獐牙菜属四种植物花蜜特征的比较

Comparative floral nectar attributes in four Swertia species(Gentianaceae)

花蜜的分泌特征在种间、种内以及植株内不同花朵间的变异决定了花朵对访花动物的吸引和访花模式,进而影响传粉效率和植物繁殖成功。然而,我们对花蜜分泌特征变异性的认识还不够深入,缺乏野外实验数据。研究选取龙胆科獐牙菜属(Swertia)4种同域分布的植物,即獐牙菜(S.bimaculata)、西南獐牙菜(S.cincta)、贵州獐牙菜(S.kouitchensis)和紫红獐牙菜(S.punicea)为研究对象,开展花蜜特征及其变异性的研究。通过比较种内套袋24 h和自然状况下花朵的3个花蜜特征,即花蜜体积、糖浓度和含糖量(重量)的异同,以及同一植株不同花朵间花蜜特征的差异,试图阐明花蜜特征在种间、种内植株间和个体内的变异性。结果显示獐牙菜属4种植物的花蜜特征有显著差异;套袋24h处理和自然状态花朵的花蜜特征大多有显著差异,仅有獐牙菜和贵州獐牙菜的糖浓度在两种处理间差异不显著;相邻两朵花的糖浓度都具有显著正相关,然而,花蜜体积和糖含量在相邻花朵间的相似性较低;相邻两朵花花蜜特征的正相关在套袋处理花中高于自然状态,显示自然状态下花蜜特征的高变异性。研究结果表明花蜜的变异性包括:(1)花蜜的种间差异可能与传粉昆虫类群有关;(2)同一植株相邻花朵间花蜜糖浓度显著相关,表明花蜜体积和含糖量相互调节使得花蜜糖浓度保持在相似区间内;(3)花蜜特征在个体间和花朵间较高的变异性可促使传粉者在植株间访问,从而提升植物繁殖成功率。

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.