Who and how much? Quantifying the role of trophic guilds in soil organic carbon mineralization

Understanding the biotic processes that drive soil organic carbon (SOC) mineralization is essential for predicting the climate warming-carbon cycle feedback. Here, we combined Tree-of-life sequencing (TOLseq; cross-domain profiling using ribosomal RNA) with quantitative conversion factors linking rRNA transcript abundance to biomass, to understand how soil food web changes affect SOC mineralization in an in situ soil warming experiment. Field observations showed that warming reduced SOC stocks, but after decades of warming SOC mineralization had acclimated. An energetic soil food web model revealed both bottom-up and top-down controls in the trophic cascades, shifting C flows from fungal and plant-associated channels towards the bacterial channel. This caused an increase in SOC mineralization rate in warmed soils of 30% per-unit biomass across the year.