Data from: An insect ecosystem engineer alleviates drought stress in plants without increasing plant susceptibility to an above-ground herbivore

Climate change models predict more extreme rainfall patterns, ranging from droughts to deluges, which will inevitably affect primary productivity in many terrestrial ecosystems. Insects within the ecosystem, living above- and below-ground, may modify plant responses to water stress. For example, some functional groups improve soil conditions via resource provision, potentially alleviating water stress. Enhanced resource provision may, however, render plants more susceptible to herbivores and negate beneficial effects. Using a model system, we tested how plants (Brassica oleracea) responded to drought, ambient and increased precipitation scenarios when interacting with both a soil conditioning ecosystem engineer (dung beetles; Bubas bison) and an above-ground herbivore, the major crop pest diamondback moth (Plutella xylostella). Dung beetles enhanced soil water retention by 10% and promoted growth in plants subjected to drought by 280%, relieving the impacts of water stress on plants. Under drought conditions, plants grown with dung beetles had c. 30% more leaves and were over twice as tall as those without dung beetles. Dung beetles produced a 2·7-fold increase in nitrogen content and more than a threefold increase in carbon content of the shoots, though shoot concentrations of nitrogen and carbon were unchanged. Carbon concentrations in roots, however, were increased by dung beetles under both ambient and increased precipitation regimes. Increased precipitation reduced root and shoot nitrogen concentrations by 16% and 30%, relative to plants under ambient regimes, respectively, most likely due to dilution effects of increased plant growth under increased precipitation. Soil carbon and nitrogen concentrations were largely unaffected. While dung beetles enhanced plant growth and nitrogen content in plants experiencing drought, the anticipated increase in plant suitability to herbivores did not arise, possibly because shoot nitrogen concentrations and C:N ratio were unaffected. To our knowledge, this is the first report of an insect ecosystem engineer alleviating the effects of predicted drought events on plants via physical manipulation of the soil matrix. Moreover, their effects did not change plant suitability to an above-ground herbivore, pointing to potential beneficial role for insect ecosystem engineers in climate change adaptation and crop protection.

气候变化模型预测，未来极端降雨格局将愈发频发，其范围涵盖干旱至洪涝的各类极端事件，这势必对众多陆地生态系统的初级生产力造成影响。栖息于陆地生态系统地上与地下的昆虫，或可改变植物对水分胁迫的响应模式。例如，部分昆虫功能群可通过资源供给改善土壤理化性状，潜在缓解植物面临的水分胁迫；但增强的资源供给或许会使植物更易遭受植食性动物侵害，进而抵消其带来的益处。本研究依托模式实验系统，探究了植物（甘蓝 *Brassica oleracea*）在与三类生物交互作用时，对干旱、正常降水及降水增加三种降水情景的响应：这三类生物分别为具备土壤调节功能的生态系统工程师——粪甲虫（*Bubas bison*），以及地上植食性昆虫、主要作物害虫小菜蛾（*Plutella xylostella*）。实验结果显示，粪甲虫可将土壤持水量提升10%，并使受干旱胁迫的植物生物量增长280%，有效缓解了水分胁迫对植物的负面影响。在干旱条件下，与粪甲虫共存的植株叶片数量较无粪甲虫的对照组多出约30%，株高更是达到对照组的两倍以上。粪甲虫使植物地上部分的氮含量提升至原水平的2.7倍，碳含量提升三倍以上，但地上部分的氮、碳浓度并未发生显著变化。而在正常降水与降水增加的情景下，粪甲虫均使根系的碳浓度有所升高。相较于正常降水情景，降水增加处理使植物根系和地上部分的氮浓度分别降低16%与30%，这一现象大概率源于降水增加促进植物生长后产生的营养稀释效应。土壤的碳、氮浓度则基本未受实验处理的影响。尽管粪甲虫提升了受干旱胁迫植物的生长量与氮含量，但并未如预期般提高植物对植食性动物的适宜性，这可能是因为地上部分的氮浓度及碳氮比未发生显著改变。据我们所知，本研究是首次报道昆虫生态系统工程师可通过物理改造土壤基质，缓解预测中干旱事件对植物的负面影响。此外，粪甲虫的作用并未改变植物对地上植食性动物的适宜性，这表明昆虫生态系统工程师在气候变化适应与作物保护领域具备潜在的有益应用价值。