Fungi colonize and form communities on and within plant leaves, and are intricately involved in host physiology and fitness. After leaves senesce and join the litter pool, leaf fungi may recolonize nearby living plant tissue, or alternatively, may affect the process of litter decomposition. However, although the fungal microbiome present in recently fallen leaves may interact with both living plants and processes of decomposition and nutrient cycling, we know very little about how communities of fungi associated with plant leaves change once a leaf drops and enters the litter pool. We sampled fungal communities from live leaves of the tropical tree species Psychotria horizontalis and P. marginata, and then forced abscission of those leaves. We experimentally placed leaves in the litter pool directly below their host, and then re-sampled their fungal communities after 1, 2, and 3 weeks. We extracted DNA from both surface-sterilized and unsterilized leaf fragments and performed Next-Generation Sequencing to examine endophytic and complete phyllosphere fungal communities across species and time.
Results/Conclusions
Fungal communities of decomposing tropical leaf litter underwent rapid successional changes. The composition of fungal communities in live leaves significantly changed once leaves entered the litter pool. Furthermore, the longer the leaf tissue remained in the litter pool, the more the fungal community composition shifted away from its original state, and fungal diversity decreased as time in the litter pool increased. Surface sterilization had a strong effect on fungal community composition, suggesting that there are fundamental differences between endophytic fungal communities and the entire phyllophere. Furthermore, diversity of fungal communities in sterilized leaf tissue was lower than that of non-sterilized leaf tissue, suggesting that only a fraction of the total fungal community is capable of existing endophytically. P. horizontalis and P. marginata hosted slightly different fungal communities, suggesting host-specificity of leaf-associated fungi, but those communities exhibited consistent patterns of succession and were affected similarly by the surface sterilization process. Finally, putative assignment of trophic level and functional guild to fungal community members suggests that endophytic fungi undergo a rapid proliferation in the first two weeks of leaf decomposition, supporting the hypothesis that many endophytes are latent saprotrophs.