Environmental fluctuations facilitate species co-existence and increase decomposition in communities of wood decay fungi.

A fluctuating environment may facilitate co-existence of species, and high species richness may be important for maintaining ecosystem processes under changing environmental conditions. A positive relationship has been found between species richness and primary production in many experiments, and there is now an increasing interest whether similar relationships also apply to microorganisms and decomposition. Basidiomycete fungi are the primary decomposers of wood with the functional groups brown and white rot fungi, which differ with respect to decay strategy. In this study, 16 species of boreal wood decay fungi, 8 brown rot fungi and 8 white rot fungi, were assembled in artificial communities. The aims were to study species persistence, wood decomposition and metabolic efficiency in fungal communities of increasing levels of species richness under constant and fluctuating temperature regimes. Species persistence was generally low, but temperature fluctuations facilitated co-existence of species. Decomposition was highest at intermediate diversity levels under the fluctuating temperature regime. Metabolic efficiency, estimated as the amount of fungal mycelium formed per amount of degraded wood, decreased with increasing community complexity under the fluctuating temperature regime. Brown and white rot fungi differed in decomposition rates and metabolic efficiency, but no synergistic effects were found where the two functional groups were mixed. This study demonstrates how niche differentiation in a variable environment may act to maintain diversity and function. In our experiment, differences in functional responses to the varying temperature rather than resource partitioning between brown and white rot fungi had significant effects. Niche differentiation is likely to be particularly important in maintaining species diversity in communities of wood decaying fungi, which are known from previous studies to be characterised by intense competition, and where otherwise metabolically costly interactions lead to species exclusion and dominance by highly competitive species.