Ecology Of Arbuscular Mycorrhizal Associations In Flaveria Bidentis, An Invasive Alien Plant

Mycorrhizal is a plant-fungal symbiont widely distributed in natural world, which come into beingwith specific soil fungi, affect the balance and stability of ecosystem by enhence the growingpower andcompetitiveness of host plants. Flaveria bidentis is a typical mycorrhizae plant native to South America,which invade our country of in recent years. There were significant theory of meaning and practicalvalues to examine the relation bewteen F. bidentis and arbuscular mycohrrizal (AM) fungi and theinfluence of arbuscular mycohrrizae on the performances of F. bidentis under changing environmentconditions. The main results were summarized below.1. By using the methods of PCR-DGGE, this paper studied the genetic diversity of AM fungi undervarious microhabitats (roadside, waterside, orchard, wasteland and farmland) in Cangzhou of HeBeiprovince, aimed to explore the AM fungi genetic diversity of F. bidentis. Results show that the AMfungi genetic diversities in all five microhabitat types were rich. The waterside soil had more kinds ofAM fungi, but less were found in the roadside one. Gene sequencing demonstrated that there were15species of AM fungi were identified from the soil samples invaded by F. bidentis. But the differentspecies of AM fungi appeared in the different ecological environments, such as Glomus etunicatum onlywas found in waterside and farmland, Glomus mosseae appeared in every microhabitats. Glomus wasthe dominant genera at the soil of growing with F. bidentis.2. We manipulated P and water availabilities to check the roles of mycorrhizal associations on F.bidentis by pot experiments, AM fungi were controlled by benomyl. It was shown that mycorrhizalassociations weaken the influence of environmental stresses on the growth of F. bidentis by increasingthe biomass accumulation and activity of protective enzymes of plant. Simultaneously, the degree ofhost plant benefits from AM fungi varied with environment condition. The contribution rate ofmycorrhizal to host plant increased with the water stress level, the treatment of serious stress is1.84and1.88times higer than the waterlogging condition respectively. But the treatment of P were different fromthe water stress, the N, P contribution rate of mycorrhizal to F. bidentis were all above to70%with Pdeprivation（P0）, which is the highest of all, but when the P were abundant（P4）, the contribution rateof mycorrhizal were reduced and the N, P contribution rate of mycorrhizal were-9.62%and-42.18%respectively.3. A pot experimentd was carried out to examine the effects of AM fungi on the competitiverelationship between F. bidentis and Amaranthus retroflexus (a native species), and AM fungi werecontrolled by benomyl as above. Experiment results indicated that relative yield (RY) of F.bidentis waslower than1.0regardless of planting proportion, Accordingly, RY of A.retroflexus were all above1.0atthe same time, the relative yield total (RYT) of both vegetations were less than1.0at differentproportion, the result implied that the F.bidentis and A.retroflexus make use of the same resource andthat the later competitiveness was stronger than the former. The competition experiments showed thatAM fungi affected the relative competitive ability of F.bidentis significantly rather than one ofA.retroflexus. Thus, AM fungi regulates the relation between alien plants and native plants by affect the different absorb mechanism of soil nutrient.Based on the results presented in these studies, it was concluded that mycohrrizal associations maycontribute significantly to the invasion of F.bidentis in newly erclaimed habitats. Mycohrrizalassociations could improve the fitness of F.bidentis to withdraw the adverse conditions. AM fungi couldalso regulate the pattems and intensity of interspecific competition between F.bidentis and nativespecies. The environment condition might affect the symbiosis status.