Who is who in litter decomposition? Metaproteomics reveals major microbial players and their biogeochemical functions

TLDR

Leaf‑litter decomposition is central to carbon cycling, yet the microbial regulation of this process remains poorly understood, and metaproteomics links enzyme activity to phylogeny. The study employed metaproteomics to investigate how environmental factors and nutrients influence decomposer structure and function in beech litter. Litter from Austrian forest sites with varying nutrient levels was processed by 1‑D SDS‑PAGE, LC‑MS/MS, and a novel bioinformatics workflow that assigned spectra to phylogenetic and functional groups, validated by complementary methods. Higher litter nutrient content and C:N:P stoichiometry shape decomposer community structure and activity, with fungi dominating extracellular hydrolytic enzyme production and increased enzyme abundance/activity driving greater microbial activity.

Abstract

Abstract Leaf-litter decomposition is a central process in carbon cycling; however, our knowledge about the microbial regulation of this process is still scarce. Metaproteomics allows us to link the abundance and activity of enzymes during nutrient cycling to their phylogenetic origin based on proteins, the ‘active building blocks’ in the system. Moreover, we employed metaproteomics to investigate the influence of environmental factors and nutrients on the decomposer structure and function during beech litter decomposition. Litter was collected at forest sites in Austria with different litter nutrient content. Proteins were analyzed by 1-D-SDS-PAGE followed by liquid-chromatography and tandem mass-spectrometry. Mass spectra were assigned to phylogenetic and functional groups by a newly developed bioinformatics workflow, assignments being validated by complementary approaches. We provide evidence that the litter nutrient content and the stoichiometry of C:N:P affect the decomposer community structure and activity. Fungi were found to be the main producers of extracellular hydrolytic enzymes, with no bacterial hydrolases being detected by our metaproteomics approach. Detailed investigation of microbial succession suggests that it is influenced by litter nutrient content. Microbial activity was stimulated at higher litter nutrient contents via a higher abundance and activity of extracellular enzymes.