Soil fungi of three native tree species inhibit biomass production and shift biomass allocation of invasive Mikania micrantha Kunth

Soil microbes contribute to native plant species successful resistance against invasive plant. Three native tree species, Heteropanax fragrans (HF), Cinnamomum burmanii (CB), and Macaranga tanarius (MT) were effective in controlling the notorious invasive vine Mikania micrantha (MM). Biomass production and allocation patterns (shoot/root biomass ratio (shoot/root)) are important indicators of MM climbing coverage and competitive light-capturing capacity. An investigation was conducted to test the role of soil microbes associated with the three native tree species to inhibit MM biomass production and shift MM shoot/root. Rhizosphere soils originating from preculture HF, CB, MT, and MM plots were collected separately for use as inocula. The inocula were mixed with sterilized river sand at a 1:9 (w/w) ratio to grow MM. The fungicide carbendazim (methyl benzimidazol-2-ylcarbamate) was applied to half the treatments to kill pathogenic soil fungi. Two nutrient levels were established based on the natural soil nutrient concentration from a field stand invaded by MM. MM were grown from seeds in a glasshouse, harvested 15 weeks after sowing, and separated into shoot and root portions. Results showed that under interaction of soil origin and nutrient levels, MM biomass production was unchanged, but biomass allocation patterns were significantly different. MM biomass production grown in the three native tree soils under two nutrient levels was similar or higher than MM biomass production in MM conspecific soil, indicating the absence of species-specific pathogens that inhibited MM biomass production in native tree soils. However, in both conspecific and tree soils, MM biomass production was significantly reduced in the presence of pathogenic soil fungi, i.e. MM experienced significant fungal inhibition, demonstrating the pathogenic soil fungi promoted native tree resistence to MM. MM exhibited decreased shoot biomass allocation when cultivated in native tree soil relative to MM conspecific soil under field stand nutrient level conditions. Reduced resource allocation to shoot biomass could result in diminished capacity to climb, cover, and subsequent smother to native trees, and reduced surface area exposed to available light. Following fungicide application, significant biomass allocation differences disappeared, suggesting the native tree soil fungi were responsible for decreasing MM shoot biomass. The overall results indicated tree soil fungi serve an integral role in controlling invasive MM through fungal inhibition on MM biomass production, and shifts in MM biomass allocation patterns.