Effects Of Planting Density On Carbon Assimilation Capacity,Distribution Of Assimilation And Nitrogen Uptake,Utilization Of Flue-cured Tobacco

Flue cured tobacco is an important economic crop in our country,and its tax revenue is an important pillar of economic development and social construction.Carbon assimilation capacity,distribution of assimilation and nitrogen uptake,utilization are the material basis of tobacco yield and quality formation.Planting density is an important cultivation measure which affects the growth and development of tobacco plants and the level of carbon and nitrogen metabolism.Reasonable planting density plays an important role in the improvement of tobacco yield and quality.In this study,we took the flue-cured tobacco K326 as tested material,and set up 3 planting density treatments（D1:16529 plants per hm2;D2:18182 plants per hm2;D3:20202 plants per hm2）.The carbon assimilation capacity,distribution of assimilates in different parts of tobacco plants and nitrogen uptake,utilization rates,distribution status of nitrogen fertilizer in the process of growth and development of tobacco plants were studied by using ¹³C and 15 N stable isotope tracer techniques.The main results are as follows:1.¹³C assimilation capacity of different parts and sections of leaves and the effects of planting density on it.The ¹³C assimilation capacity of different parts of leaves showed middle leaf > upper leaf > lower leaf,which showed middle > base > tip in 3 sections of the same leaf.The results showed that the photosynthetic mechanism of the middle leaves in the dome stage were gradually mature,so their assimilation capacity was stronger than that of the old lower leaves and the upper leaves which had not yet reached the fixed length.The ¹³C assimilation capacity of the same part leaves decreased gradually with the increase of planting density,while when the planting density was D2,the ¹³C assimilation capacity of each section in the middle and lower leaves was stronger than the other two planting levels.It was indicated that excessive planting density could affect the tobacco population structure and the coordinated development of individual growth,leading to deterioration of the microclimate of the population structure,reducing the ¹³C assimilation capacity of leaves.2.The distribution of ¹³C assimilation of different parts of leaves and the effects of planting density on it.The ¹³C assimilation produced from the all parts of leaves were mainly retained in the feeding leaves,and the assimilation produced in the upper leaves were mainly transported to the middle of the stem,and the assimilation produced in the middle and lower leaves were mainly transported to the base of stem and root system of the plant.With the increase of planting density,the amount of assimilation transported to the root system and stem decreased.Under the condition of D2 planting density,the distribution amount and ratio of assimilation formed by upper leaves were higher than that of D1 and D3.The results also showed that the ability of tobacco to supply assimilation between different parts of the leaves which had reached the fixed length is small,which means that the material basis of tobacco leaf yield and quality is mainly derived from the assimilation of tobacco leaves during their growth.3.Total nitrogen content of different parts of tobacco plant and different sections of tobacco leaf and the effects of planting density on it.The distribution amount of nitrogen absorbed by tobacco plants in different parts showed middle leaf > lower leaf > upper leaf > stem > root system,which showed middle > base > tip in the various sections of the tobacco leaves.And the total nitrogen content of each part and each section showed a high level under the condition of D2 planting density.And the average nitrogen content per leaf in the lower leaves was the highest.Under the D1 planting density,the average total nitrogen content per leaf showed middle leaf > upper leaf,while it is the opposite under the D2 or D3 planting density.What’s more,with the harvest of tobacco plants,the average nitrogen content per leaf decreased gradually.The results showed that the planting density of D2（18182 plants / hm2）was more suitable for the accumulation of nitrogen and the formation of nitrogen nutrient in the process of growth and maturity.4.The requisition ability of nitrogen fertilizer in different parts of tobacco plants and the effects of planting density on it.Before the middle leaves were harvested,the requisition ability of nitrogen fertilizer in various parts of tobacco plant showed lower leaf > middle leaf > stem > upper leaf > root system.And the requisition ability of nitrogen fertilizer in the same section of tobacco leaf and various parts of