Nectar Dynamics and Sugar Composition in Flowers of Silene and Saponaria Species (Caryophyllaceae)

Abstract: Nectar production in Saponaria officincilis and in five species of Silene (S. ciba, S. dioica, S. noctiflora, S. nutans, S. vulgaris ) was examined during two consecutive years (May to July 1993, and May to June 1994) in the Botanical Garden of the University of Giessen. Nectar volume and sugar concentration were studied in relation to time of day, flower sex, flower age, and flowering stage. Nectar amount in all species studied (except S. dioica ) increased in the afternoon or in the evening until midnight (or until the early morning in S. nutans ). After midnight and until midday, nectar volume in non-visited flowers (except S. dioica ) decreased. Nectar volume in non-visited S. dioica flowers increased constantly with flower age, indicating a stable nectar secretion rate, possibly favouring both day- and night-active flower visitors. Even at the time of highest nectar secretion, all species studied presented several nectarless flowers. Sucrose dominance in the nectar of the nocturnal species S. nutans and Saponaria officinalis fits well with the general syndrome of flowers pollinated by hawkmoths. The syndrome also applies to the nocturnal but regularly selfing, S. noctiflora . The more generalis-tic species S. dioica and S. vulgaris , which are regularly visited by bumblebees as well as nocturnal moths, secreted hexose-domi-nant nectar. Unexpectedly, Silene alba , the only nocturnal species that strictly excluded day-active flower visitors by closing flowers during the day, also secreted hexose-dominant nectar. In some cases, nectar volumes and nectar concentration differed significantly between hermaphroditic, male, and female flowers. Female flowers of S. alba, S. dioica , and S. nutans contained significantly less concentrated nectar than male or hermaphroditic ( S. nutans ) ones. In S. noctifiora and S. vulgaris the difference was not statistically significant but nectar concentration did show the same tendency.