Earthworms Enhance Global Soil Carbon Storage Through Microbial-Mineral Stabilization

Area of Science:

• Soil science
• Ecology
• Biogeochemistry

Background:

• Earthworms have a complex role in the carbon cycle, accelerating decomposition while also promoting soil organic carbon (SOC) storage.
• Previous research has had uncertainty regarding the mechanisms and scale of earthworm influence on SOC mineralization and stabilization.
• This uncertainty has hindered the inclusion of soil fauna in global carbon models.

Purpose of the Study:

• To resolve uncertainty surrounding earthworm impacts on SOC dynamics.
• To provide a quantitative global synthesis of earthworm effects on carbon cycling.
• To inform climate-smart land management and carbon modeling.

Main Methods:

• Meta-analysis synthesizing 696 paired observations from 122 global studies.
• Analysis of earthworm effects on soil organic carbon (SOC), mineral-associated organic carbon (MAOC), and particulate organic carbon (POC).
• Investigation of differences based on earthworm functional type (epigeic, endogeic) and carbon input duration.

Main Results:

• Earthworms increase SOC by an average of 5.4%, with effects strengthening over time with sustained plant carbon inputs.
• Earthworm activity significantly enhances mineral-associated organic carbon (MAOC) by 21.2%, while particulate organic carbon (POC) remains unaffected.
• Epigeic earthworms increase microbial biomass carbon, while endogeic species promote macroaggregate formation, aiding microbial necromass stabilization in MAOC.

Conclusions:

• Earthworm activity promotes a shift from short-term carbon mineralization to long-term stabilization via microbial-mineral associations.
• Earthworm functional type and sustained carbon inputs modulate the magnitude and direction of carbon cycling effects.
• This study reconciles conflicting evidence, demonstrating earthworms increase soil carbon over time and have significant implications for climate models and land management.