Jones Ian M, Koptur Suzanne
Department of Biological Sciences Florida International University Miami Florida.
Ecol Evol. 2015 Sep 4;5(18):4108-14. doi: 10.1002/ece3.1644. eCollection 2015 Sep.
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（EFN）介导了植物与昆虫之间的“食物换保护”互利共生关系，并为植物提供了一种抵御食草动物的间接防御形式。了解花外蜜分泌量变化的来源很重要，因为这种变化会影响访花昆虫的数量和种类，以及植物防御的效果。光照是调节植物防御资源分配的一个潜在关键因素，因为它不仅提供能量，还可能帮助植物预测未来的环境条件。低红光/远红光（R/FR）光比可作为竞争植物临近程度的信号。研究表明，暴露于这种光比下会促进竞争行为，同时减少对直接化学防御的资源分配。然而，对于这种信息光信号如何影响诸如花外蜜等间接防御以及它们所介导的相互作用，我们知之甚少。通过可控温室实验，我们研究了光强和R/FR光比对墨西哥决明变种查普曼决明花外蜜分泌的影响。处于光照受限条件下的植物分泌的花外蜜显著减少，且无论光照条件如何，叶片损伤都会促使花外蜜分泌量增加。然而，R/FR光比似乎并未影响受损或未受损植物的花外蜜分泌。对于佛罗里达州南部受威胁的松树岩地栖息地中的植物而言，了解光照对间接防御的影响尤为重要，在这些栖息地，经过大面积碎片化及随后的管理不善后，光照条件正以可预测的方式发生变化。这些栖息地中约27%的物种会分泌花外蜜，可能依赖昆虫群落进行防御。
