An invasive plant experiences greater benefits of root morphology from enhancing nutrient competition associated with arbuscular mycorrhizae in karst soil than a native plant

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.

Fig 1. The experimental growth microcosmic device.

The experimental device consists of three compartments, two planting compartments (one for the native E. adenophorum and one for the invasive A. annua) on opposite sides flanking one competition compartment in the center. The size of each of the three compartments was about 10 cm × 10 cm × 10 cm (length × width × height). Five circular holes were drilled on a baffle plate separating the planting compartments and the competition compartment. 20μm or 0.45μm nylon meshes were attached to both sides of the baffle plate to form an air gap to prevent the flow of nutrients among compartments. The 20μm nylon mesh allows mycelium to pass through, but the plant roots cannot; the 0.45μm nylon mesh does not allow either mycelium nor plant roots to pass through. More detailed description in the text. Pc = planting compartment; Cc = competition compartment.

Fig 2. Root dry weight of invasive E. adenophorum and native A. annua.

Abbreviations: M⁺ = Mycorrhizal fungus was used to inoculate seedlings of E. adenophorum and A. annua; M^- = Mycorrhizal fungus was not used to inoculate seedlings of E. adenophorum and A. annua; Cu = Competitive utilization nutrient treatment; Su = Single utilization nutrient treatment; Nu = Non-utilization nutrient treatment. Lowercase letters (x, y) indicate significant differences between M⁺ and M^- treatments of invasive E. adenophorum and native A. annua at the 0.05 level; lowercase letters (a, b, c) indicate that there are significant differences among Cu, Su and Nu treatments for invasive E. adenophorum and native A. annua at the 0.05 level; Greek alphabet (α, β) indicate that there are significant differences between E. adenophorum and A. annua at the 0.05 level.

Fig 3. Phenotypic traits of roots of invasive E. adenophorum and native A. annua.

See Fig 1 for an explanation of M⁺, M^-, Cu, Su and Nu, lowercase letters (a, b, c) and (x, y) and Greek alphabet (α, β).

Fig 4. Numbers of root tips and branching points of invasive E. adenophorum and native A. annua.

See Fig 1 for an explanation of M⁺, M^-, Cu, Su and Nu, lowercase letters (a, b, c) and (x, y) and Greek alphabet (α, β).

Fig 5. Specific root traits of invasive E. adenophorum and native A. annua plants.

See Fig 1 for an explanation of M⁺, M^-, Cu, Su and Nu, lowercase letters (a, b, c) and (x, y) and Greek alphabet (α, β).

Fig 6. N and P contents in roots of invasive E. adenophorum and native A. annua.

See Fig 1 for an explanation of M⁺, M^-, Cu, Su and Nu, lowercase letters (a, b, c) and (x, y) and Greek alphabet (α, β).