| The experiment was conducted at the Experimental Farm of Dezhou Academy of Agricultural Science in the years of 2004 and 2005. Studies were done in salty blocks and salty field. Seeds of three cultivars (DK961, high salt-tolerant; H6756, intermediate salt-tolerant; JN17, salt-sensitive) of winter wheat (Triticum aestivum L.) were planted into salty blocks with different NaCl concentrations (0.0%, 0.3%, 0.5%, 0.7%, w/w) and a typical salty field (salt concentration was 0.286%) in Huang-huai area. And a sand cultural experiment was conducted at a greenhouse of Shandong Agricultural University, for studying the optimal potassium concentration application in the salty solution. DK961 and H6756 were two salt tolerant winter wheat cultivars which were bred by our working group in 1996 and 1999, respectively. JN17 was a popular winter wheat variety demonstrated in Shandong Province. The salty blocks were all sized as 11 m×3 m×1 m (length×broad×height). The plant growing condition was very similar as the salty field. The results indicated that:1 The variations of yield and quality in different winter wheat cultivars under salt stress1.1 Effects of genotype and environment on yield and grain qualities of wheatThe results clearly showed that there was a close correlation between yield and salt tolerance of wheat and salt concentration. High salt tolerant winter wheat cultivar maintained high yield under 0.5% salt concentration, only 13.2% reductions occurred in comparison with non-salt treatment, while intermediate salt tolerant H6756 decreased 42.3% and salt sensitive cultivar declined 56.4%. Both of them got high yield under 0.3% salt concentration. All of them had considerable reductions under 0.7% salt concentration.The indexes of wheat quality under salt stress showed that the grain protein content of increased and the starch content decreased along with the increase of salt concentration in a range of salt concentration. Both of them decreased rapidly out of this range. The grain nitrogen contents in salt tolerant cultivar were considerably higher than in salt sensitive one in the harvesting stage of different wheat cultivars under same salt concentration stress. And the more serious the salt stress was, the more significant the influence was. The main reason of the variation of protein content was the difference of environment. The interaction of variety and environment was the main reason of variance of the farinogramme index, starch content, peak viscosity, and break down etc. On the other hand, higher temperature and more shining time in growth stage of winter wheat was benefit for improving quality. Wet gluten and dough stability time could decrease when there was more sunlight time in filling stage.1.2 Relationship between the activities of nitrogen metabolism enzymes and grain quality of winter wheat under salt stressGlutamine synthetase (GS) activity in flag leaves and grain of the three cultivars were DK961>H6756>JN17 under salt stress. Environmental factors at grain filling stage were significantly related to wheat quality and enzymes activity. Grain protein content was positively correlated to GS activity in flag leaves and grain of DK961 under 0.3% and 0.5% salt concentrations. The enzyme activities of nitrogen metabolism were promoted by suitable environment conditions, which can improve the grain qualities.2 Changes of ecological traits and physiological responses in wheat under salt stress2.1 Effects of genotypes and environments on ecological traits of wheatThe length of growth period of wheat was a key factor to influence the grain yield and quality. Salt stress accelerated the senescence of wheat plant and shortened the growth stage of wheat, reduced the time of photosynthesis. The seedling stage of wheat is the most sensitive period to salt stress.2.2 Effect of genotype and environment on physiological response of wheatSalt stress caused decrease in net photosynthetic rate (Pn), stomatal conductance (gs) and light saturation point (LSP), aggravated the"midday depression of photosynthesis", decreased the relative water content of leaves, improved the content of low osmotic regulators, increased the content of MDA and active oxygen species (AOS), increased the pressure of cleaning the AOS etc. but the responses showed differently in different wheat cultivars differing in salt tolerance. Salt tolerant cultivar acted slower than salt sensitive one in Pn, gs and LSP. There was no significant increase in the content of MDA and AOS in a suitable range of salt concentration. Salt sensitive cultivar drastically decreased in Pn, gs and LSP, considerable increase in the content of soluble sugar, proline, MDA and AOS. Some of the wheat plants could not grow normally, even dry out.3 Effects of K+ on physiological response, yield and quality of wheat under salt stress 3.1 Effects of growing mechanism at seedling stagePotassium is one of the maximum elements that plants need. And the volume of K+/Na+ is a very important mark to measure its salt tolerance. The results showed that the K+/Na+ vitro decreased rapidly under salt stress. The balance of ions was broken in wheat plant. It caused poison of single ion, decreased the growth of wheat plants. The contents of soluble sugar and proline increased. The contents of MDA and AOS were also rose. The addition of potassium to salt solution could effectively