| Among the factors known to affect tobacco quality, the most striking appeared to bethe ecological factors, the genetic factors and the cultivation practices. The ecological factorsdetermine the type of aroma style while the cultivation factors determine the degree of visibilityand highlight of style features in flue-cured tobacco. As an essential nutrient elements for thegrowth and development of crop, Calcium not only involved in many stress-related responses andenvironmental regulation process, but also participated in stomatal movement and otherphysiological process in photosynthesis, and also could effectively improve the photosyntheticcapacity of plants. The application of exogenous calcium salts could improve the resistant toadversity of plant cells, effectively relieve the decline in photosynthetic capacity of the plant, inorder to improve the performance of the photosynthesis. The situation of calcium absorption andutilization was different under different ecological conditions, and the influence of exogenouscalcium salts on the absorption,distribution and utilization of light energy was different with thechanges of light and temperature environment. In this paper, the effects of exogenous calciumsalts on the photosynthesis and quality of flue-cured tobacco under different light intensity andtemperature levels was studied.The experiment was conducted during the growing seasons2011to2012and2012to2013atscience and education demonstration zone of Henan Agricultural University, in Xuchang country,Henan provice, northest China(latitude34°01’N, longitude113°49’E). Pot experiments werecarried out in the field during previous year, subsequently, the pot-soil experiment was conductedin phytotron in the last year. In this study, including three individual test:(1) Regulating Effects ofexogenous calcium salts on the photosynthesis between different flue-cured tobacco varieties.Withflue-cured tobacco (Nicotiana tabacum) cultivar zhongyan100and yuyan10as experimentalmaterials, this soil-culture pot experiment was carried out during the development process of twocultivars in order to study the effects of three types of calcium saltsincluding calcium chloride(CaCl2),calcium nitrate(Ca(NO3)2) and calcium acetate(Ca(NO3)2) onthe photosynthetic physiology index, chlorophyll fluorescence parameters, water use efficiencyand the accumulation of dry matter of each cultivar.(2) Regulating effects of exogenous calcium salts on the photosynthesis and quality of flue-cured tobacco under the different light intensity.With flue-cured tobacco cultivar zhongyan100as experimental material, the pot experiment wascarried out during2011-2012. The experiment consists of four illumination treatments: L0:982.63-1244.44μmol·m-2·s-1; L1:786.50-996.67μmol·m-2·s-1; L2:691.67-867.89μmol·m-2·s-1; L3:480.00-618.89μmol·m-2·s-1. white gauzes were used for shading until the end of flue-curedtobacco harvest. Three kinds of calcium salts and a control were applied for each illuminationtreatment: CaCl2; Ca(NO3)2; Ca(Ac)2and contrast(distilled water).The index of photosynthetic gasexchange parameters, chlorophyll fluorescence characteristics, dry matter accumulation, mineralnutrition elements, chemical quality and neutral aroma substances have been analysed in thisexperiment in order to elucidate the feasible type of calcium salt which the quality of flue-curedtobacco could be better advanced and to ascertain the mechanism of calcium salts on light useefficiency under low light intensity.(3) Regulating effects of exogenous calcium salts on thephotosynthetic characteristics and aroma quality of flue-cured tobacco of flue-cured tobacco underthe different temperature conditions. The flue-cured tobacco cultivar zhongyan100was treated bythree kinds of temperature conditions in the artificial climate chamber,such as(low temperaturelevel:14℃/20℃; moderate temperature level:22℃/28℃; high temperature level:30℃/36℃),simultaneously, three kinds of calcium salts and a control treatment were applied for eachtemperature conditions.There has been much attention on the effects of the cooperation oftemperature and calcium salts on the plastid pigment content, photosynthetic physiology indexes,the light response curve, the initial activity of RuBP carboxylase and the acidic and neutralaroma component so as to improve the quality of flue-cured tobacco at different temperatures.Themain results are as follow:(1)Accompany with the aging process and the decline of photosynthesis, the decline of netphotosynthetic rate (Pn) was alleviatived to a certain extent by the applation of exogenous calciumsalts, moreover, the rate of descent became slowed down in the shading treatments when thematuration stage. Compared with the Zhongyan100, the decline of photosynthetic rate of Yuyan10was within a narrow range, so it still maintained a relatively high photosynthetic activity in lategrowth stage.The maximum of Pnbetween the two cultivars was appeared in Ca(Ac)2andCa(NO3)2treatment, the promotion effect of those two type of calcium salts was the best. Theexogenous calcium salts enhanced light saturation points (LSP) of two varieties and result in thegrowth of two genotypes flue-cured tobacco. The photochemical quenching coefficient (qP),actual photochemical efficiency (ФPSII) and Pnincreased of calcium salts treatments were higherthan the contrast, thereby, the photochemical efficiency of two cultivars could be improved byappropriate application of calcium salts so that the photosynthetic carbon assimilation ability could be strengthened, meanwhile, the photoinhibition could be effectively alleviated.Overall,thephotosynthetic capability and the photosynthetic capability could be improved by exogenouscalcium salts and consequently the dry matter accumulation of tobacco could be promoted.