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.

中文翻译：

---

玉米单培养中长期添加氮减少了土壤传播的放线菌对放线菌标准的体外抑制。

管理土壤微生物群落以增强对作物病害的抑制是一种有吸引力的生物防治方法，但是农业实践对土壤微生物群落的疾病抑制潜力的影响仍然未知。我们调查了长期添加氮肥（103千克ha ^-1的尿素氮比不施用化肥）和作物残茬的掺入与去除对57年玉米（玉米）放线菌体外抗菌抑制能力的影响L.）明尼苏达州东南部的单一文化。我们假设氮和作物残渣的添加都会通过增加微生物种群密度来增加抑制剂的频率，从而增加微生物之间竞争性相互作用对其适应性的重要性。我们发现，尽管氮肥使土壤碳，氮和微生物密度（放线菌和总CFU数量）趋于增加，但体外培养的频率受精地中可培养放线菌的抑制表型大约是非受精地中抑制性表型的一半。残留物掺入对土壤化学，微生物密度和抑制剂频率几乎没有影响。这些结果表明，单独的密度介导的过程不能解释抑制剂对抑制剂频率的影响。抑制性表型的适应性成本和收益可能会随时间而变化，并且可能取决于资源修正的类型。