Abstract: Alpine grassland is a unique ecosystem in the Qinghai-ibet Plateau, whose quality is determined by the distribution of total nitrogen content. Based on monitoring data, we analyzed the relationship between soil total nitrogen content and geographical factors of alpine grassland in the headwater region of the Yellow River. We used Geodetector to examine the effects of single or multiple geographical factors on the spatial distribution of soil total nitrogen. The results showed that: (1) There were obvious differences in total nitrogen content among different vegetation types, that is, Kobresia capillifolia meadow>K. pygmaea meadow>Stipa purpurea steppe>K. tibetica and Carex cinerascens meadow>Orinus kokonoricaStepp>S. aliena steppe>K. pygmaea and K. humilis meadow, which corresponded to meadow soil, chernozem, dark felty soil, alpine meadow soil and chestnut soil, respectively. (2) Soil total nitrogen content was positively correlated to altitude, slope, aspect, topography and vegetation type, and was negatively correlated to annual rainfall, ≥0 ℃ accumulated temperature, annual average temperature and soil type. Meanwhile, altitude, slope, and annual average rainfall functioned most with the coefficient 1, while the ≥0 ℃ accumulated temperature, annual average temperature, slope, vegetation, and soil type had coefficients of 0.72, 0.74, 0.59, 0.88 and 0.17, respectively. (3) The relationships between mean annual temperature, soil type, topography, and vegetation type, between topography, vegetation type and soil type, and between vegetation and soil type had nonlinear increasing effects on total nitrogen content, while the relationship among other factors had nonlinear decreasing effects. We conclude that the spatial heterogeneity of total nitrogen content is affected by the variety and complexity of environment factors.

Key words: Phyllostachys edulis invasion, soil fungi, community characteristic, broadleaf forest, Tianmu Mountain.