Impacts of Plant Exclusion on Soil Lignocellulolytic Microbial Community Composition and Function

Plant cell wall polysaccharides are the most abundant form of organic carbon in soils and their degradation by microorganisms represents a major link in the global carbon cycle. Soil carbon storage is a valuable ecosystem service, buffering against increasingly rapid climatic change, and underpinning services such as food production and flood prevention. Despite the importance of this link, little is known about the relative contributions of different microorganisms and their genes to lignocellulose degradation in soils. Here, we used a 10-year old plant-exclusion experiment on grasslands to study how reduced plant carbon inputs affects the microbial community, and genes which are putatively associated with lignocellulolysis. We show that 10-year plant exclusion consistently favours genera within the Bacillales, Thaumarchaeota, and diverse lineages of Proteobacteria, alters the repertoire of lignocellulolytic genes present, and that taxonomic and genetic changes are not clearly linked. Plant-exclusion was linked to increased hemicellulose breakdown product abundance and increased xylanase gene diversity after a single year, whereas 10 years of plant exclusion reduced xylanase gene diversity and altered lignocellulase gene composition. Additionally, this study investigates the fundamental and realised niches of specific soil microorganisms, and shows the temporal scale at which the microbial community responds to changing carbon inputs in grasslands.