| In order to explore the effects of different shading treatments on the growth and development,air-curing effect,and quality effect of cigar leaves,this study conducted a field experiment at the cigar leaf production base in Fengcheng Town,Xuanhan County,Dazhou City,Sichuan Province,from 2021 to 2022.Taking Chuanxue No.1 as the test material,five different shading intensities were set up: CK as the control(100% natural light intensity),T1(85% natural light intensity),T2(70% natural light intensity),T3(55% natural light intensity),and T4(40% natural light intensity),the dynamic changes of physiological and biochemical characteristics during the growth and development of cigar leaves under different shading intensities,the dynamic changes of quality formation during the air-curing process,and the differences in quality effects after the drying were studied,as were the photosynthetic pigment content and photosynthetic characteristic gas exchange parameters.The results are as follows:1.Effects of different shading intensities on the photosynthetic characteristics of cigar leaves during growth and developmentAt the vigorous and mature stage,the chlorophyll content,carotenoid content,net photosynthetic rate,stomatal conductance,and transpiration rate of cigar leaves in all treatments increased first and then decreased,and the change in intercellular CO2 concentration was not significant.The photosynthetic pigment content,net photosynthetic rate,stomatal conductance,and transpiration rate of tobacco leaves decreased with the decrease in light intensity between treatments.On the contrary,the intercellular CO2 concentration of tobacco leaves under shading treatment was higher,but the low light intensity environment was not conducive to the improvement of photosynthetic performance.The tobacco leaves treated with moderately weak light(70% natural light intensity)in terms of shading intensity improved the photosynthetic pigment content and intercellular CO2 concentration of cigar leaves in terms of photosynthetic characteristics,but the net photosynthetic rate,stomatal conductance,and transpiration rate decreased,which can maintain stable photosynthetic characteristics under adverse conditions.2.Effects of different shading intensities on carbon and nitrogen metabolism characteristics of cigar leaves during growth and developmentAt the vigorous and mature stage,the amylase(AL)activity and total sugar content of cigar leaves in each treatment increased first and then decreased,reaching the peak at 60 days,and the activities of neutral invertase(NI),nitrate reductase(NR),and glutamine synthetase(GS)in tobacco leaves also increased first and then decreased,but the peak was at 50 days.The total nitrogen content of tobacco leaves showed a slow downward trend,while the nicotine content of tobacco leaves showed a gradual upward trend.The activities of amylase(AL),neutral invertase(NI),and glutamine synthetase(GS)in tobacco leaves decreased with the increase of shading intensity between treatments,but shading treatment promoted the activities of nitrate reductase(NR)and plastid pigment,total sugar,total nitrogen,and nicotine content in tobacco leaves.The tobacco leaves treated with moderately low light intensity(70% natural light intensity)have weakened carbon metabolism,increased total sugar content first and then decreased,reduced carbon consumption,promoted sugar accumulation,regulated the activity of nitrogen metabolism enzymes,reduced glutamine synthetase(GS),but increased nitrate reductase(NR),increased total nitrogen and nicotine content of tobacco leaves,and improved the timely conversion of carbon and nitrogen metabolism under adverse conditions,with good coordination of carbon and nitrogen metabolism.3.Effects of different shading intensities on the antioxidant properties of cigar leaves during growth and developmentAt the vigorous and mature stage,the content of MDA and H2O2 in the leaves of each treatment showed a slow upward trend,the activity of SOD and POD in tobacco leaves showed a first upward trend and then a downward trend,and the activity of CAT showed an upward trend.With the decrease in light intensity,the activity of antioxidant enzymes increased,the content of MDA and H2O2 decreased,and the antioxidant characteristics of tobacco leaves decreased under low light intensity.The leaves treated with moderately low light intensity(70% natural light intensity)increased the activities of SOD,CAT,and POD,decreased the contents of MDA and H2O2,increased the activity of antioxidant enzymes,reduced the damage of membrane lipid peroxidation,and improved the stress resistance of tobacco