Patterns of soil and plant nitrogen isotope composition and their relationships with climate factors in Xilingol League, Inner Mongolia, China

Abstract

Background: Plant and soil nitrogen stable isotope (δ15N) can integrate several fundamental biogeochemical processes in ecosystem nitrogen dynamics, and reflect characteristics of ecosystem nitrogen cycling.Aims: We investigated how climate change influenced plant-soil nitrogen cycling by relating soil δ15N, plant δ15N and Δδ15N (difference between soil and plant δ15N) with climatic factors.Methods: Field investigation was conducted in temperate grasslands in Inner Mongolia during August 2015. Plant δ15N, soil δ15N and Δδ15N were determined, and their relationships with climatic factors were examined by simple regression analyses and general linear models.Results: Soil δ15N was significantly higher than plant δ15N, and there was a positive linear correlation between them. Soil and plant δ15N were negatively related with mean annual precipitation (MAP) and positively with mean annual temperature (MAT); conversely, Δδ15N was positively related with MAP and negatively with MAT.Conclusion: Soil δ15N was dominantly controlled by MAT, while it was MAP for plant δ15N. Climate factors influenced plant δ15N not only through their effects on soil nitrogen dynamics but also strategies of plant nitrogen acquisition. Thus, compared with plant δ15N, soil δ15N can more accurately reflect soil nitrogen dynamics, while plant δ15N may integrate soil nitrogen dynamics and plant nitrogen acquisition.