Allelopathic Effects Of Invasive Weed Solidago Canadensis L. On Native Plants And Their Arbuscular Mycorrhizae

The role of allelopathy in the invasion of exotic weed has been concerned recently. Canadensis goldenrod (Solidago canadensis L.), introduced from north America, developed quickly in southeastern China in past decades. The primary hypothesis for the astonishing success of Solidago canadensis invading into southern China is that it has developed its population by producing highly fertile seeds and propagule in its foreign land. However, in our preliminary experiment we found that S. canadensis grew in dense stands, essentially monospecific, without native coexistence. Therefore, I hypothesized that S. canadensis release allelochemicals into the surrounding environment to inhibit other species. The experiments were conducted to investigate the influence of root extract, rhizome extract and its isolated components of Solidago canadensis on seed germination, seedling growth and arbuscular mycorrhiza of native plants. Main results obtained from these experiments are as follows:1 Allelopathic effects of root and rhizome extract on native plantsBoth root and rhizome extract inhibited the seed germination and seedling growth of Trifolium repens and the inhibitory effect enhanced when the concentration increased. Furthermore, rhizome extract showed greater inhibition than root extract under the same concentration. Root and rhizome extract of Solidago canadensis inhibited Trifolium repens's root much more significantly than shoot. And root extract with high concentration (1:15, m/m) inhibited the shoot growth of Trifolium repens, while root extract of low concentration (1:60, m/m) promoted shoot growth.2 Allelopathy of rhizome extract and the tractions on different plantsEleven native plant species in orchard ecosystem, including Trifolium repens, Trifolium pretense, Medicago lupulina, Lolium perenne, Suaeda glauca, Plantago virginica, Kummerowia stipulacea, Festuca arundinacea, Ageratum conyypides, Portulaca oleracea, Amaranthus spinosus, responded differently to rhizome extract at the lowest concentration (1:60, m/m). The effect of rhizome extract on seed germination was similar to that on root growth, i. e. the suppression both on seed germination and root growth, were the greatest in grass, followed by forb. However, rhizome extract showed little effect or stimulative effect on the seed germination and root growth in legume. But for shoot, the extract could inhibit Kummerowia stipulacea, Amaranthus spinosus, Festuca arundinacea, but had nosignificant impact on Lolium perenne, Plantago virginica, Ageratum cony^oides, Vortulaca oleracta, Amaranthus spinosus and stimulated Trifolium repens, Trifolium pretense, Medicago lupulina.Five fractions isolated from rhizome extract of the lowest concentration also showed different influences on Trifolium repens, Kummerowia stipulacea and Ageratum conyyoides. The fractions isolated by dichlorome thane, ethyl acetone and normal butanol slowed down the germination of Trifolium repens, while other components showed no significant effect. All the five fractions stimulated the germination of Kummerowia stipulacea at the beginning of the germination but inhibited that of Ageratum cony^oides in the whole process of germination. Aqueous and normal butanol fraction suppressed the root growth of Trifolium repens, petroleum ether and normal butanol fraction suppressed the root growth of Ageratum cony^pides. Aqueous fraction stimulated the shoot growth of Ageratum conyyoides, and others exhibited no significant effects.3 The influence of rhizome extract on AMF colonization of native plants AMF colonization of both Echinochloa crusgalli and Ageratum cony^oides decreased significantly in the treatment with rhizome under monocultures.4 AMF colonization under species coexistenceWhen coexisting with Echinochloa crusgalli or Ageratum cony^oides, Solidago canadensis enhanced the AMF colonization of Echinochloa crusgalli but reduced Ageratum conyyoidete AMF colonization when coexisting with these species. In the coexisting with Solidago canadensis with activated carbon, Ageratum cony^oides showed great increase in AMF colonization while Echinochloa crusgalli decreased its AMF colonization. For Solidago canadensis, the treatment with activated carbon AMF colonization increased coexisting with Ageratum conyvpides, while the AMF colonization decreased coexisting with Echinochloa crusgalli.5 Response of plant species to the five fraction isolated from rhizome extract All the fraction declined belowground biomass of Ageratum cony^oides except aqueous phase. The aboveground biomass of Ageratum cony^oides 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 Ageratum cony^oides significantly, but aqueous fraction enhanced the biomass and other fractions had little effect. All the five fractions inhibited the AMF colonization of Ageratum cony^oides, following the order: aqueous phase > petroleum ether phase > dichloromethane and normal butanol > ethyl acetone phase.