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Effects Of Calcium On Physiological Characteristics, Yield And Quality And Alleviating Cadmium Stress Of Garlic

Posted on:2016-03-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:H LiFull Text:PDF
GTID:1223330461953894Subject:Vegetable science
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For most plants, calcium(Ca) is not only a necessary element, but also a central regulator of the growth and development, playing a crucial role in adaption to stress environments. Cadmium(Cd) is a nonessential element for plants, and is one of the most common heavy metal pollutants in soils worldwide, which has a serious impact on the growth and development of plants. Ca2+ and Cd2+ have the similar ionic radius and chemical property, and they compete with each other for absorption by plants, so adding calcium can reduce the absorption of Cd. This experiment was performed on garlic(Allium sativum, cultivar Jinxiang 3) cultured in nutrient solution in the greenhouse, and two questions were mainly discussed: the first one is the relationship between calcium and garlic; the other is the effect of calcium on garlic under cadmium stress.1. In this experiment, six different calcium(Ca2+) concentration treatments: 0, 1.0, 2.0, 3.0, 4.0 and 5.0 mmol·L-1 were designed, and the effects of calcium on the growth, photosynthetic characteristics, enzymes activities, nutrient absorption, yield and quality were studied using nutrient solution culture. Then the optimum calcium concentration for garlic was determined scientifically, which can provide references for the rational fertilization and the improvement of yield and quality of garlic. The main results are as follows:1) When the calcium levels were in the range of 0~3.0 mmol·L-1, the plant height, pseudostem length, pseudostem diameter, and leaf width of garlic seedlings were enhanced with the increase of calcium concentrations, which were decreased with the increase of calcium concentrations when the calcium levels were in the range of 3.0~5.0 mmol·L-1, then they got the maximum values under 3.0 mmol·L-1 treatment and were increased by 7.7%~37.8%, 28.6%~48.4%, 19.7%~38.9%, and 25.3%~53.1% respectively compared to the no calcium treatment.2) The chlorophyll and carotenoid contents of garlic leaves were increased at first and then reduced with the calcium concentrations, they were the largest when the calcium level was 3.0 mmol·L-1 and were enhanced by 29.3%~47.8% and 62.0%~84.3% respectively compared to the no calcium treatment. The net photosynthetic rate(Pn), transpiration rate(Tr), and stomatal conductance(Gs) of garlic leaves showed a similar tendency with pigment contents, and they were the biggest in the 3.0 mmol·L-1 treatment, while the intercellular CO2 concentration was diminished with the increase of calcium levels all the time.3) The contents of allicin, soluble sugar, vitamin C, free amino acid, and soluble protein in pseudostems and leaves were improved at the beginning and then reduced with the increase of calcium concentrations, these nutrient indexes under 3.0 mmol·L-1 treatment were the highest and were increased by 33.5%~50.3%, 64.2%~84.7%, 37.7%~92.7%, 22.4%~53.5%, 44.4%~69.4% and 45.8%~66.1%, 69.3%~113.1%, 49.1%~105.8%, 45.0%~66.1%, 46.0%~60.1% respectively compared to the no calcium treatment. In addition, the fresh weight of bolt, bolt diameter, bolting rate, fresh weight of bulb, and transverse diameter of bulb got their maximum values in the 3.0 mmol·L-1 treatment, which were improved by 55.1%, 39.0%, 386.6%, 106.4%, and 22.1% respectively compared to the 1.0 mmol·L-1 treatment. Meanwhile, the contents of allicin, soluble sugar, vitamin C, free amino acid, and soluble protein in bolts and bulbs also were the highest when the calcium concentration was 3.0 mmol·L-1, which were enhanced by 54.7%, 33.9%, 11.5%, 19.3%, 32.6% and 72.1%, 33.9%, 5.2%, 21.5%, 29.6% respectively compared to the 1.0 mmol·L-1 treatment.4) The activities of superoxide dismutase(SOD), peroxidase(POD), catalase(CAT), and nitrate reductase(NR) in garlic leaves were enhanced at first and then receded with the increase of calcium concentrations, they were the strongest when the calcium was 3.0 mmol·L-1, which were enhanced by 15.0%~36.6%, 65.1%~82.8%, 39.9%~47.0%, and 22.1%~58.9% respectively compared to the no calcium treatment. Moreover, the malondialdehyde(MDA) content in garlic leaves showed a contrary tendency, which got the minimum value in the 3.0 mmol·L-1 treatment and was reduced by 10.4%~34.7% compared to the no calcium treatment. Besides, the root activity of garlic also got the peak value when the calcium level was 3.0 mmol·L-1, which was increased by 47.0%.5) The Ca contents of pseudostems and leaves were positively correlated to calcium levels, they were the biggest when the calcium was 5.0 mmol·L-1, which were enhanced by 27.8%~38.2% and 28.6%~57.8% respectively compared to the no calcium treatment. The Ca contents of bolts and bulbs also were positively correlated to calcium levels and got the maximum values in the 5.0 mmol·L-1 treatment, which were increased by 216.1% and 60.4% respectively compared to the 1.0 mmol·L-1 treatment. The N, P, K, Mg contents of bolts and bulbs reached the peak values when the calcium level was 3.0 mmol·L-1, which were increased by 46.2%, 50.8%, 226.5%, 21.9% and 33.9%, 22.8%, 419.2%, 48.3% respectively compared to the 1.0 mmol·L-1 treatment.Thus it can be seen that, moderate calcium could