Study On The Characteristics And Pollination Efficiency Of The Extrafloral Nectaries In Sambucus Javanica(Caprifoliaceae)

Sambucus javanica,also known as Sambucus Lindl,is a tall perennial herb or subshrub of the genus Sambucus Linn in Caprifoliaceae.It has strong adaptability to the environment and high medicinal value.It is widely distributed in China.The extrafloral nectaries of Sambucus javanica are scattered in the inflorescence,whose color change with the growing season and do not fall off.In this study,three natural populations of Sambucus javanica were selected from Wenjiang District,Chengdu City and Yucheng District,Ya’an City(population one、population two),Sichuan Province.The experiment mainly focused on its developmental anatomy,the activity and distribution ratio,the amount and concentration of extrafloral nectar,the avoidance effect of different kinds of ants,and the pollination efficiency of bees.The results show us follows:(1)The developmental anatomy of extrafloral nectaries of S.javanica: the development time of extrafloral nectaries is slightly earlier than the flowering time,and the structure and cells of the nectaries have changed obviously in different development periods.The nectaries are located on the axis of inflorescence,which belong to the nectaries on axis according to the shape and the position of the nectaries.The nectaries are composed of secretory epidermis,nectary producing tissue and vascular bundle.The nectar producing tissue is located around the cup-shaped nectary,and the nectar is released through the stomata.(2)The active status and distribution proportion of extrafloral nectaries of S.javanica in different flowering stages: the extrafloral nectaries of two populations of Ya’an were the most active in the blooming stage,and the number of active extrafloral nectaries in the blooming stage was significantly higher than that in the early and late stage(P < 0.001),accounting for 70% of the total extrafloral nectaries,while the number of active extrafloral nectaries in the early and late stage of flowering accounted for about 30% respectively.There was a partial in the number of active extrafloral nectaries in the two adjacent flowering stages.The number of active extrafloral nectaries in the first flowering stage was significantly higher than late stage in population one(P < 0.01),but there was no significant difference in the number of active extrafloral nectaries between the two stages in population two(P = 0.15).The number of active extrafloral nectaries was 24.1±7.5(SD),51.8±14.4 and 19.4±5.9 per plant respectively in the early,blooming and late stage of population one,While the number of active extrafloral nectaries was 13.1±5.6(SD),35.2±15.5 and 15.1±7.8 per plant respectively in the early,blooming and late stage of population two.The number of total extrafloral nectaries in the two populations was72.6±22.7(SD)and 46.0±20.9 per plant,respectively.(3)The amount and concentration of nectar secreted by the extrafloral nectaries of S.javanica: the average amount of nectar secreted by a single extrafloral nectary within 24 hours was 0.037μL(SD = 0.015),and the concentration of nectar was 12.28% at 24 ℃.(4)The repellent effect of S.javanica on different kinds of ants: The results showed that there was no significant repellent effect on the four ants: Camponotus mitis Smith,pristomyrmex puncens Mayr,Pheidole nodus Smith and Myrmica bactriana ruzsky(r =0.404,df = 3,P = 0.939).(5)The pollination efficiency of bees to S.javanica in different conditions : there was no significant difference in the flowering number of the flower branches of S.javanica with and without extrafloral nectaries(P = 0.990),but there was a significant difference in the fruiting rate(P < 0.01)after one visit of bees,that is,the pollination efficiency of bees to the flower branches of S.javanica with extrafloral nectaries(32.65%)was significantly higher than that of bees to the flower branches without extrafloral nectaries(27.47%)(P <0.01).In conclusion,there are great differences between the structure of extrafloral nectaries and that of flower,and the structure of nectaries and tissue cells have changed obviously in different stages of development.At the inflorescence level,the number of active extrafloral nectaries was the largest at the flowering stage.The flower has no obvious repellent effect on the several common ants,which may be because it has the morphological characteristics of space separation between ants and flowers.The extrafloral nectaries of S.javanica can attract a large number of pollinators and improve the pollination efficiency of pollinators.