Short-term cellulose addition decreases microbial diversity and network complexity in an Ultisol following 32-year fertilization

Cellulose is an essential component of plant cell walls, and one of the major constituents of soil organic matter. Decomposition of cellulose, mediated by microorganisms, is critical to the sustainable development of arable soils. However, how exogenous cellulose addition, as a surrogate for organic material amendment, influences the diversity and community compositions of soil microorganisms and their network complexity remains largely unknown. To bridge this knowledge gap, we conducted a microcosm experiment incubated with soils that had been subjected to long-term mineral or organic fertilization. Cellulose addition increased the cumulative CO 2 emission in all treatments, with the highest value found in the pig manure amended soils. Cellulose addition significantly reduced the alpha diversity of bacteria and fungi across all fertilization treatments, with a more pronounced effect observed for fungi. Moreover, cellulose addition strongly altered bacterial community structure by increasing the relative abundance of copiotrophic bacteria such as Actinobacteria and Proteobacteria while reducing that of oligotrophic bacteria (e.g., Chloroflexi). Compared with no-fertilizer treatment, the influence of cellulose addition on bacterial and fungal community structure was stronger in long-term mineral or organic fertilized soils. Cellulose addition altered the relative abundance of bacterial and fungal functional groups by generally enriching microbes involved in chemoheterotrophy and suppressing those involved in methylotrophy, pathotroph, saprotroph-symbiotroph, and saprotroph-pathotroph. In addition, cellulose addition decreased soil microbial complexity and the number of potential keystone species, but did not change the key role of Chloroflexi in soil microbial network. Overall, our results demonstrated that cellulose addition decreased soil microbial diversity and network complexity, with possible short-term negative consequences for ecosystem functioning in Ultisols. • CO 2 emission was highest in the pig manure amended soils with cellulose addition. • Cellulose addition reduced the alpha diversity of bacteria and fungi. • Fungi were more responsive to cellulose addition than bacteria. • Cellulose addition altered microbial community structure more strongly in fertilized soils. • Cellulose addition decreased microbial complexity and the number of keystone taxa.