| Primulina leyeensis is a species,which is adaptive to the limestone habitat.It has high requirements for ecological habitat and is also very sensitive to the habitat.So it is an ideal material for the study of adaptability of plants to the ecological environment.Because of the special geological structure,Tiankeng forms different habitats.Therefore,in different locations of different Tiankeng,there are different plant community structures.To a certain extent,Tiankeng can affect the growth and distribution of plants and provide refugea for plants.Meanwhile,the distribution of plants affects the evolution of the habitat in turn.The paper studies the adaptive mechanism of Primulina leyeensis to Tiankeng from leaf morphology,photosynthetic physiological,flowering phenology and breeding system by means of field investigations and indoor experiment on blades,aiming at finding out that how does Primulina leyeensis adapt to the special Tiankeng habitat,and revealing the relationship between the Tiankeng species and the Tiankeng habitat.The main results are as follows:(1)Habitat characteristics of Primulina leyeensis in TiankengAfter observing the three habitat factors of light,temperature,humidity of Primulina leyeensis in 13 Tiankeng distribution points,we found that its habitat characteristics could be divided into three types:The bottom or cave is dark and damp,and the temperature is stable,and the main species of the community is the shade herbaceous plants.The middle of the Tiankeng or the export of karst cave is scattered light,moist,and the temperature is stable,the community species are shade grass and bush.The top of the Tiankeng has direct sunlight,dry and wet seasons aer clear,temperature fluctuations is large,and has formed a climax community.(2)The morphological adaptation mechanism of Primulina leyeensis in TiankengIn order to study the morphology adaptation mechanism of the Primulina leyeensis to the Tiankeng habitat,the surface morphology,leaf anatomical structure and leaf surface appendages were taken into observation.The results showed that Primulina leyeensis of different habitats differ greatly in their height and number of blades(P<0.01).It can be demonstrated in detail as follows:Primulina leyeensis which are in the top and middle of Tiankeng adapt themselves by reducing the height and size of the plants,increasing leaf epidermal hair and white reticulate,thickening the blade conducive for reducing the number of blades;Primutlina leyeensis which are in the dark bottom or cave,in order to increase illuminated area and absorb more light,increase the number of leaves and the height of plants,change the arrangement way of the leaves so that they can ensure the normal growth of the plant.There are remarkable differences in blade anatamoized structures such as the width of the palisade tissue and spongy tissue,upper epidermis,lower epidermis,blade transversed section.Primulina leyeensis which are in the top and middle of Tiankeng have differences of palisade tissue and sponge tissue are obvious,the number of palisade tissue layers are closely arranged in a strip shape.However,Primulina leyeensis which are in the dark bottom or cave environment have the difference of its palisade tissue and spongy tissue are unapparent and its sponge tissue is presented in merely one row in the shape of oval or round.(3)Photosynthetic physiological adaptation mechanism of Primulina leyeensis in TiankengThrough determination and comparation of the photosynthetic physiological indexes such as leaf area,chlorophyll content,layers of palisade tissue,leaf weight ratio,productivity index,the results indicate that:the physiological indexes showed significant differences(P<0.01).In environment with enough light,Primulina leyeensis have more chlorophyll content,possess more palisade cell layers,productivity index,the organic matter accumulation of photosynthesis,and leaf weight ratio compared to those in other habitat.The photosynthetic physiological indexes of Primulina leyeensis,which are in the environment without adequate light,decrease apparently,and the plants absorb more light sources by increasing leaf area and enhancing photosynthesis.(4)The flowering phenology and breeding mechanism of Primulina leyeensis in TiankengThe early flowering of Primulina leyeensis is in the end of June and the final flowering is in early August each year.A single flower lasts for 4 to 7 days,the population flowering duration is 15 to 26 days.For each plant flower,the number of inflorescence is 1 to 4,and 1 to 7 flowers per inflorescence.Corolla purple,entomophily,corolla tube height of each habitat showed significant differences(P=0.028),and the rest characteristics of the flowers show very significant differences(P<0.01).There are great differences in setting percentage due to their different habitats(P=0.001).According to bagging experiment,the plants showed self-compatibility.The setting percentage is as low as 40%under the natural selection,but the setting percentage of cross-pollination is more than 90%.The flowering phenology curve of Primulina leyeensis in the sample plots P1,P2,P3,P4 which are in the bottom or cave present bimodal "M" type curve,but other sample plots present unimodal"∧" type curve.Primulina leyeensis under different environment show different phenological periods and phenology curve,but all present a pattern of concentrated flowering.The phenophase of Primulina leyeensis which are in the top of the Tiankeng is ahead due to enough light.In order to adapt to big pollination insects,each parts of the flower thicken,flower bud differentiation Increase,pollen flow of the population Increase,evolving toward improving setting percentage.The phenophase of Primulina leyeensis which are in the bottom or cave of the Tiankeng delays,the florescence of single flower lengthens.Light and humidity cause side affect on flower bud differentiation,leading to small population,pollen flow and less attractive pollinators and lower seed setting rate.In such condition,a reproductive mechanism based on vegetative reproduction may exist. |
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