Screening Of High Tolerance Cd/Zn Mustard Cultivars And Research On The Physiological Mechanism

Soil heavy metal pollution has become a serious environmental problem in China and around the world.Soil cadmium and zinc pollution not only seriously threaten agricultural safety production,but also bring potential harm to human health through the enrichment of food chain.Phytoremediation is a low cost green repair technology,but most of the hyperaccumulator have long growth period,small biomass and sensitive to climate,which make it difficult to grow in large areas in China.Chinese mustard is rich in cultivars resources,large biomass,short growth period,strong adaptability,and the hyperaccumulator India mustard is the relative plant of mustard.So mustard is one of the potential remediation materials for Cd and Zn contaminated soil.In this study,21 kinds of common mustard cultivars in domestic market were used as materials to planted on contaminated soil that collected in polluted areas.Through pot experiments,the sensitivity distribution of different mustard cultivars on the of Cd/Zn stress in soil was investigated.Subsequently,we selected six representative cultivars,and measured the antioxidant characteristics Cd/Zn accumulation characteristics and plant rhizosphere/non-rhizosphere soil Cd/Zn forms changes.The main results are as follows:?1?The growth of 17 kinds of mustard biomass was improved by 2.0%³0.5%under low-level of Cd stress(?1.23 mg·kg^-1),while the excessive Cd stress(?6.90 mg·kg^-1)inhibited the plant growth significantly.The growth of all mustard biomass was improved by 3.6%⁷8.1%,When Zn exceeded 1314.8 mg.kg^-1,the effect of toxicity was obvious.?2?The cumulative frequencies of species sensitivity distributions of Cd/Zn stress varied significantly?P<0.05?among the tested mustard cultivars.the JTN was the most sensitive mustard cultivar to Cd stress and the BJ showed the highest tolerance.?3?In high Cd and Zn soil,based on 11 resistance indexes including plant height,root length,fresh weight and dry weight on the ground part,root fresh weight and dry weight,SPAD,MDA,SOD,POD,CAT.Resistance of these cultivars were comprehensively evaluated by methods of principal component analysis,subordinate function value analysis,comprehensive score analysis and cluster analysis.21 cultivars were clustered into 4 grades:high tolerant,tolerant,low tolerant and sensitive.Among them,1 tolerant,3 tolerant,11 low tolerant cultivars were selected,while the remaining 6 cultivars were sensitive.?4?By analyzing the activity of malonaldehyde?MDA?and antioxidant enzyme?SOD,POD,CAT?in 6 representative mustard cultivars.The toxic effects of Cd and Zn on the mustard cultivars increased with the increase of its concentration.The MDA content in the high tolerance BJ was obviously lower than that of the other 5 mustards,and the antioxidant enzyme activity in the body was high.It indicated that BJ can potentially reduce the activity of reactive oxygen species,decrease the lipid peroxidation and protect plants from oxidative damage by the synergetic effect of antioxidant enzymes.?5?The rhizosphere soil p H of 6 representative mustard was less than non-rhizosphere soil at different Cd and Zn levels,and the pH decreased most significantly in the high tolerance cultivar BJ rhizosphere,and the content of Cd form in the rhizosphere and non-rhizosphere soil of 6 kinds of mustard were:Cd-RES>Cd-OXI>Cd-RED>Cd-EXC.The content of Zn form is Zn-RES>Zn-RED>Zn-OXI>Zn-EXC.Under the stress of low concentration of heavy metals,6 kinds of mustard had the ability to activate Cd and Zn,which showed that the available and exchangeable fractions of Cd and Zn were increased.but only BJ and HJ showed a certain activation ability under the stress of high concentration of heavy metals.?6?The content of Cd and Zn in root and shoot of mustard cultivars showed significant positive correlation with the concentration of Cd and Zn in soil.The bioconcentration factor?BCF?of BJ were larger than 1 for both roots and shoots parts,the highest Cd and Zn accumulation in shoots was 468.1?g·pot^-1,49061?g·pot^-1 respectively,and the maximum of the purification rate was 14.45%and 3.37%respectively.That means BJ can be used for phytoremediation of Cd and Zn contaminated soil.