Cd-tolerance Of Salix Integra And Mitigative Effect Of Spermidine And Activated Carbon On Salix Integra Under Cd Stress

With the rapid development of enhanced industrialization and intensified agricultural production,Cd-contaminated soil is becoming more and more serious,the ecological environment and human health thus start to deteriorate.Salix Integra,as a fast-growing Salix plant with both economic and ecological values,has a great Cd tolerance,thus could be used to enhance remediation for contaminated soils.The aim of the present study is to investigate the adaptive mechanism of Salix Integra in Cd-contaminated soils and construct the enhanced remediation technology.A hydroponic experiment was carried out to investigate the effect of different Cd concentrations(0,10,20,30,40 mg L^-1)on growth,root anatomy,absorption and distribution Cd²⁺in plant,as well as the physiological response mechanism of roots and leaves of Salix Integra.The results could help to demonstrate the semi-inhibitory concentration of Salix Integra to Cd pollution.Meanwhile,a combined of hydroponic and pot experiments were conducted to reveal enhanced Cd-tolerance of exogenous spermidine(0,0.1,0.2,0.4,0.8,1.6 mmol·L^-1)in Salix Integra.Besides,a pot experiment was carried out to investigate the effect of activated carbon addition(0.5,1.0,2.0 g·kg^-1)on the reclamation of Cd contaminated soils.Together,an enhanced repair technology of Salix Integra in Cd contaminated soils could be constructed by combining application of both spermidine and activated carbon.The detailed results were as follows:（1）Salix Integra has a great Cd-tolerance with 24.76 mg·L^-11 of the semi-inhibitory concentration.The content of Cd in Salix Integra was,leaf>root>epidermis>xylem.The transmission coefficient increased with the increasing of Cd concentrations（from 1.11 to1.26）,while the enrichment coefficient followed the opposite trend,decreased with the increasing of the Cd concentrations.The largest enrichment coefficient under 10 mg·L^-11 Cd was 28.63,and ranged from 14.33 to 17.67 under 20,30,and 40 mg·L^-11 Cd concentrations.10mg·L^-11 Cd concentration significantly increased the index of root anatomy and root biomass,and decreased root volume and aboveground biomass.The growth,volume,average diameter and biomass of root were significantly decreased under higher Cd concentrations,such as 20,30 and 40 mg·L^-1.In physiology,the superoxide anion activity unit and Catalase（CAT）activity in roots and leaves of Salix Integra were significantly increased,while Glutathione（GSH）content and Glutathione reductase（GR）activity were significantly decreased under Cd stress.（2）Cd stress was obviously alleviated with the addition of activated carbon.The biomass increased by 46.00%⁶5.08%,9.38%³7.18%and 15.50%²5.60%,after the addition of activated carbon for 30d,60d and 90d,respectively.The content of superoxide anion activity unit and hydrogen peroxide（H₂O₂）decreased,and the index of root anatomy as well as the content of GSH and superoxide dismutase（SOD）increased.The Cd content in Salix Integra decreased,and the Cd removal rate o decreased by 48.82%⁵8.28%at 90d,and the removal rate was 1.73%with activated carbon added at 0.5 g·kg^-1.（3）Exogenous spermidine spraying can effectively alleviate the inhibition of Cd stress on the growth of Salix Integra was relieved though exogenous spermidine application.In the hydroponic experiment,the relative growth rate of Salix Integra increased by44.97%¹02.76%under spermidine treatment.The increase rate of nodal number,junction number and bifurcation number of roots increased by 50.33%,25.20%and 25.42%,respectively,under 0.4 mmol·L^-11 spermidine.The total protein increased by 43.43%,and the GR activity,superoxide anion activity unit and H₂O₂ content decreased by 73.90%,46.35%and 67.39%,respectively.In the pot experiment,the biomass increased by 55.27%with 0.8mmol·L^-11 spermidine.The length,surface area and volume of root were significantly increased,the content of superoxide anion activity unit and H₂O₂ was decreased,the SOD activity and GSH content were increased,and the Cd removal rate was up to 1.48%.（4）The synergistic application of spermidine and activated carbon stimulated the growth and development of Salix Integra,with the biomass increased by 66.60%⁹2.95%（30d）,47.85%⁷1.34%（60d）,39.65%⁶5.66%（90d）,root length,average diameter and fractal dimension increased by 67.33%⁸6.06%,77.45%¹06.56%and 14.09%¹7.61%（30d）,139.49%¹89.32%,33.79%⁴4.13%and 17.08%²6.61%（60d）;44.01%⁶3.37%,32.46%⁴8.54%and 15.46%¹7.84%（90d）,respectively.The synergetic application of 0.8mmol·L^-11 spermidine and 0.5·g kg^-11 activated carbon significantly decreased the unit of superoxide anion activity by 39.46%⁴5.30%,and significantly increased the content of GSH by 116.17%¹20.68%.Meanwhile,the Cd removal rate was up to 4.10%at 90d.