Study On Sexual Reproduction Ecology Of Understory Early Spring Ephemeral Erythronium Japonicum In Northeast China

Reproduction is a very important stage in the life history of plant population.It is not only the most basic behavior process for plants to reproduce and extend the population,but also the key to the regeneration of plant population.Plant sexual reproduction ecology takes plant reproduction as the core of life process and organically combines the adaptive relationship between plants and the environment as well as other organisms.Early spring ephemeral plants evolved special growth and reproduction strategies in the short above-ground life history and gradually adapted to the early spring environment in the long evolutionary process.The growth cycle of spring ephemeral plants compensates for the gaps of the forest niche during the low temperature period in early spring,avoids the loss of solar radiation energy in early spring and the loss of soil nutrients caused by snowmelt runoff,and plays a positive role in restoring the vitality of the forest ecosystem.However,most of the studies on early spring ephemeral plants in China are focused on desert areas,and less attention is paid to the understory early spring ephemeral plants.Therefore,Erythronium japonicum,one of the representative early spring ephemeral plant species in the understory of Northeast China,was taken as the research object.Field survey and laboratory experiments were conducted to investigate the pollination biology,seed dispersal process,the response of seed germination of E.japonicum to burial depth and density and its adaptation strategy to environment.This thesis systematically expounds the adaptation strategies of E.japonicum to the environment in each stage of the sexual reproductive life history,providing a scientific basis for further revealing the adaptation strategies of the early spring ephemeral plants to the environment and enrich the co-evolution theory between understory early spring ephemeral plants and pollinators.Moreover,this study can provide a scientific and effective basis for understory vegetation management,restoration and protection of degraded vegetation,cultivation of early spring flowering plant and protection of pollinators.The main research results of this paper are as follows:(1)The change of the relative position of pistil and stamen during E.japonicum flowering can effectively avoid self-pollination and reduce the interference between pistil and stamen.The results of bagging test showed that the E.japonicum were self-incompatible and apomixes does not occur.The pollen viability of long stamens and short stamens were not different during the pollen dispersal process.The activity of pollen from two phenotypic stamens changed basically the same over time.The main visitors of E.japonicum were Bombus patagiatus,Bombus ignitus and Apis cerana.B.patagiatus mainly visited the flowers at 8:00 in the morning when the flowers were just opening,B.ignitus visited the flowers between 11:00 and 13:00,and A.cerana all participated in the flower visiting activities after 9:00 in the morning.There is a certain overlap time between the periods of pollen viability,stigma acceptability and the peak period of flower visiting by insect to ensure successful reproduction.At16:00 on the first day of bloom,the length of the long stamens and short stamens were not changed,and the length of pistils has exceeded stamens when E.japonicum reached a relatively maturity state.E.japonicum began to secret a large amount of nectar after 16:00 on the first day of flowering,and the nectar continued to produce from 8:00 and stopped when the corolla are closed at 18:00 every day until the flower withered.To avoid pollen loss caused by a large number of insects visiting when the six stamens were not developed well,corolla open but not secret nectar until 16:00 on the first bloom day,which was an adaptation of this species to flower vistors.(2)Erythronium japonicum seeds with elaisome attached are protected in the capsule before dispersal.The seeds from different capsules will experience different fates.When seed capsules dehiscence normally,the seeds would fall around the maternal plant rely on gravity.The degree of seed aggregation was high,and the rate of removal was also high.During the secondary dispersal process,a total of 8 species of ants participated in dispersal of E.japonicum seeds.The larger the ant,the farther the seed dispersal distance.When seed capsules were damaged by arthropod before ripening completely and cracked prematurely,the immature E.japonicum seeds would also be handled by ants,indicating that the elaiosome mature prior to seeds.We found elaiosome plays a decisive role in the dispersal of E.japonicum seeds.Moreover,the components of elaiosome are not easily soluble in water,which can avoid the loss of the attraction of E.japonicum seeds to ants due to the rain during the seed dispersal stage.(3)There was no significant correlation between the burial depth and the germination rate of E.japonicum seeds at each seed density,but the seedling emergence rate decreased significantly with the increase of the burial depth.There was no significant correlation between the seedling emergence rate of E.japonicum and seed density at each burial depths.The germination rate of E.japonicum seeds decreased with the increase of seed density at high burial depths(8-9cm).Morphological dormancy is the main dormancy type of E.japonicum seeds,and the seed coat provides effective protection to E.japonicum seeds.Gibberellin and cytokinin had little effect on breaking dormancy of E.japonicum seeds.The endosperm of E.japonicum seeds is relatively larger,one part of endosperm is for providing the substance for ripening and the other part is for germination.