Feedback of soil biota on Ageratina adenophora growth and competitiveness with native plant: A comparison of different sterilization methods

Soil sterilization is often used to explore feedback effects of soil microbes in community successions of competitive exclusion of native plants by invasive plants. In order to choose the most suitable soil sterilization method and to further analyze feedback effects of soil microbes on invasive plant Ageratina adenophora competition with native plants, we compared the differences in biomass between A. adenophora and native plant Rabdosia amethystoides cultured in sterilized soils. The tested soil sterilization methods in the study included dry-heating sterilization, autoclaving sterilization and irradiation sterilization. Non-sterilized soil was the control. In order to mitigate effects of sterilization on soil physico- chemical properties, vermiculite was added to soils sterilized with different methods. The results showed that sterilization by the three methods significantly decreased A. adenophora and R. amethystoides biomass, regardless of vermiculite addition. For the three different sterilization methods, adding vermiculite to soil promoted the growth of A. adenophora and R. amethystoides whereas plant biomass in non-sterilized soils was not affected by vermiculite addition. A. adenophora and R. amethystoides biomass under irradiation sterilization soils plus vermiculite was 30.8% and 66.5% higher than that under dry-heating and autoclaving sterilization soils with vermiculite, respectively. Then R. amethystoides biomass under irradiation sterilization soils plus vermiculite increased by 109.5% and 63.4% compared with that in dry-heating sterilization or autoclaving sterilization soils plus vermiculite, respectively. Plants in gamma irradiated soils had the highest plant biomass among the soils subjected to the three sterilization treatments. Through mixed pot experiment of A. adenophora and R. amethystoides under irradiation sterilization soils plus vermiculite and non-sterilized soils plus vermiculite, we found that soil microbes enhanced the competitive ability of A. adenophora over the native plant R. amethystoides and relative competitive advantage increased by 16%. These results indicated that irradiation sterilization soil plus vermiculite treatment was efficient in pot experiment studies on feedback effects of soil microbes on plants. Soil microbes exerted positive feedback during invading process of invasive plant A. adenophora.