| Rorippa amphibia is an invasive plant that has attracted much attention in recent years.Rorippa amphibia is how the rapid invasion,is worth paying attention to the problem.The study of its population distribution pattern and its adaptability to different water gradients is of great theoretical significance to better reveal its invasion mechanism.In this study,we investigated the lawn communities invaded by Rorippa amphibia in different niche of some universities in Shenyang,and studied the spatial distribution pattern of Rorippa amphibia.Cluster analysis and PCA were used to explore the differences of community types and main environmental factors.During fruiting stage,fruit sequences were collected from unshaded and semi-shaded habitats,and firmness indexes were determined.PEG was used to simulate drought stress to treat seeds in different habitats.Six water gradients,namely waterlogging(5mm flooding),control(CK),2.1% PEG,6.9% PEG,15.5%PEG and 22.4%PEG,were set at 25? and 35?.Indicators related to germination and growth of seeds and seedlings were determined.In addition,the seeds with 0 germination rate after high concentration PEG stress were cleaned with water and then rewatered under the original culture conditions for germination test.At the same time,the control group was set up and the above indexes were measured.In the greenhouse,Rorippa amphibia plants were cultured in four kinds soil water contents: waterlogging(2 cm),wet(25-30%),control(15-20%,CK)and drought(5-10%).After 1 month of treatment,physiological and growth indexes of Rorippa amphibia plants under different water gradients were measured.The results were as follows:1.The Rorippa amphibia population was aggregated distribution in different habitats,and its height and coverage were the highest in semi-shaded habitats.The highest density was found in unshaded habitats.According to the cluster analysis,the Rorippa amphibia invasive community was divided into three community types,namely,Rorippa amphibia + Poa pratensis,Rorippa amphibia + Cardamine lyrata,and Viola yezoensis + Poa pratensis.PCA analysis showed that soil water content was the most important ecological factors affecting community types and the following one was the light intensity.2.The number of fruit sequence branches,pods per branch,seeds per pod,1000-seed weight and plant fecundity of Rorippa amphibia under semi-shaded habitats were significantly higher than those of unshaded plants(P < 0.01).The average number of mature seeds per plant was 12864 in semi-shaded habitat and 6410 in non-shaded habitat,indicating a significant difference between them.3.Under different treatments,the germination indicators of seeds from semi-shaded habitat were higher than that from unshaded habitat,and the difference of germination rate was significant(P < 0.01).At 35?,under different treatments,the germination rate and germination index of seeds from semi-shaded habitat,as well as the germination rate,germination potential,germination vigor,germination index and activity index of seeds from unshaded habitat were higher than those at 25?,so 35? was more suitable for germination of Rorippa amphibia seeds under various water conditions than 25?.At two temperatures,the germination rate of seeds from different habitats was decreased under different PEG stress,but the germination activity of two types seeds was significantly increased under PEG stress,indicating that the germination of Rorippa amphibia seeds had a certain ability to tolerate drought.PEG treatment significantly reduced the root length,fresh weight and dry weight of seedlings,while waterlogging treatment significantly increased them.PEG treatment significantly reduced seedling height(P < 0.01).The plant height and root length of seedlings from semi-shaded habitat were higher than those from non-shaded habitat under the same water treatment.25? was beneficial to the root growth of the two kinds of seedlings,while35? was beneficial to the growth of aboveground.4.At two culture temperatures,most germination indicators of the two kinds of seeds decreased after high PEG stress,especially germination rate.All germination indicators decreased with the increase of PEG concentration in the early stage.The germination rate,germination potential,germination vigor and germination index of rehydrated seeds at 35?were higher than those at 25?.The germination indicators of seeds from semi-shaded habitat were better than those from unshaded habitat.The plant height,root length,daily fresh weight and dry weight of seedlings per plant of the two types seedlings decreased with the increase of PEG concentration.The fresh weight and dry weight of seedlings from seeds of semi-shaded habitat were higher than those from seeds of unshaded habitat.25? was beneficial to the growth of seedling root,and the difference among each treatment was extremely significant with 35?.5.Wet treatment had little effect on physiological indexes of Rorippa amphibia plants,that means except MDA content,soluble sugar content,POD and CAT activities,most indexes had no significant difference with CK.Waterlogging and drought stress significantly increased the enzyme activities of antioxidant defense system,and the contents of Pro,soluble sugar and soluble protein were significantly increased(P < 0.01).Drought treatment significantly increased the chlorophyll content of Rorippa amphibia,but the photosynthetic capacity decreased the most seriously,the MDA and REC were the highest,and root activity was the lowest.Under drought stress,leaf RWC was the lowest,MDA content and REC content were significantly increased,chlorophyll content and root activity were the highest.6.With the decrease of soil water content,the plant height decreased,while the root length increased.CK had the highest specific leaf area and leaf longevity.Wet treatment had little effect on growth indexes of plants,and the number of green leaves per plant,rhizome length,rhizome depth and ramet number were the highest.The total number of leaves per plant,leaf area,plant height,fresh weight and dry weight of aboveground were the highest under waterlogging treatment.Under drought stress,fresh weight of aboveground was the lowest,yellow leaf number per plant,fresh weight and dry weight of underground part,root length and root weight ratio were the highest.7.Subordinate function analysis of the above indexes found that the adaptability of Rorippa amphibia to different soil water gradients from high to low was control,wet,waterlogging and drought.In conclusion,Rorippa amphibia can invade the landscape of different habitats,and easily become the dominant group.The plant can reduce the adverse effects of water stress through physiological and growth regulation mechanisms,enabling it to survive in a variety of soil water conditions which is from waterlogging to drought.It has a strong ability to reproduce sexually.Drought stress inhibited seed germination,but it still had some ability to adapt to water stress.The high temperature and humidity were beneficial to its seed germination and seedlings growth,and its seeds mature in July in the middle of summer with high temperature and high humidity in north China,which is an important reason for its rapid expansion in Liaoning Province.This study also showed its seed germination had a certain ability to adapt to water stress.This study revealed the invasion mechanism of Rorippa amphibia from the aspects of population,community,sexual reproduction and water stress,and laid a foundation for its regulation and further research. |
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