Linking molecular interactions to soil organic matter traits at the landscape scale

Plant inputs and soil characteristics influence the microbial community structure and metabolic pathways that contribute to the formation, persistence, and release of soil organic matter. Although microbial biomass and metabolites constitute a small portion of soil organic carbon, the activity and rapid turnover of microbial communities generate copious microbial residues, some of which may be relatively stable in soil. Using two long-term ecosystem experiments, we tested the hypothesis that plants and edaphic factors select for microbial communities which influences the quality and quantity of necromass production, while interactions with soil minerals dominates accrual of soil organic matter (SOM) over the long-term. We compared plant-microbe-mineral interactions at two experimental stations with a decade of identical plant treatments, but distinctly different soil environments, to understand how plant inputs and edaphic factors influence SOM dynamics. We found that differences in microbial community structure and activity in response to plant inputs were consistent across sites and amplified in soils with greater clay content. This resulted in distinct FTICR signatures for water soluble organic carbon that were strongly influenced by plant inputs, while mineral associated organic carbon clustered by plant type, with distinct site effects. Metabolic analysis via GCMS revealed elevated profiles in soils with greater clay content and highlights the microbiome influence on SOM production. ¹³C ssNMR analysis revealed that lipid like molecules were greatest in bacterial communities from clay rich soils and terminal methyl and fatty acid groups were greatest in fungal communities from sandy soils. Together our results suggest that biological interactions dominate the rate inputs into the soil, and are amplified by the physical and chemical characteristics of the soil habitat. Considering plant-microbe-mineral interactions revealed relationships that regulate the persistence of biologically derived carbon with implications for managing SOM, and even influencing the land-atmosphere exchange of carbon.