Abstract: Vegetation recovery in karst region is limited by poor availability of soil nutrients. Root plays an important role in the growth and development of seedlings. Arbuscular mycorrhizal fungi (AMF) can promote dry matter accumulation and stress resistance of karst plants, whereas the mechanism and effect of AMF infection on roots of main restoration tree species in karst area remain largely unknown. In this study, the effects of AMF on growth, root architecture of Zenia insignis in karst soil with different nutrient levels were evaluated in a greenhouse experiment. There were four inoculations of arbuscular mycorrhizal fungi: Funneliformis mosseae (Fm), Rhizophagus intraradices (Ri), their mixture inoculation (Mi) and no inoculation (CK), and two nutrient levels. Under lownutrient level, Fm treatment significantly increased root architecture parameters. The inoculated plants had the maximum colonization rate, and aboveground biomass, root biomass, total biomass, the numbers of tips, forks and crossings and projected area were increased by 2.50, 5.60, 3.67, 3.03, 3.78, 3.66 and 3.56 times than CK, respectively. Ri treatment did not affect aboveground biomass, root biomass, total biomass and the number of forks, but decreased the numbers of tips and crossings and projected area by 46.59%, 50.00%, and 38.60%, respectively. Mi treatment increased aboveground biomass, root biomass, total biomass, the numbers of forks and crossings and projected area by 3.02, 3.47, 3.14, 1.64, 1.60 and 1.70 times, respectively, but did not affect the number of tips. Under highernutrient level, Fm treatment increased root biomass and projected area by 2.38 and 1.51 times respectively, did not affect aboveground biomass, total biomass, the numbers of forks and crossings, but decreased the number of tips by 22.82%. Ri treatment increased root biomass, total biomass, the numbers of tips and crossings and projected area by 2.29, 1.37, 1.31, 1.29 and 1.66 times, but did not affect aboveground biomass and the number of forks. Mi treatment increased aboveground biomass, total biomass, the number of tips and projected area by 1.44, 1.46, 1.25 and 1.40 times, but did not affect root biomass, the numbers of forks and crossings. Collectively, inoculation with F. mosseae significantly increased root architecture parameters and plant growth under low-nutrient soil.R. intraradices had a positive impact in soils with low calcium and high phosphorus contents. F. mosseae has extensive ecological adaptability and facilitates resource uptake of roots and root spatial expansion in soils, showing high application potential for vegetation restoration under low-nutrient karst soil.

Key words: arbuscular mycorrhizal fungi, karst soil, Zenia insignis seedling, biomass, root, architecture character.