Mutualistic and antagonistic phyllosphere fungi contribute to plant recruitment in natural communities

Phyllosphere fungal communities participate in multiple ecological functions (litter decomposition, disease-causing, plant defence). However, there is a lack of knowledge on whether and how these functions contribute to plant community dynamics under natural conditions. One of the aspects of plant dynamics in which these fungi can most clearly affect is recruitment, since the success of newly germinated plants can be seriously compromised by pathogenic activity or the absence of mutualistic interactions. To determine the relationship between phyllosphere fungal communities and plant recruitment, we combined published information on the frequency of plant-plant recruitment interactions and phyllosphere fungal communities in 38 woody species from two mixed forests in southern Spain. Our results indicate that phyllosphere pathogens and saprotrophs have a negative effect on canopy-recruit interactions, while epiphytic fungi have a positive effect. Additionally, the presence of canopy species hosting high richness of epiphytes or counting with a high diversity of saprotrophic fungi favours the formation of an abundant sapling bank. Synthesis. Our results suggest that phyllosphere fungi play a relevant role in the assembly of the sapling bank in forest communities, thus, potentially influencing plant community dynamics. Beyond the well-known negative effect of pathogenic fungi on recruitment, our results show the mutualistic effect of fungal epiphytes and a dual role of saprotrophs as antagonistic, decreasing recruitment of certain species, or mutualistic, enhancing recruitment in the sapling bank. Our results suggest that phyllosphere fungi play a relevant role in the assembly of the sapling bank in forest communities, thus, potentially influencing plant community dynamics. Beyond the well-known negative effect of pathogenic fungi on recruitment, our results show the mutualistic effect of fungal epiphytes and a dual role of saprotrophs as antagonistic, decreasing recruitment of certain species, or mutualistic, enhancing recruitment in the sapling bank.image