Control For Echinochloa Caudata And Restoration For Bolboschoenus Planiculmis In Wetlands Of Songnen Plain

Bolboschoenus planiculmis is the main food species for migratory Siberian white crane(Leucogeranus leucogeranus)in Momoge National Nature Reserve(MNNR),northeastern China.B.planiculmis-dominated wetlands in MNNR has suffered severe degradation resulting from climate change and human disturbance.However,the abundance of B.planiculmis was very low in most of the rewetted sites and the population was unable to be constructed in the field.Echinochloa caudata,an annual weed propagated only from seed,became the dominant species in the majority of the rewetted site in Momoge wetland,which decreased the habitat quality for Siberian white crane.Therefore,it is urgent to carry out researches about wetland ecosystem health assessment and vegetation recovery.In this project,we study the changes of soil seed bank during the process of wetlands restoration in B.planiculmis-dominated wetlands in MNNR by intergrating in-situ observation with laboratory seedling germination method.The aim of this study is to(1)compare the characteristics of seed bank between restored wetland and natural wetland;(2)study the effects of light availability and water depth on seed germination,and reveal the factors and mechanisms influcening the seedling establishment of B.planiculmis;(3)compare the ecological response to flooding between E.caudata and B.planiculmis,and analyze the mechanisms of early flooding on the regenetaion of E.caudata;(4)clarify the potential and key factors for the vegetation restoration of B.planiculmis with seeds or tubers.Finally,the research would provide reliable data for study on soil seed bank of inland saline-alkaline wetland,promote the scientific management of wetlands,ultimately,contribute to protect the water bird habitat and biodiversity.The main conclusions include:1.The seed density of B.planiculmis in the soils of natural wetlands was 18.42 times higher than that of E.caudata,while the seed density of E.caudata in restored wetlands was 4.04 times higher than that of B.planiculmis.The dormant soil seed bank of E.caudata in invaded wetlands was significantly greater than that in natural wetlands,which indicated that the restored wetlands were heavily encroached by E.caudata.Additionally,the high seed production and lower seed buoyancy(FP0 = 5 days)of E.caudata indicated that E.caudata could not expand efficiently through water dispersal.2.Both light availability and water depth are important factors influencing seed germination in wetland plants.E.caudata showed a significant higher ability to acclimate to the stresses of shade and dark environment.For E.caudata,the effect of flooding on seed germination was reduced by a shade condition(Fig.1A).However,the combination of a shading effect and deep water(5-30cm)had an amplified effect on seed germination of B.planiculmis: the germination percentage decreased strongly as a result of a combination of the two factors and these differences confirmed that E.caudata had a higher adaptive ability than B.planiculmis to acclimate to the simultaneous stresses of shade and flooding.3.Both flooding time and water depth are important factors influencing survival and growth of E.caudata seedlings.No seedling survived when a flooding depth of 20 cm were applied at one,four,or eight DAS.A flooding depth of 10 cm significantly reduced both survival rate and seedling biomass when applied at one,four,or eight DAS.A proportion of E.caudata seedlings can survive when a 20 cm flooding depth applied at 16 DAS.E.caudata exhibited an escape strategy to avoid complete submergence when the seedlings germinated after 16 days.Flooding depths of 5-20 cm had no significant effects on the regeneration of B.planiculmis.Thus,flooding can be used to control the regeneration of E.caudata.Both earlier flooding and a constant flooding depth need to be considered to improve the habitat of the Siberian white crane.4.Both burial depth and water depth are important determinants for the emergence and growth of B.planiculmis seedlings.Emergence was most successful at a 0 cm burial depth when there was a water depth of 5-10 cm above the sediment surface.B.planiculmis seedlings do not grow to the surface under a 10 cm water depth.Thin-layer burial(0.5-1cm)promoted both seedling growth and tuber formation.Thus,seeds can be used in the revegetation of B.planiculmis.Seedling establishment depends on the use of appropriate burial and water depths.Options for maintaining soil moisture or flooding need to be considered to determine the burial depth of B.planiculmis seeds.5.Both higher water depth and density limit the regeneration of B.planiculmis from tubers.Water depth of 40 cm not only limits growth of aboveground plant,but also limits tuber formation of B.planiculmis.Growth of B.planiculmis from tuber sprouting was significantly decreased in the medium and high density treatments.Interspecific relationships were competitive among all water depth treatments.The combining effects of flooding and tuber density(competitive effects)further limits the regeneration of B.planiculmis population from tuber sprouting.Therefore,the suitable planting density should be selected according to the different water conditions for the rapid recovery of the vegetation in B.planiculmis.