Climate Effects on Subsoil Carbon Loss Mediated by Soil Chemistry

Area of Science:

• Soil Science
• Environmental Science
• Biogeochemistry

Background:

• Subsoils globally store over 50% of soil organic carbon (SOC).
• Climate change may accelerate subsoil SOC decomposition, potentially amplifying climate feedbacks.
• Predicting subsoil SOC vulnerability requires understanding mechanistic links to soil properties.

Purpose of the Study:

• To investigate the control of soil chemical properties on subsoil organic carbon (SOC_sub) decomposition under simulated climate change.
• To identify key soil properties that predict the climate sensitivity of SOC_sub decomposition.
• To understand system-specific mechanisms of mineral stabilization influencing SOC_sub vulnerability.

Main Methods:

• Collected subsoil samples from National Ecological Observatory Network (NEON) terrestrial sites.
• Assessed SOC_sub decomposition rates under elevated temperature and moisture conditions.
• Analyzed the relationship between soil chemical properties (divalent base cation-to-reactive metal gradient) and climate sensitivity.

Main Results:

• Soil chemical properties significantly controlled SOC_sub decomposition under warming and increased moisture.
• A divalent base cation-to-reactive metal gradient best predicted climate sensitivity, linked to mineral protection mechanisms.
• The SOC_sub decomposition response showed a "U"-shaped curve, with highest sensitivity at extreme cation or metal levels.
• Subsoils dominated by base cations were more sensitive to moisture, while those dominated by reactive metals were more sensitive to temperature.

Conclusions:

• System-specific mechanisms of mineral stabilization are crucial for predicting subsoil SOC vulnerability to climate change.
• Soil chemical properties, particularly the base cation-to-reactive metal ratio, are key indicators of subsoil carbon stability.
• Findings provide a basis for developing scalable tools to predict subsoil carbon responses to climate change.