Comparative floral nectar attributes in four Swertia species (Gentianaceae)

doi:10.17520/biods.2023297

Abstract

Abstract:

Aims: Floral nectar secretions at interspecific and intraspecific levels, as well as the variation among different flowers within a plant, influence pollinator attraction. By impacting pollinator visitation patterns, these factors consequently influence pollination effectiveness and plant reproductive success. However, our understanding of the variability in floral nectar production is limited by a lack of quantitative measurements.

Methods: In this study, we selected four sympatric species within the genus Swertia (Gentianaceae), Swertia bimaculata, S. cincta, S. kouitchensis and S. punicea, to study variations in floral nectar attributes. We compared volume, sugar concentration and sugar content (weight) for flowers under two treatments: (1) flowers bagged for 24 hours and (2) freshly opened flowers in natural field conditions. We examined differences among neighboring flowers to test floral nectar variations across and within individual plants.

Results: We found that floral nectar attributes were significantly different among the studied species. Except for sugar concentration in S. bimaculata and S. kouitchensis, all nectar attributes differed between treatments. Sugar concentration was similar between neighboring flowers under the two treatments for S. cincta and S. punicea. In contrast, nectar volume and sugar content showed significant difference between neighboring flowers. Furthermore, correlations for the three attributes were more commonly detected in 24 h bagged flowers than in flowers under natural conditions, suggesting a high variation of floral nectar for flowers in the field.

Conclusion: Our results indicate high variability in floral nectar within the Swertia species. Interspecific difference of floral nectar may relate to pollinator spectrum differentiation. Similarity of sugar concentration within neighboring flowers may be a result of stabilization mechanisms maintained by nectar volume and sugar content. The higher variation in floral nectar under natural conditions potentially drive floral visitors to select different plant individuals.

Key words: floral nectar, secretion dynamic, variation, nectary, sugar concentration

Shijia Wen, Minxue Deng, Ding Wu, Zhiyong Wang, Zongxin Ren. Comparative floral nectar attributes in four Swertia species (Gentianaceae)[J]. Biodiv Sci, 2024, 32(1): 23297.

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URL: https://www.biodiversity-science.net/EN/10.17520/biods.2023297

https://www.biodiversity-science.net/EN/Y2024/V32/I1/23297

Figures/Tables 5

Fig. 1 Floral characteristics of four species in the genus Swertia. The arrows indicate nectaries. A, Swertia bimaculata; B, S. cincta; C, S. kouitchensis; D, S. punicea.

Table 1 Floral nectaries, flowering phenology and habitats of four species in the genus Swertia

种名 Species	蜜腺特征 Floral nectaries	花期 Flowering phenology	生境 Habitats
獐牙菜 S. bimaculata	蜜腺斑点黄绿色、裸露于花冠裂片表面 Nectary spots yellow-green, exposed on the surface of corolla lobes	9-11月 Sep. to Nov.	林下、灌丛中 Under the woods and underbrush
西南獐牙菜 S. cincta	开口朝上的马蹄形腺窝, 位于花冠裂片基部 A horseshoe shaped nectary with an upward opening, located at the base of corolla lobes	8-11月 Aug. to Nov.	潮湿山坡、林下、灌丛中 Wet hillside, under the woods, and underbrush
贵州獐牙菜 S. kouitchensis	腺窝黄绿色, 具流苏覆盖 The nectaries are yellow-green and covered with tassels	8-10月 Aug. to Oct.	山坡草地、灌丛中 Hillside meadow and underbrush
紫红獐牙菜 S. punicea	腺窝紫红色, 具流苏覆盖 The nectaries are purple-red and covered with tassels	9-11月 Sep. to Nov.	林下、草地、灌丛中 Under the woods, grassland, and underbrush

Fig. 2 Comparison of floral nectar attributes (nectar volume, sugar concentration and sugar mass) for 24 h bagged flowers and flowers in natural conditions among four Swertia species. A-C, S. bimaculata; D-F, S. cincta; G-I, S. kouitchensis; J-L, S. punicea. NS, P > 0.05; * P < 0.05; ** P < 0.01; *** P < 0.001.

Fig. 3-4 Correlation of floral nectar attributes (nectar volume, sugar concentration and sugar mass) between two neighbored flowers in Swertia bimaculata (Fig. 3) and S. cincta (Fig. 4). A-C, Flowers bagged for 24 hours; D-F, Standing crops under the natural conditions. * P < 0.05; ** P < 0.01; *** P < 0.001.

Fig. 5-6 Correlation of floral nectar attributes (nectar volume, sugar concentration and sugar mass) between two neighbored flowers in Swertia kouitchensis (Fig. 5) and S. punicea (Fig. 6). A-C, Flowers bagged for 24 hours; D-F, Standing crops under the natural conditions. * P < 0.05; ** P < 0.01; *** P < 0.001.

