Floral nectar reabsorption and a sugar concentration gradient in two long-spurred Habenaria species (Orchidaceae)

Abstract

Background Floral nectar is the most common reward flowers offered to pollinators. The quality and quantity of nectar produced by a plant species provide a key to understanding its interactions with pollinators and predicting rates of reproductive success. However, nectar secretion is a dynamic process with a production period accompanied or followed by reabsorption and reabsorption remains an understudied topic. In this study, we compared nectar volume and sugar concentration in the flowers of two long-spurred orchid species, Habenaria limprichtii and H. davidii (Orchidaceae). We also compared sugar concentration gradients within their spurs and rates of reabsorption of water and sugars. Results Both species produced diluted nectar with sugar concentrations from 17 to 24%. Analyses of nectar production dynamics showed that as flowers of both species wilted almost all sugar was reabsorbed while the original water was retained in their spurs. We established a nectar sugar concentration gradient for both species, with differences in sugar concentrations at their spur’s terminus and at their spur’s entrance (sinus). Sugar concentration gradient levels were 1.1% in H. limprichtii and 2.8% in H. davidii, both decreasing as flowers aged. Conclusion We provided evidence for the reabsorption of sugars but not water occurred in wilted flowers of both Habenaria species. Their sugar concentration gradients vanished as flowers aged suggesting a slow process of sugar diffusion from the nectary at the spur’s terminus where the nectar gland is located. The processes of nectar secretion/reabsorption in conjunction with the dilution and hydration of sugar rewards for moth pollinators warrant further study.

Comparative floral nectar attributes in four <i>Swertia</i> species (Gentianaceae)

“…阶 段 的 糖 或 水 分 的 主 动 回 吸(Burquez & Corbet, 1991; Stpiczynska, 2003;Pyke et al, 2020a;Zhang et al, 2023)。自然状态下, 部分物种在传粉昆 虫 的 访 花 之 后 , 能 刺 激 花 蜜 快 速 补 充 (Luyt &Johnson, 2002; Ordano & Ornelas, 2005; Luo et al, 南省昆明市果东村老鸦山(102.73 °E, 25.41 °N)。实 验 对 象 为 龙 胆 科 獐 牙 菜 属 的 4 种 植 物 : 獐 牙 菜 1 材料与方法 文诗嘉等: 獐牙菜属四种植物花蜜特征的比较 2024年 | 32卷 | 1期 | 23297 | 第3页 (Swertia bimaculata)、西南獐牙菜(S. cincta)、贵州 獐牙菜(S. kouitchensis)和紫红獐牙菜(S. punicea) (2002)。4种獐牙菜属植物的花均为雌雄异熟, 且雄 图1 4种獐牙菜属植物的花部特征。A: 獐牙菜; B: 西南獐 牙菜; C: 贵州獐牙菜; D: 紫红獐牙菜。箭头所指为蜜腺。 Fig. 1 Floral characteristics of four species in the genus Swertia.…”