Data from: Increased root herbivory under elevated atmospheric carbon dioxide concentrations is reversed by silicon-based plant defences

Predicted increases in atmospheric concentrations of CO2 may alter the susceptibility of many plants to insect herbivores due to changes in plant nutrition and defences. Silicon plays a critical role in plant defence against herbivores, so increasing such silicon-based defences in plants may help remediate situations where plants become more susceptible to herbivores.
Sugarcane (Saccharum spp. hybrid) were subjected to fully factorial treatment combinations of ambient (aCO2) or elevated (eCO2) atmospheric CO2 concentrations; ambient silicon or silicon supplementation; insect-free or subject to root herbivory by greyback canegrub (Dermolepida albohirtum). A glasshouse study was used to determine how these factors affected rates of photosynthesis, growth, chemistry (concentrations of silicon, carbon, nitrogen and non-structural carbohydrates). Changes in canegrub mass were determined in the glasshouse pot study, together with more detailed assessment of how eCO2 and silicon supplementation affected performance and feeding behaviour (relative growth rate and relative consumption) in a 24-hour feeding efficiency assay.
eCO2 and silicon supplementation increased rates of photosynthesis (+32% and 14%, respectively) sugarcane biomass (+45% and 69%, respectively). Silicon supplementation increased silicon concentrations in both leaves and roots by 54% and 75%, respectively. eCO2 caused root C:N to increase by 12%.
Canegrub performance and consumption increased under eCO2; relative growth rate (RGR) increased by 116% and consumed 57% more root material (suggestive of compensatory feeding). Silicon application reversed these effects, with large decreases in mass change, RGR and root consumption (65% less root mass consumed).
Synthesis and applications. Our results suggest future atmospheric carbon dioxide concentrations could lead to increased crop damage by a below-ground herbivore. Increasing bioavailable silicon in soil stimulated silicon-based defences which dramatically decreased herbivory and herbivore performance. Our findings suggest future pest management strategies could benefit from characterising deficiencies in bioavailable silicon in agricultural soils and targeted application of silicon fertilisers. Moreover, future breeding programmes should exploit variation in silicon uptake between cultivars to enhance silicon uptake in new crop varieties. Silicon-based plant defence proved to be highly beneficial for remediating the negative effects of atmospheric change on sugarcane susceptibility to herbivory and could be applicable in other crops.

大气二氧化碳（CO₂）浓度的预计升高，可通过改变植物营养与防御机制，影响诸多植物对昆虫植食者（insect herbivores）的易感程度。硅（silicon）在植物对抗植食者的防御过程中发挥关键作用，因此强化植物的硅基防御，或可改善植物对植食者易感程度升高的状况。

本研究以甘蔗（Saccharum属杂交种）为材料，设置完全因子组合处理：大气CO₂浓度分为环境浓度（aCO₂）与升高浓度（eCO₂）；硅处理分为环境硅水平与硅补充；虫害处理分为无虫及接种灰背蔗金龟（Dermolepida albohirtum）进行根部植食。通过温室试验，探究这些因子对甘蔗光合作用速率、生长状况及化学组分（硅、碳、氮与非结构性碳水化合物（non-structural carbohydrates）含量）的影响。本温室盆栽试验还测定了蔗金龟的体重变化，并通过24小时取食效率测定，更细致地评估eCO₂与硅补充对蔗金龟生长表现与取食行为（相对生长速率（RGR，relative growth rate）、相对取食量（relative consumption））的影响。

eCO₂与硅补充分别提升了甘蔗的光合作用速率（分别提升32%与14%）与生物量（分别提升45%与69%）。硅补充使甘蔗叶片与根部的硅含量分别提升54%与75%。eCO₂使甘蔗根碳氮比升高12%。

在eCO₂处理下，蔗金龟的生长表现与取食量均有所提升：相对生长速率（RGR）提升116%，取食的根部组织量增加57%，这提示存在补偿取食（compensatory feeding）现象。施加硅肥可逆转上述效应，蔗金龟的体重变化、RGR与根部取食量均大幅下降（取食的根部组织量减少65%）。

总结与应用。我们的研究结果表明，未来大气二氧化碳浓度升高可能会加重地下植食者对作物的为害。提升土壤中生物可利用硅（bioavailable silicon）的含量，可激活植物的硅基防御系统，从而显著降低植食为害程度与植食者的生长表现。本研究结果提示，未来的害虫防治策略（pest management strategies）可通过表征农田土壤的生物可利用硅缺乏状况，并针对性施用硅肥来获益。此外，未来的作物育种项目应利用不同栽培品种（cultivars）间硅吸收能力的差异，提升新品种的硅吸收效率。硅基植物防御手段可有效改善大气变化导致的甘蔗对植食者易感程度升高的负面影响，且该手段亦可推广应用至其他作物。