The Physiological And Ecological Responses Of Phragmites Australi From The Yellow River Delta Coastal Wetlands To Salt Stress

Coastal wetland are important ecosystem and fragile eco-sensitive area with its soil salinization being a globally important ecological environment problem,which causes a series of physiological problems such as plant growth and metabolism and leads to the deterioration of regional ecological environment.On the other hand,salinization of soil as a reserve land resource,is of great significance to the sustainable development of society.According to statistics,there are about 100 million hm² of salinized soil in China,mainly distributed in arid,semi-arid and river delta regions.Therefore,studying the response of plants to salt stress can provide theoretical basis for vegetation protection and sustainable development of agriculture and forestry.In this dissertation,the coastal wetland of the Yellow River Delta is taken as the research area,and two types of Phragmites australis in tidal wetland and estuary wetland are studied.Through habitat investigation and indoor salt stress control experiments of the two P.australis,the physiological and ecological responses of P.australis to NaCl stress in the two habitats of the coastal wetland of the Yellow River Delta are analyzed.Based on the environmental condition that Na⁺and S^2-stress coexist in the tidal flat in the study area,the effects of Na⁺and S^2-stress on photosynthesis and antioxidant system of P.australis in the tidal flat?Chaotan?were investigated.The main results are as follows:?1?The phenotypic characteristics of the two kinds of P.australis are different:The investigation and detection results show that the phenotypic characteristics of P.australis in tidal wetland and estuary wetland are significantly different.The estuary wetland where the flood plain P.australis?Hetan?is located has low salinity?low salinity habitat?,and the growth of Hetan is tall and the stem is tetraploid.The tidal wetland where the Chaotan are located has high salinity?high salinity habitat?,and grow low and stem is octupled.?2?Effects of 300 mmol/L NaCl stress on the growth of P.australis seedlings:Under the 300 mmol/L NaCl stress,the relative growth rates of plant height of Hetan and Chaotan were 0.257 and 0.465 respectively,indicating that NaCl treatment significantly inhibited the growth of plant height of P.australis seedlings in Hetan and Chaotan.?3?Effects of 300 mmol/L NaCl stress on the physiological ecology of P.australis:The net photosynthetic rate?Pn?of Hetan decreased by 46.62%after the 300 mmol/L NaCl stress to the seventh day,which was caused by non-stomatal factors;the decrease of Chaotan by 28.25%is affected by stomatal factors.Chlorophyll fluorescence parameters showed that the change of Chaotan was not obvious,which indicated that only PSII reaction center was closed and the protective effect on photosynthetic apparatus was reduced.The hydrogen peroxide?H₂O₂?content of Hetan was 74.87%higher than that of the control,and that of Chaotan was 68.65%,indicating that NaCl treatment significantly induced the increase of H₂O₂ content of phragmites australis in both habitats. Malondialdehyde?MDA?of Hetan was 105.62%higher than that of the control,while that of Chaotan was 39.39%,indicating that NaCl stress caused serious damage to cell membrane of Chaotan.NaCl stress significantly increased the activities of catalase?CAT?,peroxidase?POD?,superoxide dismutase?SOD?and proline?PRO?content of Chaotan in both habitats to resist NaCl stress.However,NaCl stress can inhibit GR activity of reed leaves in tidal flat,but it is over-expressed in reed leaves in tidal flat,which is 94.92%higher than that of the control,so as to reduce osmotic stress caused by NaCl stress and improve stress resistance.Na₂S stress caused the Na⁺content of reed leaves in tidal flat to be 128.27 mg/kg,the flow rate of Na₂S in roots to be 2178.16%of that of the control,the Na₂S content of reed leaves in tidal flat to be 277.47 mk/kg,and the flow rate in roots to be1349.2%of that of the control,which indicated that reed in tidal flat could expel excessive Na₂S from body and reduce the toxicity of ions.?4?Effects of S^2-and Na⁺stress on photosynthesis and antioxidant system of Chaotan:The comparative experimental results show that:40 mmol/L and 50 mmol/LNa₂S stress significantly inhibit photosynthesis of Chaotan and significantly induce the increase of H₂O₂ content,while 50 mmol/L K₂S and 80mmol/L NaCl stress have no significant effect.The activities of POD and SOD increased significantly under 50 mmol/L Na₂S stress,but there was no significant difference under 40 mmol/L Na₂S stress,while the activities of CAT decreased significantly.Under the salt stress of 50 mmol/LK₂S and80mmol/L NaCl,there was no significant difference between the three antioxidant enzymes and the control.Under the stress of 40 mmol/L Na₂S,the plant height,leaf number and leaf length of Chaotan were significantly affected compared with the control.Therefore,their combined stress causes the photosynthesis of tidal reed to be inhibited under low concentration Na₂S stress,and the antioxidant system plays a vital role in resisting Na₂S stress.The above conclusion indicates that Chaotan is better able to adapt to NaCl stress by regulating ion balance,osmotic matter balance,photosynthetic system and antioxidant system than Hetan.As for Na₂S stress,S^2-and Na⁺cause joint stress and inhibit the photosynthesis of Chaotan,but positively respond to Na₂S in antioxidant system.Therefore,in the plant protection and restoration of coastal wetlands in the Yellow River Delta,Chaotan should be given priority to protection and the ecological restoration material should be the Chaotan with high salt-tolerance.