| In recent years,with the rapid development of pollination biology,more and more biologists have been studying the reproductive strategies and pollination mechanisms of plant survival in extreme environments.Lancea tibetica is one of the common species in alpine meadows distributed in the high altitude areas of the Qinghai-Tibet Plateau,in order to explore the reproductive strategies,pollination mechanisms and resource allocation strategies of L.tibetica under the extreme environment of alpine hypoxia,wind and strong ultraviolet radiation.In this study,L.tibetica,an alpine plant in Lhasa Valley,was taken as the research object,three study plots [sample plot 1(3790m),sample plot 2(3940m)and sample plot3(4090m)] were set up along the elevation gradient in the mountain alpine meadow of Nangeregou on the north side of Lhasa River.The flowering phenology,floral structural characteristics,flowering dynamics,pollen viability and stigma receptivity of L.tibetica were systematically studied by field observations and laboratory experiments.The species,number and pollination behavior of the main pollinating insects of L.tibetica were identified and counted.the pollen ovule ratio,hybridization index and artificial bagging experiment were used to determine the breeding system.Finally the strategies of resource allocation(sexual allocation,reproductive allocation)in flowering period were explored,and the results are summarized as follows:1.In the natural state,the first flowering period of the Lhasa Niangregou L.tibetica population begins in mid-to-early May,and the full flowering period is concentrated in earlyJune,it lasts for 14 days.The flowering period ends in mid-July,and then it enters the fruit period.The fruit mature period is long(July to October).With the increase in altitude,the flowering time of the L.tibetica in various plots will be delayed by about 7-10 days;Single flower blooming plot1(3790m)is 4 to 5 days,plot 2(3940m)and 3(4090m)are 5 to 6 days,single plant blooming time plot 1(3790m)20-25 days,15-20 days for plots 2(3940m)and 3(4090m)(mainly related to the number of buds per plant);L.tibetica is a raceme,with 3-10 flowers per inflorescence clustering and growing at the top,showing gradual opening.Before the flower of L.tibetica opens,the length of the stamens is shorter than the pistil,and the anthers are lower than the stigma.After opening,the stamens elongate rapidly and significantly.The anthers eventually grow to the lower part of the stigma or the same height as the stigma and no longer grow.The pistil stigma grows slowly to the mouth of the corolla tube and no longer grows;L.tibetica pollen is already active and high before the flower opens(the anthers are not cracked),and then gradually decreases.The anthers gradually crack and loose their powder on the day of flowering,lasting for 5 days.The stigma is basically not receivable before the flower opens,and the receptivity of the stigma at each altitude is the strongest when the flower opens for 2 to 3 days,which lasts for 6 days;To sum up,it shows that there are partial dichogamy and herkogamy phenomena of male and female in L.tibetica,which reduces the possibility of self-pollination of L.tibetica to a certain extent,and the overlapping functions of pistils and stamens in the later stage can make up for the defects of sexual reproduction in the condition of limited pollinators and insufficient outcrossing.2.The hybridization index(OCI)of L.tibetica is equal to 4.Showed that the breeding system of L.tibetica is self-compatible,facultative outcrossing,and sometimes requires pollinator type;The number of pollen in a single flower of L.tibetica is about28830.09±961.175,the number of ovules is 249.79±4.17,and the pollen-ovule ratio(P/O)is117.52±4.34.Showed that the breeding type of L.tibetica belonged to the Facultative autogamy;The seed setting rate was 0 in the experiment of emasculating and bagging,which indicated that there is no apomictic reproduction in L.tibetica;The seed setting rate of L.tibetica in the natural state is 92.5%,and the seed setting rate without emasculation and bagging is 77.5%,which is not much different from the seed setting rate in the natural state,indicating that the reproductive process of L.tibetica had a high self-affinity,which required the participation of pollinators;The seed setting rate of L.tibetica in the experiment of removing the corolla and not bagging is 10%,compared with natural pollination of seed setting rate is low,corolla plays an important role in successful pollination.The L.tibetica corolla is not only for pollinators to visit flowers provide a stopping point and because of the white beard on the lower lip of abdomen,it can stick to the pollen,and it can greatly increase the pollination rate relative to the direction of the stigma;The seed setting rate of castration without bagging is 22.5%,which is lower than that of natural pollination,indicating that the pollen of the L.tibetica will affect its own fruit setting.According to the results of hybridization index,pollen ovule ratio(P/O)and bagging experiment,it can be concluded that the breeding system of L.tibetica is dominated by outcrossing,and self-crossing is supplemented.3.Halicus sp.and ants are the main pollinators of the L.tibetica,and the most effective pollinator is the Halicus sp.;The body size and structural characteristics of the Halicus sp.and the ant are extremely similar,and they can be well adapted to the floral characteristics of the L.tibetica.They can smoothly penetrate into the deep part of the L.tibetica corolla tube.They are entering or leaving the corolla tube of L.tibetica,and in the process of turning around and foraging in it,all parts of its body that are contaminated with pollen can touch the anthers and stigma to complete the pollination;The number of single visits by Halicus sp.is large and the time interval is short,with each visit duration is about 1 to 2 minutes.The daily activity pattern was unimodal,which usually appears around 11:30 AM and peaked around13:30 PM,then quickly reduced to no visit;The number of ants in the population is large and the activity is frequent.The tracks of ants can be found throughout the day.The number of visits to flowers is mostly from morning to noon,and a single visit lasts about 1 to 1.5minutes.4.The correlation between the allocation of flowering resources and altitude showed that the individual size of L.tibetica decreased gradually with the increase of altitude,and a extremely significant positive correlation between reproductive distribution of L.tibetica and altitude(P<0.01),and a extremely significant negative correlation between nutritional distribution of L.tibetica and altitude(P<0.01).That is,with the increase of altitude,the relative resource input of the L.tibetica to the reproductive organs shows an increasing trend,while the relative resource input to the vegetative organs shows a decreasing trend;Comparing the biomass of various organs of L.tibetica at different altitude gradients showed that the biomass of each part of L.tibetica in the three plots all accounted for the largest proportion is leaf biomass and the smallest proportion is stem biomass.The ground biomass,vegetative organs biomass and reproductive organ biomass are decrease with the increase of altitude;The relationship between individual size and biomass allocation in the three plots indicates that both reproductive allocation and sex allocation in flowering period of L.tibetica are dependent on the individual size.That is,the larger the individual(the more aboveground biomass),the lower the reproductive allocation and the higher the reproductive input,and the resource input in the pistil and stamen biomass(b>0),but the sex allocation(the proportion of total flower dry weight to stamens)decreases with the increase of individual size(b<0),and larger individuals had more allocation to pistil biomass(total stamen biomass/total carpel biomass b<0).The statistical insignificance may be caused by the different flowering dates between individuals at the time of sampling. |
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