Data from: Quantity over quality: light intensity, but not red/far-red ratio, affects extrafloral nectar production in Senna mexicana var. chapmanii

Extrafloral nectar (EFN) mediates food-for-protection mutualisms between plants and insects and provides plants with a form of indirect defense against herbivory. Understanding sources of variation in EFN production is important because such variations affect the number and identity of insect visitors and the effectiveness of plant defense. Light represents a potentially crucial tool for regulating resource allocation to defense, as it not only contributes energy but may help plants to anticipate future conditions. Low red/far-red (R/FR) light ratios can act as a signal of the proximity of competing plants. Exposure to such light ratios has been shown to promote competitive behaviors that coincide with reduced resource allocation to direct chemical defenses. Little is known, however, about how such informational light signals might affect indirect defenses such as EFN, and the interactions that they mediate. Through controlled glasshouse experiments, we investigated the effects of light intensity, and R/FR light ratios, on EFN production in Senna mexicana var. chapmanii. Plants in light-limited conditions produced significantly less EFN, and leaf damage elicited increased EFN production regardless of light conditions. Ratios of R/FR light, however, did not appear to affect EFN production in either damaged or undamaged plants. Understanding the effects of light on indirect defenses is of particular importance for plants in the threatened pine rockland habitats of south Florida, where light conditions are changing in predictable ways following extensive fragmentation and subsequent mismanagement. Around 27% of species in these habitats produce EFN and may rely on insect communities for defense.

花外蜜腺（Extrafloral nectar, EFN）介导植物与昆虫间的食饵保护型互惠共生关系，为植物提供了一种抵御植食危害的间接防御手段。探明花外蜜腺分泌量的变异来源具有重要学术意义，因为此类变异会影响访食昆虫的数量与类群组成，以及植物防御的有效性。光照是调控防御相关资源分配的潜在关键因子，其不仅可为植物提供能量，还可帮助其预判未来环境条件。低红光/远红光（Red/Far-red, R/FR）光强比可作为邻近竞争植物的信号。已有研究表明，暴露于此类光强比环境下的植物会增强竞争行为，同时减少对直接化学防御的资源分配。然而，目前对这类信息性光信号如何影响花外蜜腺这类间接防御，以及其所介导的种间互作，仍知之甚少。本研究通过可控温室实验，探究了光照强度与红光/远红光光强比对查普曼墨西哥决明（Senna mexicana var. chapmanii）花外蜜腺分泌量的影响。结果显示，光照受限环境下的植株，其花外蜜腺分泌量显著降低；且无论光照条件如何，叶片损伤均会诱导花外蜜腺分泌量上升。但红光/远红光光强比似乎并未对受损或未受损植株的花外蜜腺分泌量产生显著影响。探明光照对间接防御的调控效应，对于佛罗里达州南部受威胁的松岩栖息地中的植物尤为关键——该栖息地因大规模生境片段化及后续管理失当，其光照条件正以可预测的模式发生改变。该栖息地中约27%的植物类群可产生花外蜜腺，并可能依赖昆虫群落实现防御功能。