Strengthened plant-microbe interactions under organic nutrient management lead to soil carbon sequestration

Dynamic plant-microbe interactions determine carbon sequestration, wherein plants input carbon to soil as rhizodeposits and, in return, nutrients are liberated by microbial metabolic processes. Microbial processing of plant-derived soil organic carbon is critical to understanding soil carbon sequestration as it governs whether carbon remains in soil or is respired to the atmosphere. For example, microbial biomass carbon can become stabilized on soil mineral surfaces following turnover (mineral-associated organic matter, MAOM) and remain in soil for decades or even centuries. Agricultural nutrient amendments can impact this process by shaping plant-microbe interactivity. Understanding how nutrient amendments impact plant-microbe interactions and linking this to soil carbon sequestration is critical as we seek to manage the environmental impacts of agriculture. We investigated the impact of conventional (mineral N-P-K) and organic (composted dairy manure) nutrients on soil carbon sequestration through the lens of plant-microbe interactions. Organic amendments simulated carbon assimilation by known plant-growth promoting bacteria as determined via quantitative stable isotope probing. Further, organic amendments increased plant productivity and microbial activity, resulting in a 21% increase in soil carbon stocks compared to plots without nutrient additions, and a 66% increase since the beginning of Miscanthus cultivation under organic fertilizer management. Carbon in the MAOM pool accounted for 44% of the total increase in soil carbons stocks, suggesting the bolstered microbial activity was a strong driver of carbon sequestration in the organically fertilized soils. All told, these results directly link organic amendments to strengthened plant-microbe interactions leading to increased plant yields and soil carbon sequestration.