Effects of the conversion of a degraded alpine Kobresia meadow on the organic carbon and nitrogen of soil and plants

摘要

Three sites with both degraded alpine Kobresia meadow (DM) and adjacent mix-seeded perennial grasses pastures (MSP) in the headwater region of the Yellow River, Qinghai-Tibetan Plateau, were selected to investigate plant and soil organic carbon (SOC), total nitrogen (TN) and their isotope composition. The SOC and TN in the top soil layer to a depth of 10 cm were significantly affected by ploughing and planting mix-seeded perennial grasses. The SOC content in 0-10 cm soil layer of MSPs was 25.6%, 5.5% and 12.9% lower than those of DMs at the I-III sites, respectively, and the rate of OC density loss was 23.8, 14.5 and 18.2%, respectively. The soil TN content in 0-10 cm soil layer of MSPs was 16.6%, 2.2% and 9.4% lower than those of the DMs at three sites, respectively, and the TN density was 15.6, 10.6 and 15.3% lower than those of DMs, respectively. The plant and soil C-13 values (-27.03 parts per thousand, -25.16 parts per thousand, respectively) suggest that the vegetation of both DMs and MSPs are C-3 plant communities. The N-15 value in the soil (>4 parts per thousand) was significantly greater than in plants (<2 parts per thousand). No differences of either C-13 or N-15 abundance between MSPs and DMs at Site I and II, but were found at Site III, indicating that the effects were site specific. The rehabilitation of a degraded Kobresia meadow has a significant influence on the soil properties, SOC and TN. Caution should be taken in site selection before performing conversion.