Changed spatial configurations at sowing have been investigated as a strategy to minimize interspecific competition and improve the establishment and persistence of multi-species plantings in pastures, but the impact of this practice on the soil microbiome has received almost no previous research attention. Differences in populations of bacteria and fungi in the surface 10 cm of soil in the third year following pasture establishment were quantified using quantitative polymerase chain reaction and terminal restriction fragment length polymorphism methods. Populations were compared on, and between, drill rows sown to either the perennial grass phalaris (Phalaris aquatica L.), perennial legume lucerne (alfalfa; Medicago sativa L.) or the annual legume subterranean clover (Trifolium subterraneum L.). Results showed that soil microbial abundance and diversity were related to plant distribution across the field at the time of sampling and to soil chemical parameters including total carbon (C), mineral nitrogen (N), pH, and available phosphorus (P), potassium (K) and sulfur (S). Despite the 27-month lag since sowing, pasture species remained concentrated around the original drill row with very little colonization of the inter-row area. The abundance and diversity of bacterial and fungal populations were consistently greater under drill rows associated with higher total C concentrations in the surface soil compared with the inter-row areas. Our results showed that the pH and available nutrients were similar between the subterranean clover drill row and the inter-row, suggesting that soil microbial populations were not impacted directly by these soil fertility parameters, but rather were related to the presence or absence of plants. The abundance of bacteria and fungi were numerically lower under phalaris rows compared to rows sown to legumes. The richness and diversity of fungal populations were lowest between rows where lucerne was planted. Possible explanations for this observation include a lower C:N ratio of lucerne roots and/or a lack of fibrous roots at the soil surface compared to the other species, illustrating the influence of contrasting plant types on the soil microflora community. This study highlights the enduring legacy of the drill row on the spatial distribution of plants well into the pasture phase of a cropping rotation and discusses the opportunity to enhance the microbiome of cropping soils on a large scale during the pasture phase by increasing plant distribution across the landscape.

中文翻译：

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播种后第三个生长期牧草排上和排间土壤微生物丰度和多样性对比

播种时改变空间配置已被研究作为一种策略，以尽量减少种间竞争并改善牧场中多品种种植的建立和持久性，但这种做法对土壤微生物组的影响几乎没有受到先前的研究关注。使用定量聚合酶链反应和末端限制性片段长度多态性方法对牧场建立后第三年土壤表面 10 cm 中细菌和真菌种群的差异进行量化。在播种到多年生草蜉（鲶鱼L.)、多年生豆科植物苜蓿（紫花苜蓿；紫花苜蓿L.) 或一年生豆科植物地下三叶草 (三叶草L.)。结果表明，土壤微生物丰度和多样性与采样时田间植物分布和土壤化学参数有关，包括总碳（C）、矿质氮（N）、pH值和有效磷（P）、钾（ K) 和硫 (S)。尽管播种后滞后了 27 个月，但牧草物种仍然集中在原始的播种行周围，行间区域的定植很少。与行间区域相比，与表层土壤中较高的总 C 浓度相关的钻排下细菌和真菌种群的丰度和多样性始终较高。我们的结果表明，地下三叶草钻行和行间行之间的 pH 值和有效养分相似，表明土壤微生物种群不受这些土壤肥力参数的直接影响，而是与植物的存在与否有关。与播种豆科植物的行相比，在趾骨行下细菌和真菌的丰度在数值上较低。种植苜蓿的行间真菌种群的丰富度和多样性最低。对这一观察结果的可能解释包括与其他物种相比，苜蓿根的 C:N 比较低和/或土壤表面缺乏须根，这说明了不同植物类型对土壤微生物群落群落的影响。