References 23

[1]	Burquez A, Corbet SA (1991) Do flowers reabsorb nectar? Functional Ecology, 5, 369-379. DOI URL
[2]	Liu CQ, Niu Y, Peng DL, Sun H (2018) Are superior ovaries damaged by the bills of flower-visiting birds and does this preclude adaptation to bird pollinators? Botanical Journal of the Linnean Society, 187, 499-511. DOI URL
[3]	Lunau K, Ren ZX, Fan XQ, Trunschke J, Pyke GH, Wang H (2020) Nectar mimicry: A new phenomenon. Scientific Reports, 10, 7039. DOI PMID
[4]	Luo EY, Ogilvie JE, Thomson JD (2014) Stimulation of flower nectar replenishment by removal: A survey of eleven animal-pollinated plant species. Journal of Pollination Ecology, 12, 52-62. DOI URL
[5]	Luyt R, Johnson SD (2002) Postpollination nectar reabsorption and its implications for fruit quality in an epiphytic orchid. Biotropica, 34, 442-446. DOI URL
[6]	Nepi M, Stpiczynska M (2008) Do plants dynamically regulate nectar features through sugar sensing? Plant Signaling & Behavior, 3, 874-876.
[7]	Nicolson SW, Nepi M (2005) Dilute nectar in dry atmospheres: Nectar secretion patterns in Aloe castanea (Asphodelaceae). International Journal of Plant Sciences, 166, 227-233. DOI URL
[8]	Ollerton J (2021) Pollinators and Pollination:Nature and Society. Pelagic Publishing, Exeter, UK.
[9]	Ordano M, Ornelas JF (2005) The cost of nectar replenishment in two epiphytic bromeliads. Journal of Tropical Ecology, 21, 541-547. DOI URL
[10]	Plos C, Stelbrink N, Römermann C, Knight TM, Hensen I (2023) Abiotic conditions affect nectar properties and flower visitation in four herbaceous plant species. Flora, 303, 152279. DOI URL
[11]	Pyke GH, Kalman JRM, Bordin DM, Blanes L, Doble PA (2020a) Patterns of floral nectar standing crops allow plants to manipulate their pollinators. Scientific Reports, 10, 1660. DOI
[12]	Pyke GH, Ren ZX (2023) Floral nectar production: What cost to a plant? Biological Reviews, 98, 2078-2090. DOI URL
[13]	Pyke GH, Ren ZX, Trunschke J, Lunau K, Wang H (2020b) Salvage of floral resources through re-absorption before flower abscission. Scientific Reports, 10, 15960. DOI
[14]	Pyke GH, Waser NM (1981) The production of dilute nectars by hummingbird and honeyeater flowers. Biotropica, 13, 260-270. DOI URL
[15]	Pyke GH (2016a) Floral nectar: Pollinator attraction or manipulation? Trends in Ecology & Evolution, 31, 339-341. DOI URL
[16]	Pyke GH (2016b) Plant-pollinator co-evolution: It’s time to reconnect with Optimal Foraging Theory and Evolutionarily Stable Strategies. Perspectives in Plant Ecology, Evolution and Systematics, 19, 70-76. DOI URL
[17]	R Core Team (2022) R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/. (accessed on 2023-08-01)
[18]	Stpiczyńska M (2003) Nectar resorption in the spur of Platanthera chlorantha Custer (Rchb.) Orchidaceae— Structural and microautoradiographic study. Plant Systematics and Evolution, 238, 119-126. DOI URL
[19]	Wang S, Fu WL, Du W, Zhang Q, Li Y, Lyu YS, Wang XF (2018) Nectary tracks as pollinator manipulators: The pollination ecology of Swertia bimaculata (Gentianaceae). Ecology and Evolution, 8, 3187-3207. DOI URL
[20]	Wickham H (2016) ggplot2:Elegant Graphics for Data Analysis. Springer-Verlag, New York.
[21]	Xue CY, He TN, Li DZ (2002) Floral nectaries in Swertia: Anatomy and morphology. Acta Botanica Yunnanica, 24, 359-369. (in Chinese with English abstract)
	[薛春迎, 何廷农, 李德铢 (2002) 獐牙菜属植物花蜜腺形态及解剖学. 云南植物研究, 24, 359-369.]
[22]	Zhang FP, Cai XH, Wang H, Ren ZX, Larson-Rabin Z, Li DZ (2012) Dark purple nectar as a foraging signal in a bird- pollinated Himalayan plant. New Phytologist, 193, 188-195. DOI URL
[23]	Zhang HP, Wen SJ, Wang H, Ren ZX (2023) Floral nectar reabsorption and a sugar concentration gradient in two long-spurred Habenaria species (Orchidaceae). BMC Plant Biology, 23, 331. DOI