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The Study Of Saline And Alkaline Tolerant Eco-physiological Metabolism In Four Gramineae In The Songnen Grasslands

Posted on:2011-02-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:R GuoFull Text:PDF
GTID:1100360305489467Subject:Ecology
Abstract/Summary:PDF Full Text Request
Arable land has been tightly coupled with the socio-economic development and the rapid growth of the world's population, but it has been severely affected by soil salinity. The arable land is affected by salt throughout the world; plants growth and productivity are severely affected by soil salinity. The detrimental effects of high salinity on plants can be observed at the whole-plant level as the death of plants and/or decrease in productivity. The effects of saline and alkaline stress on plants were multiple pathways, so the ability of plants to tolerate stress is determined by multiple biochemical pathways. Different plant species may have completely different stresses adaptation mechanisms, it is necessary to summarize and compare the responses and adaptive adjustment mechanisms of saline-alkaline stress in different plant species. Gramineae plants are the type which have been more concentrated studied, it includes many saline stress tolerate types. In order to summarize and compare the adaptive adjustment mechanisms of saline-alkaline stress in gramineae plants, we chose four different gramineae plants they were Triticum aestivum Linn, Leymus chinensis, Leymus secalinus and Setaria viridis. Based on the saline soils of grasslands in northeast China, the natural salinity stress in natural saline soils is very complex. Two neutral salts were mixed at a 1:1 molar ratio of NaCl: Na2SO4 and applied to the saline stress group. Similarly, two alkaline salts were mixed at a 1:1 molar ratio of NaHCO3 to Na2CO3 and applied to the alkaline stress group. There were five concentrations for the saline and alkaline stresses: 30, 60, 90, 120 and 150 mM. To further explore the saline-alkaline stress adaptation mechanisms of gramineae plants(four species)by measuring the germination rate, relative growth rate, water content, photosynthesis parameters, ionic balance and organic acids.Germination is one of the most critical periods in the life cycle of plants, but it can be affected by abiotic stresses. Under saline-alkaline stress, low water potential is a decisive factor to inhibit the seed germination. The results indicated that alkaline stress more significantly affected seed germination than saline stress. Non-germinated seeds in dormancy to avoid adverse environment. Perhaps alkaline stress (high pH value) on seed germination could be extremely complex, and the low pH value didn't inhibit the germination of wheat seeds, on the contrary to the high salinity. Under low-intensity alkaline stress, the germinated seeds can decline pH value by metabolic activities. The high pH stress may decompose the seed structure, eventually leading to seed death, may be it is a complex reaction process, and be worth studying in-depth. Under saline-alkaline stress, the relative growth rate and water use efficiency of four gramineae plants decreased with increasing salinity, and the decrease for alkaline stress is much greater than for saline stress at the same concentration. Salt stress is mainly osmotic stress and ion toxicity, the harmful of alkaline-stress on plants is greater than saline-stress, the main reason may be alkaline-stress includes high-pH stress. The high pH in soil can be direct cause Ca2+ and Mg2+ precipitated, destroy plant absorb nutrients and then cause nutritional imbalances around the root in the plants.Except saline and alkaline stress obviously inhibited the growth of plants, we also discovered that the saline-alkaline stress is significantly affects on photosynthetic carbon assimilation in plant. Photosynthetic capacity of four plants had changed little under low and moderate concentrations of saline stress or low concentrations of alkaline stress; but photosynthetic parameters declined rapidly with increasing salinity, the extent of reduction under alkaline stress was significantly greater than under saline stress. These results appeared to confirm that the high pH value of alkali-stress can be a strong inhibition of plant photosynthesis. Alkaline stress can restrict photosynthesis processes by damaging the photosynthetic apparatus and stomatal conductance in plants; this may be related to excessive accumulation of Na+ in cells, and then causing poison. The Chlorophyll fluorescence experiments can also prove this point, high-pH stress caused a large number of Na+ influx into plant cells, causing photoinhibition and impede the absorption of light energy and cause the activity of the maximal photochemical efficiency of PSâ…¡reactor decreased. And the saline-alkaline stress severely hampered self-repair of the injury of PSâ…¡reaction center.The results indicated that the contents of Na+ in plants increased with increasing stress intensity, and the contents of K+ decreased rapidly. The Na+ increase and K+ decrease under alkaline stress were greater than under salt stress with increasing stress intensity. This showed that the high pH value of alkaline stress may interfere with the absorption of Na+ in roots, make the accumulation of intracellular Na+ to the poison level. Under alkaline stress, the increasing Na+ may not be the response to osmotic stress, but the response to high pH value. The absorption and transportation of Na+ in roots are promoted under alkaline stress, but inhibit K+, and eventually result in ion imbalance and unstable pH in plants. The response to two stresses of Ca2+, Mg2+ and Fe2+ was different from the previous reports, they increased with increasing stress intensity in this experiment, and this may be plants response to alkaline stress in order to avoid stress threat. It may be a specific adaptive response, so it is worth studying in-depth. Although the contents of Ca2+, Mg2+ and Fe2+ increased under alkaline stress, they have little effect on the osmotic adjustment; mainly because of they have a low proportion of the ion contents.The four gramineae plants didn't accumulated organic acids under saline stress, but accumulated substantial organic acids under alkaline stress, malic acids and citric acids are the main components. In order to balance substantial Na+, compensate the deficit of inorganic anions, and maintain intracellular stable pH, plant enhanced the synthesis of the organic acids (OA) anions, indicating that OA metabolic regulation played a central role in intracellular pH adjustment of plant. The accumulation of organic acids in the stems and leaves not a simple passive response to salt stress, it is a positive result of metabolic regulation under alkaline stress. The metabolic regulation of OA under alkaline stress may involve in one or more basal metabolic pathways. It is easy to identify and clone the key gene of anti-saline and anti-alkaline in plants, if the response of organic acids could be clearly explained. Thus, the research on organic acids may be the main direction or branch of salt-alkaline stress in the future.
Keywords/Search Tags:Saline stress, Alkaline stress, Triticum aestivum Linn, Leymus chinensis, Leymus secalinus, Setaria viridis, Eco-physiological
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