| Magnolia officinalis subsp. biloba is belong to Magnoliaceae, Magnolia. M. officinalissubsp. biloba is recorded as the2ndendangered species for conservation in China. And it onlyoccurs in a few counties in Shanxi, Gansu, Sichuan, Guizhou, Hubei, Hunan, Guangxi. In thispaper, We conducted field observations and artificial pollination experiments on the floralbiology, pollination process and breeding system of M. officinalis subsp. biloba in threepopulations in Zhejiang Province. We collected fruits and seeds of M. officinalis subsp. bilobafrom different populations to study the morphological differentiation of fruits and seeds amongpopulations. We divided the orientation into east, west, south and north, the canopies into toplayer, middle layer and bottom layer, fruits and seeds were collected from different orientationand canopy, and their morphological indexes were measured. Based on the above-mentionedstudies, we analyzed the factors resulting in the endangering of M. officinalis subsp. biloba.The purpose of the research is to understanding why this species is endangered and to developsuccessful conservation strategies for this species, to rich the theory of endangered plantprotection, to set up new ideas for studying other plants' endangered mechanism. The resultsshow as followings:1) The floral syndrome of M. officinalis subsp. biloba: the flower is bisexual, their flowersare big and grow in the top of branches alonely. Every flower has9~12fleshy petals, and thepetals are oblong obovate, outer3petals are pale green or light purple, inner petals are white.The flowers are herkogamy, the number of stamen is usually more than90, the arrangement ofcoalescent pistil is spiral, the part of papillations could accept pollens.2) The flowering traits of M. officinalis subsp. biloba: The flowering lasted4~5d and theprocess for one flower of this species can be divided into four periods by the flowermorphology and dehiscence: bud swelling, flower opening, full blooming, flower withering.According to the study of the flowering phenology of M. officinalis subsp. biloba at populationlevel, we can see that there was no flowering peak and M. officinalis subsp. biloba belongs to continue blooming type. The population flowering started in April and came to an end in May,the flowering span among population is about30days. The mean floral quantity was171.4~188.8, the mean flowering amplitude was5~7per plant per day and synchronous indexwas0.839. Those results had differences in different sites and years.3) The aromatic compounds and its traits of M. officinalis subsp. biloba: Both thearomatic compounds and their relative content in M. officinalis subsp. biloba wild specie andcultivated specie were distinctly differert, terpenes were the major compounds of flower bud ofM. Officinalis subsp. biloba, camphene,(Z)-3,7-dimethyl-1,3,6-Octatriene, caryophyllene,3,7-dimethyl-1,6-Octadien-3-ol were identified in both the wild specie and cultivated specieand their relative content was high; there are obvious differences in constituents and theirrelative contents of aroma between pistil-stamen and petal of M. officinalis subsp. biloba wildspecie during different flowering stages, the components in aroma from pistil-stamen and petalcan be divided into eight types, viz. terpenes, alcohols, arenes, ethers, aldehydes and ketones,esters, alkanes and nitrogenous-containings and terpenes are the main constituents. Accordingto organoleptic evaluation and GC-MS analysis results, it is comprehensively judged thatterpenes are the major compounds in aroma of M. officinalis subsp. biloba flower, and petal isprobably the most important part for releasing aroma, while pistil-stamen plays an additionalrole in releasing aroma process.4) The breeding system of M. officinalis subsp. biloba: It would be termed xenogamy, itspollination needs pollinators. The outercrossing index(OCI) was4and pollen-ovuleratio(P/O)is5726.86, the artificial pollination studies showed that fruit set rate of bagged butunemasculation was0, fruit set and seed set of cross-pollination increased14.25%and43.66%than those of natural condition. Based on the those results, the breeding system is xenogamy.5) The pollen and stigma of M. officinalis subsp. biloba: The pollen viability of the flowerwas high, and stigma receptivity was strong, but there were only5-6h overlap of stigmareceptivity with pollen dispersal. The pollen viability was best in the day of pollination, meanviability was94%, they could keep vigor of6days. The stigma receptivity was strong at bud stage, but it decreased significantly after pollination, so the time of pollen and stigma keepinghigh viability was short.6) The pre-fertilization barriers of M. officinalis subsp. biloba: There were only a fewpollens adhered on stigmas after open pollination, after self-pollination all pollens adered onstigmas were not germinate, after cross pollination in one plant many pollens adered onstigmas could germinate, but their germination was tardy, and after4hours of pollination, mostpollen tubes stopped growing, and there were many expand pollen tubes and twist pollen tubes,few of pollen tubes could enter into styles through stigmas,but callose was also found inpapillose cells of stigma.7) Variation of fruit and seed characters of M. officinalis subsp. biloba: The number offruits in wild environment is rarely, there were significant differences of characteristics of allthe traits in different populations and the variation came from both among individuals andwithin an individual, fruit was easily affected by the environment. Crown densities, soilnutrient, orientation and canopy have an important effect to fruit traits. altitude, orientation andcanopy have an important effect to seed traits.In conclusion, the factors resulting in the endangering of M. officinalis subsp. biloba areas follows: Herkogamy and heterogamy, the small mean floral quantity cause the pollination behindered; Self-pollination and cross pollination in one plant cause the growth of pollen tubesbe hinderec; Insufficient light in the wild cause low setting and seeds' dysplasia. |
PDF Full Text Request