The interactive effect of tree mycorrhizal type, mycorrhizal type mixture and tree diversity shapes rooting zone soil fungal communities in temperate forest ecosystems

Abstract The underlying processes of plant‐microbe associations particularly their interactions with their mycorrhizal fungal partners have been extensively studied. However, considerably less is known about the consequences of tree‐tree interactions on rooting zone soil microbiota when tree species of different mycorrhizal type (myco‐type) grow together as mono and mixed myco‐type mixtures along a tree diversity gradient. Using the MyDiv tree diversity experiment, where arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) trees and their mixtures were planted in monocultures, two‐species and four‐species mixture plots, we investigated the interplay of target tree myco‐type, myco‐type mixture, tree diversity and rooting zone compartment (target tree dominated and its interaction zones with neighbour trees) on the rooting zone soil mycobiota employing meta‐barcoding of the ITS2 rDNA fragment of the fungal internal transcribed spacer (ITS). Our results revealed significant individual and interaction effects of tree myco‐type, myco‐type mixture and tree diversity but not rooting zone compartment on the fungal taxonomic and functional alpha and beta diversity. This implies intermingling of roots of target and neighbouring tree species there by reducing the target tree species effect in its rooting zone. As tree diversity increases, we found convergence of the fungal community in general, where the fungal community dissimilarity varies depending on the co‐existing tree species myco‐type and tree species diversity. Furthermore, the fungal community composition in the two and four species mixtures were consistently influenced by soil pH, whereas in the mixed multi‐species stands basal respiration, N, PO 4 − , NO 3 − were found to be equally important unlike in AM and EcM multi‐species stands. Comparative analysis of the fungal taxa specialisation between mono and mixed myco‐type multi‐species stands revealed that the mixed myco‐type plots shared 23.5% (AM) and 19.7% (EcM) of the generalist fungal communities However, the percentage of specialised fungal community in mixed myco‐type plots (13.2%) was significantly higher as compared to EcM (9.5%), and significantly lower (9%) as compared to AM (11.7%) plots, resulting in myco‐type and myco‐type mixture specific fungal communities and functional guild patterns Our results provide novel insights on the significance of tree species and its co‐existing trees preferred mycorrhizal association in shaping the target tree rooting zone soil mycobiome along a tree diversity gradient. Furthermore, it highlights the significance of generalist and specialist fungal communities in mono and mixed myco‐type stands in modulating tree‐tree interaction, tree species co‐existence and regulating soil properties and ecosystem functions. Read the free Plain Language Summary for this article on the Journal blog.