Fungi are the primary decomposers of dead plant material (i.e., litter) in terrestrial environments, controlling a major flux of carbon (C) between the biosphere and atmosphere. While decomposer fungi exhibit predictable community succession patterns as litter decay progresses, the processes by which these communities assemble in the field remain poorly understood. We hypothesized that decomposer fungi become dominant in field communities due to high growth rate and high activity of C-degrading enzymes compared to rare species. Furthermore, we hypothesized that dominant species have similar abilities to degrade major plant cell wall biopolymers, and that these abilities were fundamentally different than rare species, which might specialize on less abundant resources. To test these hypotheses, we created laboratory microcosms with 18 fungal species identified in litter-degrading communities in a boreal forest in Alaska, USA. Nine species were dominant in the field communities, and nine species were rare. Microcosms were supplemented with Arabidopsis thaliana litter as the sole C source. We measured fungal growth rate, activity of 10 extracellular C-degrading enzymes, litter mass loss, and CO2 respiration rate after 30 days of incubation.
Results/Conclusions
Our primary finding was that fungal growth rate was significantly correlated with average field relative abundance, suggesting that the ability to claim territory and resources is an important factor in fungal community assembly. In contrast to our other predictions, we found no significant differences between dominant and rare species with respect to litter mass loss or CO2 respiration rate when normalized to biomass area. However, we did find markedly different enzymatic capability among the species, with each species displaying its own unique enzyme activity profile. Rather than enzyme activity correlating with dominant or rare status in the field, we found that both dominant and rare species were largely specialists, exhibiting strong enzyme activity against specific sugars, proteins, or phenolics. Together, these results suggest that the ability to use certain (but not all) resources is important in predicting field abundance. Future work will continue to investigate the combined roles that growth rate and specific resource utilization ability play in decomposer fungi community assembly.