The Ecological Adaptation Strategies Of Lilium Concolor Var.megalanthum In Wetland

In the process of long-term evolution,plants have formed a variety of effective ecological adaptation strategies to cope with environmental changes.As an important category of flowering plants in wetland,Lilium is an important component of wetland biodiversity.Lilium concolor var.megalanthum is the only species of Lilium growing in wetland in Changbai Mountain area.Currently,the wild population of L.concolor var.megalanthum is small and its distribution range is narrow.It can be used as an indicator species of environmental changes in wetland.The ecological adaptation strategy of L.concolor var.megalanthum to wetland environment is a key scientific problem to study the mechanism of population regeneration of wetland plants and the restoration of wetland plant diversity.In this paper,the sexual system characteristics and population spatial distribution characteristics of L.concolor var.megalanthum were studied based on the wild population surveys,and the response mechanisms of functional traits,biomass allocation,sex conversion and seed germination to environmental changes(such as nutrition,light,water level and temperature changes)were explored by control simulation experiment.The main research results are as follows:(1)At the individual level,L.concolor var.megalanthum has three sexual phenotypes: male flower,hermaphrodite flower and andromonoecy.At the population level,the plants with male flower act as male parent and transmit genes to the next generation through pollen,while the plants with hermaphrodite flower mainly act as female parent and transmit genes through ovules.The proportion of male plants in L.concolor var.megalanthum population increased significantly by 22.80% from 2012 to 2020.There was no significant change in the proportion of male plants from 2020 to 2021.The population of L.concolor var.megalanthum mainly showed aggregated distribution in small scale,and tended to random distribution with the increase of scale.There was no significant difference in the spatial distribution pattern of L.concolor var.megalanthum population in the same habitat between 2020 and 2021.However,there were differences in the spatial distribution pattern of L.concolor var.megalanthum population between four different habitats in 2021.(2)L.concolor var.megalanthum with male flower is significantly smaller than the plant with hermaphrodite flower,but its resource allocation to bulb is significantly higher than that of the plant with hermaphrodite flower.The sexual expression of L.concolor var.megalanthum followed the hypothesis of size-dependent sexual allocation.That is,the smaller plant produces male flower,while the larger plant produces hermaphroditic flower or is andromonoecious.The pollen number of hermaphroditic plant was significantly larger than that of male plant,but there were no significant differences in flower longevity,pollen size and pollen germination percentage between hermaphrodite plant and male plant.The results of seed set and germination under different pollination treatments showed that the seed set and fruit set of self-pollination treatment are significantly lower than those of cross-pollination treatment.There was no significant difference in pollen fertility between male and hermaphroditic plant.There was also no significant difference in the viability of seed pollinated by pollen from male and from hermaphroditic plant.The reproduction system of L.concolor var.megalanthum is outcrossing type,some of them are self-compatible,and pollinators are needed in the sexual reproduction process.(3)Nutrient treatments affected the functional traits,biomass allocation and sex conversion of L.concolor var.megalanthum.When plants derived from bulbs of hermaphrodite plants were treated with lower nutritional conditions than those in the field,the morphological size of more than 90% of the plants decreased compared with the previous year,while the bulb size of 96.25% of the plants increased compared with the previous year,and sex conversion occurred in 40% of the plants.It can be seen that after nutrients were reduced,hermaphrodite plants will allocate relatively more resources to the bulbs,while reducing the investment in sexual reproduction of the aboveground parts in the next year.The combined reduction of any two elements of nitrogen,phosphorus and potassium has a more significant effect on the sex conversion of individuals derived from the bulbs of hermaphrodite plants than the reduction of single nutrient elements of nitrogen,phosphorus and potassium,and they would produce male flowers or no flowers.After applying relatively higher nutrients than the field habitat,the height of 36.5% of the plants derived from the bulbs of male plants were higher than that of the previous year,their bulbs were all larger than that of the previous year,and 67.5% of the plants underwent sex conversion and produce hermaphrodite flowers.Compared with the combined increase of any two elements of nitrogen,phosphorus and potassium,the increase of the content of any single nutrient element of nitrogen,phosphorus and potassium could promote the sex conversion of plants,resulting in the proportion of plant with hermaphrodite flower exceeding 80%.Light,water level and their interaction had certain effects on the functional traits,biomass allocation and sex conversion of L.concolor var.megalanthum.With the increase of shading intensity,plant height,leaf number,leaf length,leaf width,base diameter,stem biomass allocation and flower biomass allocation of L.concolor megalanthum increased.All the above growth indexes reached the maximu when the light transmittance was 30%.With the decrease of water level,the biomass allocation of stem,leaf,underground stem and aboveground parts decreased,while the biomass allocation of bulb,fibrous root and underground parts increased.When water level is-10 cm,the plant growth was promoted.In conclusion,L.concolor megalanthum grow best at 30% light transmittance and-10 cm water level,with a high proportion of hermaphrodite flowers.By 2021,97.92% of the hermaphrodite plants in 2020 reduced their morphological size,69.79% of the plants had enlarged bulbs,and84.38% of the plants had sex conversion,with male flowers or no flowers in 2021.By2021,93.75% of the male plants in 2020 reduced the morphological size,61.45% of the plants had enlarged bulbs.21.88% of the plants had hermaphrodite flowers,16.66% of the plants had male flowers,and 61.46% of them had no flowers.Plants that produce male or no flowers allocate more resources to bulbs growth,and make reproductive reserve for the next flowering season.(4)Temperature,simulated drought stress by polyethylene glycol-6000,(PEG-6000),and their interaction had significant impacts on the day first germination(DFG),germination percentage(GP),coefficient of germination rate(CGR),germination energy(GE),germination index(GI),and vigor index(VI)of L.concolor var.megalanthum seed.By analyzing the effects of temperature,drought stress and their interaction on seed germination of L.concolor var.megalanthum,it was found that 25℃ and simulated drought stress by 5% PEG-6000 solution concentration was the most suitable condition for seed germination of L.concolor var.megalanthum.The strongest tolerance of seed germination to simulated drought stress of PEG was detected at 10℃ and 15℃.Moderate drought can promote seed germination at low temperature,seeds are more sensitive to drought stress at high temperature,and the increase of temperature will enhance the inhibitory effect of drought stress on seed germination of L.concolor var.megalanthum.The inhibition of lower temperature,higher temperature and drought stress on the seed of L.concolor var.megalanthum did not destroy the seed structure,and the seed vigor was still good,and the seed germination could be resumed after the stress was released.The occurrence of male plant may be the result of L.concolor var.megalanthum adaptation to limited environmental resources,which reflects the trade-off strategy of resource allocation between growth and reproduction of this plant species under the stressful conditions in wetland.The emergence of this sexual system and the response mechanism of growth,sex conversion,and seed germination to environmental factors have a certain adaptive significance for L.concolor var.megalanthum during the long-term wetland succession.