Global evidence for joint effects of multiple natural and anthropogenic drivers on soil nitrogen cycling

Abstract

Global soil nitrogen (N) cycling remains poorly understood due to its complex driving mechanisms. Here, we present a comprehensive analysis of global soil ￎﾴ15N, a stable isotopic signature indicative of the N input￢ﾀﾓoutput balance, using a machine￢ﾀﾐlearning approach on 10,676 observations from 2670 sites. Our findings reveal prevalent joint effects of climatic conditions, plant N￢ﾀﾐuse strategies, soil properties, and other natural and anthropogenic forcings on global soil ￎﾴ15N. The joint effects of multiple drivers govern the latitudinal distribution of soil ￎﾴ15N, with more rapid N cycling at lower latitudes than at higher latitudes. In contrast to previous climate￢ﾀﾐfocused models, our data￢ﾀﾐdriven model more accurately simulates spatial changes in global soil ￎﾴ15N, highlighting the need to consider the joint effects of multiple drivers to estimate the Earth's N budget. These insights contribute to the reconciliation of discordances among empirical, theoretical, and modeling studies on soil N cycling, as well as sustainable N management.