| The cultivated area of tomato is very large, which is second only to that of potato. The uptake of potassium for tomato is the topmost, so oversupplying potassium is very common in agricultural production recently. Besides, in agricultural production of China, due to the excessive pursuit of production, unreasonable irrigation exists generally. These practices not only lead to the waste of water resources, but also cause quality decline of agricultural products. In order to achieve water-fertilizer-saving and higher quality of agricultural products, how to irrigate and apply fertilizer reasonably and scientifically, and how to realize the joint control and regulation of water and fertilizer need to be addressed urgently in the modern agricultural production. For this purpose, according to the law of growth and development of tomato and development dynamic of the first sipke fruits, tomato growth was divided into five stages, i.e. vegetative growth stage, blooming and fruit setting stage, early fruit growth stage, fruit development stage and fruit maturity stage. Pot experiment was conducted. Based on the design of two factors and three levels, three potassium levels(0.92 g K2O/kg soil 、 0.46 g K2O/kg soil 、 0 g K2O/kg soil, respectively) and three water levels(80~90%θf, 70~80%θf, 60~70%θf, respectively) were set at fruit development stage and fruit maturity stage. High amount of water and no potassium application were conducted at other stages. Besides, traditional method of water and potassium application was CK2. Water and potassium status of tomato plant, soluble sugar content and sugar metabolizing enzymes activity in fruit were determined in order to study the effect of water, potassium and their interaction on soluble sugar content. Besides, the mechanism of water and potassium regulating sugar accumulation was analyzed based on water and potassium status of tomato plant, sugar metabolizing enzymes activity. The main results are as follows:(1) The study of the effect of water and potassium application on soluble sugar content of mature fruit showed that, water and potassium application at fruit development stage had bigger impact on soluble sugar content and the interaction of water and potassium had significant impact. 4WlK0 and 4WmKm got higher soluble sugar content(3.62% and 3.17%).When small amount of water was supplied, soluble sugar content increased with the increase of the amount of potassium application. When middle water was supplied, soluble sugarcontent first increased and then decreased with the increase of the amount of potassium application. When high water was supplied, potassium did not have obvious effect on soluble sugar content. Water application at fruit maturity stage had significant effect on soluble sugar content and water deficit was conducive to the accumulation of soluble sugar content.Potassium application at fruit maturity stage had little regulating effect on soluble sugar content. However, when different amount of water was supplied, high potassium treatment had higher soluble sugar content than middle or no potassium treatment. Traditional practice is against the accumulation of soluble sugar.(2) The study of the effect of water and potassium application on yield and dry matter accumulation showed that water supply and the interaction of water and potassium had significant effect on yield. When none potassium was applied, the treatment of high amount of water obtained a higher yield, which was 51.2% and 47.6% higher than treatments of middle and low amount of water; when middle amount of potassium was applied, soil water did not have significant effect on yield; when high amount of potassium was applied, the treatment of middle amount of water significantly exceeded treatments of high and low amount of water by 22.1% and 45.6%. Water supply at fruit maturity stage had significant effect on yield. When none potassium was applied, the treatment of high amount of water obtained a higher yield, which was 37.1% higher than the treatment of low amount of water;when middle or high amount of potassium was applied, there was no significant difference between different soil water contents, but treatments of high soil water content achieved higher yield, compared to treatments of middle or low soil water content.For the two stages, the order of the amount of dry matter of different organs was fruit>stem ≥leaf > root, and fruit dry matter accumulation accounted for 44-55%. Water and potassium application at fruit development stage had significant effect on fruit and total dry matter accumulation, and did not have significant effect on root, stem and leaf. When none or high amount of potassium was applied, high amount of water was conducive to the transfer of photosynthate to fruit; when middle potassium, low water could increase the distribution of photosynthetic products to fruit; low water and high potassium could cause higher root dry weight, but lower fruit and total dry matter accumulation were also determined. For treatments of fruit maturity stage, water and potassium application had significant effect on stem dry matter accumulation and the interaction of water and potassium had significant effect on fruit and total dry matter accumulation. When high amount of water was applied,stem dry matter accumulation increased with the increase of potassium supply; when middle or low water, it declined with the increase of potassium supply. When high or middle amount of potassium was applied, high water was conducive to the distribution of photosynthate tofruit, but if high potassium was applied, water deficit was conductive to the distribution of photosynthate to fruit.