Fungi are the major decomposers of wood in terrestrial ecosystem. There are two major groups of fungi that accomplish this – brown rot fungi and white rot fungi. In most of the cases, they are not substrate-specific, but remarkably little is known about how they coexist and compete. Because they degrade wood in unique ways and generate distinct residues, understanding their colonization and competition is important.

Here, we studied the decomposition of pine, oak and birch invaded by two fungi that coexist in the boreal forest of Minnesota - a brown rot Gloeophyllum trabeum and a white rot Irpex lacteus. Fungi were cultured as single-species and as mixed treatments for 8 weeks. The biomass of specific fungi was quantified by quantitative PCR. Sample weight loss, lignin, ergosterol and solubility of wood samples were also measured. Our hypotheses were: 1) both wood type and fungal combination will have significant effect on decomposition.2) if one fungi is out-competed by another, the decayed wood will have more similar properties as wood invaded by the single winner fungus.

Results/Conclusions

Both fungi and wood type had significant effect on decomposition. G. trabeum caused 40~50% of weight loss on pine and birch, twice the weight loss of I. lacteus and mixed treatment in the same wood. All fungal treatments caused similar weight loss on oak. On the contrary, lignin loss is similar in pine and birch for all fungi treatments, while I. lacteus and mixed treatment had 20% more lignin loss than G. trabeum on oak. qPCR and ergosterol analyses revealed that G. trabeum was outcompeted by I. lacteus in every mixed scenario. Samples invaded by I. lacteus or mixed fungi have a similar level of solubility while G. trabeum has dramatically increased the solubility of all types of woods.

Our research indicates that wood type and fungi combination both have significant effect on fungi behavior. Samples invaded by mixed fungi showed similar weight loss, lignin loss, fungi biomass and solubility as single I. lacteus treatment. Solubility was a good indicator of fungi competition according to our data. Most importantly, qPCR allowed us to weight the presence of both fungi in a mixture and gave results that matched observed changes in the wood.