Long-term nitrogen addition in maize monocultures reduces in vitro inhibition of actinomycete standards by soil-borne actinomycetes

Abstract

Management of soil microbial communities for enhanced crop disease suppression is an attractive approach to biocontrol, but the effects of agricultural practices on the disease-suppressive potential of the soil microbial community remain unknown. We investigated the effects of long-term nitrogen addition (103 kg ha−1 nitrogen as urea versus no fertilizer) and crop residue incorporation versus removal on in vitro antibiotic inhibitory capacities of actinomycetes from 57-year maize (Zea mays L.) monocultures in southeastern Minnesota. We hypothesized that both nitrogen and crop residue addition would increase inhibitor frequencies by increasing microbial population densities and thus increasing the importance of competitive interactions among microbes to their fitness. We found that although soil carbon and nitrogen and microbial densities (actinomycete and total CFU counts) tended to be greater with nitrogen fertilizer, the frequency of in vitro inhibitory phenotypes among culturable actinomycetes in fertilized plots was approximately half that in non-fertilized plots. Residue incorporation had little to no effect on soil chemistry, microbial density, and inhibitor frequency. These results suggest that density-mediated processes alone cannot explain the effects of amendments on inhibitor frequencies. Fitness costs and benefits of inhibitory phenotypes may vary over time, and may depend on type of resource amendment.

The climate‐driven distribution and response to global change of soil‐borne pathogens in agroecosystems

“…In pathogen‐poor soils, the abundance and richness of pathogens might be less affected by competition among pathogens and biotic interactions with other microbes when faced with adverse conditions such as warming and nutrients (Delgado‐Baquerizo et al, 2020; Lekberg et al, 2021). By contrast, the more complex biotic interactions in pathogen‐rich soils could cause the abundance and richness of pathogens to gradually reach an upper asymptote limit in suitable environments, with competition leading to declines (Gieske & Kinkel, 2020; Wardle, 2006). More significant relationships found in the subsoil suggested that subsoil pathogens were more affected by the abrupt environment change, which might be associated with their indirect contact with the external environment.…”

Editorial to the Thematic Topic “Towards a more sustainable agriculture through managing soil microbiomes”

“…Elsayed, Grosch and Smalla (2021) demonstrated using cultivation-dependent techniques that the potato plant sphere, and to a lesser extent the soil type, affected the diversity and proportion of bacteria showing in vitro antagonistic activity towards the soil-borne pathogen Ralstonia solanacearum. Another study described that long-term nitrogen fertilization in soils under maize monoculture resulted in fewer actinomycetes with in vitro inhibitory capacities towards other actinomycetes compared to non-fertilized soils while crop residue incorporation showed no effect (Gieske and Kinkel 2020).…”