The Study On Diversity And Effectiveness Of Pollinators In Geranium Delavayi

A generalized pollination system usually involves various flower visitors,among which bees remove amounts of pollen from anthers.There is a conflicting interest of pollen between bees and stigmas.If high amounts of pollen are collected by bees in a plant species,less pollen would be available for deposition on the stigmas.To understand how bee-pollinated plants reduce pollen loss from bee collection,we investigated plant-pollinator interactions in Geranium delavayi.We measured floral traits,including nectar volume and sugar concentration,the chemical components of pollen,observed the pollinator visitation frequency and pollination efficiency,and determined the diversity and effectiveness of pollinators.We also explored the possible reasons why bumblebees do not actively groom pollen of G.delavayi.The main results are as follows:We observed that pollen gradual presentation in G.delavayi may reduce the amount of pollen removal per visit by bees.It is protandrous with almost no overlap between male and female function,avoiding intra-flower selfing.Our pollination experiment showed that this herb was partly self-compatible and seed production needed pollinator visits.Open radial flowers with pink petals produce nectar and pollen grains are exposed,to diverse insect visitors.Floral visitors were diverse including bumblebees,honeybees,solitary bees,hoverflies,flies,butterflies visited the flowers.Bumblebees visited flowers with highest frequency.They only absorbed nectar when visiting flowers,instead of actively grooming pollen grains stuck to their bodies.Due to their larger body size,they were easy to touch stigma and anthers,and had higher pollination efficiency.Thus,bumblebees were effective pollinators.Nectar concentration did not differ between male and female phases,but the nectar volume in male phase was significantly higher than in female phase,consistent with the higher visitation frequency in male phase.The highest component of nectar was sucrose,followed by fructose and glucose.The nectar with high sucrose content is favored by long-tongue bees.High performance liquid chromatography(HPLC)analysis showed the contents of geraniin,corilagin and gallic acid were relatively high in pollen,but lower in nectar than in leaf,petal and pollen.The toxic pollen may deter bumblebees grooming pollen into corbiculae.In addition,the protein and the lipid content in pollen was 22.6%and 13.9%,and the protein-lipid ratio was about 1.64,not the pollen type that bumblebees perfer feeding.Our experiments show that G.delavayi has a variety of pollinators,and bumblebees are the most effective pollinators in the natural environment.The presence of toxic substances or low quality in pollen of G.delavayi may effectively reduce bee collecting.However,further studies on the effects of pollen intake on bumblebees are needed in the future.