation gradients

The alpine sod layer is spongy,tough,and resistant to the shifting surface soil layer formed under natural vegetation in the alpine cold region. Understanding the ecological functions of this layer is necessary to promote sustainable methods of grass production and animal husbandry that can restore and protect existing grasslands,and to suggest new projects to implement these goals. After conducting extensive preliminary investigations regarding the alpine vegetation on the Zoige Plateau on the Eastern Qinghai-Tibetan Plateau,China,we established community sample plots along the existing soil moisture gradient: swamp,degraded swamp,swampy meadow,wet meadow,dry meadow,and degraded meadow. We also established community sample plots along the existing elevation gradient: subalpine meadow,subalpine shrub meadow,alpine shrub meadow,and alpine meadow. We determined sod layer thickness,bulk density,soil particle composition,and soil organic carbon(SOC) content in the community plots to compare carbon sequestration capacity along the moisture and elevation gradients. The results indicated that the average thickness of the sod layer was 30 cm. The bulk density of swampsoil was the lowest among the communities studied,and the SOC content of swamp soil was greater than 300 g/kg. The bulk density of degraded meadow soil was the highest among the communities studied,and the SOC content of degraded meadow soil was significantly lower than that of the other communities. The SOC density of the different communities ranged from 10 to 24 kg C/m~2,and decreased with decreasing soil water availability. Degraded meadow soil had significantly lower SOC storage in the sod layer. The SOC density of alpine shrub meadow soil was 15% higher than that of alpine meadow soil. The minimum mass water content needed to maintain a stable sod layer was 30%,and the minimum SOC was 30 g/kg. In alpine vegetation regressive succession,the bulk density and compactness of the sod layer became increased. SOC content,density,and storage decreased along the soil moisture gradient from swamp to degraded meadow. The higher the gravel content of swamp soil,the more easily it was degraded. Similarly,the higher the sand content of meadow soil,the more easily it was degraded. The carbon sequestration capacity of alpine shrub meadows was greater than that of alpine meadows;however,the productivity of shrub meadows was lower. To maintain sustainable development of grassland production and protect the carbon