| In recent years,due to global climate change and long-term human disturbance,such as grazing,random reclamation,etc.,the natural grassland has seriously degraded,with a large number of poisonous weeds invading and spreading,seriously threatening the balance of grassland ecosystem and sustainable development of livestock husbandry.As one of typical poisonous weeds in degraded grassland,Stellera chamaejasme is often regarded as an indicator of grassland degradation.In this thesis,the floral traits and their variability,characteristics of mating system,pollination ecology,and selection on traits relevant to reproduction of S.chamaejasme in alpine grassland were determined.Then,both reproductive ecological mechanism underlying the plant’s invasion and diffusion in alpine degraded grassland and its evolutionary adaptation were discussed.The main results are as follows:1.Floral characters and its variability in S.chamaejasme.Among these measured traits related to reproduction of the species,the variability(i.e.variation coefficient)of inflorescence number per plant(i.e.an indicator of individual size)was the largest(CV >75%),followed by that of flower number per inflorescence(CV > 25%),and the variability of floral structural traits,such as corolla tube length,corolla mouth and inflorescence-head diameter,as well as that of plant height,were the smallest(CV: 4%-18%).In addition,there were significant inter-annual variation in corolla tube length,inflorescence-head diameter and individual size.Taken together,the reproduction-related traits of S.chamaejasme had large variation among different individuals in the population,and the variability of floral structural traits was overall smaller than that of individual size.2.Pollen viability and longevity of S.chamaejasme.By measuring pollen viability at different flowering stages of the single flower of S.chamaejasme,the results showed that pollen viability of the species was no less than 90% upon anthesis,and last 9-10 days until the inflorescence is fully open.Fourteen to fifteen days after flowering,i.e.when the single flower withered,its pollen viability was still high(at 79.08%).It was implied that the pollen of S.chamaejasme could maintain high viability over the whole flowering period of single flower,which contributed to the realization of reproduction of the species.3.The characteristics of mating system in S.chamaejasme.By pollination manipulation experiment,the results showed that seed set of S.chamaejasme was 39.16 ±4.91% under open pollination,and 26.52 ± 4.06 % under the hand-supplemented cross pollination,and both were of no significant difference(P > 0.05).The seed set of S.chamaejasme was all close to zero in treatments of hand-assisted self-pollination,bagging on the emasculated flower(i.e.no pollination)and bagging before anthesis without pollination.It was suggested that S.chamaejasme had self-incompatibility or complete self-incompatibility mating system,and it did not show the characteristics of apomixis and autonomous selfing.4.Pollinator assemblage and pollination in S.chamaejasme.Through pollination observation in studied natural population of S.chamaejasme,it was showed that the visiting insects included long-tongued butterflies and the insects of Thysanoptera.The butterflies included 9 species,i.e.Everes argiades Pallas,Pontia edusa Fabricius,Brenthis daphne,Coenonympha amaryllis Stoll,Coenonympha semenori Alpheraky,Aporia crataegi Linnaeus,Colias fieldii Ménétriēs,and Aglais urticae and Cynthia cardui Linnaeus.Compared with open pollination,the bagging treatment with either macroporous or microporous bags could significantly reduce seed set of S.chamaejasme,implying that the two types of insects could serve as effective pollinators for the species.5.Selection on floral traits and their adaptation in S.chamaejasme.By estimation of selection differentials and selection gradients for the reproduction-related traits in natural population,such as corolla tube length,corolla entrance size,inflorescence-head diameter and floret number,the results showed that the number of florets per inflorescence had significant selection differentials and selection gradients in two years,that is,it was undergoing positive directional selection.Meanwhile,a significant nonlinear selection gradient(minimum adequate model)was also detected on this trait.The corolla entrance had a directional selection differential in one year,which was nearly significant.However,a significant non-linear selection was detected on the trait in another year,showing a tendency of disruptive selection pattern.The corolla tube length and inflorescence head diameter had opposite selection differentials and selection gradients between two years.Similarly,the selection differential and selection gradient of plant height also showed annual variation.Significant positive selection gradients were detected for the combination characters of inflorescence number per plant with corolla entrance in two years,while significant selection gradients were detected on the combination of inflorescence number per plant with inflorescence-head diameter,and the combination of plant height with floret number per inflorescence.In conclusion,this study shown that the reproduction-related traits of S.chamaejasme showed great variation among individuals in the natural population in the alpine degraded grassland,which was the material basis for evolution of the species to adaption to changing environment.S.chamaejasme has a typical outcrossing mating system,and its high pollen vitality,long-lasting floral longevity,as well as diverse pollinator groups,were the key to ensure reproduction success of the species.In addition,the reproductive traits in S.chamaejasme,especially the number of flowers,corolla entrance size and corolla tube length showed a large potential to adaptive evolution.Overall,it was implied that long floral longevity in S.chamaejasme and its capability of reproduction under different pollination environment jointly contributed to its invasion and spreading in alpine degraded grasslands. |
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