alleviate this harmful effect. The application of potassium increased the K+ concentration in the solution, improved the K+ absorption from the solution, and recovered the K+/Na+ ratio. The trait of salt stress was lighter, the contents of soluble sugar and proline were decreased, and the contents of MDA and AOS were also reduced in comparison with non-potassium treatment. Excessive potassium application was also harmful for plant growth. The result of our experiment was that the optimal K+/Na+ ratio was 1:10.3.2 Effects of potassium fertilizer on grain yield and quality of wheat under salt stressThe results of this experiment showed that 0.1% potassium nitrate foliar application under 0.5% salt concentration stress could improve the grain yield and quality. The seed numbers per spike of three cultivars increased by 1.94%,7.46% and 7.09%, respectively. The 1000-seed weight of three cultivars increased by 2.27%,4.19% and 2.76%, respectively. The yield of three cultivars increased by 4.49%,12.8% and 12.28%, respectively. Potassium application also improved the protein and starch quality of grain. Protein contents of three cultivars were improved by -2.54%, 5.15%, 8.33% in comparison with non-potassium application, respectively. Potassium application was also benefit for increasing the quality index of wet gluten, sedimentation volume, dough development time and dough stability time.3.3 Effects of potassium on photosynthesis and C, N assimilation under salt stress The ability of photosynthetic assimilation was significantly decreased after anthesis under salt stress, and the duration of midday depression was prolonged, and the duration of photosynthesis of leaves was reduced. Potassium foliar application on the wheat under salt stress could significantly improve the ability of photosynthesis, and maintain a long-term high net photosynthetic rate, and alleviated the influence of midday depression. This measurement improved the content of soluble sugar and sucrose in flag leaves and grain. It was benefit for the starch formation in grain.On the other hand, the ability of nitrogen mechanism was decreased by salt stress, and the ability of grain starch formation was also reduced. 1000-seed weight decreased, but the content of protein was increased. Potassium application in wheat jointing stage under salt stress could improve the ability of nitrogen metabolism. The rate of starch formation increased. Meanwhile, the content of free amino acids in flag leaves and grains in grain filling stage, the protein content in grain was improved. Proper treatment of potassium under salt stress could improve the ability of absorbing nitrogen, accelerate the transportation rate from vegetative organ to the reproductive organ, improve the contents of protein and starch in grain.3.4 Effects of potassium application on enzymes of wheat quality formation in senescent process under salt stressProper potassium concentration application under salt stress condition significantly improved the grain GS activity and grain nitrogen assimilation, so improved the grain protein content. The GS activity of high salt tolerant cultivar, DK961, was improved by 3.15% in comparison with non-potassium treatment; The GS activity of intermediate salt tolerant cultivar, H6756, was improved by 2.26% in comparison with non-potassium treatment; The GS activity of salt sensitive cultivar, JN17, was improved by 2.12% in comparison with non-potassium treatment. So we concluded that the treatment of potassium application improved the ability of nitrogen assimilation, increased the protein content of grain and NR and GS activities.More active oxygen species were produced in wheat plant under salt stress condition. In order to getting rid of them, the protection enzymes SOD, POD and CAT activities were improved. But excessive salt concentration could destroy the structure of membrane, the activities of these enzymes decreased significantly, and the content of MDA increased. The treatment of potassium application could considerably improve the activities of antioxidant enzymes, decrease the content of MDA.4 The measurements of getting high yield and quality of wheat under salt stress4.1 High salt tolerant winter wheat cultivars were usedSelecting a salt tolerant wheat cultivar was the key measurement in getting higher yield and quality of wheat under salt stress. Higher net photosynthetic rate and photosynthetic period were required in getting high seed number per spike and 1000-seed weight.4.2 Potassium fertilizer applicationProper concentration of potassium fertilizer application could effectively alleviate the harmful effects to wheat plant under salt stress. It increased the net photosynthetic rate and light efficiency. It accelerated the substance metabolism and energy transportation. According to the method of"sink-source"relative, vegetative organ strongly improved its ability of producing organic matter, through the photosynthetic products in vegetative organ were transported to grain. The mechanism of wheat plant was in a perfect cycle, decreased the traits of salt stress. Our results also showed that proper concentration of potassium fertilizer supply could effectively increase the rate of spike formation, seeds per spike and 1000-seed weight, as a result, improved the yield and quality of wheat.
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