Nitrogen increases soil organic carbon accrual and alters its functionality.

Area of Science:

• Soil science
• Biogeochemistry
• Ecology

Background:

• Nitrogen availability critically influences soil organic carbon (SOC) cycling and storage, but its effects on the SOC pool are variable.
• Understanding SOC dynamics requires differentiating the pool into functional components like particulate organic carbon (POC) and mineral-associated organic carbon (MAOC).
• The impact of nitrogen-induced changes in SOC component ratios on overall soil functionality remains poorly understood.

Approach:

• A global meta-analysis synthesized 803 paired observations from 98 studies.
• Assessed the effects of nitrogen addition on SOC components (POC and MAOC) and their ratios.
• Investigated correlations between SOC component responses and environmental factors like plant biomass, enzymes, and microbial biomass.

Key Points:

• Nitrogen addition significantly increased POC (16.4%) and MAOC (3.7%) pools globally.
• Nitrogen enrichment decreased the ratios of MAOC to total SOC (4.1%) and MAOC to POC (10.1%).
• POC increases correlated with aboveground plant biomass and hydrolytic enzymes, while MAOC increases linked to microbial biomass.

Conclusions:

• Nitrogen deposition can enhance soil carbon sequestration to a degree.
• However, it may reduce the SOC pool's nutrient density, turnover time, and resistance to disturbance.
• Mechanistic insights into nitrogen's effects on SOC functionality are crucial for predicting soil carbon dynamics under future perturbations.