Inter-species root interaction can shift feedback effect of arbuscular mycorrhizal fungi from neutral to positive or negative

Aims: The growth-improvement of Robinia pseudoacacia in the presence of Platycladus orientalis is well documented, but the effects of arbuscular mycorrhizal (AM) fungi and roots on the growth of these trees remain largely unexplored. Here, we show different effects of changed AM fungi under distinct belowground interaction pathways. Methods: An AM fungal community native to grassland and a remodeled AM community from an adjacent R. pseudoacacia and P. orientalis mixed stand were collected and used in a pot experiment to estimate the role of AM fungi in the co-existence of conspecific and heterospecific neighbor trees. Using pots compartmented with mesh of different pore sizes, we also investigated how the feedback effects of remodeled AM fungi on R. pseudoacacia and P. orientalis growth were affected by different belowground interaction pathways between plants. Results: The biomass of P. orientalis coexisting with conspecific plants decreased under the remodeled AM treatment while that of R. pseudoacacia increased. The contrasting response of these tree species is attributable to different tree-tree interaction patterns. P. orientalis and R. pseudoacacia also experience d different AM-induced plant-soil feedback responses (APSF) in the presence of interspecific root interaction. Furthermore, we found the mechanisms of how AM colonization, photosynthesis and root morphology affected APSF in presence of different intra- and interspecific interaction pathways. Conclusion: There is a critical influence of neighbor tree identity and of tree-tree interaction pathways in the feedback effects induced by AM fungi on R. pseudoacacia and P. orientalis . The use of high proportion of P. orientalis is not advisable in R. pseudoacacia × P. orientalis mixed stands.