Promotion effect of AM fungi and rhizobia co-inoculations on alfalfa (Medicago Sativa L.) growth

Arbuscular mycorrhizal fungi (AMF) and rhizobia have been widely used in agriculture in recent years to increase production, reduce fertilizer consumption and control plant diseases. However, it is unclear whether there are differences in the effects of AMF and rhizobia inoculation alone and in combination. In this study, alfalfa seedlings were inoculated with AMF Glomus mosseae (G.m), Glomus intraradices (G.i) and co-inoculated with AMF and rhizobia Sinorhizobium meliloti (S.m) before being transplanted outdoors. The growth characteristics, fine root yield and fine root death of alfalfa were measured throughout the experiment, and the results showed that co-inoculation with AMF and rhizobia promoted alfalfa growth, while increasing plant height, branch number and total biomass. However, the growth promoting effects of AMF and rhizobia differed; AMF inoculation displayed no advantage over S.m inoculation in increasing aboveground biomass (P > 0.05) but did lead to an increase in underground biomass (P < 0.05). Compared with that observed following the single inoculations with G.m or S.m, the annual fine root production following co-inoculation with G.m and S.m increased by 15.38% and 47.06%, respectively, although there was less effect following co-inoculation with G. i and S.m. These results indicated that there was mutual selectivity and interaction between AMF and rhizobia. G.m and S.m inoculation treatment has a positive effect on alfalfa growth, on the one hand, it is because that AMF-Rhizobia synergically promoted alfalfa root system to absorb nutrients (N), then improve the plant growth, on the other hand, their vaccination can reduce the death of alfalfa fine roots, significantly improve the alfalfa biomass of underground part.