Plants can have strong effects on soil biota and thus subsequent plant growth in those soils. In agroecosystems, these microbe-mediated plant-soil feedbacks (PSFs) can have strong positive or negative effects on subsequent crop growth, but how multiple factors including the identity of the species involved, crop diversity and soil characteristics influence PSF is poorly understood. To address this knowledge gap, we focus on alfalfa (Medicago sativa), the globally most common forage legume. We sampled plants and soils from 24 alfalfa stands evenly split between alfalfa monocultures and grass-alfalfa mixtures of varying ages. Using the soils from these sites, we conducted an experiment to quantify how the conditioning plant community and soil characteristics altered PSF effects on four alfalfa varieties and five additional native and non-native grass and legume forage species. Alfalfa monocultures generated more negative PSF than mixtures overall, indicating dilution of antagonistic soil biota in more diverse stands. Differences among varieties and species were idiosyncratic: one alfalfa variety had positive PSF in mixture soils, whereas one legume species (Trifolium pratense) had positive PSF in monoculture and another (Onobrychis viciifolia) had positive PSF in mixture. Among varieties, PSFs were mediated by soil texture, soil phosphorus, and alfalfa fiber content. Similarly, PSFs among species were mediated by alfalfa fiber and nitrogen content, stand age, plant species richness and weed abundance. These relationships, however, were highly dependent on the variety or species selected and whether the field was seeded to monoculture or mixture. Interestingly, PSFs of native species were negatively impacted by weed abundance, suggesting that weeds may have deleterious effects on native plants via soil biota legacies, thus limiting the utility of native species when reseeding pastures to restore productivity (i.e., pasture rejuvenation). Combined, these results show that the impacts of soil biota on crop productivity depend on previous cropping practices and the variety or species of subsequent crops. As plant-soil feedback is context dependent, variety and species selection combined with diversity-related management practices are critical for successful pasture rejuvenation. Such an approach may sustainably reduce the impact of negative soil biota in agroecosystems.

植物可以对土壤生物群产生强烈影响，从而影响这些土壤中的后续植物生长。在农业生态系统中，这些微生物介导的植物-土壤反馈 (PSF) 可能对随后的作物生长产生强烈的正面或负面影响，但对包括所涉及物种的特性、作物多样性和土壤特征在内的多种因素如何影响 PSF 的了解甚少。为了解决这一知识差距，我们专注于紫花苜蓿（Medicago sativa)，全球最常见的牧草豆类。我们从 24 株紫花苜蓿中取样植物和土壤，这些植物和土壤均匀分布在紫花苜蓿单一栽培和不同年龄的草-紫花苜蓿混合物之间。使用这些地点的土壤，我们进行了一项实验，以量化调节植物群落和土壤特性如何改变 PSF 对四种苜蓿品种和另外五种本地和非本地草和豆类牧草品种的影响。紫花苜蓿单一栽培产生的 PSF 比混合物总体上的负 PSF 更高，表明在更多样化的林分中拮抗土壤生物群的稀释。品种和物种之间的差异是特殊的：一种紫花苜蓿品种在混合土壤中具有阳性 PSF，而一种豆科植物（Trifolium pratense）在单一栽培中具有阳性 PSF 和另一种（Onobrychis viciifolia) 在混合物中具有阳性 PSF。在品种中，PSF受土壤质地、土壤磷和苜蓿纤维含量的调节。同样，物种间的 PSF 受紫花苜蓿纤维和氮含量、林龄、植物物种丰富度和杂草丰度的影响。然而，这些关系高度依赖于所选择的品种或物种以及该田地是种植单一种植还是混合种植。有趣的是，本地物种的 PSF 受到杂草丰度的负面影响，这表明杂草可能通过土壤生物群遗产对本地植物产生有害影响，从而限制本地物种在重新播种牧场以恢复生产力（即牧场复兴）时的效用。结合，这些结果表明，土壤生物群对作物生产力的影响取决于以前的种植方式和后续作物的品种或种类。由于植物-土壤反馈依赖于环境，品种和物种选择与多样性相关的管理实践相结合对于成功的牧场复兴至关重要。这种方法可以可持续地减少负面土壤生物群对农业生态系统的影响。