Nitrogen Availability Modulates Root-Mediated Soil Organic Carbon Formation

Area of Science:

• Soil Science
• Biogeochemistry
• Agronomy

Background:

• Living roots play a role in soil organic carbon (SOC) formation under straw incorporation.
• The precise mechanisms of root influence on SOC stabilization remain unclear.

Purpose of the Study:

• To investigate how root activity affects the allocation of straw-derived carbon into different soil organic carbon pools.
• To elucidate the mechanisms of root-mediated SOC formation under varying nitrogen conditions.

Main Methods:

• Utilized isotopically labeled maize straw to trace carbon fate in soil cores.
• Incubated soil cores in a soybean field to simulate field conditions.
• Analyzed the distribution of straw-derived carbon into stable SOC pools, including occluded particulate organic carbon (oPOC) and mineral-associated organic carbon (MAOC).

Main Results:

• Root ingrowth did not significantly alter total SOC accumulation but enhanced the proportion of SOC in stable pools.
• In low-nitrogen soils, roots promoted stable SOC by increasing straw-derived carbon in oPOC and MAOC.
• In high-nitrogen soils, roots decreased straw-derived carbon in stable SOC, but rhizodeposits compensated.
• Observed differences were linked to microbial carbon-to-nitrogen stoichiometric imbalances.

Conclusions:

• Root presence influences the stabilization pathways of straw-derived carbon into SOC pools.
• Nitrogen availability critically modulates the interaction between roots, straw, and SOC formation.
• Findings offer mechanistic insights into root-mediated SOC sequestration, crucial for soil carbon management.