Previous cover crop studies mainly focused on the links between plant uptake and soil fertility, and there is a clear knowledge gap regarding the role of microbes in these processes. Our aim was then to better understand the effects of plant mixtures (versus monoculture) and the specific effects of each plant species on nitrogen (N) and phosphorus (P) partitioning between plant, soil, and more particularly microbial pools. Monocultures and mixtures composed of black oat, field pea and Indian mustard were grown during two months in a greenhouse. The concentrations of carbon (C), N and P were measured in both plant and microbial biomass at final harvest, together with soil available N and P. Overall, our findings highlight stronger selection effect (i.e., presence of key species) rather than complementarity effects (i.e., species mixture) to affect the measured parameters. The presence of pea increased the biomass production of oat and mustard, as well as the nutrient concentration of oat, whereas pea P concentration decreased in presence of oat and mustard N and P concentrations were negatively impacted respectively by the presence of oat and pea. We also observed a strong competition between plants and microbes for both soil N and P. The oat-pea and the oat-pea-mustard mixtures represented the best compromise between biomass production, nutrient storage and biomass C:N ratio, thus insuring a good organic matter decomposition and nutrient provision for the following main crop.

中文翻译：

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物种身份，而不是物种混合物，驱动覆盖作物对未施肥农业土壤中养分分配的影响

以前的覆盖作物研究主要集中在植物吸收和土壤肥力之间的联系上，关于微生物在这些过程中的作用存在明显的知识差距。我们的目标是更好地了解植物混合物（相对于单一栽培）的影响以及每种植物物种对植物、土壤，尤其是微生物库之间的氮 (N) 和磷 (P) 分配的具体影响。由黑燕麦、豌豆和印度芥末组成的单一栽培和混合物在温室中生长了两个月。在最终收获时测量了植物和微生物生物量中的碳 (C)、N 和 P 浓度，以及土壤有效 N 和 P。总体而言，我们的研究结果强调了更强的选择效应（即关键物种的存在）而不是互补性效果（即 物种混合物）影响测量参数。豌豆的存在增加了燕麦和芥末的生物量产量，以及燕麦的营养浓度，而豌豆 P 浓度在燕麦存在下降低，芥末 N 和 P 浓度分别受到燕麦和豌豆的负面影响。我们还观察到植物和微生物之间对土壤 N 和 P 的强烈竞争。燕麦-豌豆和燕麦-豌豆-芥末混合物代表了生物量生产、养分储存和生物量 C:N 比之间的最佳折衷，从而确保了良好的为以下主要作物提供有机质分解和养分。而豌豆 P 浓度在燕麦和芥菜中下降，N 和 P 浓度分别受到燕麦和豌豆的负面影响。我们还观察到植物和微生物之间对土壤 N 和 P 的强烈竞争。燕麦-豌豆和燕麦-豌豆-芥末混合物代表了生物量生产、养分储存和生物量 C:N 比之间的最佳折衷，从而确保了良好的为以下主要作物提供有机质分解和养分。而豌豆 P 浓度在燕麦和芥菜中下降，N 和 P 浓度分别受到燕麦和豌豆的负面影响。我们还观察到植物和微生物之间对土壤 N 和 P 的强烈竞争。燕麦-豌豆和燕麦-豌豆-芥末混合物代表了生物量生产、养分储存和生物量 C:N 比之间的最佳折衷，从而确保了良好的为以下主要作物提供有机质分解和养分。