Abstract: Taking the typical peat land in Zoige National Nature Reserve at the eastern edge of Qinghai-Tibet Plateau as test object, four sites with different ground water tables were selected in summer 2009 to study the distribution patterns of organic carbon and total nitrogen in soil profile (0-50 cm), aimed to understand the effects of underground water table fluctuation on peat land soil carbon and nitrogen. In the soil profiles, both the organic carbon and the total nitrogen decreased exponentially with decreasing ground water table, and the coefficient of variation presented an increasing trend, implying that the decrease of ground water table was the main cause of the losses of soil carbon and nitrogen. There was a significant positive correlation between soil organic carbon and soil total nitrogen, and the two of them were significantly negatively correlated with soil pH and soil bulk density. The soil C/N ratio at the four sites had a small variation (from 15.76 to 18.16), implying low decomposition rate of soil organic carbon under the plateau climate and little effects of ground water table and soil pH on the soil C/N ratio.

Key words: Citrus grandis, Phosphorus supply, Doubled CO₂ partial pressure, Photosynthetic parameter