Soil pH Modulates the Global Stabilized Soil Organic Carbon

Area of Science:

• Soil Science
• Biogeochemistry
• Environmental Science

Background:

• Mineral-associated organic carbon (MAOC) is crucial for long-term soil organic carbon (SOC) stabilization, representing over 50% of total SOC.
• Soil pH is a master variable in biogeochemical cycles, yet its large-scale influence on MAOC and SOC remains poorly understood.

Purpose of the Study:

• To investigate the influence of soil pH on MAOC and SOC dynamics across continental and global scales.
• To identify the key environmental factors regulating MAOC formation under varying pH conditions.

Main Methods:

• Conducted a continental-scale survey in China and synthesized 1300 global observations from existing literature.
• Analyzed relationships between SOC, MAOC, and environmental factors (pH, mineralogy, texture, climate, NPP) across pH gradients.

Main Results:

• Higher SOC content generally correlates positively with MAOC, but this relationship is modulated by soil mineralogy, texture, and climate.
• Distinct pH-dependent pathways control MAOC: Fe/Al (hydr)oxides dominate in acidic soils (pH ≤ 5.5), while clay content and temperature are key in neutral-to-alkaline soils (pH > 6.5).
• Net primary productivity (NPP) can dilute the MAOC fraction by increasing the particulate organic carbon (POC) pool.

Conclusions:

• The universal applicability of clay-centric SOC models is challenged, particularly in acidic soils.
• A conceptual framework integrating pH-dependent metal oxide dynamics is needed for improved SOC persistence predictions in biogeochemical models.