Studies On Dark Septate Endophytes (DSE) In Munai And Gejiu Mine Area In Yunnan

Bioremediation of heavy metal contaminated soil is an important way to heavy metal pollution control, making use of the association of microorganisms and plants to restore heavy metal contaminated soil was an important aspect in this field. Dark septate endophytes (DSE) comprise a heterogeneous assemblage of fungi that inhabit the roots of health plants. DSE may assume the role of AMF in certain habitats. Choosing Munai and Gejiu, two major mine areas of Yunnan province as the studied sites, we surveyed the colonization of DSE in plant roots, isolated the DSE strains from the roots, identified based on morphological observation and molecular analysis. Nine dominant DSE strains were selected to test their tolerances to Cd2+ in vitro, besides, the effects of Cladosporium sp. (z113) inoculation on both growth performance and Cd2+ tolerance of maize were studied by pot cultivation experiments. Results of the thesis were as follows:1. The DSE colonization frequencies of sampled plants in Munai and Gejiu were 71% and 90% respectively. This result indicated that most of plants in two studied sites were colonized by DSE, moreover, all dominant plant species were colonized by DSE.2. In this thesis, 40 and 55 strains of DSE were isolated from 110 plant root samples collected in Munai and 108 plant root samples collected in Gejiu respectively. Morphological characters and phylogenic analysis based on their sequences of ribosome ITS1-5.8S rDNA-ITS2 showed that most of the isolates belong to ascomyetes, including Phoma, Schizothecium, Exophiala, Lophiostoma, Thysanorea, Cladophialophora, Phialophora, Phialocephala, Leptodontidium, Leohumicola, Pleosporales, Pyrenochaeta. Cladosporium and Leptodontidium were the dominant genera of Munai and Gejiu respectively. Presumably, plant species or many ecological factors including the physico-chemical properties of soils and contents of heavy metals may influence the diversity and communities of endophytic fungi colonized in the plant roots. 3. The nine tested dominant strains belonging to Cladosporium, Helicoma, Exophiala and Cladophialophora could colonize the roots of maize in vitro. Typical structures of DSE were observed in the roots of maize, without causing plant disease symptoms. Moreover, the tested fungi could be re-isolated from roots of maize. Among the tested isolates, Exophiala,Cladophialophora were generally accepted as DSE by informed studies, however, Cladosporium and Helicoma were proved to be plant pathogens in previous reports, which suggested that judged by the morphological characteristics within root cells of host plants, more fungi can possibly be categorized into DSE.4. Promising inoculation effects of Cladosporium sp. (Z113) on maize were observed in pot experiments. Under Cd2+ stress of 7 different concentrations, Cladosporium sp. (Z113) unexceptionally enhanced the biomasses of maize, and improved the tolerance of host plant to Cd2+, and the excessive Cd2+ were mainly biostabilized in the roots which effectively alleviated the toxicity to host plant.