Abstract: The objectives were to investigate the effects of applying AMF and phosphorus on AMF infection of oat roots, soil microbial biomass, soil enzyme activity, as well as oat yield under drought stress, so as to develop AMF and phosphorus application guidelines for growing oat under drought. The experiment was conducted in pots for a total of 12 treatments, consisted of two levels of water supply, normal water supply (75% soil relative water content, W1) and drought stress (55% soil relative water content, W2), three levels of phosphorus supplement, 0, 20, and 40 mg·kg^-1 (P0, P1, P2), and two levels of AMF, inoculated (AMF) and not inoculated (NAMF). Root and soil samples were collected at the jointing, filling, and maturity stages to determine the AMF infection rate of oat roots, the soil MBC, MBN, and MBP, the soil sucrase, urease, and alkaline phosphatase activities. Oat yield was determined at maturity stage. The results showed that significant effects of soil water content, phosphorus, and AMF treatment were found on these indicators. Significant interactions among three factors were found on soil MBN  and soil sucrose activities. Under drought stress, compared with non-inoculated AMF, inoculated AMF significantly increased these indicators. Compared to P0, the AMF infection rate, the soil MBC, MBN, and MBP, the soil sucrase, urease, and alkaline phosphatase activities and yield significantly increased by 13.21%, 52.26%, 47.07%, 88.94%, 23.15%, 15.44%, 11.15% and 17.16% (the maximum value) with P1 application in oat growth period, respectively. However, these indicators tended to be reduced with further increasing of phosphorus application (P2). Therefore, AMF inoculation and a moderate application of phosphorus were effective ways to increase the  soil MBC, MBN and MBP, improve the activities of soil sucrase, urease and alkaline phosphatase, and increase oat yield under drought stress; however, the oat yield did not reach the level in normal water supply without AMF inoculation.

Key words: oat, drought stress, AMF, phosphorus, soil microbial biomass, soil enzyme activity