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.

Diffuse competition for heterogeneous substrate in soil among six species of wood-decomposing basidiomycetes.

Competition among six wood decay fungi was studied using 15×15 mm wood blocks placed in 250×250 mm plastic trays filled with unsterilized sand or clay. The wood blocks were preinoculated with Heterobasidion annosum (Fr.) Bref., Resinicium bicolor (Alb. & Schw. ex Fr.) Parm., Phanerochaete sanguinea (Fr.) Hjortstam, Coniophora sp. DC. ex Me"rat, Armillaria borealis Marxmuller and Korhonen and Hypholoma capnoides (Fr.) Kummer before they were combined in all possible combinations in the trays. Two methods were used, one with all wood blocks inoculated, and one with sterilized non-inoculated wood blocks distributed between the inoculated ones. Wood blocks preinoculated with the six species were also used in a pairwise competition test. Following incubation for 9 months in darkness at 21°C, mycelia were reisolated and identified. R. bicolor was most successful at invading through the soil and replacing other species in the wood blocks. P. sanguinea, Coniophora sp. and H. capnoides also had some success.

Population structure and mating system in Marasmius androsaceus Fr.

Isolates of the rhizomorph-forming fungus Marasmius androsaceus were obtained from four different sites in stands of either Norway spruce or Scots pine of different age. The mating system and the mycelial interactions within each site were studied. The fungus had a bifactorial mating system and genetically different dikaryons were strongly mutually antagonistic in culture. On the basis of such antagonism, up to 18 different individual genets could be found within an area of 2.8 m2 . No differences between the four sites could be detected with respect to the size of the genets. Isolates belonging to the same genet were frequently found in close proximity in areas from which other types were excluded. However, the older plots contained genets with a discontinuous distribution in the plots. The likely origin of this distribution is discussed in relation to the pattern of dispersal, establishment and spread of this saprophytic fungus in different woodland habitats.