| With the influence of climate and human activities,a large number of wetlands are suffering from salinization,drought and desertification,and the salinity of saline-alkali wetlands were raising which lead the degeneration of plant.In addition,global warming may result in the changes of soil freeze-thaw processes in seasonal frozen soil area.Therefore,the changes of water-salt conditions and soil freeze-thaw may affect the ecological structure and functions of saline-alkali wetlands in seasonal frozen soil area.For a better understanding on responses of plant to the changes of freeze thawing,water and salt,Scirpus planiculmis which is the representative plant in Momoge wetland was chosen as research sample and simulation experiments were performed.To study the effects of freeze thawing-water-salt conditions on the germination and seedlings,the influence of water-salt conditions on mature plant of Scirpus planiculmis,the responses of soil nutrients to freeze thaw-water-salt conditions,and the relationship between soil nutrients and the eco-physiological characters of Scirpus planiculmis will provide theoretical foundation for the mechanism of degraded saline-alkali wetlands response to climate change and human activities.Furthermore,the study results will provide basic theory for the vegetation restoration in degraded saline-alkali wetlands.The main conclusions showed as follows:(1)Although the germination and seedlings growth of Scirpus planiculmis influenced by the coupling effects of freeze thawing-water-salt conditions significantly and the water-salt conditions also affected Scirpus planiculmis in mature stage,the freeze-thaw and water were the main factors which influenced the germination and seedlings of Scirpus planiculmis and the water was the main factor which influenced the mature stage of Scirpus planiculmis.(2)The freeze-thaw might influence the growth of plant in the following growing season,and adverse to the gemination and growth of Scirpus planiculmis which overwintered under the non-flooding condition.Besides,the increasing water level and the contents of salt might have negative impact on the seedlings including the decrease of germination number,height,leaf number and the ability of photosynthetic.For the various element contents in different organs of Scirpus planiculmis seedlings,the effect of freeze-thaw promoted the accumulation of N in stem under non-flooding condition,reduced the accumulation of S in leaf under flooding condition,reduced the accumulation of S in stem and P in stem and leaf under 10 cm water level.N in stem,C,P,S in leaf were influenced by salt,and they were increasing with the salt contents except S in leaf.(3)Coupling effects exists in water,salt and stress time influencing the photosynthetic of mature Scirpus planiculmis significantly.Within short stress time,water and salt might not influence or influence the photosynthetic slightly,but might have significantly negative effects with long stress time.Scirpus planiculmis might maintain the ability of exchanging gas by improving the photosynthetic and increasing the stem diameter under the high water level.In addition,Scirpus planiculmis might distribute more biomass to the aboveground than underground with the increasing of water level.For the various element contents of mature Scirpus planiculmis,element contents in different organs showed different trends with the changes of water level,and the distribution of C,N,P in plant organs significantly effects by the water level.For example,the increasing water level might negative to the accumulation of C in stem,prompt the accumulation of N and P in stem and bulb,and S in bulb.(4)Freeze-thaw effected soil nutrients significantly which prompted the accumulation of S under non-flooding and organic carbon in 10 cm water level,and the loss of N in flooding condition.In addition,soil nutrients may be influenced by watersalt conditions more severely when freeze-thaw effects exist.(5)The changes of freeze-thaw,water and salt altered the relationship of soil nutrients and eco-physiological characters of plant according by influencing them significantly.According to the results above all,this thesis could provide some advices for protecting and restoration of Scirpus planiculmis in Momoge wetland:(1)Planting and restoration of Scirpus planiculmis should pay attention to the regulation of water level and salt concentration,especially the control of water level.In addition,the water level should not too high when restoration during seedling.(2)Scirpus planiculmis could be planted to different water levels according to the stem diameter in the process of transplanting.For example,the thicker stem could be transplanted to places with deeper water level,and the thinner stem converse.(3)Suitable flooding or litters covering during wintering could relieve the effects of freeze-thaw,and reduce negative influences of freeze-thaw on germination and growth of Scirpus planiculmis in the following growing season. |
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