Interactions between microbial diversity and substrate chemistry determine the fate of carbon in soil

Nanette C Raczka,Ljiljana Pasa-Tolic,Rosalie K Chu,Edward Brzostek,Mary S Lipton,Malak M Tfaily,Juan Piñeiro,Ember Morrissey

doi:10.1038/s41598-021-97942-9

Abstract

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 (e.g., enzymatic capabilities, growth rates). Here, we explicitly test these theories by coupling quantitative stable isotope probing and metabolomics to track the fate of 13C enriched substrates that vary in chemical composition as they are assimilated by microbes and transformed into new metabolic products in soil. We found that differences in forest nutrient economies (e.g., nutrient cycling, microbial competition) led to arbuscular mycorrhizal (AM) soils harboring greater diversity of fungi and bacteria than ectomycorrhizal (ECM) soils. When incubated with 13C enriched substrates, substrate type drove shifts in which species were active decomposers and the abundance of metabolic products that were reduced or saturated in the highly diverse AM soils. The decomposition pathways were more static in the less diverse, ECM soil. Importantly, the majority of these shifts were driven by taxa only present in the AM soil suggesting a strong link between microbial identity and their ability to decompose and assimilate substrates. 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.

Highlights

Microbial decomposition drives the transformation of plant-derived substrates into microbial products that form stable soil organic matter (SOM)
Our results support our conceptual model in that the diversity of microbes is greater in arbuscular mycorrhizal (AM) than ECM soils (Fig. 1) and that microbial diversity is tightly coupled to the breadth of functional capabilities and the resulting shift in SOM chemistry with microbial degradation (Fig. 2)
The soils differed in C: N stoichiometry with AM soils having a lower C:N ratio (− 24%, p value < 0.05; Table S1) relative to ECM soils, a pattern commonly observed in forest e cosystems[32]

Summary

Introduction

Microbial decomposition drives the transformation of plant-derived substrates into microbial products that form stable soil organic matter (SOM). We explicitly test our conceptual model (Fig. 1) using a novel approach that couples quantitative stable isotope probing[26] (qSIP), to quantify the amount of litter C that is assimilated by active bacterial and fungal taxa, with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) to track changes in metabolite composition during microbial degradation.

Results

Conclusion