Abstract Balanced communities of natural enemies (i.e., greater evenness) can strengthen biological control. Natural enemy evenness is generally higher on organic than conventional farms, but the reason(s) for this are unclear. One possibility is that applications of composted manure on organic farms provide habitat for predators as well as food for detritus-feeding arthropods that are important supplemental prey. We searched for potential links between soil organic matter and ground beetle biodiversity in 65 broccoli (B. oleracea) fields, spanning the U.S. west coast, on mixed-vegetable farms using organic or conventional management practices. We measured soil organic matter in each field while also collecting predatory ground beetles (Coleoptera: Carabidae) and detritus-feeding springtails (Collembola), which are potential alternative prey resources for ground beetles. We found that carabid activity density, species richness, and species evenness were higher on organic than conventional farms. Some organic farms integrated livestock alongside vegetable production, however this did not detectably impact ground beetles, springtails, or organic matter. In a path analysis built from our on-farm data, carabid community evenness correlated with soil organic matter, and subsequently, carabid evenness positively correlated with carabid activity density. However, springtail activity-density had no apparent relationship to soil organic matter, carabid activity, or carabid evenness. It is possible that increasing organic matter improved soil microclimate to the benefit of ground beetles, although we cannot exclude the possibility that carabids on organic farms were responding to other ecological or management practices that differed from those on conventional farms. More broadly, among its myriad soil-health benefits, enhancing organic matter could be one strategy for re-balancing natural enemy densities to increase evenness.

中文翻译：

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土壤有机质将有机农业与增强捕食者均匀度联系起来

摘要 天敌的平衡群落（即更大的均匀度）可以加强生物控制。有机农场的天敌均匀度通常高于传统农场，但原因尚不清楚。一种可能性是，在有机农场使用堆肥可为捕食者提供栖息地，并为作为重要补充猎物的以碎屑为食的节肢动物提供食物。我们在美国西海岸的 65 块西兰花（B. oleracea）田中使用有机或传统管理方法在混合蔬菜农场中寻找土壤有机质与地甲虫生物多样性之间的潜在联系。我们测量了每个田地的土壤有机质，同时还收集了掠食性地甲虫（鞘翅目：Carabidae）和以碎屑为食的跳虫（Colembola），这是地面甲虫的潜在替代猎物资源。我们发现有机农场的甲虫活动密度、物种丰富度和物种均匀度高于传统农场。一些有机农场将牲畜与蔬菜生产相结合，但这并没有明显影响地甲虫、跳虫或有机物质。在根据我们的农场数据构建的路径分析中，carabid 群落均匀度与土壤有机质相关，随后 carabid 均匀度与 carabid 活动密度正相关。然而，弹尾活动密度与土壤有机质、甲虫活动或甲虫均匀度没有明显关系。增加有机质可能会改善土壤小气候，从而有利于地面甲虫，尽管我们不能排除有机农场的carabids对其他不同于传统农场的生态或管理实践做出反应的可能性。更广泛地说，在其无数的土壤健康益处中，增加有机质可能是重新平衡天敌密度以增加均匀度的一种策略。