13C-cellulose stable isotope probing was applied to Californian forest soil from both organic and mineral soils. The data identifies cellulolytic taxa and impacts of three different timber harvesting strategies contrasted to unharvested pristine forest.. Impacts of Timber Harvesting on Cellulolytic Community of Forest Soils

Soil management is vital for maintaining the productivity of commercial forests, yet the long-term impact of timber harvesting on soil microbial communities remains largely a matter of conjecture. Decomposition of plant biomass, comprised mainly of lignocellulose, has a broad impact on nutrient cycling, microbial activity and physicochemical characteristics of soil. Within the framework of the Long-term Soil Productivity Study, we tested whether timber harvesting, accompanied by varying degrees of organic matter (OM) retention, affected the activity and structure of the cellulose-degrading microbial populations sixteen years after harvesting. Using a variety of experimental approaches, including stable isotope probing with 13C-labelled cellulose in soil microcosms, we demonstrated that harvesting led to a decrease in net respiration and cellulolytic activity. The decrease in cellulolytic activity was associated with an increased relative abundance of thermophilic, cellulolytic fungi (Chaetomiaceae), coupled with a decreased relative abundance of cellulolytic bacteria in harvested plots, namely members of Opitutaceae, Caulobacter and Streptomycetaceae. In general, harvesting led to an increase of other stress-tolerant non-cellulolytic taxa. Stable-isotope probing improved shotgun metagenome assembly by 20-fold and enabled the recovery of ten metagenome-assembled genomes of cellulolytic bacteria and fungi. Our study demonstrates the putative cellulolytic activity of a number of uncultured taxa and highlights the mineral soil layer as a reservoir of uncharacterized diversity of cellulose-degraders. It also demonstrates the mitigating potential of OM retention, and contributes to a growing body of research showing persistent changes in microbial community structure in the decades following timber harvesting prior to canopy closure.