Keystone microbial taxa drive the accelerated decompositions of cellulose and lignin by long-term resource enrichments.

Lignin and cellulose are the most important component of crop straw entering arable soil. The decomposition of lignin and cellulose are related to carbon sequestration and soil fertility. The keystone microbes decomposing lignin and cellulose in cropland and their impact on agricultural management, however, remains largely unclear. In this study, we traced the carbon (C) from highly enriched C-labeled (atom% C = 99 %) lignin and cellulose to functional keystone microbes in soils of a 26-year fertilization field experiment with stable isotope probing (SIP). C-cellulose and C-lignin decomposition were significantly accelerated with the long-term application of fertilization, especially with the combination of organic and chemical fertilization (NPKM). The C was mainly assimilated by bacteria Acidobacteria (i.e. GP1, GP3, GP6), Proteobacteria (i.e. unidentified gamaproteobactiera, Bradyrhizobium), and fungi Ascomycota (i.e. Talaromyces and Fusarium, etc.). The keystone bacteria taxa decomposing cellulose and lignin were large overlapped, but substantially shaped by fertilization. For instance, GP3 was the dominant bacterium that decomposed both cellulose and lignin in no fertilizer control (CK), while GP1 and GP6 were the ones in chemical fertilization (NPK) and NPKM, respectively. The decomposition rates of cellulose in different fertilizations were majorly predicted by soil total phosphorus (TP), functional fungi abundance, total nitrogen (TN), whereas functional bacterial and fungal abundance, TP, and community structure of functional fungi manipulated the decomposing rate of lignin. Together, we demonstrate that keystone functional microbes decomposing cellulose and lignin were largely concurring and significantly altered by long-term resources enrichment, which drives the similar patterns of decomposition rates of these two substrates along the resource enrichment gradient.