Abstract
Common mycorrhizal networks of ectomycorrhizal (EcM) fungi could be of great benefit to trees growing in the shallow soils of Sub-Mediterranean Karst ecosystems, potentially playing a crucial role in the survival of trees in this harsh environment. The first step to confirm the existence of such networks is to assess the extent and nature of symbiont sharing in the mycelial community. To address this question, we incubated in-growth mesh bags under the native Ostrya carpinifolia and Quercus pubescens, and the non-native Pinus nigra, over two consecutive years. In Q. pubescens and P. nigra, but not in O. carpinifolia, mycelium production was significantly higher in the year with higher spring precipitation, indicating the influence of climatic conditions, but also the identity of the host tree. We observed a complex interaction between tree species and sampling year in structuring the composition and diversity of mycelial communities. Local environmental conditions contributed additionally and were responsible for 21.46% of the community variation between samples. Although ~ 70% of fungal operational taxonomic units were shared across the studied tree species, distinct community compositions emerged, emphasizing the role of host tree specificity. Q. pubescens exhibited greater stability in EcM richness between sampling years, whereas P. nigra showed lower EcM richness, likely due to limited availability of compatible fungi and reliance on introduced fungal partners. Additionally, differences in EcM fungal exploration strategies were observed. O. carpinifolia and Q. pubescens mainly hosted non-specific EcM fungi with short distance exploration types. In contrast, EcM fungi of P. nigra had higher spatial spread, and were predominantly conifer specific. Overall, our results emphasize the importance of host specificity, soil parameters, spatial proximity, and climatic variability for the structuring of mycelial communities in fragmented forests.