Enhancing diversity within crop systems can have benefits including increased resource use efficiency and productivity, and increased control of weeds, pests and diseases. Some benefits are expected to operate through biodiversity-driven insurance effects, whereby enhanced diversity increases the chance that a system component can compensate for the impacts of adverse environmental conditions. Studies of insurance effects in natural and agricultural systems have provided equivocal results. As insurance effects are expected to play a key role in helping to maintain crop production in more variable future climates (for example under periodic drought), it is essential to know when and how they operate and interact with other potentially beneficial biodiversity-function effects. Using barley as a model crop, and pot-based plant communities, we studied the interactive effects of barley cultivar diversity and drought stress on plant productivity and the response of agricultural weeds, fungal disease, and aphids. Drought reduced barley and weed biomass, but there were no interactive effects of drought and cultivar diversity on plant productivity. Increased cultivar diversity enhanced weed suppression, potentially as a result of reduced functional space availability, and reduced disease severity on a susceptible cultivar; these effects were consistent irrespective of drought. Aphid responses were more complex, with idiosyncratic response patterns on individual cultivars. Overall, we found no evidence of an insurance effect of enhanced cultivar diversity for the negative impact of drought on crop productivity, but our results indicate that other positive biodiversity effects (weed and disease suppression) are maintained under drought. However, it is clear that not all potentially-beneficial biodiversity effects respond in the same manner. Field trials are now needed to explore whether a range of responses also occur in crop field settings, whether these can be expected to occur predictably under a range of environmental conditions, and how these then impact on crop production.

增强作物系统内的多样性可能会带来好处，包括提高资源利用效率和生产力，以及加强对杂草，病虫害和疾病的控制。预计通过生物多样性驱动的保险效应将产生一些收益，从而增加多样性将增加系统组成部分可以补偿不利环境条件的影响的机会。对自然和农业系统中保险影响的研究提供了模棱两可的结果。由于预计保险影响将在帮助维持未来变化多端的气候条件下（例如在周期性干旱下）的农作物生产中发挥关键作用，因此必须了解保险的运行时间和方式以及与其他潜在有益的生物多样性功能的影响，以及与之相互作用的关键。使用大麦作为典范作物和盆栽植物群落，我们研究了大麦品种多样性和干旱胁迫对植物生产力以及农业杂草，真菌病和蚜虫的响应的相互作用。干旱减少了大麦和杂草的生物量，但干旱和品种多样性对植物生产力没有交互作用。品种多样性的增加可能是杂草的抑制作用，这可能是由于功能空间利用率降低以及易感品种的病害严重程度降低所致；无论干旱如何，这些影响都是一致的。蚜虫的反应较复杂，个别品种有特异反应模式。总体而言，我们没有发现增加品种多样性对干旱对作物生产力造成负面影响的保证作用的证据，但是我们的结果表明，干旱条件下还能保持其他积极的生物多样性影响（杂草和疾病抑制）。但是，很明显，并非所有潜在的有益生物多样性影响都以相同的方式做出反应。现在需要进行田间试验，以探索在田间环境中是否还会发生一系列响应，是否可以预期在一系列环境条件下会发生可预见的响应，以及这些响应如何影响作物生产。