Research On The Effects Of Three Bee Species On The Reproduction Of Medicago Sativa

Plants and pollinators are important components of terrestrial ecosystems,and has formed an inseparable reciprocal relationship between them during long-term envolution.Pollinators can not only obtain nectar from plant flowers,but also transmit pollen to plants,thus affecting plant reproduction.Bee pollinators are an important part of pollinators.More species and wider distribution of bee pollinators make them have high pollinator efficiency,which play a central role in pollen transmission and reproduction of plants.Medicago sativa L.is one of the most cultivated herbage in China,but its industrialization is restricted due to its lower seed yield.M.sativa is an entomophilous plant,and its pollinators may play an important role in seed yield of M.sativa.In this study,the effects of bee pollination insects(including domesticated bee: Bombus lucorum and Apis mellifera,and wild bees: Megachile eutricharaea sp.1)on M.sativa reproduction were studied through different groups of pollinators,different densities of the same group,and different community composition,and the mechanism of pollinators was revealed from the pollinators' behavior and insect characteristics.This research not only theoretically discusses the interaction relationship between bee pollinatiors and flowering plants,reveals underlying mechanism of bee pollinators visiting plant flowers,which provide an important foundation for further understand the co-evolution between flowering plants and pollinators.And moreover,it can also provide a theoretical basis for improving the M.sativa seed production,in order to impel the industrialization of M.sativa.The main results of this study are as follows:(1)The seed yield of M.sativa was significantly different under different bee pollinators treatments.The number of pod per tiller of M.sativa under B.lucorum treatments was the highest,with increased by 1647.91%,compared to the no pollinator treatments,and the number of pod per tiller increased by 890.58% under the treatments of M.eutricharaea.There was no significant difference in germination rate,germination potential and vigor index between different species of bee pollinators.The effect of bee pollinators on seed yield of M.sativa was related to pollination efficiency.First,B.lucorum has good adaptability to M.sativa flowers(tripping phenomenon).Secondly,the visiting behavior of B.lucorum(the visiting frequency to the floret and the transfer times on the floret)was higher than that of A.mellifera and M.eutricharaea,which may make the visiting efficiency higher.Inaddition,B.lucorumis large in size and carry a large amount of pollen,which is beneficial to pollinate M.sativa.(2)The effect of domesticated bees on M.sativa seed yield was dependent on its density.The number of pod per tiller of M.sativa was the highest in B.lucorum treatments with 10 number,and there was no significant difference in the yield of M.sativa seed when the number B.lucorum is 15 and 20.The number of A.mellifera increased from 5 to 20,and the number of pod per tiller of M.sativa increased gradually.This indicatesthat the density of B.lucorum is different from that of A.mellifera when M.sativa seed production is at its highest.For seed quality,the number of B.lucorum and A.mellifera had no significant effect on seed germination rate,germination potential and vigor index.There are two possible reasons for the difference in seed yield due to different density of domesticated bees: First,when the number of domesticated bees is large,the frequency of visit to M.sativa floret increases,which may increase the pollination efficiency of M.sativa.Secondly,the competition for resources among bee pollinators increases the frequency of visiting floret,which increases the pollination opportunities of M.sativa floret.(3)The seed yield of M.sativa was different under different proportion of B.lucorum and A.mellifera.The pod number per tiller and seed number per pod of M.sativa were the highest when the ratio of B.lucorum to A.mellifera was 2:1,but the thousand kernel weight was lower.There was no significant difference in seed quality(germination rate,germination potential and vigor index)between different treatments.Since there was no significant difference in the pollination behavior of B.lucorum in the treatment of different proportions,the pollination behavior of B.lucorum did not play a major role.In contrast,A.mellifera had a longer residence time on floret in 2:1 treatment,which may improve the pollination efficiency of M.sativa.Therefore,both the number of B.lucorum and the visiting behavior of A.mellifera play a major role in the seed yield of M.sativa.In conclusion,the reproductive effect of bee pollinators on M.sativa depends on the species,density,and composition of pollinators,such effects are driven by flower characteristics,pollinator behavior and pollinator characteristics.This study provided important theoretical basis for enriching the reciprocal mechanism between plants and pollinators and has practical significance in the seed production of M.sativa.