Li Yikang

Characteristics of soil respiration in different degraded alpine grassland in the source region of Three-River

摘 要 为了研究高寒草原退化对土壤呼吸的影响, 对三江源区不同退化程度的高寒草原土壤呼吸进行了测定, 分析了土壤 呼吸与生物量、土壤温度以及土壤湿度的相关性, 结果表明: 1)不同退化程度的高寒草原土壤呼吸均表现出一定的月动态, 这 种月动态在不同退化程度间各有不同。2)高寒草原在退化演替序列上生长季平均土壤呼吸速率呈先增加后降低的变化趋势, 其中在中度退化程度下达到最高值((2.46 ± 0.27) μmol·m·s), 显著高于未退化((1.92 ± 0.11) μmol·m·s)和重度退化((1.30 ± 0.16) μmol·m·s)水平(p 0.05), 重度退化程度下呼吸速率显著 低于其他退化水平(p < 0.01)。3)地上生物量和土壤呼吸存在极显著线性正相关关系(p = 0.004), 而地下生物量与土壤呼吸的相 关性不很显著(p = 0.056)。4)除重度退化外, 未退化、轻度退化和中度退化高寒草原土壤呼吸与土壤温度显著正相关; 土壤呼 吸与土壤湿度的二项式拟合方程在轻度退化程度下达到显著水平(p < 0.05), 而在未退化、中度退化和重度退化程度下均达到 极显著水平(p < 0.01)。 关键词 高寒草原, 草地退化, 土壤湿度, 土壤呼吸, 三江源区, 温度

Dominant process and mechanism of nitrous oxide flux in an alpine meadow on the Tibetan plateau

Nitrous oxide emission (N2O) and its main process in a Kobresia humillis meadow were measured by acetylene inhibition during the growing season in 2009, and the DNDC model was validated by the N2O fluxes of 2004 and 2005. The average fluxes were 2.91±0.46 and 1.97±0.58 μg/m2/h from nitrification-denitrification and soil denitrification process, thus indicating that the potential nitrification might be the dominant process in the alpine meadow. DNDC model also revealed that nitrification contributed 52.85% to N2O flux, while denitrification contributed about 47.15%. The N2O flux could be well captured considering the main affecting factors by a linear regression model (r2=0.663), which demonstrated that soil temperature and biomass played a large part in N2O emission, while biomass, soil organic matter and mineral nitrogen concentration could also simulate the emission. Nevertheless, warming and increasing precipitation would mitigate the emission.