Data from: Legacy effects of diversity in space and time driven by winter cover crop biomass and nitrogen concentration

Plant diversity can increase nitrogen cycling and decrease soil-borne pests, which are feedback mechanisms influencing subsequent plant growth. The relative strength of these mechanisms is unclear, as is the influence of preceding plant quantity and quality. Here, we studied how plant diversity in space and time influences subsequent crop growth.

During 2 years, we rotated two main crops (Avena sativa, Cichorium endivia) with four winter cover crop (WCC) species in monocultures and mixtures. We hypothesized that, relative to monocultures, WCC mixtures promote WCC biomass (quantity) and nitrogen concentration (quality), soil mineral nitrogen, soil organic matter, and reduce plant-feeding nematode abundance. Additionally, we predicted that preceding crops modified WCC legacies. By structural equation modelling (SEM), we tested the relative importance of WCC shoot biomass and nitrogen concentration on succeeding crop productivity directly and indirectly via nitrogen cycling and root-feeding nematode abundance.

WCC shoot biomass, soil properties and succeeding Avena productivity were affected by first-season cropping, whereas subsequent Cichorium only responded to the WCC treatments. WCC mixtures’ productivity and nitrogen concentration showed over- and under-yielding, depending on mixture composition. Soil nitrogen and nematode abundance did not display WCC mixture effects. Soil organic matter was lower than expected after Raphanus sativus + Vicia sativa mixture. Subsequent Avena productivity depended upon mixture composition, whereas final Cichorium productivity was unresponsive to WCC mixtures. SEM indicated that WCC legacy effects on subsequent Avena (R2 = 0.52) and Cichorium (R2 = 0.59) productivity were driven by WCC biomass and nitrogen concentration, although not by the quantified soil properties.

Synthesis and applications. Through understanding plant–soil feedback, legacy effects of plant species and species mixtures can be employed for sustainable management of agro-ecosystems. Biomass and nitrogen concentration of plants returned to the soil stimulate subsequent plant productivity. Winter cover crop quantity and quality are both manipulable with mixtures. The specificity of spatial and temporal diversity effects warrants consideration of plant species choice in mixtures and rotations for optimal employment of beneficial legacy effects.

植物多样性可提升氮循环（nitrogen cycling）效率并抑制土传害虫（soil-borne pests），二者均为影响后续植物生长的反馈调控机制。目前学界对这些调控机制的相对强度尚不明确，对前茬植物的生物量与养分质量的影响亦缺乏清晰认知。本研究旨在探究时空尺度下的植物多样性如何作用于后续作物生长。

本研究为期两年，设置了两种主栽作物（燕麦（Avena sativa）、菊苣（Cichorium endivia））与四种冬季覆盖作物（winter cover crop, WCC）的单播及混播轮作体系。我们提出假说：相较于单播处理，冬季覆盖作物混播可提升覆盖作物的生物量（即数量指标）与氮浓度（即质量指标）、土壤矿质氮含量与土壤有机质水平，并降低植食性线虫（plant-feeding nematode）的丰度。此外，我们预测前茬作物会改变冬季覆盖作物的遗留效应。本研究通过结构方程模型（structural equation modelling, SEM），检验了冬季覆盖作物地上部生物量与氮浓度，如何通过氮循环与食根线虫（root-feeding nematode）丰度，对后续作物生产力产生直接与间接影响，并明确二者的相对重要性。

冬季覆盖作物地上部生物量、土壤理化性质与后续燕麦的生产力均受首季种植处理的影响，而后续菊苣仅对冬季覆盖作物处理产生响应。冬季覆盖作物混播的生产力与氮浓度表现出超产与低产的分化，具体结果取决于混播组合的构成。土壤氮含量与线虫丰度未受冬季覆盖作物混播处理的影响。在萝卜（Raphanus sativus）+箭舌豌豆（Vicia sativa）混播处理后，土壤有机质水平低于预期。后续燕麦的生产力取决于混播组合的构成，而最终菊苣的生产力则不受冬季覆盖作物混播处理的影响。结构方程模型分析显示，冬季覆盖作物遗留效应对后续燕麦（R²=0.52）与菊苣（R²=0.59）生产力的驱动作用，来自覆盖作物自身的生物量与氮浓度，而非本研究量化的土壤性质。

结论与应用展望。通过解析植物-土壤反馈（plant-soil feedback）机制，可利用植物物种及其混播组合的遗留效应，实现农业生态系统的可持续管理。返还至土壤中的植物生物量与氮浓度可提升后续植物的生产力。通过混播手段，可同时调控冬季覆盖作物的生物量（数量）与养分质量（质量）。时空尺度下的多样性效应具有物种特异性，因此在优化利用有益遗留效应时，需审慎考量混播与轮作体系中的植物物种选择。