Juan Piñeiro, Nanette Raczka, Ember Morrissey, Edward Brzostek, Mary Lipton, Ljiljana Pasa-Tolic, Malak Tfaiky

Microbial decomposition drives the transformation of plant-derived substrates into microbial products that form stable soil organic matter (SOM). Recent theories have posited that decomposition depends on an interaction between SOM chemistry with microbial diversity and resulting function. Here, we explicitly test these theories by coupling quantitative stable isotope probing and metabolomics to track the fate of 13C labeled substrates that vary in chemical composition as they are assimilated by microbes and transformed into new metabolic products in the lab. We found that mycorrhizal-driven differences in forest nutrient economies (e.g., nutrient cycling, microbial competition) led to arbuscular mycorrhizal (AM) soils harboring greater microbial diversity than ectomycorrhizal (ECM) soils. When incubated with 13C labeled substrates, the greater diversity in AM soils led to substrate type driving shifts in the identity of active decomposers and their metabolic products. The decomposition pathways were more static in the less diverse, ECM soil. Importantly, the majority of these shifts were driven by non-co-occurring taxa suggesting a strong link between microbial identity and specialized function. Collectively, these results highlight an important interaction between ecosystem-level processes and microbial diversity; whereby the identity and function of active decomposers impacts the composition of decomposition products that can form stable SOM.