| The absolute symbiosis between majority of land plants and arbuscular mycorrhizalfungi (AMF) is probably the most abundant and wide spread mutualism on earth.AMF not only enhance plant productivity and plant nutrition, AMF can also promoteplant disease suppression, drought resistance and influence plant community structure,plant diversity and ecosystem functioning. The aim of this studies are (1) to isolateAM fungal species from Hubei cultivated soil, screen efficient isolates for inoculationin agricultural practice, and detect AM fungi in fields at molecular level; (2) toinvestigate the competitive behavior of several AM fungi using nested PCR withspecies-specific primers, which cannot be distinguished based on fungal structures; (3)to investigate the influence of agricultural practices on soil microbial activitymeasured by calorimetry.25 AM fungal isolates were obtained from more than 80 soil samples. The majorityof them were the members of Glomus. 15 isolates were identified as new species inChina and 17 species were registered in International Bank for the Glomeromycota(IBG).High efficient isolates HAU-01 (Glomus constrictum) and HAU-E4 (G. etunicatum)were screened as species for filed trial by pot culture in glasshouse conditions. Thefield trials were carried out by means of producing pre-inoculated seedlings prior totransplanting. The yield of the maize inoculated with HAU-01 and HAU-E4 wassignificantly enhanced 10.84% and 5.06%, respectively. The content of starch ingrains was also increased 4.23% and 3.54%, respectively.Three species of AM fungi, G. intraradices, G. mosseae and Acaulospora laeviswere detected in fresh root fragments by means of nested PCR with species-specificprimers. The competitive behavior of three AM fungi cannot be distinguished basedon fungal structures within same root system was monitored in this work. Roughlyextracted DNA from fresh root was amplified by using universal eukaryotic primers.The PCR products were diluted and used as template for the second PCRamplification using species specific primers respectively. The results showed below.(1) The infection rate of G. intraradices was higher than the rate of G. mosseae whenthey were co-inoculated plant, the difference was larger especially in new colonizedroots. (2) Three AM fungi were detected within same root fragment 1 cm in length. (3)The infection rate of three fungi was changed at different harvested stage. Thecompetitive interaction between G. intraradices and G. mosseae was observed, but the interaction between fungus of A. laevis and other fungi was not tight when three fungico-existed in root system. In addition, the ability of mycorrhizal effect of these fungiis different. The effect of G. intraradices is persistent compared with slow increaseshowed by other fungi.Two introduced species of AM fungi, G. intraradices and G. mosseae weresuccessfully detected in the plant roots from fields using nested PCR technique. Thisstudy hasmade it possible to assess potential ability of introduced efficient species ofAM fungi at molecular level and understand the interactions between AM fungi andother microorganisms in fields.To investigate the influence of different agricultural practices and vegetations onsoil microbial activity, soil samples from different land were studied by calorimetry.All power-time curves presented typical changes of microbial activity. The curves ofsoil samples could be divided into two groups differing in agricultural practices andvegetations. The most soil samples showed a significant positive correlation betweenthe values of microbial growth rate and the number of bacteria. A very highdissipative metabolism for sample F1 was observed, which suggest F1 is degradingorganic matter under stress. The values of total heat agreed with vegetation abundanceand probably with microbial diversity. In conclusion, microbial activity of the soilsamples determined by calorimetry reflected differences in soil due to agriculturalmanagement.
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