A pyrosequencing insight into sprawling bacterial diversity and community dynamics in decaying deadwood logs of Fagus sylvatica and Picea abies.

Jürgen Bauhus,Tiemo Kahl,Björn Hoppe,Dirk Krüger,Tesfaye Wubet,François Buscot,Tobias Arnstadt

doi:10.1038/srep09456

Abstract

Deadwood is an important biodiversity hotspot in forest ecosystems. While saproxylic insects and wood-inhabiting fungi have been studied extensively, little is known about deadwood-inhabiting bacteria. The study we present is among the first to compare bacterial diversity and community structure of deadwood under field conditions. We therefore compared deadwood logs of two temperate forest tree species Fagus sylvatica and Picea abies using 16S rDNA pyrosequencing to identify changes in bacterial diversity and community structure at different stages of decay in forest plots under different management regimes. Alphaproteobacteria, Acidobacteria and Actinobacteria were the dominant taxonomic groups in both tree species. There were no differences in bacterial OTU richness between deadwood of Fagus sylvatica and Picea abies. Bacteria from the order Rhizobiales became more abundant during the intermediate and advanced stages of decay, accounting for up to 25% of the entire bacterial community in such logs. The most dominant OTU was taxonomically assigned to the genus Methylovirgula, which was recently described in a woodblock experiment of Fagus sylvatica. Besides tree species we were able to demonstrate that deadwood physico-chemical properties, in particular remaining mass, relative wood moisture, pH, and C/N ratio serve as drivers of community composition of deadwood-inhabiting bacteria.

Highlights

Deadwood is an important biodiversity hotspot in forest ecosystems
Using a very comprehensive dataset of physico-chemical wood properties, we were able to identify key wood properties that correlate with bacterial community structure and abundances of dominant bacterial phyla
In line with the results of our recent study on the distribution of nifH genes[29], we found that members of the order Rhizobiales became significantly more abundant during the intermediate to advanced stages of decay, indicating that they may play an important ecological role and contribute significantly to Ncycling

Summary

Introduction

Deadwood is an important biodiversity hotspot in forest ecosystems. While saproxylic insects and wood-inhabiting fungi have been studied extensively, little is known about deadwood-inhabiting bacteria. The role of prokaryotes in deadwood and related ecosystem processes has only been examined in a few case studies such as the investigation into bacterial communities in deadwood of an East Asian pine species[13] and the presence of coexisting bacteria with Hypholoma fasciculare sampled in seven tree stumps by Valaskovaet al.[14] Substrate properties such as nutrient and water content have been shown to strongly influence wood colonization by microbes[10,15]. The study we here present is among the first to investigate bacterial diversity and community structure in deadwood under field conditions and applying deep 16S rDNA metabarcoding It compares the bacteria in deadwood logs of two common temperate timber tree species grown in geographic proximity, the deciduous Fagus sylvatica and the conifer Picea abies, at different stages of decay and under different forest management. In relation to a previously conducted study on the distribution of nifH genes in deadwood[29], we assumed that N-fixing bacteria from the order Rhizobiales are more abundant during the intermediate stages of wood decay, when fungal sporocarp richness is known to be highest and the provision of nitrogen is crucial[29]

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Conclusion