Effect Of Nitrogen Potassium Ratio On Cotton Seedlings Growth And Carbon And Nitrogen Metabolism

Nitrogen and potassium are the two major mineral elements that affect the growth of cotton,the coordinated utilization of nitrogen and potassium,and the ratio of nitrogen and potassium affect the growth of cotton seedlings.The test selected Huamian 2270,under the Hoagland nutrient solution,the fixed phosphorus concentration of 1 mmol·L^-1,set 3 nitrogen concentrations(low nitrogen 7.5 mmol·L^-1（N0.5）,medium nitrogen 15mmol·L^-1（N1.0）,high nitrogen 30 mmol·L^-1（N2.0）)and 3 potassium concentrations(low potassium 3 mmol·L^-1（N0.5）,medium potassium 6 mmol·L^-1（N1.0）,high potassium 12 mmol·L^-1（N2.0）)is combined in two pairs for a total of nine treatments.The effects of different nitrogen-potassium ratios on morphological characteristics,carbon metabolism and nitrogen metabolism of cotton seedlings（cotyledons flattened to8 true leaf stage,and each treatment appeared in the 8-leaf stage）were studied,and the effects of nitrogen-potassium ratios on the growth of cotton seedlings were clarified.The key results are as follows:1 Phenotypic characteristics of cotton seedlings.N1.0K0.5 treatment had the largest root length(4129.6 cm plant^-1)and root surface area(344.9 cm² plant^-1),which were162%and 138%higher than the lowest treatment（N2.0K1.0）,respectively.The average diameter of the root system in the N0.5K2.0 treatment is up to 0.4 mm,which is 100%higher than the lowest treatment（N1.0K2.0）.The height and stem thickness of the seedlings treated with N0.5K1.0 were the highest（41.2 cm and 4.0 mm）,which were11.11%and 32.18%higher than those of the lowest treatment（N2.0K0.5）,respectively.At the eight-leaf stage,N2.0K0.5 seedlings had the largest total leaf area(506.6 cm2plant^-1)and 19%higher than the lowest treatment（N1.0K1.0）.The linear fitting equation shows that there is no difference in total leaf area of seedlings with the growth process and the increase of nitrogen and potassium concentration.2 Dry matter of cotton seedlings.At the eight-leaf stage,N1.0K0.5 root dry matter was the largest(259.4 mg plant^-1)and 123%higher than the lowest treatment（N0.5K0.5）;N0.5K1.0 has the largest stem substance(913.5 mg plant^-1)and is 135%higher than the lowest treatment（N0.5K0.5）;N2.0K1.0 treatment had the largest leaf dry matter(1321.9mg plant^-1)and 60.7%higher than the lowest treatment（N0.5K0.5）.Linear fitting showed an exponential correlation between nitrogen-potassium ratios and seedling dry matter quality,and dry matter increased with increased nitrogen-potassium ratios.3 Carbon metabolism of cotton seedlings.The soluble sugar,sucrose and starch content of cotton seedlings are manifested as leaf>stems>roots.The root soluble sugar content of the N1.0K1.0 treatment was the highest,which was 69.23%higher than that of the lowest treatment（N0.5K1.0）;The root and leaf sucrose content was the highest in the N2.0K1.0 treatment,89.64%and 71.42%higher than that in the lowest treatment（N0.5K1.0）;The soluble sugar content of stems in the N0.5K1.0 and N0.5K2.0treatments was higher than that in other treatments,and the soluble sugar content and starch content in the leaves of the N0.5K2.0 treatment were 40.01%and 54.54%higher than those in the lowest treatment（N1.0K2.0）,respectively.4 Nitrogen metabolism in cotton seedlings.The free amino acid and protein content,GS and GOGAT activities of cotton seedlings were manifested as leaf>stems>roots.The N2.0K1.0 treatment had the highest content of SPAD values,free amino acids and soluble proteins,among which the leaf SPAD values were 20.5%higher than those of the lowest treatment（N0.5K0.5）,the free amino acid content of roots and stems was 77%and 50%higher than that of the lowest treatment（N0.5K2.0）,and the soluble protein content of roots was 121%higher than that of the lowest treatment（N0.5K1.0）.At N2.0concentrations,GS and GOGAT enzyme activities were the highest,and the root ratio of N2.0K1.0 treatment was 38.46%and 54.54%higher than that of the lowest treatment（N1.0K2.0）.The NR enzyme activities in the roots were strong,among which the N1.0K2.0 treatment was the highest,96.4%higher than the lowest treatment（N2.0K0.5）,and its stems and leaves were 87.52%and 80.91%higher than the lowest treatment（N1.0K1.0）,respectively.In summary,High nitrogen(30 mmol·L^-1)and potassium(6 mmol·L^-1)increased the activities of GS and GOGAT enzymes,increased SPAD value,promoted protein synthesis,and promoted the synthesis of soluble sugar and sucrose.Thus,seedling height and total leaf area were increased,leaf dry matter was increased,and seedling stage was shortened（33 days）.