Evaluation And Screening Tolerant Clones Of Salix Caprea In Heavy Metal Mining Area And Their Physiological Response To Phosphorus Deficiency

Environmental pollution of toxic heavy metals is increasing in recent years due to the increase of human activities.According to the 2014 National Survey Bulletin on Soil Pollution,16.1 percent of the country’s soil exceeded the national standard,mainly due to heavy metal pollution,which affected an estimated 1.2 billion a unit of area of land covering more than 70percent of the counties,covering factories,mines,roads,arable land,woodland,pastures and other sites.Through plant investigation in mining area,this study recorded community characteristics and confirmed that Salix caprea is the dominant tree species in mining area.The concentrations of heavy metals in roots,stems and leaves and the physical and chemical properties of rhizosphere soil were analyzed.According to the accumulation characteristics of heavy metals in the aboveground of Salix chinensis,168 and 169 populations with typical Cd phytoremediation potential were identified.By establishing the relationship between heavy metal accumulation and soil mineral nutrition,it is clear that the accumulation of heavy metal Cd in the aboveground is positively regulated by soil P.Cuttings and propagation were made from 168 and 169 populations to obtain different clones of Salix caprea.The Cd tolerance of clones 168-HH-A and 168-HH-B with strong Cd resistance were tested by examining the differences of Cd tolerance of different clones.The regulation of phosphorus on Cd tolerance of the two clones was illustrated.Specific research results are as follows:（1）Through the rightness of Liao Ning,He Bei,He Nan,Shan Xi heavy metals such as iron ore,gold,copper,gold mining area on the vegetation investigation,summed up the community characteristics of the typical natural vegetation around:The representative plants were Populus simonii Carr、Salix matsudana Koidz、Ulmus pumila L.;Salix caprea、Sorbaria sorbifolia（L.）A.Br、Lespedeza bicolor Turcz、Salix integra、for arbor layer;Saussurea japonica（Thunb.）DC、Dendranthema chanetii Kochia scoparia（L.）Schrad.、for brushwood layer etc.31 species of plants belonging to 26 genera and 20 families were found in this study.A total of 59 Clones of Salix were collected,including 48 Clones of Salix caprea.Among all the shrub species in the mining area,Salix caprea is the most widely distributed,which is distributed from Liao Ning,He Bei,He Nan to Shan Xi.It has the strongest adaptability.It can grow in a variety of harsh site conditions such as open pit mine,mineral dressing plant,slag turning line and tailings pond,and can be planted and survive on steep slope.The largest population.（2）The characteristics of heavy metal accumulation in the collected Salix caprea clones were evaluated.The results showed that the heavy metals Cd and Zn were highly mobile in Salix caprea clones,and were easily transported to the aboveground through the root system,while the heavy metals Pb was easily trapped by the root system.According to the specific characterization of different clones,Salix caprea clones 168-HH-1、169-HH-1 and 169-HH-2were selected as suitable for remediation of Cd contaminated soil.Clones 175-HH-1 and 182-HH-1 were suitable for the repair of heavy metal Zn,and clones 176-HH-1 and 176-HH-5 were suitable for the repair of heavy metal lead.Establish a chrysanthemum Salix caprea clones aboveground heavy metal enrichment and the relationship between soil physical and chemical properties,results show that the enrichment of branches of Zn and Cd and Zn concentration in the soil,branches of the concentration of lead is regulated by the total phosphorus and total potassium in soil negative,is regulated by the concentration of soil Cd,Zn is,branches and leaves of Cd enrichment is regulated by the total phosphorus and total potassium in soil.（3）Under Cd stress,branch growth rate,SPAD value and Cd concentration in each organ of eight clones 168 and 169 were measured and analyzed.Compared with CK,the growth rate of 168-HH-A and 168-HH-E branch length under Cd treatment increased by 15.61%and 9.75%,respectively.However,the diameter growth rate of 168-HH-E,168-HH-A and 169-HH-A branches was slightly affected by Cd stress,which increased by 24.14%,decreased by 4.17%and 7.29%,respectively.168-HH-B only reduced by 6.97%in SPAD changes and was least affected.Based on the standard of high cadmium concentration in both leaves and branches,the Salix caprea Clone 168-HH-F was selected as suitable for phytoremediation of cadmium contaminated soil.The cadmium concentrations of 168-HH-F branches and leaves were 340.99mg·kg^-1 and 604.37 mg kg^-1,respectively,and the transport coefficients were 0.36 and 0.62,respectively.（4）The Cd tolerant clone 168-HH-A and Cd sensitive clone 168-HH-B were compared and analyzed with different concentrations of Cd and different concentrations of phosphorus.Compared with CK treatment,the growth rate of branch length,the growth rate of branch diameter and the decrease degree of SPAD value of the clone of Salix caprea under Cd-P treatment were greater than that under Cd treatment,which proved that phosphorus could reduce the toxicity of Cd to Salix caprea and promote its growth.Cd tolerant clone 168-HH-A and Cd sensitive clone 168-HH-B have different dependence on phosphorus.Increasing phosphorus concentration of 168-HH-A under Cd stress does not reduce the damage of Cd stress.Phosphorus can reduce Cd toxicity on photosynthetic physiology and chlorophyll fluorescence of Cd sensitive type 168-HH-B,and improve its Cd tolerance.Phosphorus promoted the transport of Cd to the aboveground,and the concentration of Cd in 168-HH-B roots,branches and leaves was10.92%,26.67%and 71.25%higher than that in the absence of phosphorus,respectively.The transport coefficients of branches and leaves increased by 19.33%and 69.13%,respectively.In conclusion,Salix caprea is the dominant species of vegetation in the mining area.Clones 168-HH-F and 169-HH-M with high Cd concentration in leaves and branches were selected as phytoremediation materials for Cd contaminated soil.Phosphorus can alleviate the damage of Cd stress to Salix caprea and improve the transport of Cd to the overground.This study can provide plant materials and supporting technical support for the remediation of heavy metal Cd contaminated soil.