Allelopathic Effects Of Invasive Weeds On Arbuscular Mycorrhizae Of Native Plants

The role of allelopathy in the invasion of exotic weed has been concerned recently. The invasion of Solidago canadensis and Alternanthera pbiloxeroides, the most invasive weeds in South China, were thought due to their quick growth and population development. However, in our preliminary experiment we found that S. canadensis and A. pbiloxeroides inhibited native plants strongly. Therefore, we hypothesized that S. canadensis and A. pbiloxeroides may release allelochemicals into the surrounding environment to . inhibit other species. Several experiments were conducted to investigate the potential influence of S. canadensis and A. pbiloxeroides on seed germination, seedling growth and arbuscular mycorrhiza of native plants. Main results obtained from these experiments are as follows.1. Allelopathic effects of rhizome extract on native plants and their arbuscular mycorrhizae Biomass, AMF colonization and AMF spore numbers of Ageratum conyzoides decreased significantly in the treatment with rhizome extracts of Solidago canadensis. But extracts from rhizome of A. pbiloxeroides didn't impact on biomass and mycorrhizae of A. conyzoides.2. Responses of plant species and their AMF to the five fractions isolated from rhizome extractAll isolated fractions from extracts of Solidago canadensis inhibited the germination of A. conyzoides in low concentration. Fractions petroleum ether and normal butanol suppressed the root growth of A. conyzoides, but aqueous fraction stimulated the shoot growth of A. conyzoides, and other fractions exhibited no significant effects.All the fractions declined belowground biomass of A. conyzoides except aqueous fraction. The aboveground biomass of A. conyzoides was enhanced by aqueous fraction but was inhibited by ethyl acetone and normal butanol fractions. Ethyl acetone and normal butanol fraction reduced the biomass of A. conyzoides significantly. But aqueous fraction enhanced the biomass and other fractions had no significant effect. All the five fractions inhibited the AMF colonization of A. conyzoides, following the order aqueous phase > petroleum ether phase > dichloromethane and normal butanol > ethyl acetone phase.3. In-situ allelopathic effect of exotic weeds on native plants and their AMFS. canadensis and A. pbiloxeroides were cultivated for four months. The aboveground was removed and native plants were grown. The result show that native seed germination and biomass were reduced, the AMF colonization and spore number of native plants were inhibited under S. canadensis, but enhanced under A. pbiloxeroides.4. Native plants and their arbuscular mycorrhiza under species coexistenceBiomass and AMF colonization of A. conyzoides decreased in the mixture with S. canadensis without activated carbon. However, in the treatments with activated carbon biomass and AMF colonization of. A. conyzoides increased in the mixture with S. canadensis. No significant effects of A. pbiloxeroides was found in the mixture experiment.