plants.4.Effects of different shading intensities on the leaf tissue structure of cigar leaves during growth and developmentThe tissue structure of cigar leaf was measured during the mature and non-aging periods of tobacco leaf.The thickness of the leaf decreased significantly with the increase in shading intensity,but the effect on the thickness of palisade tissue,sponge tissue,the upper epidermis,and the lower epidermis was different.The thickness of palisade tissue,sponge tissue,the upper epidermis,and the lower epidermis of tobacco leaves treated with moderate light intensity(70% natural light intensity)decreased significantly compared with CK treatment.They decreased by 46.02%,16.26%,29.36%,and 17.44%,respectively,and the blade thickness decreased significantly by 27.51%.5.Effect of different shading intensities on the discoloration characteristics of cigar during air-curingDuring the air-curing process,the color change of tobacco leaves goes gradually from green to yellow and then deepen to brown.There are some differences in the discoloration characteristics of tobacco leaves among different shading intensities,and the transformation of the yellowing and browning characteristics of tobacco leaves is more smooth under 55%-70% natural light intensity.The moisture content of tobacco leaves treated with 55%-70% natural light intensity was significantly higher than that of other treatments.The moisture loss rate of tobacco leaves treated with 70% natural light intensity was moderate,and the drying speed was appropriate,which was conducive to improving the coordination of color change and material transformation in tobacco leaves.Treatment of tobacco leaves with 55%-70% natural light intensity increased LOX and PPO activities during the drying process,which was conducive to enzymatic browning reactions and plastid pigment degradation.The plastid pigment treated with 55%-70% natural light intensity had a large amount of degradation and a fast degradation rate,which promoted the color transformation and quality formation of tobacco leaves.The content of chlorogenic acid,rutin,and hyoscyamine in 70% natural light intensity during the air-curing process was maintained at an appropriate level at all stages,which was conducive to the color transformation and quality formation of tobacco leaves.6.Effects of different shading intensities on membrane lipid peroxidation of cigar leaves during air-curingDuring the air-curing process,the MDA content of tobacco leaves in each treatment increased gradually,the activities of POD and CAT increased first and then decreased,and the activities of SOD decreased gradually.There were certain differences in the membrane lipid peroxidation characteristics of tobacco leaves among different treatments.The MDA content of tobacco leaves in the treatment of 55%-70% natural light intensity was significantly lower than that of other treatments,and the activities of POD,CAT,SOD,and PPO remained high,which was conducive to reducing the level of membrane lipid peroxidation.7.Effect of different shading intensities on the quality of cigar leaves after air-curingThrough the analysis of the quality effect of air-cured tobacco leaves treated with different shading intensities,the comparison of different treatments showed that the content of total sugar,total nitrogen,nicotine,chlorine,and potassium in the air-cured tobacco leaves treated with 70% natural light intensity increased,the ratio of nitrogen to alkali,potassium,and chlorine was better,and the coordination of chemical components was better.The thickness of tobacco leaves treated with 70% natural light intensity decreased significantly,and the balanced moisture content increased.The comprehensive performance of physical characteristics was good,which was beneficial to the usability of tobacco leaves.The appearance quality of the tobacco leaves treated with 70% natural light intensity is uniform and full;the color difference between the front and back sides of the tobacco leaves is small;the identity,structure,chroma,length and width,color uniformity,branch vein thickness,branch vein angle,and branch vein flatness are greatly improved;and the appearance quality performance is the best.The sensory quality of tobacco leaves treated with 70% natural light intensity had a better aroma,coordinated the irritation and impurity,improved the aftertaste and gray,and promoted the sensory quality of tobacco leaves.The output value,average value,and proportion of eggplant coats of tobacco leaves treated with 70% natural light intensity were better,and the economic characteristics were the best. |
PDF Full Text Request