Data from: Can above-ground ecosystem services compensate for reduced fertilizer input and soil organic matter in annual crops?

Above-ground and below-ground environmental conditions influence crop yield by pollination, pest pressure, and resource supply. However, little is known about how interactions between these factors contribute to yield. Here, we used oilseed rape Brassica napus to test their effects on crop yield. We exposed potted plants to all combinations of high and low levels of soil organic matter (SOM) and fertilizer supply, and placed all treatments at a variety of field sites representing a gradient in pollinator visitation rate and pest exposure. We determined the relative contribution of pollinators and pests, SOM and fertilizer supply to yield. We also tested whether SOM can moderate effects of fertilizer on yield and whether soil conditions influence the relationship between above-ground conditions and yield. Increases in pollinator visitation rate and decreases in pest pressure enhanced yield more than increase of fertilizer supply. Although higher SOM content resulted in plants with more biomass and flowers, under our experimental conditions SOM neither enhanced yield, nor influenced effects of fertilizer, pollinators or pests on yield. The relationships between yield, pollinator visitation rate and pest pressure did not depend on the level of fertilization suggesting that the effects of fertilizer application and above-ground (dis)services on yield were additive. In contrast, pollinator visitation rate was more strongly related to yield at low pest pressure than at high pest pressure indicating trade-offs between above-ground services and disservices. Synthesis and applications. Our results show that it is possible to increase oilseed rape yield by enhancing pollination, irrespective of supplying mineral fertilizer. Moreover, the fact that below-ground conditions did not alter the effect of above-ground conditions, suggests that farmers may obtain even higher yields by maximizing both above-ground ecosystem services and external inputs. Further studies are needed to understand at which point the positive relationships between pollinator visitation and yield, as well as between fertilizer and yield will level off. Considering above-ground and below-ground services and inputs in agro-ecosystems in conjunction is crucial in order to optimize external inputs for crop yield from an economic and ecological perspective.

地上与地下环境条件可通过传粉、虫害压力及资源供给三条途径影响作物产量，但目前学界对这些因素间的交互作用如何调控作物产量的机制仍知之甚少。本研究以甘蓝型油菜（Brassica napus）为实验材料，探究上述因素对作物产量的影响。我们将盆栽植株置于土壤有机质（SOM）与肥料供给量高低的全组合处理中，并将所有处理组放置于覆盖传粉者访花频率与虫害暴露水平梯度的多个田间试验点。本研究量化了传粉者、虫害、土壤有机质与肥料供给对产量的相对贡献度；同时验证了土壤有机质是否会调节肥料对产量的效应，以及土壤条件是否会影响地上环境条件与产量间的关联。

传粉者访花频率的提升与虫害压力的降低，对产量的增益效果优于肥料供给量的增加。尽管土壤有机质含量更高会使植株拥有更大的生物量与更多花朵，但在本实验条件下，土壤有机质既未提升产量，也未影响肥料、传粉者或虫害对产量的效应。产量、传粉者访花频率与虫害压力间的关联不受肥料施用水平的影响，这表明肥料施用与地上（正反）服务对产量的效应为加性效应。与之相反，在低虫害压力条件下，传粉者访花频率与产量的相关性显著高于高虫害压力条件，这反映出地上服务与有害服务间存在权衡关系。

综合与应用
本研究结果表明，无需额外施用矿质肥料，仅通过强化传粉服务即可提升甘蓝型油菜产量。此外，由于地下环境条件并未改变地上环境条件的效应，这提示农户可通过最大化地上生态系统服务与外部投入，进一步提升作物产量。未来仍需开展进一步研究，以明确传粉者访花与产量、肥料与产量间的正相关关系会在何种临界点趋于平缓。从经济与生态视角出发，将农业生态系统中的地上与地下服务及投入纳入统一考量，对于优化作物产量相关的外部投入至关重要。