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No abstract

The Eupatorium adenophorum have widespread invaded the karst ecosystem of southwest China and threatened the regional native community stability. Arbuscular mycorrhizae (AM) plays an important role in promoting growth for host plants via root external mycelia. However, whether AM regulates plant root traits underlying competition between invasive and native species via mycorrhizal networks in karst habitats, remains unclear. An experiment was conducted in a microcosm composed of two planting compartments flanking a competition compartment. The invasive E. adenophorum and native Artemisia annua were each placed in one of the two planting compartments with or without Glomus etunicatum fungus. The nutrient access treatments included the competitive utilization (Cu), single utilization (Su) and non-utilization (Nu) by using different nylon meshes allowed or prevented mycelium passing to acquire nutrients from the competition compartment. Root traits and nutrients of the two species were analyzed. The results showed that AM fungi had differential effects on root traits and nutrients of E. adenophorum and A. annua seedlings, which increased dry weight, length, surface area, volume, tips and branching points in roots, specific root length and volume, root nitrogen (N) and phosphorus (P) contents under Cu, Su and Nu treatments. AM fungus was also associated with decreases in the average diameter for both species. Under the Cu treatment, E. adenophorum had significantly greater length, surface area, volume, tips and branching points of roots, specific root traits, and root N and P than A. annua. AM fungi changed root phenotypes and nutrient uptake for both invasive and native plant species via interconnected mycorrhizal networks. Overall, our results suggest that through mycorrhizal networks, the invasive plant experiences greater benefits than the native plant in the nutrient competition, which fosters root morphological developments in karst soil.

In the karst landscape, widespread in the world including southern China, soil nutrient supply is strongly constrained. In such environments, arbuscular mycorrhizal (AM) fungi may facilitate plant nutrient uptake. However, the possible role of different AM fungal species, and their interactions, especially in transferring nitrogen (N) from litter to plant, is poorly understood. We conducted two microcosm experiments to investigate the role that two karst soil AM fungi, Glomus etunicatum and Glomus mosseae, play in the transfer of N from decomposing litter to the host plant and to determine how N availability influences these processes. In experiment 1, Cinnamomum camphora tree seedlings were grown in compartments inoculated with G. etunicatum. Lolium perenne leaf litter labeled with δN was added to the soil in unplanted compartments. Compartments containing the δN labeled litter were either accessible to hyphae but not to seedling roots or were not accessible to hyphae or roots. The addition of mineral N to one of the host compartments at the start of the experiment significantly increased the biomass of the C. camphora seedlings, N content and N:P ratio, AM mycelium length, and soil microbial biomass carbon and N. However, significantly, more δN was acquired, from the leaf litter by the AM hyphae and transferred to the host when mineral N was not added to the soil. In experiment 2, in which C. camphora seedlings were inoculated with both G. etunicatum and G. mosseae rather than with G. mosseae alone, there was a significant increase in mycelial growth (50.21%), in soil microbial biomass carbon (417.73%) in the rhizosphere, and in the amount of δN that was transferred to the host. These findings suggest that maintaining AM fungal diversity in karst soils could be important for mediating N transfer from organic material to host plants in N-poor soils.