Bacterial communities of decaying Norway spruce follow distinct slope exposure and time‐dependent trajectories

Abstract

Deadwood decay employs a complex metabolism and provides carbon and nutrients for soils. Although being highly diverse, the contribution of the bacterial deadwood colonizing community is underexplored compared with the fungal one. Therefore, we performed an in-field mesocosm study and monitored the bacterial communities in decaying experimental Picea abies wood blocks and their underlying soil on north- and south- exposed slopes in the Italian Alps over a 2-year period. The faster deadwood decay at the south-facing slope was associated with a higher bacterial richness and a higher number of specialist operational taxonomic units (OTUs) which were more strongly correlated to environmental parameters than other bacterial community members. With progressing decay, the wood and soil bacterial communities became more similar in terms of richness, diversity and evenness and especially at the south-facing slope, they also became more similar in terms of community composition. Exposure-specific OTUs suggest wood-soil interaction. However, despite the strong influence of exposure on the soil bacterial communities, the P. abies wood blocks shared a comparably high number of OTUs with the soil irrespective of the slope. At finer taxonomic scale, we identified Pseudomonas, Microbacteria, Sphingomonas, Xanthomonas, Methylovirgula and Burkholderia as decay associated, although their functional role needs further studies.

Complementary Roles of Wood-Inhabiting Fungi and Bacteria Facilitate Deadwood Decomposition

“…In particular, the wood density, indicating the progress of decomposition, showed high variation, ranging from 290 to 470 kg m 23 . This is not surprising, since individual deadwood logs are under the complex influence of the individual history of the microbial community assembly and microclimate conditions, including sun exposure and soil contact (20,21). Both CO 2 production from deadwood and N fixation showed a significant correlation with pH (r = 20.720, P = 0.016 and r = 20.832, P = 0.003, respectively).…”

Site-Specific Microbial Decomposer Communities Do Not Imply Faster Decomposition: Results from a Litter Transplantation Experiment

“…N-fixing bacteria such as Sphingomonas or Luteibacter could provide N that is known to be limited in the litter environment, while they could receive secondary metabolites from fungi [50]. This has recently been shown for deadwood colonisation [10] and in the rhizosphere where diazothrophs and mycorrhiza, together, promote the growth of the host plant [53]. Positive interactions between microbial species with different functional roles were reported to affect process rates in soil nutrient dynamics [54].…”

“…However, recent work has shown that bacterial genomes contain cellulase genes [8] and they are capable of cellulolytic activity [9]. Bacteria could probably dominate the first phase of decomposition, where more soluble compounds are still available [9,10]. Despite a long history of research focusing on the dynamics of litter degradation, the role microbial communities play is still debated, especially regarding their local adaptation to litter inputs.…”

Determinants of Deadwood-Inhabiting Fungal Communities in Temperate Forests: Molecular Evidence From a Large Scale Deadwood Decomposition Experiment

“…In deadwood, bacteria and archaea may also contribute to pH changes through the two versions of ammonification: (i) N fixation and (ii) anaerobic assimilatory and dissimilatory nitrite reduction to ammonium ( Stein and Klotz, 2016 ). N fixing bacteria ( Hoppe et al, 2014 , 2015 ; Mäkipää et al, 2018 ; Probst et al, 2018 ) and known bacteria involve in dissimilatory nitrite reduction to ammonium (e.g., Clostridium, Klebsiella ) ( Spano et al, 1982 ; Johnston et al, 2016 ) are detected in conifer and broadleaved deadwood logs. Ammonium in deadwood can be then potentially converted to nitrate via nitrification process, hydrogen (H + ) is released, which can decrease wood pH ( Stein and Klotz, 2016 ).…”