Effects Of Cadmium Stress On Seed Germination And Seedling Growth Of Different Mulberry Varieties

Cadmium is one of the five major heavy metal pollutants,which has a wide range and high toxicity,it is easily absorbed by plants and transferred.Thereby achieving the effect of repairing polluted soil.This has attracted widespread attention from researchers.Mulberry has certain tolerance and transfer ability to heavy metal cadmium and can be used to repair cadmium contaminated soil.In this study,10 mulberry varieties（Guisang 5,Guisang 6,Yue Sang 51,Guisangyou 12,69851,Yuesang 11,Santeyou 2,Guisang 62,Sha 2×Len 109）was used as experimental materials to investigate the effects of different concentrations of cadmium on seed germination and seedling growth of mulberry.Analysis the cadmium enrichment and transfer ability of different mulberry.At the same time,the cadmium tolerance was analyzed and evaluated by the membership function method,in order to screen out the mulberry varieties with strong cadmium tolerance.The main results are as follows:1.In the germination experiment of 10 varieties of mulberry seeds,the stress was treated with 0¹00 mg/L Cd²⁺concentration.The results showed that different concentrations of cadmium stress had different inhibitory effects on the seed germination of 10 mulberry varieties.With the increase of cadmium stress,the seed germination rate,germination index and vigor index decreased gradually.Under the low cadmium treatment（5 mg/L）,the germination rate of Yuesang 11 and Danbaisang were eliminated.The germination index of Yuesang 11,Guisangyou 12 and Guisang 6 increased slightly compared with the control,and the other varieties decreased.The higher the concentration,the larger the decrease,The decrease of vitality index was higher than that of germination rate and germination index,indicating that the activity index was most inhibited by heavy metal cadmium.The growth of radicle and hypocotyl decreased with the increase of cadmium concentration.Under low cadmium treatment（5 mg/L）,the hypocotyl length of Guisang 5increased significantly by 50.48%compared with the control.The length of the radicle and hypocotyls decreased of other mulberry varieties,and The higher the concentration,the lower the drop.And the decrease of radicle was greater than that of the hypocotyl,indicating that the radicle of the cadmium treatment was inhibited more than the hypocotyl.Through the membership function method in fuzzy mathematics,the comprehensive cadmium tolerance values of 10 varieties were comprehensively calculated.It was found that Guisang 6 and Yuesang 11 had the strongest cadmium resistance,with comprehensive values of 8.19 and 8.01,respectively,Sha 2×Lun 109 was the smallest,only 1.94.Cluster analysis divided 10 varieties into three categories:cadmium-tolerant:Guisang 6 and Yuesang 11,medium cadmium-resistant:69851,Guisangyou 12,Danbaisang,Sangteyou 2,Guisangyou62,Guisang 5 and Yuesang 51,sensitive type:Sha 2×Lun 109.2.Using mulberry seedlings as test materials,the effects of cadmium on the growth of different mulberry seedlings were investigated by pouring cadmium solution with Cd²⁺concentration of 0-500 mg/kg.The results showed that low cadmium treatment（5 mg/kg）was applied to mulberry plants.The increase of high increment and total biomass was promoted,and then decreased gradually.At high concentration（500 mg/kg）,the plant height increment and total biomass decreased significantly compared with the control,but the increase of plant height of Yuesang 11 was changed under cadmium treatment,not significant.Among the physiological indicators,the mulberry trees of different varieties had different trends under different cadmium treatments,antioxidant enzymes（SOD,POD,CAT）,osmotic adjustment substances（soluble protein,soluble sugar,proline）and stress indicators（MDA）.The variation law is also different due to the variety of cultivars and cadmium concentration.Therefore,the cadmium tolerance of different mulberry trees cannot be evaluated by a single index.The multi-index membership function method and the standard deviation weighting method were used to comprehensively evaluate the cadmium tolerance of different varieties of mulberry trees,and finally expressed by the comprehensive value D.The higher the D value,the stronger the cadmium resistance,according to the D value.The cadmium tolerance of 9 mulberry trees was ranked as follows:Sangteyou 2>Guisang 6>Guisang 5=Guisangyou 12>Danbaisang=Yuesang 11>Guisang 62>Yuesang 51>69851.Cluster analysis is divided into three categories:cadmium-tolerant:Sangteyou 2 and Guisang 6,medium cadmium-resistant:Danbaisang,Guisang 5,Guisangyou 12,sensitive:Yuesang 11,Yuesang 51,69851 and Guisang 62.3.The cadmium content in various organs of mulberry was determined by inductively coupled plasma mass spectrometry（ICP-MS）.The results showed that the cadmium content in roots,stems and leaves of mulberry trees increased with the increase of cadmium concentration,but at any concentration.The cadmium content in different organs of mulberry trees was root>stem>leaf,indicating that the roots were the main organs of mulberry accumulation of heavy metal cadmium,and under the high concentration of cadmium treatment,the cadmium content of roots of Guisangyou 12 was significantly higher than the other 8 varieties,and it was 109.27 mg/kg,indicates that the roots of Guisangyou 12 have strong ability to absorb cadmium.With the increase of cadmium concentration,the transfer coefficient of different mulberry trees showed a trend of increasing first,then decreasing and then increasing.The average transfer coefficient of each variety was 0.166-0.319,of which Guisang 6 was the highest and 69851 was the lowest;while the enrichment coefficient was The performance showed a gradual decline.The average enrichment coefficient of mulberry roots in different varieties ranged from 0.27 to 0.58,of which Guisangyou 12 was the highest,and its root cadmium enrichment ability was strong.Yuesang 51 was the lowest,and its enrichment ability was higher.weak.The average value of the above-ground enrichment factor of different mulberry trees ranged from 0.08 to 0.17,with Guisang 6 and Guisangyou 12 being the highest,reaching 0.17.Compared with the root enrichment ability,the above-ground part of the mulberry tree has a weak enrichment ability,and the mulberry tree mainly absorbs and enriches the heavy metal cadmium by the root.