Thestudy Of Reproductive Ecology On Nectar Presenting Strategiesin Four Nectariferous Plants

Nectar is an important reward produced by plant to attract visitor.The variation of nectar volume on the temporal and spatial scales is known as thenectar presenting strategies.By regulating the secretion dynamics and distribution pattern of nectar,the plant can manipulate foraging behavior of pollinators during or following a visit to it,thereby achieve its own reproductive success.In this paper,4 typical nectar nectariferous plants were used as materials.To provide a new insight into the role of pollination in plant reproduction and evolution,we systematically studiedthe role of nectar presenting strategies in plant reproductive ecology from the perspective of ecology and evolutionary biology.The main results and conclusions are as follows:1)For nectariferous plants,the nectar volume per flower is not constant,and there are even some nectarless flowers.However,the variation of nectar volumeamong the flowers or inflorescences has an important influence on the reproduction of the plant.Through the investigation on the natural population of Corydalis ambigua Chem.& Schlecht(Fumariaceae),we found that there was a significant variation in nectar volume of this species.The nectar accumulation per flower is 0.61?l,and the Coefficient of variation is 1.48.There is a certain frequency of nectarless flowers in the natural population of C.ambigua.We investigate the distribution patterns of nectarless flowers in natural populations and their variation among the populations and years in a spring-flowering self-incompatible perennial herb plant,C.ambigua,we observed the foraging behavior of bumblebees to nectariferous and nectarless inflorescences.We also examined the differences in reproductive success between inflorescence types and the effect of nectar production on flower production of the next flowering season.The results indicated that the distribution frequencies of three inflorescence types with refer to nectar containting varied among years and populations,and also between the sizesof inflorescence,furthermore,the distribution frequencies of nectarless flower varied among positions of inflorescence.However,nectarless flower is ubiquitous in the natural population of this species.Although the characteristics of the single flower nectar production were stable during the growing season,there were about 20% variationsin the nectar production status of plants between years.The results indicatedthat the nectar production status of C.ambiguawas not entirelydetermined by genetic factors,and also explain the reasons for the fluctuation of the frequency of nectarless floweramong the populations and years.Bumblebees visited both inflorescence types with equal frequency but different foraging behavior,which resulted in lower seed production in nectarless inflorescences.However,nectarless inflorescences may save more energy and result in larger bulbs,which produce more flowers in the next flowering season.Furthermore,we found that nectarless floweris conducive to breaking pollinators' regional visitingbehavior,reduce their numberof successive visits within inflorescence and handling time on each flower,thus the distance of the pollen flow andmale fitness would be enhanced.However,nectariferous flower is beneficial to improve seed set and enhance the female fitness.2)In many plants,the flowers at different stages of development will show different color and nectar volume.Floralcolorchanges during anthesisarecommonin Weigelaandtheretentionofpost-changeflowers for a few days hasbeeninterpretedas a mechanism to increase attractiveness from a long distance and shorten pollinators' lingering time on theinflorescence(s)of individual plants.In the present study,we investigated the temporal pattern and stabilityof floral color changein the shrub Weigela japonica var.sinica.We also investigated the relationship among flower color change,nectar volume,fecundity andflower-visiting behavior of Bumblebees.The significance of flower color change in reproductive ecology to this species was discussed.The results indicated thatover the 4-day anthesis,thecolor of the corolla in this species changes from white to red and the color cue changes from yellow to purple.Theduration of both the white phase and the intermediate phase is approximately 1 day and the duration of the red phaseis approximately 2 days.Our studies showed that color change in Weigela japonica var.sinica is age-dependent butindependent of pollinator visits and flower pollination.At different developmental stages,the flower color,nectar volume,and fecundity are related events.Bumblebees could discriminate and showfeeding preference for different color flowers,thus improve the foraging efficiency and pollination efficiency.TheM-phase flower was helpful to furthemore improve the rate of reproductive success.The R-Phase flower lost most of both the male and femaleresidual reproductive ability and retained no rewards for pollinators,but could reduce the geitonogamy and increased pollen flow.It took at least 3 days for a pollen tube to growto the ovules and achieve