Nitrogen isotopic composition of plant-soil in the Loess Plateau and its responding to environmental change

The nitrogen isotope of soil is of emerging significance as an indicator of climatic change and biogeochemical cycle of nitrogen in nature systems. In this paper, the nitrogen content and isotopic composition of modern ecosystems from arid and semiarid Loess Plateau in northwestern China, including plant roots and surface soil, were determined to investigate trends in δ¹⁵N variation of plant roots and soil along a precipitation and temperature gradient in northwestern China under the East Asian Monsoon climate condition. The δ¹⁵N values of surface soil from the study area vary from −1.2‰ to 5.8‰ but from −5.1‰ to 1.9‰ in the plant roots. Our results indicate that (1) although the isotopic compositions of both plant roots and surface soil change with a similar trend along the climate gradient, the apparent nitrogen difference between plant roots and soil existed, with Δδ¹⁵N values ranging from 0.3‰ to 7.2‰ with average of 4.1‰ and (2) mean annual precipitation (MAP) is the dominant factor for isotopic composition of plant-soil nitrogen in the Loess Plateau, and the δ¹⁵N values are less correlated with MAT; we suggest that nitrogen isotopic composition of soil is a potential tracer for environmental changes. Supported by National Natural Science Foundation of China (Grant Nos. 40673012 and 40599422), and National Basic Research Program of China (Grant No. 2004CB720200)