Priority effects of foliar fungal endophytes in leaf litter decomposition

PI: Gerald M. Cobián, PhD, California State University, Chico, Department of Biological Sciences

Foliar endophytic fungi live inside plant leaves and are invisible to the unaided eye. These fungi can defend against pathogens and help plants retain water in arid environments, but many of their ecological roles remain unclear. We hypothesized that certain endophytes persist in leaves as dormant commensals, becoming active upon senescence to initiate decomposition and influence subsequent fungal community assembly via priority effects. We tested this through a 36-week field experiment using Quercus lobata leaf litter in mesh bags exposed to different fungal treatments. Using high-throughput sequencing, we tracked fungal community shifts and found that while distinct taxa were associated with each treatment, decomposition rates were similar. Site-level effects and stochastic processes played a larger role in shaping community composition than endophyte presence. Our findings suggest that endophytes exert weak priority effects under natural conditions and highlight the complexity of fungal interactions in litter decomposition.

Fig 1. The role of historical contingency in community assembly. Adapted from Fukami (2010), this conceptual diagram illustrates how the sequence and timing of species arrival, priority effects, can shape ecological community structure. The hypothetical species pool includes all potential colonizers (1–9), each capable of establishing under similar environmental conditions. Immigration pathways (A, B, C) represent different colonization sequences drawn from the same pool. Despite identical starting conditions, variation in arrival order leads to distinct local communities, such as 1–3, 4–6, and 7–9. These outcomes result from the interplay between stochastic and deterministic processes, highlighting the role of historical contingency in driving community divergence.

Fig 2. Fungal endophytes as early colonizers in the leaf litter community. This schematic illustrates how fungal endophytes, already present in green leaves, transition into the leaf litter community upon leaf abscission (Tennakoon et al., 2021). Their early establishment influences subsequent colonization by external fungal decomposers, shaping community composition and contributing to carbon cycling during the decomposition of litter (Swift et al., 1979).