Abstract:

Soil organic carbon and labile organic carbon components decreased inevitably as the grassland degradation degree intensified, but their response mechanisms to topography type remain unclear. In this study, plant and soil samples with soil depth of 0-40 cm were collected from alpine degraded grasslands across different topography types on the Qinghai-Xizang Plateau. The mass fraction of soil organic carbon and the ratio of labile organic carbon components to total organic carbon were analyzed to explore the influence of grassland degradation and topography on the stability of soil organic carbon pool. Results showed that 1) compared with non-degraded beachland, the mass fraction of soil organic carbon (SOC), the ratios of microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidized organic carbon (EOC) to SOC in the heavily degraded beachland decreased by 18.8%, 62.1%, 36.6% and 38.1%, respectively. While in the heavily degraded steep-slopeland, these decreased by 41.8%, 51.3%, 34.2% and 11.6%, respectively compared with non-degraded steep-slopeland. This indicates that grassland degradation increases the stability of soil organic carbon pool, relatively. 2) The mass fraction of SOC in the steep-slopeland was 30.0% higher than that in the beachland, but the w_(MBC)/w_(SOC), w_(DOC)/w_(SOC), w_(EOC)/w_(SOC) in the steep-slopeland were 66.9%, 43.0%, and 36.7% lower than those in the beachland, respectively. This indicates that the stability of the soil organic carbon pool in the steep-slopeland increased relatively. 3) Labile organic carbon components were positively correlated with above-ground biomass, below-ground biomass, soil organic carbon, soil moisture mass fraction, total carbon, total nitrogen, and negatively correlated with pH value, and below-ground biomass was the key factor affecting mass fraction of soil organic carbon and labile organic carbon components. In conclusion, the grassland degradation and topography affected the mass fraction of soil organic carbon and the ratio of labile organic carbon components to total organic carbon. The ratio of labile organic carbon components to total organic carbon can be used as key indicators to reflect the degradation of alpine grassland. For the restoration of alpine degraded grasslands under different topography types, appropriate methods should be adopted to reduce soil carbon emissions according to local conditions to cope with global climate change.

Key words: alpine grassland, grassland degradation, topography, soil organic carbon, soil labile organic carbon component

摘要：

土壤有机碳及活性有机碳组分质量分数必然随草地退化程度加剧而下降，但是它们对地形类型的响应机制尚不明确。该研究以青藏高原不同地形类型高寒退化草地为研究对象，采集植物样品和土层深度0－40 cm的土壤样品，分析土壤有机碳质量分数及活性有机碳组分占总有机碳的比值，探讨草地退化和地形对土壤有机碳库稳定性的影响。结果表明：1）重度退化滩地与原生滩地相比，土壤有机碳（SOC）质量分数以及微生物生物量碳（MBC）、溶解有机碳（DOC）、易氧化有机碳（EOC）占SOC的比值分别下降了18.8%、62.1%、36.6%、38.1%，重度退化陡坡地与原生陡坡地相比分别下降了41.8%、51.3%、34.2%、11.6%，这说明草地退化使土壤有机碳库稳定性相对增加；2）陡坡地SOC质量分数较滩地高30.0%，但陡坡地w_(MBC)/w_(SOC)、w_(DOC)/w_(SOC)、w_(EOC)/w_(SOC)分别比滩地低66.9%、43.0%、36.7%，这表明陡坡地土壤有机碳库稳定性相对增加；3）活性有机碳组分与地上生物量、地下生物量、土壤水分质量分数以及土壤有机碳、总碳、总氮质量分数呈正相关关系，与pH值呈负相关关系，且地下生物量是影响土壤有机碳和活性有机碳组分质量分数的关键因素。综上所述，草地退化和地形影响土壤有机碳质量分数和活性有机碳组分占总有机碳的比值。活性有机碳组分占总有机碳的比值可作为反映高寒草地退化的关键指标。对于不同地形类型高寒退化草地的修复，应采取因地制宜的方式，选取合适的方法减缓土壤碳排放，以应对全球气候变化。

关键词: 高寒草地, 草地退化, 地形, 土壤有机碳, 土壤活性有机碳组分