fertilization.Thus,retention of post-change flowers is necessary for the completion ofpollen tube growth.Our results indicate that the temporal pattern of color change,reproductive potential and nectar presenting strategies are related events.Thus,flower color change is an adaptive reproductive strategy for W.japonica var.sinica.3)The foraging behavior of most pollinators is regulated by the volume of nectar.As to the nectariferous plants with a variety of pollinators,their specific nectar presenting strategies may have different effects on different kinds of pollinators.We chose the Blueberry growing in the greenhouse as the experimental material.By using different kinds of bees(Bombus terrestris,Apisceranaand Apis mellifera)to provide pollination services in 3 greenhouses,we simultaneously examined the effects of nectar presenting strategies of Blueberry on visiting behavior of three kinds of bees.We also inspected the pollination efficiency of different kinds of pollinators and their effects on fruit quality and yield.Furthemore,artificial pollination with different pollen grains number(low,medium and high)were conducted to test the effects of pollination on fruit yield and quality.The results indicated thatBlueberry is a kind of plant with along single flowering period.The flower secretes nectar throughout the anthesis(6-8 days).Among the three kinds of bees,B.terrestrishas the lowest handing time per flower and the most number of pollinated flowers per minuteamong the three kinds of bee.The pollination efficiency of B.terrestris(buzz-pollination)is higher compared with the A.ceranaand A.melliferathe(contact polliantion).Under the polliantion ofB.terrestris,the larger quantity of pollendeposited on stigma result in the better fruit quality and yield.The results of artificial pollination showed that although the larger quantity of pollen could improve the yield and quality of fruit,the excessive amount was not effective.At the group level,thepollination can be completed earlier by B.terrestristhan the other two kinds of bees,thereby shortening the single flowering period to reduce the resource consumption of nectar production.Our results show that the floral traits of blueberry limit thesingle-visit pollination efficiency of polliantor.Therefore,it is necessary to continuously secrete nectar to attract more efficient access to maximize reproductive fitness.4)The pattern of resource allocation has an effect on the nectar presenting strategiesof flower growing in different position of the inflorescences,which may affect the pollinator visiting behavior and plant reproductive success.This study selected Hosta undulata Bailey as experimental materials to test the spatial position effect of nectar.The results indicated that the physiological structure of inflorescence lead to the quantity of resources available for flowers in different position of inflorescence is different.Thereby,the flower in lower positon of inflorescence priori to access resources and with more nectar than the middle and upper.However,the flowers in different position of inflorescence had similar nectar secretion dynamics(nectar secretion rate showed a single peak distribution and the nectar accumulation increased with time).The foraging behaviors of pollinators changed the spatial distribution pattern and secretion dynamics of nectar.For each pollinator(Bombus ignitus Smith,Apis mellifera ligustica Spin.andXylocopa sinensis Smith.),the handling times per flower among three positions of inflorescence were significantly different,which resulted in the number of pollen removal and pollen deposition of lower flower were significantly higher than that in the middle and upper.In the morning,the visited frequency and handling time of flower were higher than in the afternoon,which result in the speedrate of pollen removaland pollen depositionwere higher in the morning than in the afternoon.The quantity of pollen removal and pollen deposition showed a trend of increasing with time,but in the afternoon almost stopped growing.The study demonstrates that the flowers of H.undulatawith rapid nectar secretion in the morning but stop the nectar secretion and appearabsorption phenomenon in the afternoon.The significance of this kind of nectar presenting strategiesin the species is that its flowers with ephemeral flowering period and long style which limits the time for effective pollination.Therefore,theflowers need to get a large number of efficient accesses as soon as possibleto achieve the maximization of reproductive fitness.However,the pollen depostion on stigmaduiring later time of the day can not achieve fertilization.Absorption of nectar at this time may be beneficial to the subsequent seed production and reduce invalid access to avoid damage to reproductive components.In conclusion,the nectar presenting strategies of plants have an important influence on reproductive success,The plants can adjust the variation of nectar volume(temporal and spatial)to affects the visiting behavior of pollinators and regulate their own porcess of pollen removal,transmission and deposition to achieve the maximization of reproductive fitness.