Plants, not just environment, select the interacting fungal pool along altitude
Plant-fungal interactions are shaped by both abiotic and biotic variables, but often the focus is on how abiotic variables influence the pool of available symbionts rather than how the abiotic environment structures the complex interaction system between a host plant and its symbiotic fungi. The question of whether plant-associated fungal communities are primarily driven by partner availability or by the selection of partners offering ecological advantages remains unclear. Here, a large-scale field survey investigated how the selected fungal communities within different Bistorta vivipara plant compartments (bulbils, leaves, and roots) varied with altitudinal stressors, respective to the available fungal species pool in the soil and other nearby plants. Our results revealed that while the selected species pool was largely determined by the available species pool, the occurrence probability of some fungi increased under specific conditions, relative to the respective available species pool. Furthermore, while we found that plant compartment is a major selective force shaping plant fungal interactions, environment-driven selection for specific fungi was observed across all compartments. We conclude that plant-fungal interaction networks along environmental gradients are not exclusively shaped by passive responses to partner availability but rather by more strategic selection of partners that may offer ecological advantages.