How Do Litter Chemistry and Soil Texture Influence Soil Organic Matter Formation Dynamics?.

Soil organic matter (SOM) is the largest store of carbon (C) in terrestrial ecosystems, representing 2/3 of the total terrestrial C pool. SOM is important for ecosystem balance as it supplies plants with nutrients, maintains soil structure, and helps control the exchange of CO₂ with the atmosphere. New frameworks have recently been proposed regarding the mechanisms controlling the formation and persistence of SOM, which point to the role of plant litter chemistry and soil C saturation deficit as major controls. However, they have not been tested with a comprehensive approach. This study analyzes the fate of litters of different chemistries as they form SOM fractions characterized by different mechanisms of stabilization (i.e. inherent litter chemical recalcitrance or mineral-association), in soil with contrasting textures and degree of C saturation. The role of microbes in mediating this process is also examined. We hypothesized that labile litter components (i.e. hot water-extractable fraction) will be preferentially incorporated in microbial biomass and ultimately contribute more to mineral-associated SOM, in fine-textured soils with a higher C saturation deficit. In order to test these hypotheses, we incubated isotopically (¹³C and ¹⁵N) labeled wood, leaf and root litters with differing chemistries in two soils that vary in texture and C saturation deficit, and are tracking the fate of the litter-derived C and N as they mineralize, incorporate into microbial phospholipid fatty acids (PLFAs), or stabilize into particulate or mineral-associated SOM fractions. We will present the results from the first 5 months of incubation on litter decay, CO₂ production, and SOM formation.