Effect Of Nitrogen On Cadmium Uptake And Accumulation In Sweet Sorghum

Soil is an important natural resource for human survival.With the rapid development of global modernization,a variety of pollutants continue to enter the soil,among which the heavy metal cadmium(Cd)has attracted much attention because of its strong mobility,difficult degradation and high toxicity.Heavy metal Cd pollution mainly comes from the abuse of agricultural chemical fertilizers and pesticides.Cd pollution will not only inhibit plant growth,but more importantly,Cd will enter the human body through the food chain,causing serious damage to human health.Plant extraction remediation technology is widely used to treat Cd contaminated soil,but the CD hyperaccumulator plants found at present are generally short and grow slowly,which greatly restricts the remediation efficiency.If sweet sorghum,a high-biomass crop,is used to repair Cd contaminated soil by plant extraction,the remediation efficiency can be greatly improved.In addition,nitrogen is closely related to the absorption and accumulation of Cd by plants,but it is not clear whether nitrogen can further promote Cd,accumulation in sweet sorghum and improve phytoremediation efficiency.Therefore,the mechanism of nitrogen on the absorption and accumulation of Cd in sweet sorghum was studied in this paper.The main results are as follows:1.In sweet sorghum,compared with ammonium nitrogen,the application of nitrate nitrogen significantly increased plant fresh weight and Cd concentration,indicating that nitrate nitrogen was more beneficial to the growth and Cd accumulation of sweet sorghum.In the study of antioxidant enzyme system,it was found that the antioxidant capacity of nitrate treatment was higher than that of ammonium nitrogen treatment under Cd stress..2.In the study of the role of sulfur metabolism in sweet sorghum under Cd stress,it was found that there was a close relationship between nitrogen metabolism and sulfur metabolism,and the application of nitrate nitrogen significantly increased the activity of nitrate reductase in the nitrogen metabolism pathway,but did not make the glutamineglutamate cycle play a role again after being inhibited by cadmium stress.In the process of sulfur metabolism,the activity of ATP sulfurase in the first step of sulfur assimilation did not change significantly after the application of nitrate,indicating that the application of nitrate did not enhance the metabolism of sulfate in sweet sorghum,but significantly increased the activity of O-acetylserine thiohydrolase,the key enzyme for the synthesis of cysteine,and promoted the synthesis of more glutathione.The results showed that in the study of nitrate nitrogen on Cd accumulation in sweet sorghum under Cd stress,nitrate nitrogen not only increased the ability of sweet sorghum to accumulate Cd,but also synthesized glutathione by promoting nitrogen and sulfur metabolism,further synthesized plant chelating peptide,and detoxified Cd by storing Cd in vacuoles in the form of PCs-Cd complex.3.The suitable concentration of nitrate nitrogen promoted the shoot dry weight and cadmium concentration of sweet sorghum,which significantly increased the accumulation of cadmium,but nitrate nitrogen did not change the transfer ability of cadmium from root to shoot,so nitrate nitrogen probably promoted the ability of sweet sorghum root to absorb cadmium.Further study on the genes closely related to cadmium uptake and transport showed that there was no correlation between the expression level of Sb Nramp1,Sb Nramp5,Sb HMA3 and cadmium uptake,but the expression of nitrate transporter gene Sb NRT1.1B was consistent with the change of cadmium concentration in aboveground parts,indicating that Sb NRT1.1B may be the key gene for nitrate nitrogen to promote the absorption and accumulation of cadmium in sweet sorghum.