Effects Of Water Environmental Factors And Plant Growth Regulators On Turion Formation And Sprouting Of Potamogeton Crispus

Eutrophication often causes the decline of submerged plants,which results in heavy deterioration of water ecosystem.Potamogeton crispus L.is a submerged macrophyted of Potamogetonaceous family,and has a strong ability to adapt or repair polluted water.P.crispus relies mainly on turions for its population spreading,therefore,the formation and sprouting of turions have an important impact on the rise and fall of its populations in waters.In this study,the effects of different nitrogen and phosphorus levels in overlying water and sediment,light intensities and plant growth regulators on turion formation and sprouting were investigated.We expected that the findings of this study could elucidate the decline mechanisms of submerged plants in eutrophic water and provide guidelines for the restoration of contaminated waters.The main results are as followes:1.Under the condition of nitrogen(N)?2.5 mg/L,the growth and biomass of stems and leaves were little affected by N concnetratins in water.However,when water N increased to 25 mg/L,plant vegetative biomass and Chla content reduced significantly.Plant carbohydrate,soluble protein and nitrogen and phosphorus contents increased at first but then fell down with increasing water N with the treatments of 0.25 mgN/L or 2.5 mgN/L being the highest.Jasmonic acid(JA)content in shoot tops decreased,while,trans-zetin(t-Z)increased at first but then decreased along with increasing water N concentration.Turion number and propagule biomass per plant increased at first with increasing water N but decreased significantly when water N reached 25mg/L.Moreover,starch content in propagules decreased significantly under 25mg/L of water N concentration.2.In the range of 0.01?10 mg/L water phosphorus(P)concentratiuon,the growth and biomass accumulation of stems and leaves were not significantly different.Plant phosphorus content increased significantly,carbohydrates and soluble proteins increased at first but decreased later along with increasing water P concentration.When water P concentration was 1.0 mg/L,plant carbohydrates and soluble proteins reached their higheast levels.The JA content in shoot tops decreased gradually,t-Z content increased at first but then decreased with increasing water P concentration.The t-Z reached its highest level when water P was 0.1 mg/L.Water P concentration had a significant impact on the formation of standart turions but did not on that of phyllocladium turions.The number of standart turions and starch accumulation in propagules per plant decreased significantly when water P increased to 0.1 mg/L,whereas,the dry weight of standart turion decreased when water P increased to 1.0 mg/L.It suggested that progagule formation was more sensitive to high water phosphorus level than plant vegetative growth of P.crispus.3.When cultivated plants were treated with lovastatin ?10?M prior to turion formation,plant height,stem and leaf biomass and plant N and P contents did not change significantly.However,when lovastatin increased to 100 ?M,plant vegetative growth was significantly inhibited.Lovastatin treatments resulted in lower t-Z in shoot tops.The number of turion per plant increased when plants were treated with 1?M lovastatin but decreased when treated with 100?M lovastatin.It suggested that relatively lower endogenous cytokinin is conducive to turion formation of P.cripus.4.When dormant turios were cultivated under different light intensities and matrix nutritions in summer,the sprouting of turions and axillary buds were strongly inhibited under the low light intensity.Relatively high matrix N concentration was beneficial to the turion sprouting under medium light intensity,while,higher N and P concentrations in matrix impeded turion sprouting under high light intensity.Seedling growth was promoted under moderate light intensity but not significantly affected by the N and P concentrations in matrix.Nevertheless,the propagule production was significantly lower under moderate light intensity than under high light intensity.It suggested that less turion sprouting rate and fewer turion formations under low water transparency resulting from eutrophication may be important reasons that P.cripus declines in polluted waters.5.Exogenous application of 6-benzyladenine(6-BA)exceeding 10 ?M could break turion dormancy rapidly and promoted axillary buds sprouting,while,metyrapone,an inhibitor of zeatin-type cytokinins biosyntheis,restrained turion sprouting induced by 6-BA,which demonstrated that cytokinins are important substances that regulate turion sprouting of P.cripus.Appropriate lower endogenous cytokinins by metyrapone could promoted turion sprouting induced by 50 ?M 6-BA,implying that there is an optimum acting concentration in cytokinin promoting turion sprouting.When turions sprouted under 6-BA stimulation,the degration of turion starch reserve,the growth and carbohydrates content of young shoots were promoted.Application of appropriate 6-BA could be used to promote turion sprouting and increase propagation efficieney for the restoration of P.cripus population in eutrophic waters.