Effects Of Cadmium And Nickel Single/compound Stress On Alfalfa Seeds And Seedlings

Soil is the material basis and guarantee for the sustainable development of China’s economy.Reducing soil pollution and protecting soil environment is an important part of the national ecological and environmental construction.Soil environment in China is in poor condition as a whole,and heavy metals such as cadmium,nickel,lead,mercury and arsenic are seriously polluted in some areas.Pollution prevention and control should be strengthened to improve the quality of soil environment.Alfalfa,known as the"king of forage",is widely planted in China and has a long history.It is mainly distributed in Northwestern China,North China,Northeastern China and the Jianghuai River basin.In this study,hydroponic method was adopted and Hoagland nutrient solution was used as the nutritional basis to study the effects of single/compound stress of Cd and Ni on the absorption capacity of heavy metals and various growth physiological indexes of alfalfa under certain temperature and light intensity,and to compare the corresponding differences of alfalfa under single/compound stress of Cd and Ni.The study results are as follows:（1）Response of alfalfa to growth index under single/combined stress of Cd and Ni showed that:Under the single stress of Cd and Ni,the germination rate,germination potential and germination index of alfalfa showed a phenomenon of"low promotion and high inhibition"with the change of stress concentration,and the vigor index showed a negative correlation,while the inhibition index of root,stem and leaf increased with the increase of stress concentration,and showed a positive correlation.When the concentration of Cd was 15 mg/L and the concentration of Ni was 10 mg/L,the germination rate,germination potential and germination index reached the maximum value.Under C1N10 stress,the germination rate,germination potential and germination index of alfalfa reached the maximum value,the leaf inhibition index was negative,and the root and stem of alfalfa did not show significant inhibition,indicating that the two concentrations of heavy metals contribute to the growth of alfalfa.（2）Response results of alfalfa to physiological indexes under single/combined stress of Cd and Ni showed that:Under single stress of Cd and Ni,under the same mass concentration（50 mg/L）stress,the heavy metal content in alfalfa increased compared with CK control group,and the content of O^2-also increased,resulting in the increase of SOD,POD and proline.Alfalfa adsorption of Ni is higher than on Cd adsorption amount,but in alfalfa root cell vitality,H₂O₂,CAT,soluble protein,soluble sugar,chlorophyll content of each index is less than Cd stress levels,the indicators show that Cd damage in alfalfa than Ni damage in alfalfa,and alfalfa is better for adsorption of Ni,have a higher resistance.Under the combined stress of Cd and Ni（C1N25）,the adsorption capacity of Cd and Ni to alfalfa was the highest,which promoted the growth of alfalfa.Under C5N25 stress,the contents of proline and soluble protein in alfalfa reached the highest level,and the content of soluble sugar decreased compared with CK control group.Under C10N25 stress,root cell viability and chlorophyll content in alfalfa were the lowest,but O^2-content reached the maximum,indicating that root cell viability and chlorophyll content were negatively correlated with O^2-content.（3）Correlation analysis of alfalfa growth indexes and physiological indexes,principal component analysis and heat map analysis under single/combined stress of Cd and Ni showed that:The correlation between alfalfa germination rate and germination potential was the highest under the stress of Cd.The correlation between alfalfa germination potential and germination index was the highest under Ni stress.The correlation between the activity index of alfalfa and root inhibition index was the highest under Cd-Ni stress.Under the single/combined stress of Cd and Ni,the higher the heavy metal stress concentration,the lower the activities of chlorophyll a,chlorophyll b,total chlorophyll,root cell activity,CAT and soluble sugar content in alfalfa,but the O^2-content increased significantly,which showed a negative correlation.Under single stress of Cd,root inhibition index and activity index were the growth indexes,and total chlorophyll and proline were the physiological indexes.Under Ni stress alone,the growth index,the growth index,the physiological index,the total chlorophyll and proline;Under the combined stress of Cd-Ni,the germination potential and vigor index in the growth indexes can be used as the main indexes,and the content of Cd,SOD and soluble protein in the physiological indexes can be used to determine the resistance strength of alfalfa to Cd-Ni.In conclusion,the toxicity to alfalfa under the single stress of Cd and Ni is Cd>Ni.Under C1N25 stress,has the highest absorption of heavy metals.Under C5N25 stress,alfalfa had the highest resistance to heavy metals.The root cell viability and chlorophyll content of C10N25 alfalfa were the lowest and the toxicity was the highest.