Studies On Dark Septate Endophytes (DSE) In The Dry-hot Valley Of Yuan River, Yunnan Province

An area of valley-type savanna and an over-grazed area in the dry-hot valley of Yuan River were chosen as the study site to study the colonization status of dark septate endophytes (DSE) and arbuscular mycorrhizal fungi (AMF).DSE strains were isolated from these areas and their possible taxonomic placements were phylogenetic analysized based on their sequences of ribosome ITS1-5.8S rDNA-ITS2.Two isolations among these strains were selected for the study of fungal solution ability of the insoluble inorganic phosphorus and dissolved organic phosphorus. The results were as follows:The colonization status of DSE and AMF in these areas showed that the colonization frequency of DSE and AMF in plants representing 25 species, 16 families were respectively 64% and 92% in the savanna-type vegetation area and the colonization frequency of DSE and AMF in plants representing 22 species, 12 families were respectively 68% and 95% in the over-grazed area. All plants in the sampled sites were colonized either by AMF or DSE. Differences of AMF and DSE colonization extents in plants were not exist between the two sampled sites. Variance analysis indicated that few differences in the colonization extent of AMF hyphae, vesicles and arbuscular. Difference was observed only in a few plants.Forty-three DSE strains were isolated from natural growth plants roots in the two sample areas. Fourteen strains were isolated from the savanna area and 29 were isolated from the over-grazed area. The isolating rate was 15.4% and 18.8% respectively. Most strains were sterile. According to the phylogenetic tree of these strains based on their ribosome ITS1-5.8S rDNA-ITS2, strains grouped with Phialocephala fluminis and Cercophora mirabilis were dominant in the dry-hot valley of Yuan River. Two representative strains, 6-26 and 7 were selected to study the fungal solubility of the insoluble inorganic phosphorus and dissolved organic phosphorus. It was found that both of them were able to dissolve the insoluble inorganic phosphorus and dissolved organic phosphorus to some extent. For the strain 7, the ability of dissolving inorganic phosphorus was stronger. While the ability of dissolving inorganic phosphorus and organic phosphorus was almost the same for the strain of 6-26. These results expended our knowdege about of fungi which could dissolve phosphorus and supplied theoretic evidence to the assumption that DSE might improve the host plants on the absorption of insoluble phosphate in dry-hot ecosystem.