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

Area of Science:

• Forest ecology
• Biogeochemical cycles
• Environmental science

Background:

• Human activities, particularly since the Industrial Revolution, have significantly altered atmospheric nitrogen (N) deposition patterns globally.
• Nitrogen deposition influences soil respiration (SR), a major component of the terrestrial carbon cycle, but its effects on SR are debated, with studies showing both increases and decreases.
• Understanding the net impact of N deposition on forest SR is crucial for predicting future carbon fluxes and climate change feedbacks.

Purpose of the Study:

• To develop a generalized framework for understanding soil respiration (SR) responses to nitrogen (N) deposition across global forests.
• To synthesize data from numerous N addition experiments to assess the worldwide effects of N deposition on SR.
• To investigate the relationship between natural N deposition gradients and observed SR in global forests.

Main Methods:

• Synthesized data from 168 N addition experiments conducted worldwide.
• Analyzed soil respiration (SR) data across a global gradient of natural nitrogen (N) deposition.
• Developed a framework to generalize the responses of SR to varying levels of N deposition.

Main Results:

• Nitrogen deposition was found to decrease SR in 2.9% of global forested areas, notably in eastern China, western Europe, and the eastern USA.
• The net effect of N deposition across all global forests resulted in an approximate 5% increase in soil respiration (SR), equivalent to 1.7 ± 0.1 PgC yr⁻¹.
• A significant portion of global forest SR is influenced by N deposition, highlighting the sensitivity of this carbon flux to anthropogenic changes.

Conclusions:

• Controlling nitrogen pollution could lead to a decrease in global forest soil respiration (SR).
• Reducing N deposition may offer a pathway to mitigate terrestrial carbon emissions, potentially aiding in climate change mitigation efforts.
• The findings underscore the complex and significant role of nitrogen deposition in regulating global carbon cycling through its impact on forest soil respiration.