Eupatorium adenophorum is an alien species that threatens community stability and diversity in karst areas. Arbuscular mycorrhizal (AM) fungi form interconnected mycorrhizal network, connecting adjacent plants and plant species. How mycorrhizal networks affect the competition for nutrients between invasive and native plants in karst habitat remains unclear at present. An experiment was conducted using a compartmental growing device, which was composed of two planting compartments (for the invasive E. adenophorum or native Artemisia annua) and a competitive compartment (for the interconnected mycorrhizal network). The experiment contained mycorrhizal fungus treatments, with AM fungi (M⁺) and without AM fungi (M⁻) using the species Claroideoglomus etunicatum, and the nutrient utilization treatments using nylon mesh to interconnective mycorrhizal networks, including common utilization (Cu), single utilization (Su), and non-utilization (Nu). The results showed as follows: AM fungi differentially increased biomass, nitrogen (N) acquisition and phosphorus (P) acquisition and significantly reduced N/P ratio of the invasive E. adenophorum and native A. annua under Cu, Su, and Nu conditions. Additionally, the biomass, N acquisition and P acquisition of E. adenophorum was greater than A. annua and the N/P ratio of E. adenophorum was significantly lower than A. annua under Cu condition, which AM fungi promoted the accumulation of biomass, N and P for E. adenophorum and A. annua, and E. adenophorum experienced a greater reduction of P limitation than A. annua via the interconnected mycorrhizal network. In conclusion, we suggest that AM fungi endow invasive plants greater alleviation of P limitation and enhancement of nutrient competition than native plants via mycorrhizal network in low-P karst soil.

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.

How arbuscular mycorrhizal (AM) fungi affect litter nutrient release and soil properties in the nutrient-deficient karst soil, is unclear. An experiment was conducted in this study using a dual compartment device composed of a planting compartment (for the Cinnamomum camphora seedlings with or without Funneliformis mosseae fungus) and a litter compartment (with or without the litter of Arthraxon hispidus). The center baffle between the compartments was covered with a double layer of 20-µm or 0.45-µm nylon mesh, which controlled the entrance of AM mycelium into the litter compartment. The results are as follows: AM mycelium significantly increased the mass loss and carbon and nitrogen releases and decreased the nitrogen concentration in the litter. AM mycelium could significantly increase soil organic carbon, total nitrogen and availability of phosphorus during litter decomposition in the litter compartment. Redundancy analysis showed that the effect of AM mycelium on the soil organic carbon, total nitrogen in the litter compartment was closely associated with the increase in carbon and nitrogen release from litter. It was concluded that AM mycelium can enhance litter decomposition and nutrient releases, contributing to greater nutrient input to the soil and then subsequently higher soil organic carbon and nutrient content in the nutrient-poor karst soils. STATEMENT OF NOVELTY This study firstly estimated the impacts of arbuscular mycorrhizal fungi on litter nutrient releases and soil properties through root external mycelium