(3) The study of the effect of water and potassium application on water and potassium status of plant and their relationship with soluble sugar content of mature fruit showed that,water and potassium application at fruit development stage had little influence on leaf relative water content when monitored fruit matured. There was no obvious relation between soluble sugar content and leaf relative water content. Differences of leaf relative water content were bigger among treatments of fruit maturity stage. Higher soil water content led to higher leaf relative water content, and there was negative relation between leaf relative water content and soluble sugar content.Among all treatments, the order of the amount of potassium content of different organs was fruit>stem≥ leaf>root, which was consistent with dry matter. Water application at fruit development stage had significant effect on root potassium content, and potassium application had significant effect on root, stem and leaf potassium content. For root potassium content, on different water supply levels, it increased with the increase of the amount of potassium applied; on different potassium supply levels, it increased with the decrease of soil water content. When high amount of water was applied, stem and leaf potassium content first increased and then decreased with the increase of the amount of potassium applied; when middle or low water, it had an increase tendency with the increase of the amount of potassium applied. Water supply at fruit maturity stage had significant effect on potassium content of every organ. Potassium supply had significant effect on root and fruit. The interaction of water and potassium had significant effect on root and stem. For stem potassium content, it decreased with the increase of water supply when none or high amount of potassium was applied; when middle amount of potassium was applied, it increased with the increase of water supply. Leaf potassium content increased with the increase of water supply when high amount of potassium was applied, and other change status was same as stem. Root and fruit potassium content both increased with the increase of water and potassium supply.Among all treatments, the order of the amount of potassium accumulation content of different organs was fruit>stem≥ leaf>root, which was consistent with potassium content.For treatments of fruit development stage, when none potassium was applied, the percent of root, stem and leaf potassium accumulation content was lower, compared to middle or high potassium supply level, but fruit showed an adverse trend, showing that when less potassium applied, tomato would preferentially transfer potassium to fruit. During fruit maturity stage,when none or middle amount of potassium was applied, root, stem and leaf potassium accumulation content decreased with the increase of water supply, but fruit showed anadverse trend. When high potassium, root and stem potassium accumulation content first increased and then declined with the increase of water supply, but leaf and fruit showed an adverse trend, showing that when less potassium applied at fruit maturity stage, improving water supply could enhance the transfer of potassium to fruit.Path analysis showed that for treatments of fruit development stages, leaf relative water content and soluble sugar content had significant correlation. Leaf relative water content and potassium content of each organ, root, stem and leaf, fruit and root, had significant correlation. The incidence of the direct effect on soluble sugar content was leaf relative water content>root>leaf>stem>fruit; the incidence of the indirect effect was root>leaf relative water content>stem>leaf>fruit. For treatments of fruit maturity stage, there was significant relation between soluble sugar content and fruit potassium content. Leaf relative water content did not have significant correlation with potassium content of each organ and each two potassium content of every organ had significant correlation. The incidence of the direct effect on soluble sugar content was fruit>leaf>stem>root>leaf relative water content; the incidence of the indirect effect was leaf>fruit>leaf relative water content>stem>root.For treatments of fruit development stage, soluble sugar content and leaf potassium accumulation content had significant correlation. Leaf relative water content had significant correlation with each potassium accumulation content. For root, stem and leaf, every two had significant correlation, but fruit and stem did not have significant correlation. The incidence of the direct effect on soluble sugar content was leaf>stem>root>leaf relative water content>fruit; the incidence of the indirect effect was stem>root>leaf>leaf relative water content>fruit. For treatments of fruit maturity stage, soluble sugar content did not have significant correlation with other independent variables. Stem had significant correlation with root, leaf and fruit respectively. Leaf and fruit had significant positive correlation. The incidence of the direct effect on soluble sugar content was leaf>fruit>root>leaf relative water content>stem; the incidence of the indirect effect was leaf>fruit>root>leaf relative water content>stem.(4) The study of the response mechanism of fruit sugar accumulation to physiological indexes showed that, soluble sugar content of every monitored treatment did not have obvious difference during 35-40 d, and they opened gap during 40-49 d. 4WmKm was the highest(3.17%), and 5WmKm and CK1 centered, and 4WmK and CK2 were lower. With the development of fruit, the leaf relative water content of every monitored treatment appeared a decreasing trend, and CK2 declined fastest. Among all monitored treatments, potassium accumulation content of stem and leaf had a trend of U-shape, but fruit showed a reverse trend, indicating that during the monitored period potassium in stem and leaf was firsttransported into fruit and then transported out. With the development of fruit, activities of AI and NI of every monitored treatment increased, and SS* and SPS decreased.There was no obvious correlation between the change of leaf relative water content and soluble sugar content. When high amount of potassium was applied at fruit development stage, fruit would accumulate large amount of potassium during 40 d after anthesis, and this may be bad for the accumulation of sugar. Soluble sugar content had significant positive correlation with AI and NI respectively, and had significant negative correlation with SPS and SS* respectively. Moderate potassium supply was conducive to regulate activities of sugar metabolizing enzymes and then enhance sugar accumulation. High potassium or none would cause too high or too low potassium accumulation in organs, and these would have negative effect on to enzyme activity. |
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