Effects Of Multi-walled Carbon Nanotubes On Nutritional Quality And Nitrogen Assimilation And Utilization Of Brassica Campestris Under Different Nitrogen Supply Conditions

Nowadays,there are lots of irrational phenomena in nitrogen fertilizer application in China.Farmers often overuse nitrogen fertilizer for high yield,which reduces the utilization rate of fertilizer and increases the production cost.Nanotechnology is a new technology,and many studies have found that applying nano-materials to soil is an effective way to reduce agricultural nitrogen loss and maintain nitrogen bioavailability in soil.Multi-walled carbon nanotubes（MWCNTs）are one of the most widely used nanomaterials at present.Although there have been a few studies on the effects of MWCNTs on crop growth,there are few studies on the effects of MWCNTs on the nutritional quality and nitrogen assimilation and utilization of Brassica campestris,and its molecular mechanism has not been fully understood.In this study,pot experiment was adopted and four treatments were designed to add MWCNTs under the conditions of conventional N application,N reduction by 10%（0.27 g/kg）,N reduction by 20%（0.24 g/kg）and N reduction by 30%（0.21 g/kg）with ¹⁵N labeled urea as nitrogen fertilizer and farmers’conventional nitrogen application（0.3 g/kg）as control to study the effects of MWCNTs on the physiological quality and nitrogen absorption and utilization of Brassica campestris by measuring the physical and chemical properties of soil,activities of N metabolism related enzymes in plants,Brassica campestris growth and nutritional quality.The molecular mechanism of MWCNTs for nitrogen assimilation and utilization of Brassica campestris were studied to provide theoretical basis for rational application of N fertilizer in agricultural production.The results are as follows:（1）After 45 days of Brassica campestris harvest,the soil p H increased by 3.32%,11.40%and 13.71%respectively,and the content of ammonium nitrogen in soil increased by 24.77%,43.51%and 29.47%respectively,when treated with MWCNTs to reduce N by 10%,20%and30%compared with the control.The soil organic matter in the soil with conventional N application and MWCNTs treatment increased by 9.43%,while the content of nitrate nitrogen in the soil with 10%N reduction and MWCNTs treatment decreased by 29.41%.（2）After 45 days of Brassica campestris growth,the activities of soil urease,sucrase,protease and nitrate reductase increased by 27.10%,12.06%,55.64%and 33.62%respectively with 20%N reduction and MWCNTs treatment as compared with the control.The application of MWCNTs also increased the activities of nitrate reductase,glutamine synthetase and glutamic acid synthetase in plants.The activities of three kinds of plant enzymes related to nitrogen metabolism were increased by 70.65%,60.89%and 67.29%respectively by reducing N by 20%treatment.（3）Compared with the control,the plant height,fresh weight,dry weight,leaf width and leaf area of Brassica campestris increased by 13.16%,53.97%,35.11%,55.09%and 66.63%respectively in the treatment of reducing nitrogen by 20%and adding MWCNTs,while there was no significant difference in other treatments compared with the control.At the same time,MWCNTs can significantly increase the content of soluble sugar and organic acids in Brassica campestris plants.The content of soluble protein in Brassica campestris was increased by 26.39%and 24.68%by 20%and 30%of N reduction and adding MWCNTs,and the content of vitamin C was increased by 19.32%by 30%of N reduction and adding MWCNTs.（4）Compared with the control,10%,20%and 30%N reduction treatments with MWCNTs increased the nitrogen use efficiency of Brassica campestris by 62.84%,36.61%and 46.21%,respectively.In addition,the nitrogen loss of 10%,20%and 30%N reduction treatments with MWCNTs treatments decreased by 72.24%,79.28%and 59.26%respectively,and the nitrogen loss efficiency of the above three treatments were 9.28%,7.62%and 17.47%respectively.To sum up,MWCNTs can improve the growth quality and NUE of Brassica campestris under different N application by adjusting the physical and chemical properties of soil and the activities of related enzymes involved in N metabolism in soil and plants,among which the N₂+C treatment has the best effect on the growth quality and NUE of Brassica campestris.