| Magnesium has an important influence on the carbon and nitrogen metabolism pathway of flue-cured tobacco.It not only participates in the formation of chloroplasts,but also promotes the improvement of many enzyme activities in plants.Flue-cured tobacco is more sensitive to magnesium than other crops.The lack of magnesium affects the formation,transformation,absorption and utilization of mineral nutrients,which restricts the formation of high-quality tobacco leaves and quality.In order to clarify the contribution of magnesium to high-quality tobacco under the existing soil conditions and planting system,and discuss the mechanism of the effect of increasing magnesium fertilizer on the yield and quality of flue-cured tobacco.The field application and pot experiment were conducted to study the impacts of magnesium application carbon and nitrogen metabolism of flue-cured tobacco,the following conclusions were reached:(1)In root elongation stages,the chlorophyll a and total chlorophyll content in tobacco leaves were significantly positively correlated with the amount of magnesium applied.Magnesium could promote the chlorophyll synthesis of tobacco leaves during extension and had a greater influence on the synthesis of chlorophyll a.The content of photosynthetic pigments in flue-cured tobacco leaves was significantly increased by appropriate magnesium application during its vigorous growth period,especially the middle period of vigorous growth.In the middle period of vigorous growth,the content of chlorophyll and carotenoids increased first and then decreased with the increase of magnesium application.High magnesium and magnesium deficiency inhibited the synthesis of photosynthetic pigments in tobacco leaves,but the inhibition of high magnesium stress was less than that of magnesium deficiency.In the budding period,the chlorophyll and carotenoids contents of tobacco leaves were not significantly negatively correlated with magnesium concentration,and the chlorophyll content of tobacco leaves was not significantly different.The carotenoids increased first and then decreased with the increase of magnesium application.The suitable magnesium application could promote the synthesis of carotene that helps the tobacco leaves fall yellow at the right time.(2)The effect of magnesium on the photosynthesis parameters of tobacco leaves in the rosette stage and the middle period of vigorous growth was larger than that of the bud stage,which could significantly improve the photosynthesis of tobacco plants,but the optimum magnesium concentration affecting the photosynthesis rate of flue-cured tobacco at different growth stages was slightly different.In the rosette stage,the photosynthesis parameters such as net photosynthetic rate,stomatal conductance and intercellular carbon dioxide concentration increased with the increase of magnesium application rate.The higher the magnesium concentration,the better the growth of tobacco plants;In the middle period of vigorous growth,the photosynthesis intensity of tobacco leaves showed an inverted“V”trend with the increase of magnesium application.Magnesium can promote the increase of photosynthetic intensity of tobacco,but when the magnesium concentration exceeds8mmol/L,the promoting effect begins to decrease;The net photosynthetic rate of tobacco leaves had a trend of increasing first and then decreasing with the amount of magnesium applied in the bud stage,but the difference is not significant.As the net photosynthetic rate of tobacco leaves increased,the stomatal conductance and intercellular carbon dioxide concentration also increased,and the stomatal conductance did not increase with the increase of net photosynthetic rate during the bud stage,and intercellular carbon dioxide the sharp drop in concentration indicates that the effect of magnesium on photosynthesis of tobacco leaves is mainly limited by stomatal.(3)Magnesium application can significantly increase the activity of enzymes involved in the strong carbon and nitrogen metabolism during the growth and development of flue-cured tobacco.The key period of the effect of magnesium on the activity of carbon metabolism enzymes in tobacco leaves is the bud stage.During this period,the amount of magnesium applied is significantly positively correlated with the activities of SS and SPS,and the activity ofα-amylase,β-amylase and total amylase is significant.Positive correlation,the correlation with S-AI activity is not significant;the key period of the effect of magnesium on nitrogen metabolism is the middle and late growth of flue-cured tobacco,which can significantly increase the GS activity in the mid-term and the bud stage,and the NR activity of tobacco leaves is gradually increased with the increase of magnesium application rate,which helps the flue-cured tobacco to transition from nitrogen metabolism to carbon metabolism in a timely manner,which is conducive to the formation of high-quality tobacco leaves.(4)Appropriate amount of magnesium can increase the accumulation of carbon metabolites.After the preparation,the content of reducing sugar and total sugar in tobacco leaves increase first and then decrease with the increase of magnesium application,and the content of reducing sugar and total sugar of tobacco leaves was the highest at the dosage of 3.6 kg/667m~2;The content of tobacco leaves was increased as a whole with the increase of magnesium application level and was significantly positively correlated with the amount of magnesium applied.Magnesium can significantly increase the starch content of tobacco leaves.With the increase of magnesium application rate,the content of nitrogen metabolites in tobacco leaves increased,and the amount of magnesium applied was positively correlated with the content of nitrogen metabolites,and was significantly correlated with protein content.Magnesium significantly increased nitrogen assimilation and absorption capacity in tobacco leaves that can increase the total nitrogen content of tobacco leaves.(5)The effect of magnesium on the plant height,stem circumference and maximum leaf area of flue-cured tobacco was larger than that of effective leaves.Magnesium application was positively correlated with plant height at root elongation stage and cluster stage,but it was not significant.Plant height at root elongation stage increased first and then decreased with the increase of magnesium application rate,and reached the highest level at cluster stage when magnesium application rate was7.2kg/667m~2.Magnesium application was positively correlated with stem circumference at elongation stage.The stem circumference of tobacco increased from cluster stage to vigorous period with the increase of magnesium application.The value of stem circumference of tobacco increased first and then decreased with the increase of magnesium application at budding stage.Suitable application of magnesium could promote the increase of stem circumference of tobacco and benefit the growth of Flue-cured tobacco.The maximum leaf area of tobacco leaves was positively correlated with the amount of magnesium applied in the root elongation stage and rosette stage.The maximum leaf area of the middle and long buds was less correlated with the amount of magnesium applied,and the application of magnesium was obviously increased the maximum leaf area in the early stage of flue-cured tobacco growth,which was conducive to increasing tobacco yield.(6)With a magnesium content of 1.8kg/667m~2and 2.7kg/667m~2the plant height was 101.09cm and 109.60cm,the stem circumference was 8.31cm,8.35cm,and the maximum leaf area was 1026cm~2,1124.97cm~2in the bud stage.The growth is best;the carbon and nitrogen metabolites are more suitable after preparation,the nitrogen content is 2.32%,2.64%,the protein content is 8.88%,8.75%.The reducing sugar content is 20.31%,23.25%,and the total sugar content is 23.27%,25.85%.The chemical quality of tobacco leaves was the most coordinated.That is,the amount of magnesium applied is 1.8～2.7kg/667m~2,which is most beneficial to coordinate the carbon and nitrogen metabolism of flue-cured tobacco,improve the growth of tobacco plants,and optimize the quality of tobacco leaves. |
