Biodiversity is thought to help regulate the impacts of disease through the dilution effect, where biodiversity among potential host species helps limit the impacts of pathogens. However, our knowledge is fragmentary about the direction and magnitude of the effects of plant species richness on disease impact. Here, we gathered data from 145 comparisons presented in 21 papers to conduct a systematic meta‐analysis on the effect of plant species richness on aboveground plant disease impact. We estimated the effect size using Pearson's correlation coefficient (r) with Fisher's z‐transformation. We evaluated how the magnitude of effect size varies between systems, including ecosystem type (grassland versus forest), pathogen taxon (virus versus fungus), study design (observational versus manipulative), parasite life history (biotroph versus necrotroph) and kinds of symptoms associated with the disease. We also tested whether there was a latitudinal trend of the effect size. We found there was a significant overall dilution effect in plant communities, but the magnitude varied among systems. Studies based on manipulative experiments and those in grassland ecosystems showed a significant dilution effect, as did both viral and fungal pathogens. Furthermore, obligate biotrophic pathogens but not necrotrophs showed a significant dilution effect. Diseases with different kinds of symptom manifestation differed, but not in a consistent pattern to the life history of the pathogens. The dilution effect was notably stronger at lower latitudes in the mid‐temperate region than at higher latitudes. This latitudinal trend existed in forest ecosystems, both observational and manipulative experiments, and necrotrophs. Dilution effects occur prevalently in plant communities, although the magnitude depends on ecosystem type, pathogen life history and kinds of symptoms associated with the disease. In conclusion, this study shows the importance of preserving the biodiversity of plants for maintaining ecosystem health.

中文翻译：

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植物多样性对传染病的稀释作用：纬度趋势和生物背景依赖性

人们认为生物多样性通过稀释效应有助于调节疾病的影响，潜在宿主物种中的生物多样性有助于限制病原体的影响。但是，我们对植物物种丰富度对疾病影响的影响的方向和程度的知识是零碎的。在这里，我们从21篇论文中进行的145个比较中收集了数据，对植物物种丰富度对地上植物病害的影响进行了系统的荟萃分析。我们使用皮尔逊相关系数（r）和Fisher的z估计效应大小-转型。我们评估了效应大小的大小如何在系统之间变化，包括生态系统类型（草地与森林），病原体分类群（病毒与真菌），研究设计（观察性与操纵性），寄生虫的生活史（生物营养素与坏死菌）以及相关的症状与疾病。我们还测试了效应量是否存在纬度趋势。我们发现植物群落中存在显着的总体稀释效应，但是其强度在系统之间有所不同。基于操作性实验和草地生态系统的研究表明，病毒和真菌病原体均具有明显的稀释作用。此外，专性的生物营养性病原体而不是坏死性生物显示出显着的稀释作用。具有不同症状表现的疾病有所不同，但与病原体的生活史却不一致。在中温带低纬度地区，稀释作用明显强于高纬度地区。这种横向趋势存在于森林生态系统中，无论是观察性实验还是操纵性实验，以及坏死菌。尽管其影响程度取决于生态系统类型，病原体的生活史以及与疾病相关的症状种类，但稀释作用普遍发生在植物群落中。总之，这项研究表明了保护植物生物多样性对于维持生态系统健康的重要性。观察性和操纵性实验以及坏死菌。尽管其影响程度取决于生态系统类型，病原体的生活史以及与疾病相关的症状种类，但稀释作用普遍发生在植物群落中。总之，这项研究表明了保护植物生物多样性对于维持生态系统健康的重要性。观察性和操纵性实验以及坏死菌。尽管其影响程度取决于生态系统类型，病原体的生活史以及与疾病相关的症状种类，但稀释作用普遍发生在植物群落中。总之，这项研究表明了保护植物生物多样性对于维持生态系统健康的重要性。