Effects of arbuscular mycorrhizal fungi on antioxidant metabolism and rhizo-spheric micro-organism of soybean (Glycine max) under drought stress

Arbuscular mycorrhizal fungi (AMF) not only improves nutrient absorption, but also enhances the resistance of host plant to stress such as drought. AMF inoculation has become one of the effective ways to resist drought stress. To explore the drought resistance mechanism of soybeans (Glycie max) inoculated with AMF, an experiment involving soybean variety 'Guichundou 103' as material was conducted. After inoculation with Claroideoglomus etunicatum (C.e), the effects of C.e on activities of antioxidant enzymes and C/N/P-cycle-related enzymes were investigated by collecting rhizospheric soil of soybean under drought stress. The changes in bacterial and fungal community diversities in rhizospheric soil were analyzed by denaturing gel gradient electrophoresis (DGGE) and other technologies. The results showed that activities of SOD, POD, sucrase, urease and phosphatase, free proline (FP) content, number and indexes of Shannon-Wiener diversity, richness and evenness of microorganisms in rhizospheric soil, as well as biomass and plant height of soybean with C.e inoculation (+AM) treatment were significantly higher than those without C.e inoculation (-AM) treatment under normal water supply condition. On the contrary, MDA content decreased significantly. Under drought stress (+D), MDA content with +AM treatment was lower and higher than that with -AM+D and +AM treatment, respectively. FP content was both higher than those of two treatments. The other indexes mentioned above along with band numbers of rDNA fragments of rhizospheric soil bacteria and fungi population were significantly higher than those with -AM+D treatment, and lower than those with +AM treatment. The bacterial and fungal communities of rhizospheric soil of -AM and -AM+D treatments belonged to different groups, while those of +AM treatment were clustered together with those of +AM+D treatment. In conclusion, +AM+D treatment obviously promoted the activities of antioxidant enzyme system, alleviated inhibition of drought on soil enzyme activities, kept high stability of cell membrane system, retained high population number and microbial structure diversity, promoted circulation and transformation of C, N and P in rhizospheric soil, improved drought resistance and effectively stimulated soybean growth. These results will lay a critical foundation for promoting sustainable development of agroecological systems.