Molecular fungal community and its decomposition activity in sapwood and heartwood of 13 temperate European tree species.

Sabrina Leonhardt,Claus Bässler,Francois Buscot,Martin Hofrichter,Lisa Noll,Andreas Dahl,Elisa Stengel,Julia Moll,Björn Hoppe,Harald Kellner,Daniel Cullen

doi:10.1371/journal.pone.0212120

Abstract

Deadwood is an important structural component in forest ecosystems and plays a significant role in global carbon and nutrient cycling. Relatively little is known about the formation and decomposition of CWD by microbial communities in situ and about the factors controlling the associated processes. In this study, we intensively analyzed the molecular fungal community composition and species richness in relation to extracellular enzyme activity and differences in decomposing sapwood and heartwood of 13 temperate tree species (four coniferous and nine deciduous species, log diameter 30–40 cm and 4 m long) in an artificial experiment involving placing the logs on the forest soil for six years. We observed strong differences in the molecular fungal community composition and richness among the 13 tree species, and specifically between deciduous and coniferous wood, but unexpectedly no difference was found between sapwood and heartwood. Fungal species richness correlated positively with wood extractives and negatively with fungal biomass. A distinct fungal community secreting lignocellulolytic key enzymes seemed to dominate the decomposition of the logs in this specific phase. In particular, the relative sequence abundance of basidiomycetous species of the Meruliaceae (e.g. Bjerkandera adusta) correlated with ligninolytic manganese peroxidase activity. Moreover, this study reveals abundant white-rot causing Basidiomycota and soft-rot causing Ascomycota during this phase of wood decomposition.

Highlights

Deadwood, or coarse woody debris (CWD), is an important structural component in forest ecosystems that influences a large number of ecosystem functions and contains diverse microhabitats for various organisms [1,2,3]
Wood-decaying fungi are usually divided into three major ecological categories: white-rot or white-rot like fungi (WRF, subtypes, simultaneous and selective white rot) [19], brown-rot fungi (BRF) and soft-rot fungi (SRF; type I and II), depending on modification of the lignocellulose complex and the technique used for decomposition, i.e. via multiple different secreted enzymes (e.g. WRF, SRF) or by the combined action of only few enzymes but strong radical-based mechanisms (e.g. BRF) [3,6,20,21,22,23]
We investigated the in-depth relationships between fungal biomass, enzyme activities and CWD properties in sapwood and heartwood of these decomposing logs exposed for six years on the ground [10]

Summary

Introduction

Coarse woody debris (CWD), is an important structural component in forest ecosystems that influences a large number of ecosystem functions and contains diverse microhabitats for various organisms [1,2,3]. The microbial decomposition of CWD is dominated by filamentous Dikarya fungi, especially Agaricomycotina and xylariaceous Ascomycota [5,12,13,14,15,16]. These organisms have the ability to break down the recalcitrant lignocellulose complex by an effective toolbox of extracellular oxidoreductases and hydrolases that are encoded in high numbers in their genomes [10,11,14,17,18]. Wood-decaying fungi are usually divided into three major ecological categories: white-rot or white-rot like fungi (WRF, subtypes, simultaneous and selective white rot) [19], brown-rot fungi (BRF) and soft-rot fungi (SRF; type I and II), depending on modification of the lignocellulose complex and the technique used for decomposition, i.e. via multiple different secreted enzymes (e.g. WRF, SRF) or by the combined action of only few enzymes but strong radical-based mechanisms (e.g. BRF) [3,6,20,21,22,23]

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Conclusion