Plant-soil feedback contributes to intercropping overyielding by reducing the negative effect of take-all on wheat and compensating the growth of faba bean

Abstract

Overyielding in intercropping compared to monoculture has been widely reported. One of the mechanisms may be the alteration of the microbial community in intercropping and especially the amelioration of the negative effects of pathogens that can accumulate in monocultures. Here we test whether inoculation with arbuscular mycorrhizal fungi (AMF) and wheat take-all disease influences overyielding and whether changes in the microbial communities generate feedbacks on plant growth. In Experiment 1, wheat and faba bean were grown in monoculture or intercropping to form three planting patterns. Plants were inoculated with or without wheat take-all disease (Gaeumannomyces graminis), and one, six, or no AM fungi, to create 6 soil conditioned treatments. Soils from Experiment 1 were used as inocula in Experiment 2 to test the feedback on plant growth from monocultures and the legacy benefits of intercropping. No significant influence of AMF on plant growth was observed in either experiment. In Experiment 1, AMF had no significant effect in suppressing take-all but take-all tended to decrease AMF colonization. Shoot biomass and competitive ability of wheat was suppressed by take-all in both experiments. Wheat and faba bean showed overyielding in both the take-all and non-take-all treatment in Experiment 1 but only overyielding in the take-all treatment in Experiment 2. Growth of wheat and faba bean were suppressed in conspecific soil, and this negative feedback was observed across all take-all and AMF treatments, and regardless of competition. Biomass of wheat and faba bean was higher in soil from intercropping than in monoculture soil, and this positive legacy benefit of intercropping did not depend on take-all, AMF or plant competition. We find support for alterations of the soil community causing negative plant soil feedback and positive legacy benefits of intercropping. Our results are consistent with microbial dynamics generating overyielding in intercropping by reducing the negative influence of soil pathogen build-up on conspecific host plants and simultaneously compensatively improving growth of neighbor plants.