Activity, diversity and function of arbuscular mycorrhizae vary with changes in agricultural management intensity

Many beneficial soil microbes are sensitive to chemical and mechanical disturbances associated with conventional row crop agriculture, including arbuscular mycorrhizal (AM) fungi. AM fungi provide agricultural benefits through multiple mechanisms including increasing crop pathogen resistance, helping with crop nutrient acquisition, and increasing soil carbon storage. Conversion to less intensive row crop agricultural management systems such as biologically-based organic and no-till may reduce the negative effects of conventional management to AM fungi. In this study, AM fungus activity (via glomalin production), spore diversity, community structure, and community stability were surveyed over 20 years in no-till, biologically-based organic, and conventionally managed plots at the W.K. Kellogg Biological Station Long Term Ecological Research Site in Michigan, USA. A complementary greenhouse experiment tested for direct effects of AM fungal inocula from these different agricultural management treatments on growth of corn and wheat plants. Soil glomalin increased in no-till and organic management systems, most likely due to decreases in disturbance associated with tillage and chemical inputs. No-till management slightly increased AM fungus diversity and community stability. AM fungus community structure significantly differed between conventional and no-till treatments, with an indicator species analysis showing that Acaulospora spp. were characteristic of conventional management, while Glomus spp. and Gigaspora spp. were associated with no-till management. AM fungal inocula from organically-managed treatments increased wheat, but not corn, growth. Overall, conversion from long-term conventional row crop agricultural management to no-till or biologically-based organic systems increased soil glomalin, but did not uniformly improve AM fungus diversity or crop plant benefits. In the future, novel agricultural systems combining organic management with conservation tillage may further improve AM fungal benefits to soils and crops.