Effects Of Light Intensities And Water Nitrogen And Phosphorus Levels On Plant Growth And Propagation Formation Of Potamogeton Crispus L.

The eutrophication of water caused by nitrogen and phosphorus enrichment often results in algal blooms,water transparency decline,and water quality deterioration,damage to aquatic ecosystems.Submerged aquatic macrophyte as an important component in lake ecosystems can absorb mineral nutrients from the water,therefore,purify water quality,inhibit algal growth,and maintain the stability of aquatic ecosystems.Potamogeton crispus L.is a submerged aquatic plant that has a strong ability to purify and adapt polluted water.It has very important function in lakes especially when other submerged plants decline in winter.P.crispus mainly relies on turion,a kind of vegetative propagule,for its population propagation,thus,the turion formation and germination are two key processes in the lifecycle of the plant.In this thesis,the effects of different nitrogen(0.2 mg N/L and 20 mg N/L)and phosphorus(0.02 mg P/L and 2 mg P/L)levels in overlying water,light intensities(high,medium and low)on the growth and propagule formation of P.crispus were studied under the artificial culture.Meanwhile,the regulation of cytokinin inhibitor was also studied.The purposes of this study is expected to elucidate the physiological mechanism of water eutrophic factors affecting the plant growth and propagule formation of P.crispus,and to provid theoretical guidance for the rational use of the plant and the ecological remediation of eutrophic lakes.The main results are as followes:1.The biomass accumulation of P.crispus stems and leaves were significantly affected by the interaction between water N and P levels.Under the low water N and P,the photosynthetic pigment contents in leaves,soluble sugar content in plants increased,but N and P uptakes and ABA and JA contents in stems and leaves decreased.Under the high water N and P,the N and P uptakes by plant and ABA and JA contents in stems and leaves increased;while,leaf photosynthetic pigment and plant carbohydrate contents decreased.Low water N promoted the formation and growth of propagules;while,high water N level promoted plant growth but delayed propagule formation.Under the low water N and P,IAA content in stem apexes increased significantly.Under the high water N and P,the number,biomass and the carbohydrate content and accumulation of propagules were significantly reduced.Under the condition of low water N and high P or high water N and low P,the number of propagules formation was the most in this studys,but the dry weight and the biomass of propagules were lower than those under low water N and P.The combination high water N and high water P inhibited the formation and growth of propagules,therefore,hinders the population propagation of P.crispus.2.Under different levels of N and P in overlying water,low light intensity affected significantly the plant growth and inhibited propagule formation,resulting in the low fertility of P.crispus.Under low water N levels,low light intensity decreased the N and P uptakes by plant,the contents of photosynthetic pigment and carbohydrates in plants,but increased the contents of ABA and JA in stems and leaves.Under low water N and P,high light intensity increased plant carbohydrate content,promoted the formation and growth of apical standard turions and increased propagules biomass,carbohydrate content and accumulation.Medium light intensity significantly promoted plants to take up N and P from the water,increased the photosynthetic pigment content in leaves and ABA,IAA contents in stem apexes,and promoted plant growth and the formation of axillary standard turions and phylloclade turions.Under low water N and high P,high light intensity increased N and P uptakes and carbohydrate content of plants and the biomass of stems and leaves,promoted plants to form propagules.Medium light intensity increased the photosynthetic pigment content in leaves,IAA content in stem apexes and the growth of propagules.Under high water N and low P,high light intensity was favorable for plant growth and propagule formation,increased the number,biomass and carbohydrate accumulation of propagules.Medium light intensity increased the photosynthetic pigment content in leaves,promoted N and P uptakes by plants and soluble sugar content in plant and starch accumulation in propagules.Under high water N and P,medium light intensity increased the biomass and N and P uptake of plants,the photosynthetic pigment content in leaves,promoted propagule formation and growth and increased the biomass and carbohydrate accumulation of propagules.High light intensity was harmful to plant growth and propagule formation,caused rot in basal part of stems.The combination of high light intensity and high water N and P significantly affected plant growth in the later period and inhibited the formation and growth of propagules,resulting in significant fertility decline of the plant.3.Lowering endogenous cytokinin metabolism in plants before the propagugle formation is helpful for the propagule formation of P.crispus under high water P.Treatment with 1 ?M lovastatin at 15 days,10 days and 5 days before propagule formation,respectively,increased N and P uptakes by plants and the soluble sugar content and the biomass of the plant,promoted the formation,biomass and starch accumulation of propagules,but did not change propagule morphology,size and starch content.The most significant effect was found in the treatment at 10 days before propagule formation.Treatment with 1 ?M lovastatin at 18 days,13 days and 8 days before the propagule formation,the plant biomass,the N and P uptakes by plants and the soluble sugar content in plants decreased to different degrees,but the plant starch content increased.The treatment at 8 days before propagule formation significantly increased the turion formation and the carbohydrate contents in turions.However,the biomass of turions did not increase.4.The transcriptome sequencing and data analysis were performed on the stem apexes and leaves of P.crispus under different light intensities.The unigenes were annotated and classified using seven databases.A total of 472,570 unigenes were obtained and 286,796 genes were annotated.In the KEGG database,anabolic-related differentially expressed genes of auxin,cytokinin,abscisic acid,jasmonic acid and sucrose metabolism were enrichment analysis,and a total of 13 differentially expressed genes were screened.It lays a foundation for further studies on the molecular mechanism of plant hormones regulating propagule formation of P.crispus under different environmental conditions.