Boreal forests contain an estimated 28% of the world's soil carbon, and currently act as a significant global carbon sink. Plant-derived lignocellulose is a major component of soil carbon, and its decomposition is dependent on soil bacteria and fungi. In order to predict the fate of this soil carbon and its potential feedbacks to climate change, the identities, activity, and interactions of soil microbial decomposer communities must be better understood. This study used stable isotope probing (SIP) with ¹³C-labeled lignocellulose and two of its constituents, cellulose and vanillin, to identify microbes responsible for the processing of lignocellulose-derived carbon and examine the specific roles that they perform. Results indicate that multiple taxa are involved in lignocellulose processing, and that certain taxa target specific portions of the lignocellulose macromolecule; specifically, fungi dominate the degradation of lignocellulose and cellulose macromolecules, while bacteria scavenge aromatic lignocellulose monomers. Major fungal taxa involved in lignocellulose degradation include Ceratobasidium, Geomyces, and Sebacina, among others. Bacterial taxa processing lignocellulose and cellulose included Cellvibrio and Mesorhizobium in high abundance relative to other taxa, although Burkholderia were the primary vanillin consumers. These results elucidate some of the major players in lignocellulose decomposition and their specific roles in boreal forest soil. This information provides knowledge of small-scale microbial processes that dictate ecosystem-level carbon cycling, and can assist in predictions of the fate of boreal forest carbon stocks.
