Comparative floral nectar attributes in four Swertia species(Gentianaceae)
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.
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