effectively improve the growth, photosynthesis, enzymes activities, nutrient absorption, yield and qualities of garlic, and 3.0 mmol·L-1 calcium level was the best treatment to garlic under hydroponic condition.2. In the experiment, the effects of cadmium(Cd) in nutrient solution on growth, photosynthetic characteristics, root indexes, enzymes activities, nutrient absorption, chemical forms of Cd, yield and quality of garlic were studied, as well as the alleviation effects of exogenous calcium(Ca). Then the optimum dosage of exogenous calcium was determined scientifically, which can provide references for reducing Cd toxicity to garlic and the reduction of Cd pollution in garlic productions. The results are as follows:1) Cadmium could obviously inhibit the growth indexes of garlic seedlings(plant height, pseudostem diameter, pseudostem length, and fresh weight), decrease the pigment contents(chlorophyll and carotenoid) and photosynthetic parameters(Pn, Tr, Gs) of leaves, reduce the root indexes(fresh and dry weight, root volume, the greatest length, and root activity), recede the enzymes(SOD, POD, CAT) activities and increase the MDA content of leaves, reduce the mineral elements(N, P, K, Ca, Mg) contents and increase the Cd accumulation of roots, increase the chemical forms of Cd with stronger activities, also could lower the appearance qualities(the fresh weight of bolt, bolt diameter, bolting rate, fresh weight of bulb, and transverse diameter of bulb) and nutritional qualities(allicin, soluble sugar, vitamin C, free amino acid, and soluble protein) of bolts and bulbs.2) The growth was promoted significantly after adding exogenous Ca to garlic seedlings under Cd stress, plant height, pseudostem diameter, pseudostem length, and fresh weight were increased at first and then decreased with the increase of exogenous Ca levels, they got the maximum values when the exogenous Ca was 2 or 3 mmol·L-1, which were increased by 39.0%~68.1%, 25.1%~26.0%, 42.8%~48.0%, and 53.5%~95.2% respectively compared to the Cd treatment with no exogenous Ca.3) Exogenous calcium improved the chlorophyll and carotenoid contents of garlic leaves under Cd stress, the change tendency was similar to the growth indexes, and the largest increases under 2 or 3 mmol·L-1 exogenous calcium treatment were 25.7%~38.5% and 37.0% respectively compared to the Cd treatment with no exogenous Ca. Adding exogenous calcium also increased the net photosynthetic rate(Pn), transpiration rate(Tr), and stomatal conductance(Gs) of leaves under Cd stress, which were the biggest when the exogenous Ca was 2 mmol·L-1.4) Exogenous calcium increased the root indexes(fresh weight, root volume, the greatest length, dry weight, and root activity) of garlic under Cd stress, they got their peak values when the exogenous Ca was 2 or 3 mmol·L-1, which were increased by 31.2%~43.7%, 63.2%~73.3%, 27.0%~48.6%, 51.3%~58.7%, and 28.7%~55.3% respectively compared to the Cd treatment with no exogenous Ca. In addition, adding exogenous calcium to garlic under Cd stress enhanced enzymes activities and decreased MDA content of leaves. SOD, POD, and CAT activities were the strongest when the exogenous Ca was 2 or 3 mmol·L-1, which were enhanced by 22.9%~43.9%, 12.3%~18.0%, and 4.9%~27.4% respectively compared to the Cd treatment with no exogenous Ca, while MDA content was the least and was decreased by 12.9%~25.0% when the exogenous Ca was 2 mmol·L-1.5) Exogenous calcium improved the absorption of mineral elements and decreased the accumulation of Cd of garlic under Cd stress. The N, P, K, Mg contents of roots were increased at the beginning and then decreased with the increase of exogenous calcium levels, which got the peak values when the exogenous calcium was 2 or 3 mmol·L-1 and were enhanced by 9.1%~15.5%, 21.3%~50.3%, 19.6%~31.2%, and 20.2%~62.3% respectively compared to the Cd treatment with no exogenous Ca. What was more, the Ca content of roots was positively correlated to exogenous calcium levels, and the Cd content of roots showed a completely contrary tendency. Furthermore, exogenous calcium also changed the chemical forms of Cd in roots that decreased the forms with stronger activities.6) The appearance qualities of bolts and bulbs were improved significantly after adding exogenous to garlic under Cd stress, and then the fresh weight of bolt, bolt diameter, bolting rate, fresh weight of bulb, and transverse diameter of bulb got the peak values when the exogenous calcium was 2 or 3 mmol·L-1, which were improved by 32.4%, 17.6%, 96.3%, 158.7%, and 38.6% respectively compared to the Cd treatment with no exogenous Ca. Moreover, exogenous calcium also increased the nutritional qualities of bolts and bulbs, specifically the contents of allicin, soluble sugar, vitamin C, free amino acid, and soluble protein in bolts and bulbs got their maximum values when the exogenous calcium was 2 or 3 mmol·L-1, the biggest increases of which were 57.7%, 29.7%, 21.3%, 22.5%, 28.8% and 22.0%, 23.8%, 28.8%, 26.7%, 23.2%, respectively.In short, Cd stress could have serious negative effects on the growth, photosynthesis, root indexes, enzymes activities, nutrient absorption, chemical forms of Cd, yield and quality of garlic, while exogenous calcium significantly relieved the toxic effects of Cd in many aspects and reduced Cd pollution in garlic.
Keywords/Search Tags:Garlic, Calcium, Physiological characteristic, Yield & Quality, Alleviating, Cadmium stress
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