Resource availability and physiological traits determine strength of priority effects in fungal community assembly

Background/Question/Methods

The stochastic sequence and timing of species arrival may have important consequences for community dynamics and ecosystem-level processes in soils due to priority effects, the competitive advantage obtained by early colonizers. However, understanding the factors that contribute to the strength of priority effects remains unknown. By altering establishment success of colonizers, the extent to which priority effects alter microbial dynamics may be dependent on resource availability and traits of initial colonizers. Using saprotrophic fungi as a model system, we constructed a microcosm experiment to investigate the importance of initial colonizer traits and litter biochemistry in the degree to which community assembly history alters community dynamics. We expected that initial colonizers exhibiting rapid growth and high lignolytic capacity would result in larger deviations in community composition and functional characteristics, relative to a “control” community. Secondly, we expected that competitive dynamics were dependent on resource availability, such that the impact of a particular initial colonizer varied with litter biochemistry. Consequences of assembly history on fungal dynamics were quantified according to fungal richness and b-diversity, as well as rate of decomposition and potential enzyme activity of litter communities.

Results/Conclusions

Priority effects had persistent consequences for fungal community assembly, wherein the physiological traits of the initial colonist accounted for the early trajectories of community composition and rates of litter decay. Support for this claim comes from evidence that the initial fungal colonist suppressed fungal community richness and enhanced litter decay, although the degree of divergence was highly dependent on the colonist’s identity. During the early stages of community assembly (1 and 3 months), deviations from control community assembly were positively related to colonist growth rate (r² = 0.54, P = 0.007) and metabolic potential to degrade plant detritus (r² = 0.28, P = 0.076). Importantly, lignin-rich leaf litter generated increasingly divergent trajectories of community assembly, as initial colonizer identity resulted in a broader range of community composition and enzyme potential in oak litter communities relative to maple litter communities (dispersion analysis; Pseudo-F_1,68 = 5.73, P = 0.019). Together, our results indicate the important roles that physiological traits of initial colonist, as well as resource availability, play in shaping the balance between habitat filtering and priority effects during the process of community assembly.