Data from: Still armed after domestication? Impact of domestication and agronomic selection on silicon defences in cereals

1. Plant phenotypes reflect trade-offs between competing resource-intensive physiological processes. A shift in resource allocation, away from anti-herbivore defences and towards growth and reproduction, is predicted through plant domestication, such that crops are faster growing and higher yielding than their wild ancestors. These changes are hypothesized to have come at the cost of defence investment, leaving crops ‘disarmed by domestication’. Silicon is the principal anti-herbivore defence in grasses, including many of our most important staple cereal crops, but the impact of domestication on silicon-based defences is unknown. 2. We measured the effects of both domestication and modern agronomic selection on growth rate and a suite of anti-herbivore defences, specifically leaf toughness, silicon and phenolic concentrations. Our comparison of wild, landrace and modern cultivated cereals spanned multiple cereal species, including wheat, barley and maize, sampling eight independent domestication events and five examples of modern agronomic selection. 3. Leaf silicon concentration showed a small, but significant, 10% reduction through domestication, but there was no effect of modern agronomic selection, and phenolic concentration was not affected by either factor. Silicon concentration correlated positively with leaf tensile strength, but negatively with foliar phenolic concentrations, suggesting a trade-off between chemical and physical defences. Size-standardised growth rate was independent of domestication status, and did not trade-off with silicon or phenolic defences. However, modeling showed that relative growth rate slowed more with increasing size in plants with higher silicon levels, so that they reached a smaller final size, implying a cost of silicon-based defence. We found the opposite pattern for phenolic-based defence, with increasing phenolic concentrations associated with a greater plant size at maturity, and faster maximum relative growth rates. 4. Silicon-based defences have been reduced in cereals through domestication, consistent with our predicted costs of these defences to growth. However, modern agronomic selection has not influenced silicon defences in cereal crops and the small decrease in silicon concentration associated with domestication is unlikely to have a major effect on the ability of cereals to withstand a range of abiotic and biotic stresses. These findings have broad implications for crop protection and our understanding of plant trade-offs.

1. 植物表型体现了多种相互竞争的资源消耗型生理过程之间的权衡。研究预测，在植物驯化（plant domestication）过程中，资源分配会发生转向：从抗草食动物防御（anti-herbivore defences）转向生长与繁殖，因此栽培作物相较其野生祖先生长更快、产量更高。学界假设这类变化是以防御投入为代价的，使得作物“因驯化而解除武装”。硅是草本植物（包括诸多重要的主粮谷类作物（staple cereal crops））的主要抗草食动物防御手段，但驯化对硅基防御（silicon-based defences）的影响尚不明晰。
2. 本研究评估了驯化与现代农艺选择对生长速率以及一系列抗草食动物防御指标的影响，具体包括叶片韧性、硅含量与酚类物质浓度。研究比较了野生种、地方品种（landrace）与现代栽培谷类作物，涵盖小麦、大麦、玉米等多个物种，共采集了8次独立的驯化事件样本与5例现代农艺选择案例。
3. 叶片硅含量在驯化过程中出现了小幅但显著的10%下降，但现代农艺选择未对其产生影响；酚类物质浓度则不受这两个因素的影响。硅含量与叶片抗拉强度（leaf tensile strength）呈正相关，而与叶片酚类浓度呈负相关，这表明化学防御与物理防御之间存在权衡。以体型标准化后的生长速率与驯化状态无关，且未与硅基或酚类防御形成权衡。不过模型分析显示，在硅含量更高的植株中，相对生长速率（relative growth rate）随体型增大下降得更快，最终达到的成熟体型更小，这暗示了硅基防御存在生长成本。我们在酚类防御中观察到了相反的模式：酚类浓度越高，植株成熟时的体型越大，最大相对生长速率也越快。
4. 谷类作物的硅基防御已因驯化而减弱，这与我们提出的“这类防御会带来生长成本”的预测相符。不过，现代农艺选择并未对谷类作物的硅基防御产生影响，且与驯化相关的硅含量小幅下降不太可能对谷类作物抵御多种非生物胁迫（abiotic stresses）与生物胁迫（biotic stresses）的能力造成显著影响。这些发现对作物保护以及我们对植物权衡机制的理解具有广泛的启示意义。