Aims Floral nectar plays a vital role in plant reproductive success by attracting pollinators.Nectar traits of a flower can depend directly on plant characteristics other than environmental factors and exhibit extensive flower-and plant-level variations.studies on nectar traits frequently focused on intraplant variation for dichogamous plants,but few have paid attention to both intra-and interplant nectar variations in relation to plant characteristics.revealing within-and among-plant variation and its relative magnitude is important for our understanding of how pollinator-mediated selection can act on nectar traits and evolution of nectar traits.Methods Through investigating protandrous Aconitum gymnandrum populations at the alpine meadows and Wetland Ecosystems research station of lanzhou university,we examined the relationships between nectar production per flower and plant characteristics(e.g.flower position within inflorescences,flo-ral sexual phases,flowering time,inflorescence size and floral attractive traits).Important Findings A.gymnandrum exhibited a declining gradient in the nectar volume along inflorescences,with more nectar in basal flowers than distal ones.Protandrous flowers of A.gymnandrum did not show gender-biased nectar production while the nectar volume varied with differ-ent stages of floral sexual phases.The significant correlation between the first flowering date of individuals and the mean nectar volume per flower was positive in 2013,but became negative in 2014,sug-gesting complex effects of biotic and abiotic factors.The mean nectar volume per flower was not related to inflorescence size(the num-ber of total flowers per plant).Furthermore,nectar production was weakly associated with floral attractive traits(the petal width and the galea height),even if the effect of flowering time of individuals was removed,suggesting that the honesty of floral traits as signals of nec-tar reward for pollinators is not stable in this species.
Aims sex allocation in plants is often plastic,enabling individuals to adjust to variable environments.However,the predicted male-biased sex allocation in response to low resource conditions has rarely been experimentally tested in hermaphroditic plants.in particular,it is unknown whether distal flowers in linear inflorescences show a larger shift to male allocation relative to basal flowers when resources are reduced.in this study,we measure position-depend-ent plasticity of floral sex allocation within racemes of Aconitum gymnandrum in response to reduced resource availability.Methods using a defoliation treatment in the field applied to potted plants from a nested half-sibling design,we examined the effects of the treatment,flower position,family and their interactions.Important Findingsallocation to male function increased with more distal flower posi-tion,while female allocation either did not change with position or declined at the most distal flowers.Defoliation significantly reduced the mass of both the androecium and gynoecium,but not anther number or carpel number.gynoecial mass declined more strongly with defoliation than did androecial mass,resulting in a significant increase in the androecium/gynoecium ratio as predicted by sex allocation theory.Plastic responses of androecium mass and gynoecium mass were affected by flower position,with less mass lost in basal flowers,but similar plastic magnitude in both sexual traits across flower position lead to consistent variation in the androecium/gynoecium ratio along the inflorescence.a sig-nificant treatment*paternal family interaction for the androecium/gynoecium ratio is evidence for additive genetic variation for plastic floral sex allocation,which means that further evolution of alloca-tion can occur.