(2)The content of chlorophyll and carotenoid increased significantly with the lightintensity decreased and exogenous calcium salts increased, the application of calcium salts wasstimulate the synthesis of photosynthetic pigments, so that more solar energy was absorbed bytobacco leaves, at the same time, the photochemical activity was improved and the light energytransfer efficiency relatively increased; More light energy of which absorbed by Photosystem IIwas allocated to photosynthetic electron transport for photosynthesis under the condition of lowlight intensity. exogenous calcium could promote light energy convert to chemical energy withgreater speed and efficiency, thereby, tobacco could be provided with relatively higher electrontransport rate and photochemical efficiency. The photochemical quenching coefficient (qP),maximum photochemical efficiency (Fv/Fm) and the PSII electron transmit rate(ETR) wereincreased with the application of calcium salts, however, the original fluorescence(Fo) wasdecreased, calcium salts could facilitate the photosystem II exert greater photochemical potentialof flue-cured tobacco in the moderate weak light environment which close to the saturationintensity. Generally, The combination of70%light intensity(L2:691.67-867.89μmol·m-2·s-1) inthis experiment with proper application of calcium salt (Ca(Ac)2in this experiment) couldimprove the degree of utilization of light energy and increase the accumulation of dry matter influe-cured tobacco.(3)Exogenous calcium was conducive to promote the initial activity of RuBP carboxylase,thereby, the net photosynthetic rate (Pn) increased and the light utilization efficiency(LUE)sustain a relatively high rate. The values of transpiration rate (E), Stomatal conductance(Gs) andPnexpressed as such a change regulation that firstly increased and then decreased, on the contrary,the intercellular CO2concentration(Ci) reflected the trend of decline after a period ofcontrol of different temperatures. The value of Pnat T2treatment was the highest.Compared to thecontrast, the tobacco of calcium treatments showed higher photosynthetic potential, the highestvalue of maximum photosynthetic rate(Amax) appared in Ca(Ac)2treatment, and maximum of thelight saturation point (LSP) and the apparent quantum yield (AQY) achieved the highest levels attreatment of CaCl2.With the application of exogenous calcium salts the content of chlorophyll andcarotenoid component increased in flue-cured tobacco leaves, it is beneficial to the ability toabsorb light energy, on the other hand, it is also contribute to avoid the damage of photooxidation,definitively, the photosynthetic capacity could be maintained in tobacco leaves. Between differentcalcium treatments, the Ca(Ac)2treatment manifested the best promoting effects for photosynthetic ability.(4)the regulation effects of exogenous calcium on the balance of carbon and nitrogen and itspromoting effect on the quality of tobacco was more significant under low light conditions. Thecontent of total sugar and reducing sugar of calcium salts treatment was significantly higher thanthe control, and accompanied with the light intensity declined the the rate of increase increased inthe low light intensity, at the same time, the nitrogen and nicotine content was decreased. Thetreatment of Ca(Ac)2and Ca(NO3)2have more significantly positive effects for the balance ofcarbon and nitrogen between different calcium salts. with the light intensity decreased the mineralnutrient content in tobacco leaves increased, the micro-element and macro-element were higherthan the contrast, while the content of calcium in tobacco leaves was not remarkable increased.The neutral volatile aroma components achieved the maximum amount at50%light intensity (L3),exogenous calcium was conducive to the formation of aroma components,and also the quality oftobacco aroma could be effectively improved.(5)Low temperature is the primary factor affecting the quality of tobacco, the content ofvarious monosaccharides and disaccharides increased in the appropriate temperature conditions(T2in this test),the significantly improvement of such sweet substances in tobacco betweenexogenous calcium treatments could reduce the bitter taste in smell brought by excess content ofnitrogen compounds.The content of multiple carboxylic acids and organic acids of exogenouscalcium salts treatments were higher than the contral, but the higher fatty acid content was lowerthan the contrast, that is conducive to the balance of tobacco gas. The neutral volatile content ofaroma increased with increasing temperature, simultaneously the exogenous calcium salts couldpromote acidic and neutral aroma ingredients increased. generally, the treatment of Ca(Ac)2exerted the best positive effects, and effectively improved the quality and quantity of aroma intobacco, consequently, conducive to the formation of good quality. |
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