The Hyphosphere Interactions Between An Arbuscular Mycorrhiza Fungus And Phosphate Solubilizing Bacteria In Relation To Improving Organic Phosphate Utilization

Arbuscular mycorrhizal (AM) fungi produce massive extraradical hyphae in the soil which secrete carbon (C) compounds and attract other soil microbes to colonize in the hyphosphere. The intimate relationships between AM fungi and hyphosphere microbes have significant influence on the ecological functions of AM fungi. More than 40% of soil culturable bacteria have the ability to mobilize soil organic phosphorus (P) (the so called phosphate solubilizing bacteria, PSB), and the interaction between AM fungi and PSB may play important roles in organic P utilization.Three systems, the microcosm and bi-compartment Petri plate to culture the plant and the bi-compartment Petri plate to culture the Ri T-DNA transformed root and the AM fungal strains Rhizophagus intraradices BEG 141, Rhizophagus irregularis DAOM 197198 and PSB strains Bacillus megaterium C4, Rahnella aquatilis HX2 were selected to study the AM fungi-PSB interactions from the soil chemical processes, microbial physiological and biochemical processes to microbial genes expression. The main results were following:(1) AM fungal strain R. irregularis DAOM 197198 doesn’t have the ability to mobilize organic P and PSB play a role in organic P hydrolyzation. After hydrolyzing by phosphatases to release inorganic P, the organic P can be used by AM fungi. Under axenic condition, however, AM fungi had no influence on phosphatase activities in the medium; PSB increased phosphatase activities significantly and enhance the hydrolyzation of organic P.(2) AM fungi hyphal exudate contains high concentration of C compounds which can stimulate PSB to mobilize organic P. On the one hand, bacteria used hyphal exudate as C source to enlarge the bacterial number. On the other hand, fructose in the hyphal exudate could play a role as signal molecular to stimulate bacterial phosphatase genes expression in a short time.(3) PSB increased inorganic P uptake and transfer by extraradical hyphae of AM fungi. On the one hand, PSB stimulated the hyphal length to enlarge the absorbed volume. On the other hand, PSB increased the hyphal high-affinity P transporter and polyP synthetase genes expression.(4) AM fungi-PSB interactions can be regulated by adding inorganic P. In the low available P soil, though PSB mobilized organic P, they acquired the released inorganic P and competed with AM fungi. When a small amount of inorganic P was added to decrease the soil C:P, the competition between AMF and PSB could be lessened.In the present study, three systems were used to study the interactions between AM fungi and PSB to improve organic P utilization. The results increased our knowledge of the ecological functions of AM fungi and the biological interactions in the hyphosphere. The regulation of the AMF-PSB interactions by adding a small amount of inorganic P may have significance on improving organic P utilization by playing roles of AM fungi in the fields.