Fragile foundations: Succession patterns of bacterial communities in fine woody debris and soil under long-term microclimate influence

Background Fine woody debris (FWD) is a crucial yet often overlooked component of forest ecosystems, providing a dynamic habitat for microbial communities and playing a key role in carbon and nutrient cycling. In managed forests with low deadwood stocks, FWD decomposition enhances soil fertility by facilitating microbial nutrient cycling. Climate change increases the prevalence of forest disturbances enhancing the area of early succession forests with low canopy cover, but the consequences on the microbial communities and related processes is insufficiently understood. Results Here we conducted a ten-year experiment manipulating canopy cover to examine the decomposition of FWD of Fagus sylvatica and Abies alba . Our study revealed that canopy openness significantly affected bacterial diversity in the decomposing wood as well as in the surrounding soil. While community structure in FWD was primarily influenced by decomposition time, tree species and canopy density also played a role. We identified bacterial taxa associated with carbohydrate utilization, fungal biomass degradation, and nitrogen fixation, highlighting the diverse functional roles of FWD bacteria in nutrient cycling. Bacterial community in almost completely decomposed FWD remains clearly distinct from soil bacterial communities. Conclusions Complex ecological interactions shape deadwood decomposition and nutrient cycling. The interplay between FWD decomposition time, tree species, and microclimatic variability influences microbial community dynamics, with bacteria acting as a more stable component of the decomposer community compared previously studied fungi. This stability may be critical for sustaining decomposition and nutrient turnover despite environmental fluctuations associated with global change.