Studies of the Italian ryegrass–rice rotation system in southern China: Arbuscular mycorrhizal symbiosis affects soil microorganisms and enzyme activities in the Lolium mutiflorum L. rhizosphere

•Viable AMF species especially G. versiforme could infect roots of Italian ryegrass.•Effects of the single and mixed AMF species differed in plant and soil properties.•Soil microorganism abundance and enzyme activities were promoted by AMF infection.•AMF did contribute to increases in N and P uptake of Italian ryegrass.

Greater understanding of roles of arbuscular mycorrhizal fungi (AMF) in roots of Italian ryegrass (Lolium mutiflorum L.) is required, particularly in the Italian ryegrass–rice rotation (IRR) system applied in southern China. Therefore, we examined growth of Italian ryegrass inoculated with either or both of two AMF species (Glomus mosseae and G. versiforme), and AMF-free controls, in pots. AMF in the roots promoted ryegrass biomass accumulation and affected both the soil microorganisms and rhizosphere enzyme activities. Inoculation with G. versiforme alone resulted in the highest percentage of mycorrhizal root colonization and highest soil urease activity. Inoculation with either AMF species alone also resulted in much higher ryegrass root dry weights than use of both species (P < 0.05), but the reverse was true for soil invertase activity and the abundance of soil fungi and actinomyces. We also explored effects of AMF on N and P uptake by the ryegrass, soil microbes and enzymes in a multi-compartment rhizobox experiment with two treatments: inoculation with viable and autoclaved G. versiforme. Despite a low root colonization percentage, the presence of viable AMF markedly increased: alkaline phosphatase and urease activities in the rhizosphere (P < 0.05); the abundance of ammonifying bacteria, nitrosobacteria, denitrifying bacteria and inorganic phosphobacteria; and both N and P uptake of the plants. Root N contents were positively correlated with both soil urease activity and soil denitrifying bacteria (P < 0.05), while shoot and root P contents were positively correlated with soil total P and available P, respectively (P < 0.05). Thus, AMF colonization clearly increased the abundance of soil microorganisms and enzyme (excluding invertase) activities, thereby enhancing N and P uptake of the ryegrass.