Unprotected carbon dominates decadal soil carbon increase.

Area of Science:

• Soil Science
• Environmental Science
• Ecology

Background:

• Soil organic carbon (SOC) fractions, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), influence SOC storage and stability.
• Understanding changes in these fractions is crucial for soil carbon sequestration and climate change mitigation.

Purpose of the Study:

• To analyze global trends in SOC fractions (POC and MAOC) from 2000 to 2022.
• To assess the impact of land management practices on SOC fractions and overall SOC storage.
• To identify key factors driving changes in SOC stability.

Main Methods:

• Compilation of a global SOC fraction dataset from 7219 soil samples across six continents.
• Statistical analysis of changes in POC and MAOC over time and their relationship with land use and management.

Main Results:

• Global SOC storage increased by 11.0% between 2000 and 2022, primarily driven by a 21.8% increase in POC.
• MAOC decreased by 5.3%, leading to a 29.1% rise in the POC/MAOC ratio, indicating reduced SOC stability.
• SOC declined in planted forests, grazed grasslands, and croplands under intensive management, mainly due to POC loss.

Conclusions:

• While global SOC storage is increasing, this is mainly due to labile POC, which is more vulnerable to environmental changes.
• Decreasing SOC stability, evidenced by the rising POC/MAOC ratio, poses risks under climate change and intensive land use.
• Targeted strategies focusing on preserving and enhancing POC are essential for maintaining soil carbon sinks.