Soil organic matter (SOM) represents a large proportion of the terrestrial carbon pool. The rates of carbon input versus output are heavily influenced by soil microorganisms. High microbial carbon use efficiency (CUE) has been proposed as an indicator of the microbial communities ability to store soil organic carbon through biomass production and the stabilization of microbial. Although microbial biodiversity is posited as a driver of ecosystem processes, evidence connecting variation in microbial community composition and CUE remain scarce. To address this knowledge gap we manipulated microbial biodiversity by selectively removing microorganisms from a innocula from soil based on cell size to produce microbial communities composed of only ‘small’ microbes (< 0.8 um), as well as those with medium (< 3um), and relatively large (< 5 um) community members. The cell size of a microbe can influence reproductive strategies, nutrient acquisition and interaction with the soil environment. Consequently, this manipulation of biodiversity was predicted to influence the overall function of the microbial community and the soil carbon biogeochemistry. The experimental communities along with an unmanipulated ‘whole community’ inoculum was added to a sterile artificial mineral soil and maintained for three months with regular substrate additions.
Results/Conclusions
Selective removal of microorganisms based on size reduced alpha diversity, altered community composition and changed CUE. Phylogenetic diversity and phylotype richness were lowest in communities with only ‘small’ microbes and increased with less restrictive size filtering. The composition of the communities was also influenced by the treatments, when considering both the membership and the relative abundance of microbial groups. The reductions in phylogenetic diversity were strongly associated with decreases in the CUE (adj R2 = 0.54). The exclusion of larger microorganisms also decreased the soil microbial biomass. The reductions CUE and biomass with alpha diversity show that microbial biodiversity is a driver of soil carbon stabilization processes. Inclusion of fungi in the ‘whole’ and ‘large’ cell size communities may contribute to the higher CUE observed in these treatments if fungi use carbon substrate more efficiently than bacteria. Alternatively, the exclusion of comparatively large microorganisms such as protozoa could change predator-prey relationships and trophic dynamics within the community reducing community level CUE. In summary, the results from this experiment suggest that microbial biodiversity and microbial traits such as cell size can be an important determinants of soil carbon stabilization processes.