Effect Of Nitrogen And Phosphorus Ratio On Cotton Seedling Growth And Its Carbon And Nitrogen Metabolism

Cotton is an important cash crop in China and even the world.As an important mineral nutrient element for cotton growth and development,the concentration and ratio of nitrogen and phosphorus have an important impact on cotton seedling growth and carbon and nitrogen metabolism.Taking HM 2270（a variety popularized in the Yangtze River Basin）as the material,the hydroponic culture method was adopted in the artificial climate room.Based on Hoagland nutrient solution,the potassium level of the three major nutrient elements was fixed to 6 mmol l L^-1,and three different nitrogen levels were set up to treat 7.5 mmol L^-1（low nitrogen）,15.0 mmol L^-1（medium nitrogen）and30.0 mmol L^-1（high nitrogen）,which were recorded as N0.5,N1.0,N2.0;Three different phosphorus levels were set to treat 0.5 mmol L^-1（low phosphorus）,1.0 mmol L^-1（medium phosphorus）and 2.0 mmol L^-1（high phosphorus）,which were recorded as P0.5,P1.0,P2.0.The effects of 9 treatments on budding time,morphological characteristics and carbon and nitrogen metabolism of cotton seedlings were studied.The main results are as follows:1.Budding time and morphological characteristics of cotton.All treatments showed buds at 8 leaf stage and 33-35 days,and there was no significant difference.When buds appear,N2.0P0.5 has the thinnest stem diameter and N0.5P2.0 is the thickest;N2.0P0.5 is the shortest,N0.5P0.5 is the highest;The root length and volume of N2.0P1.0 and N2.0P2.0 were the smallest,and the root surface area was the largest,which was significantly different from N2.0P0.5.2.Dry matter of cotton seedlings and its distribution.Dry weight of cotton seedling leaves>stems>roots.N0.5P2.0 has the highest total dry weight and N1.0P1.0 has the lowest total dry weight,with significant difference.3.Related indicators of carbon metabolism in cotton seedlings.The content of starch and soluble sugar increased with the increase of the number of leaves,and decreased at the 5-6 leaf stage.The content was leaf>stem>root.At budding,under the condition of constant P concentration,the content of soluble sugar and starch in leaves of N1.0treatment was significantly lower than that of N0.5 and N2.0;Under the condition of constant N concentration,the content of soluble sugar in leaves,P1.0,was significantly higher than P0.5 and P2.0;The starch content of P2.0 was significantly higher than that of P0.5 and P1.0.4.Indexes related to nitrogen metabolism in cotton seedlings.The content of free amino acids,soluble protein and the activities of GS and GOGAT were leaf>stem>root.Under the condition of constant P concentration,the content of free amino acids in leaves of N2.0 was significantly higher than that of N0.5 and N1.0;The content of soluble protein in leaves of N1.0 was significantly higher than that of N0.5 and N2.0;Under the condition of constant N concentration,the content of free amino acids in leaves P2.0 was significantly higher than P0.5 and P1.0;The content of soluble protein in leaves,P0.5,was significantly higher than P1.0 and P2.0.5.Nutrient accumulation of cotton seedlings.The accumulation of nitrogen and phosphorus in cotton seedlings increased with the increase of nitrogen and phosphorus concentration.The accumulation of nitrogen and phosphorus was leaf>stem>root.In conclusion,all treatments did not affect the growth process and budding time of cotton seedlings.The dry weight,carbohydrate content,nitrogen compounds content,nitrogen and phosphorus accumulation and GS and GOGAT activities of cotton seedlings were leaf>stem>root.At budding stage,the nitrogen content of carbohydrate in leaves was lower,while the phosphorus content of soluble sugar in leaves was higher,and the starch content was higher;The content of free amino acids in leaves is high,and the content of nitrogen and phosphorus is high,while the content of soluble protein in leaves is low,and the content of nitrogen and phosphorus is high.