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Mixing Effects And Stress Mechanisms Of Four Major Harmful Salts In Salt-alkaline Soil On Chloris Virgata

Posted on:2010-04-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:C Y LiFull Text:PDF
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Sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium bicarbonate (NaHCO3) and sodium carbonate (Na2CO3) are the main harmful salts in many inland areas; these four salts may cause complex interactions to plants, when mixed, the stress might be stronger or lower. To verify this interaction, Chloris virgata, a naturally alkali-resistant halophyte, was studied. The single and mixed stresses of four salts (NaCl, Na2SO4, NaHCO3 and Na2CO3) in various proportions were applied to C. virgata seedlings. The effects of these salt-alkali conditions on the state of mineral elements in nutrient solutions were analyzed using the GEOCHEM-PC2.0; and to examine the influence of salt-alkaline mixed stress on plant mineral nutrition. Physiological parameters such as matter accumulation rate (MAR), energy accumulation rate (EAR), leaf area and net photosynthetic rate (PN) of C. virgata under stresses were determined and analyzed by statistical methods, and to examine mixed-effects of four salts to C. virgata. Germination rate, relative growth rate (RGR), Na+, K+, proline and organic acid were also determined, and to examine physiological responses and adaptive mechanisms of C. virgata to salt-alkaline mixed stress.Experimental results and conclusions as follows:1. Comparative effects of four single salts stressesThe results indicated photosynthesis, leaf expansion, matter accumulation and energy accumulation of C. virgata were all inhibited under four single salt stresses, but the degrees of inhibition were different, from strong to weak as follows: Na2CO3, NaHCO3, NaCl and Na2SO4. Na+ concentration and the ratio of Na+/ K+ both increased under four single salt stresses, but the increases were significant higher under alkali stress than those under neutral salt stress. The results convincingly demonstrated that: the stress action of alkaline salt is stronger than that of neutral salt; especially ion balance of plant was destructed seriously.2. Effects of salt-alkaline mixed stress on the status of mineral elementsGEOCHEM-PC2.0 analysis predicted that the effect of salinity on the status of mineral elements is relatively small, maybe it is only between ions affinity; while alkalinity (high pH) effects ion-pair formation and results in many mineral ions to precipitate. With increasing alkalinity, phosphorus and metal ions except Na+ and K+ were precipitated and the effect was more significant when pH>8.7, this indicated alkalinity (high pH) caused severe nutrient stress. Based on these, we can consider nutrient stress from alkali stress is one main reason why it is more severe than salt stress.3. Effects of salt-alkaline mixed stresses on seed germination and seedling of C. virgataThe stress actions of four single salts were significant different and the effects on germination and seedling of C. virgata were also different under salt-alkaline mixed stress. The results showed moderate salinity or pH stimulated seeds to germinate, when salinity>100mM, germination rate significantly decreased with increasing salinity or pH, and the role of salinity was greater than pH. The results proved that the optimum germination condition of C. virgata was pH 8.6, 50mM salinity. This may be the key to determine its ecological distribution. The physiological responses of C. virgata to salt-alkaline mixed are different from Helianthus annuus and Leymus chinensis. At moderate pH (pH 6.65-8.74), relative growth rate (RGR), tillering rate and net photosynthetic rate (PN) of seedlings were decreased with in creasing salinity, but they did not decrease with increasing alkalinity (pH). At this time, salinity is the dominant factor, but pH plays a minor role. However, when pH was higher than 9.7, alkalinity became a dominant factor and relative growth rate (RGR), tillering rate and net photosynthetic rate (PN) were decreased significantly and even resulted in death. This seems to indicate that the alkali-resistant mechanism of C. virgata may be different from other plants, such as L. chinensis and Helianthus annuus. This may be related to the characteristics of pH regulation outside the roots which may be a key physiological character to determine it to resist alkaline.4. Interaction analysis of anionAfter systematically analyzing matter accumulation rate (MAR), energy accumulation rate (EAR), leaf area and net photosynthetic rate (PN), we found the degrees of inhibition from strong to weak were Na2CO3, NaHCO3, NaCl and Na2SO4. But after mixing four single salts, the stress effects of mixtures were lower than the combined effects of the single salts. The four salts were all sodium salts, this showed an interaction among the different anions, and as a result, their stress impacts were abated. Thus, relative to single ion stress, mixed ions had a relaxation effect on plants. The results also demonstrated that the relaxation effect decreased with increased salinity, and increased with increased alkalinity. According to mathematical analysis, we found the mathematical relation between the relaxation rate of growth parameters and salinity is series of hyperbolic equations, all coefficients from the equations can also be clear that when the salinity>0, the relaxation rate is positive constant, that is when cation is the same, mixed-anion reduces stress is established under any stress intensity.
Keywords/Search Tags:Chloris virgata, single salt stress, mixed salt stress, anion toxicity, nutrition stress, interaction, relaxation effect
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