Root‐associated fungi modulate plant recruitment in Mediterranean forests

Abstract Established plants affect directly and indirectly the success of juvenile plants recruiting in their close vicinity, what is defined as a canopy–recruit interaction. Such interactions affect plant species demography and community dynamics. Root‐associated fungi (RAF) can influence plant performance and survival, thus contributing to the sign and intensity of canopy–recruit interactions. Pathogenic RAF negatively affect individual plants and their neighbours, while mycorrhizal fungi can positively counteract those effects. Additionally, saprotrophic RAF decompose organic matter, modifying nutrient availability in the soil, possibly enhancing recruitment. Therefore, understanding the role of RAFs in canopy–recruit interactions will help us understand their potential effect on the dynamics of natural plant communities. We combined information on canopy–recruit interactions for 24 woody species in two Mediterranean mixed forests with high‐throughput sequencing of root DNA from each species. We determined the relationships between plant recruitment and the similarity and richness of RAF communities among woody species associated with different mycorrhizal types. The probability of canopy–recruit interactions decreased between plants sharing more similar pathogenic RAF communities. However, their effect on the frequency of recruitment was modulated by the mycorrhizal association of the recruit, being negative for plant species associated with AM fungi but not significant for those associated with ECM. At the plant species level, plants hosting higher richness of pathogenic RAF presented scarcer recruitment and recruited under a narrower set of canopy species; on the other hand, canopy species associated with ECM fungi or hosting higher richness of saprotrophic RAF promoted denser recruit banks of any species in their vicinity. Our findings provide evidence of the importance of RAF for plant recruitment in natural habitats, and thus for plant population and community dynamics. They support the hypothesis that pathogenic RAF interact with mycorrhizal associations, and that plant species susceptibility to multiple pathogens limits its recruitment success. They also suggest that the positive effect of certain plant species on the recruitment of others (i.e. nurse effect) is likely mediated by a higher diversity of saprotrophic RAF. Read the free Plain Language Summary for this article on the Journal blog.