The influence of climate, topography, parent material and vegetation on soil nitrogen fractions

Abstract

Soil nitrogen (N) is controlled by climate, topography, parent material and vegetation in less-disturbed ecosystems. However, a comprehensive understanding of the interactions among these soil-forming factors on soil N fractions (SNFs) is still unclear. We measured SNFs at 89 sites across a 3300-m gradient elevation in the southeastern Tibetan Plateau, which spans a large range of climates, parent materials and plant communities. The results showed that different SNFs were correlated with different predictors. Inorganic N was related to elevation and plant species diversity; labile organic N was mainly controlled by parent material; and moderate and recalcitrant organic N were governed by mean annual temperature, parent material and plant species diversity. We concluded that the combined effects of the soil-forming factors controlled SNFs; plant species diversity and parent material were the first and second crucial factors for predicting SNFs. Aspect, elevation and mean annual temperature not only directly affected some fractions, but also indirectly influenced them via plant species diversity. Our results stress the importance of incorporating abiotic and biotic factors when predicting soil N–environment feedback across a large scale.