Effects Of Nitrogen Forms On Cadmium Tolerance,Absorption And Enrichment Efficiency Of Poplar

The heavy metal pollution is one of the most serious pollution that has adverse effects on environment,agriculture and forestry.Cadmium is one of the most common heavy metal pollution and it is usually accumulated in leaves or roots of plants at high levels.Plants usually exhibited growth inhibition,root depression and yield decrement when grown in Cd-polluted soils.As Cd eventually enter the human body through the food chain after it is absorbed by plants,it will lead to a serious threat to human health.Therefore,remediation of Cd polluted soils will be crucial for agricultural production.Phytoremediation may be a better way to solve this problem..It is reported that the Populus is a typical hyper-accumulators as it might accumulate large quantity of heavy metals in contaminated soil,mainly due to their gigantic root system,high growth rate and large biomass.Therefore,Populus can be used to remedy cadmium contamination in an efficient and cost-effective way.Compared with annual crops or other herbaceous plants,the environmental factors faced by the growth and development of trees are more complicated and changeable.Soil nutrients such as nitrogen and phosphorus are often more scarce and deficient.How does the shortage of soil nutrients such as nitrogen and phosphorus affect the absorption and enrichment efficiency of cadmium ions by trees? This is a key scientific problem faced by phytoremediation of heavy metal pollution,which needs to be studied urgently.In this study,84 K poplar was used as the research object for pot experiment.Through the determination and analysis of relevant physiological indexes,the effects and laws of different nitrogen forms on cadmium stress tolerance of poplar were summarized.The main conclusions of the study are as follows:(1)Exogenous addition of different proportions of nitrate nitrogen and ammonium nitrogen can significantly increase the accumulation of cadmium in poplar leaves and roots.Among them,100% ammonium nitrogen is much better than the other two nitrogen forms:50% nitrate nitrogen,50% ammonium nitrogen and 100% nitrate nitrogen.Therefore,application of ammonium nitrogen with appropriate concentration is a simple and efficient repair measure for cadmium contaminated soil.(2)The superoxide anion content and malondialdehyde MDA content in poplar leaves and roots showed different degrees of reduction under different ratios of nitrate nitrogenand ammonium nitrogen treatment,indicating that different forms of nitrogen have certain mitigation effects on heavy metal cadmium toxicity in poplar leaves and roots.(3)Exogenous addition of different forms of nitrogen can improve antioxidant enzyme activity to a certain extent,accelerate the removal of reactive oxygen species and free radicals,and relieve the oxidative stress of heavy metals on plants.POD plays a leading role in the removal of active oxygen when nitrate nitrogen concentration is low and ammonium nitrogen concentration is high.(4)The addition of exogenous nitrogen had no significant effect on hormone content in shoot leaves of poplar under cadmium stress,while the addition of exogenous 50% nitrate nitrogen: 50% ammonium nitrogen and 100% ammonium nitrogen could significantly increase the content of most hormones in roots and enhance the resistance of roots to heavy metal stress.