The role of interspecific competition in fungal communities in natural substrates is poorly understood because fungi do not form easily definable populations. A new approach to investigating fungal competition, using natural substrates containing a range of known biomass concentrations of each of two species, is described. Relative competitive success of each species is assessed over time in terms of propagule production and substrate colonisation by each species. In an agricultural soil Mucor hiemalis usually out-competed Trichoderma harzianum. After 27 days, the success of both species in the mixtures was independent of the initial biomass concentration of either species, although the success of T. harzianum in these mixtures was substantially inhibited relative to the T. harzianum monocultures. In a forest soil, T. polysporum maintained a competitive advantage over M. hiemalis, and induced M. hiemalis to produce propagules rather than mycelia. Coexistence of both species always occurred in both experiments, and in the forest soil experiment the two-species mixtures all contained a higher total microbial biomass than the monocultures of either species by day 47, suggesting some niche differentiation.
Keywords: Competition; Fungi; Microbial ecology; Mixture experiment; Niche differentiation.