BACKGROUND: Fine woody debris (FWD; deadwood < 10 cm diameter) is a crucial but often overlooked component of forest ecosystems. It provides habitat for microbial communities and enhances soil fertility through nutrient cycling. This role is especially important in managed forests, which typically have limited deadwood stocks. Climate change is increasing forest disturbances and expanding early successional forests with low canopy cover, yet the effects on microbial communities and related processes remain poorly understood. RESULTS: In a ten-year canopy manipulation experiment, we examined the decomposition of FWD of Fagus sylvatica and Abies alba. Increased canopy openness significantly decreased bacterial diversity in decomposing FWD and altered the community composition in surrounding soil. Decomposition time was the main factor shaping bacterial community structure in FWD, with tree species and canopy cover also contributing. We identified bacterial groups involved in carbohydrate degradation, fungal biomass breakdown, and nitrogen fixation. Importantly, bacterial communities in fully decomposed FWD remained distinct from soil communities. CONCLUSIONS: Deadwood decomposition and nutrient cycling are driven by complex ecological interactions. Microbial community dynamics are influenced by the interplay of FWD decomposition stage, tree species, and microclimatic conditions. Bacterial communities, although less frequently studied in this context, appear more stable over time than previously studied fungi. This stability may help sustain decomposition processes and nutrient turnover under the environmental variability associated with global change.

• Klíčová slova
• Bacterial community, Canopy cover, Deadwood, Decomposition, Ecology, Fine woody debris, Microclimate, Succession, Temperate forest,
• Publikační typ
• časopisecké články MeSH

Deadwood decomposition is responsible for a significant amount of carbon (C) turnover in natural forests. While fresh deadwood contains mainly plant compounds and is extremely low in nitrogen (N), fungal biomass and N content increase during decomposition. Here, we examined 18 genome-sequenced bacterial strains representing the dominant deadwood taxa to assess their adaptations to C and N utilization in deadwood. Diverse gene sets for the efficient decomposition of plant and fungal cell wall biopolymers were found in Acidobacteria, Bacteroidetes, and Actinobacteria. In contrast to these groups, Alphaproteobacteria and Gammaproteobacteria contained fewer carbohydrate-active enzymes and depended either on low-molecular-mass C sources or on mycophagy. This group, however, showed rich gene complements for N2 fixation and nitrate/nitrite reduction-key assimilatory and dissimilatory steps in the deadwood N cycle. We show that N2 fixers can obtain C independently from either plant biopolymers or fungal biomass. The succession of bacteria on decomposing deadwood reflects their ability to cope with the changing quality of C-containing compounds and increasing N content.

• Klíčová slova
• bacterial genomes, cellulose, deadwood, mycophagy, nitrogen fixation,
• Publikační typ
• časopisecké články MeSH

The bacterial genus Sodalis is represented by insect endosymbionts as well as free-living species. While the former have been studied frequently, the distribution of the latter is not yet clear. Here, we present a description of a free-living strain, Sodalis ligni sp. nov., originating from decomposing deadwood. The favored occurrence of S. ligni in deadwood is confirmed by both 16S rRNA gene distribution and metagenome data. Pangenome analysis of available Sodalis genomes shows at least three groups within the Sodalis genus: deadwood-associated strains, tsetse fly endosymbionts and endosymbionts of other insects. This differentiation is consistent in terms of the gene frequency level, genome similarity and carbohydrate-active enzyme composition of the genomes. Deadwood-associated strains contain genes for active decomposition of biopolymers of plant and fungal origin and can utilize more diverse carbon sources than their symbiotic relatives. Deadwood-associated strains, but not other Sodalis strains, have the genetic potential to fix N2, and the corresponding genes are expressed in deadwood. Nitrogenase genes are located within the genomes of Sodalis, including S. ligni, at multiple loci represented by more gene variants. We show decomposing wood to be a previously undescribed habitat of the genus Sodalis that appears to show striking ecological divergence.

• Klíčová slova
• Sodalis, deadwood, free-living, insect symbionts, nitrogen fixation, non-symbiotic,
• Publikační typ
• časopisecké články MeSH