September 19, 2024
Journal Article

The path from root input to mineral-associated soil carbon is dictated by habitat-specific microbial traits and soil moisture

Abstract

Soil microorganisms help transform plant inputs into mineral-associated soil organic carbon (SOC) – the largest and slowest-cycling pool of organic carbon on land. However, the microbial traits that influence this process are widely debated. While current theory and biogeochemical models have settled on carbon-use efficiency (CUE) and growth rate as positive predictors of mineral-associated SOC, empirical tests are sparse, with contradictory observations. Using 13C-labeling of a grassland soil under two moisture regimes, we found that microbial traits associated with mineral-associated SOC varied by soil habitat, as did active microbial taxa and SOC composition. In the habitat surrounding living roots (‘rhizosphere’), bacterial-dominated communities with fast growth, high biomass, and high extracellular polymeric substance (EPS) production were positively associated with mineral-associated SOC. In contrast, the habitat around decaying roots (‘detritusphere’) held communities dominated by fungi and more filamentous bacteria with greater exoenzyme production; there, mineral-associated SOC was associated with slower microbial growth and lower microbial biomass. CUE was a negative predictor of mineral-associated SOC in both habitats. Using 13C-quantitative stable isotope probing, we found that most C assimilation in the rhizosphere and detritusphere was performed by very few bacterial and fungal taxa (0.6–1.7% of the total taxa present). Our findings challenge current theory by demonstrating that microbial traits linked with mineral-associated SOC are not universal, but vary with soil habitat and moisture conditions, and are shaped by a small number of active taxa. Emerging SOC models that explicitly reflect these interactions may better predict SOC storage, since climate change causes shifts in soil moisture regimes and the ratio of living versus decaying roots.

Published: September 19, 2024

Citation

Sokol N., M. Foley, S.J. Blazewicz, A. Bhattacharyya, N. DiDonato, K. Estera-Molina, and M. Firestone, et al. 2024. The path from root input to mineral-associated soil carbon is dictated by habitat-specific microbial traits and soil moisture. Soil Biology and Biochemistry 193. PNNL-SA-194739. doi:10.1016/j.soilbio.2024.109367