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，未来将出现从干旱到暴雨的各类极端降雨模式，这势必会对众多陆地生态系统的初级生产力造成不可避免的影响。栖息于生态系统中的昆虫，涵盖地表与地下类群，或可改变植物对水分胁迫的响应策略。例如，部分功能类群可通过资源供给改善土壤条件，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者侵害，进而抵消其带来的有益效果。
本研究依托模式实验系统，探究了甘蓝（Brassica oleracea）在干旱、常态降水及增加降水三种情境下，与土壤改良生态系统工程师（ecosystem engineer）——蜣螂（dung beetles; Bubas bison），以及地上植食者、主要作物害虫小菜蛾（Plutella xylostella）共同作用时的响应特征。
实验结果显示，蜣螂可将土壤持水量提升10%，并使受干旱胁迫的植株生长量提升280%，有效缓解了水分胁迫对植物的负面影响。在干旱情境下，与蜣螂共生的植株叶片数量较无蜣螂处理组多约30%，株高更是达到后者的两倍以上。蜣螂使植株地上部分的氮含量提升2.7倍，碳含量提升三倍以上，但地上组织的氮、碳浓度并未发生显著变化。不过，在常态降水与增加降水的情境下，蜣螂均提升了植株根系的碳浓度。相较于常态降水处理组的植株，增加降水使根系与地上部分的氮浓度分别降低16%与30%，该现象大概率源于增加降水下植物生长速率加快所产生的稀释效应。土壤的碳、氮浓度基本未受实验处理的影响。
尽管蜣螂提升了受干旱胁迫植株的生长量与氮含量，但预期中植株对植食者的适宜性并未出现提升，这可能是因为地上组织的氮浓度与碳氮比并未发生改变。据我们所知，本研究首次报道了昆虫生态系统工程师通过物理改造土壤基质，缓解预测中的干旱事件对植物的不利影响。此外，蜣螂的作用并未改变植物对地上植食者的适宜性，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作用。