tobacco plant increased obviously with the increase of planting density.The requisition ability of nitrogen fertilizer in stem and root system was stronger than that in upper leaf after the middle leaves were harvested.In addition,under the D2 planting density,the requisition ability of nitrogen fertilizer in various parts of tobacco plant and same section of tobacco leaf has obvious advantage.However,there was no significant difference between the three sections of the same leaf.The results showed that the requisition ability of nitrogen fertilizer of lower leaf and middle leaf was stronger in the early and middle stage,which was beneficial to the growth and development of the tobacco leaves.The results also showed that the decreasing magnitudes of requisition ability of nitrogen fertilizer of all parts of tobacco plants under D3 planting density was the largest in the process of growth and development,followed by D2 and then D1,which indicated that planting density had an important influence on the requisition ability of nitrogen fertilizer of various parts of the tobacco.The maturity and harvest of tobacco leaves is a long-lasting process,and planting density of D2（18182 plants per hm2）not only ensured the requisition ability of nitrogen fertilizer of the various parts of tobacco plants,but also took into account the decreasing magnitudes of requisition ability of nitrogen fertilizer during the maturity of plants.5.The distribution of nitrogen derived from fertilizer of various parts of tobacco plants in different stages and the effects of planting density on it.Under the condition of medium and high planting density（D2,D3）,the distribution of nitrogen derived from fertilizer of various parts of tobacco plants was significantly better than that of low planting density（D1）.The distribution of nitrogen derived from fertilizer in the tobacco plants showed lower leaf > middle leaf > upper leaf > stem > root system.The distribution ratio of nitrogen derived from fertilizer in the leaves decreased gradually from the dome to the middle leaves were harvested,but that in the stem and root increased gradually.However,the distribution of nitrogen derived from fertilizer in the leaves still accounted for a large proportion,which indicated that nitrogen derived from fertilizer absorbed during the growth and maturity of tobacco plants was mainly used for leaf growth.The decreasing amplitude of distribution ratio of nitrogen derived from fertilizer in leaves was the smallest under the medium planting density（D2）,while the increasing amplitude of distribution ratio of nitrogen derived from fertilizer in stem and root system was relatively small,which was beneficial to the distribution of nitrogen derived from fertilizer in the leaves and contributed to the growth of them.6.Changes of nitrogen derived from fertilizer uptake and utilization during the growth and maturity of tobacco plants and the effects of planting density on it.Since the dome stage,the absorption of nitrogen derived from the soil had been significantly greater than that of the nitrogen from the fertilizer.With the maturity and harvest of tobacco plants,the absorption of nitrogen in fertilizer gradually decreased,while the absorption of nitrogen in soil increased gradually.It is suggested that the nitrogen needed for the growth of flue-cured tobacco was mainly from the soil during the middle and later stage.The ratios of Ndff/Ndfs varied with different planting densities.And with the harvest of tobacco leaves,the utilization of nitrogen in fertilizer gradually decreased.The nitrogen use efficiency of the tobacco plants with medium and high planting density（D2,D3）was significantly higher than D1 density,which showed that medium and high density cultivation measures could promote the use of nitrogen fertilizer in tobacco plants and reduce the waste of resources.7.Effects of planting density on yield and quality of flue-cured tobacco.The yield of flue-cured tobacco increased with the increase of planting density,but the yield difference between medium and high density（D2,D3）was not significant,while the first-class tobacco proportion was reduced.And the medium and low density（D2,D1）kept the higher first-class tobacco proportion.The results indicated that the increase of planting density could promote the total yield of flue-cured tobacco to some extent,while affected the formation of high quality tobacco leaves,and reduced the quality of flue-cured tobacco leaves.In addition,the output value of D2 planting density was the highest,followed by D3.In general,the cultivation of D2 planting density（18182 plants per hm2）could not only guarantee the higher yield and the first-class proportion,but also increase the output value,which is the suitable planting density.