Abstract
Biomass production and decomposition are key processes in ecology, where plants are primarily responsible for production and microbes act in decomposition. Trees harbor foliar microfungi living on and inside leaf tissues, epiphytes, and endophytes, respectively. Early researchers hypothesized that all fungal endophytes are parasites or latent saprophytes, which slowly colonize the leaf tissues for decomposition. While this has been proven for some strains in the terrestrial environment, it is not known whether foliar microfungi from terrestrial origin can survive or perform decomposition in the aquatic environment. On the other hand, aquatic hyphomycetes, fungi which decompose organic material in stream environments, have been suggested to have a plant-associated life phase. Our aim was to study how much the fungal communities of leaves and litter submerged in streams overlap. Ergosterol content on litter, which is an estimator of fungal biomass, was 5–14 times higher in submerged litter than in senescent leaves, indicating active fungal colonization. Leaves generally harbored a different microbiome prior to than after submergence in streams. The Chao1 richness was significantly higher (93.7 vs. 60.7, p = 0.004) and there were more observed operational taxonomic units (OTUs) (78.3 vs. 47.4, p = 0.004) in senescent leaves than in stream-immersed litter. There were more Leotiomycetes (9%, p = 0.014) in the litter. We identified a group of 35 fungi (65%) with both plant- and water-associated lifestyles. Of these, eight taxa had no previous references to water, such as lichenicolous fungi. Six OTUs were classified within Glomeromycota, known as obligate root symbionts with no previous records from leaves. Five members of Basidiomycota, which are rare in aquatic environments, were identified in the stream-immersed litter only. Overall, our study demonstrates that foliar microfungi contribute to fungal diversity in submerged litter.
Highlights
Biomass production and decomposition are key processes in ecology
How large is the proportion of foliar microfungi that thrives in decomposing leaves in an aquatic environment, and do aquatic hyphomycetes of litter originate from the plant? Our aim was to study these questions by sequencing the fungal communities of alder (Alnus incana L.) leaves prior to and after submergence in pristine boreal streams
Samples from senescent leaves and stream-immersed litter were clearly separated in the Non-metric Multidimensional Scaling (NMDS) ordinations space (Figure 2)
Summary
Biomass production and decomposition are key processes in ecology. Whereas plants are primarily responsible for production of biomass, microorganisms together with animals decompose the organic material in various ecosystems (Gessner et al, 2010). Papers hypothesized that all fungal endophytes are saprophytes or parasites, which slowly colonize the living leaf tissues and gain a head start over soil-dwelling saprophytes that invade the fallen, dead leaves (Sherwood-Pike et al, 1986; Saikkonen et al, 1998; Müller et al, 2001; Koide et al, 2005). This hypothesis was based on results made by early classification methods, leaning on morphological characteristics that erroneously classified fungal species into pathogens, saprophytes or parasites of the host tree (Berbee, 2001; Baayen et al, 2002). Modern classification methods, which are based on sequencing of DNA and ribosomal RNA genes, have revealed that most endophytes are different from parasites of the host tree (Ganley et al, 2004)
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