# A general framework for nitrogen deposition effects on soil respiration in global forests

## TL;DR

Nitrogen pollution from human activities increases soil CO2 emissions in global forests, with a 5% overall rise despite regional differences.

## Contribution

A new framework generalizes soil respiration responses to nitrogen deposition using global experimental and observational data.

## Key findings

- Nitrogen deposition increased global forest soil respiration by ~5%.
- Negative effects of N deposition on SR were observed in 2.9% of global forested areas.
- Controlling N pollution could reduce terrestrial carbon emissions.

## Abstract

Since the Industrial Revolution, human activities have altered atmospheric nitrogen (N) deposition to global forests, affecting carbon dioxide emissions from soils (soil respiration or SR) – one of the largest land-atmosphere carbon fluxes. However, experimental studies have demonstrated both positive and negative effects of N deposition on SR in global forests, leading to debates on how N deposition increases or decreases SR. We developed a framework for generalizing SR responses to N deposition using synthesized data from 168 N addition experiments worldwide and observed SR across the global natural N deposition gradient. The findings indicate that N deposition decreased SR in 2.9% of global forested areas, particularly in eastern China, western Europe, and the eastern USA. However, the net effect of N deposition increased the global forest SR by ~5% (1.7 ± 0.1 PgC yr–1). If N pollution could be effectively controlled, global forest SR would decrease, potentially contributing to a reduction in the terrestrial carbon emissions.

Using synthesized experimental and observational data, Cen et al. revealed that anthropogenic nitrogen deposition has increased global forest soil CO2 emissions by ~5%, despite considerable spatial variation in the effects of nitrogen deposition.