Global patterns of nitrogen saturation in forests

Xiaoyu Cen, Nianpeng He, Kevin Van Sundert, César Terrer, Kailiang Yu, Mingxu Li, Li Xu, Liyin He, Klaus Butterbach-Bahl

ABSTRACT:

Organisms require nitrogen (N) for survival and growth. Since the Industrial Revolution, human activity has considerably increased the supply of N to terrestrial ecosystems through atmospheric N deposition, and forests are particularly affected. When N supply exceeds biological N demand, forests change from N limited to N saturated. This change in N status could affect forest productivity and could influence future climate. Nevertheless, the global patterns of N saturation in forests have remained unclear. In N-saturated forests, high N availability leads to extravagant N use by organisms, so that a higher proportion of the supplied N is lost in forms such as N2O as compared to N-limited forests. In this work, we synthesized experimental and observational data to determine the N status of global forests using the sensitivity of soil N2O emissions to N deposition as an indicator. We found that 47.5% of global forests are N saturated, especially tropical and temperate forests impacted by human activities. In N-saturated forests, excessive N may be detrimental to organisms and cause biodiversity loss and N pollution, while in N-limited forests, low N availability may still limit forest growth and carbon sequestration. The global map of forest N status produced in this study provides a basis for implementing optimized, region-specific N management practices.

https://www.cell.com/one-earth/abstract/S2590-3322(24)00531-1