Functional carbon pools and microbial communities in persistent carbon rich erosion buried topsoils

Abstract

Storing more C in subsoils can offset greenhouse gas emissions and C-rich buried horizons provide a unique opportunity to investigate the nature of subsurface C persistence. We identified five sites with varying soil texture across a climatic gradient that had C-rich buried surface horizons. We profiled the microbial community and characterized the soil organic matter of surface Ah, buried surface Ahb, and buried subsoil Bwb horizons to gain insight into these C-rich subsoils. Similar concentrations of C remained in Ahb horizons relative to Ah horizons, despite significant viable microbial biomass in Ahb horizons capable of decomposing the C at depth where little fresh C input has occurred in the decades since burial. The microbial community composition had shifted in Ahb horizons to be more similar to subsoil Bwb than surface Ah communities, indicating the SOC composition in Ahb horizons and conditions at depth strongly influenced their current status. Ahb horizons stored a greater proportion of C in mineral-associated organic matter (MAOM) than Ah horizons. Although similar microbial necromass quantity and concentration in Ah vs. Ahb soils, muramic acid was reduced in Ahb horizons, indicating significant recycling of microbial necromass. Commonalities in C-rich buried surface horizons between microbial and C profiles across a wide range of textures and climates, demonstrates that the general processes of C cycling and persistence are ubiquitous across buried surface horizons. These soils may provide an opportunity to examine microbial communities associated with persistent C that is difficult to isolate due to low concentration in surface soils.