Study Of Growth Physiological Response And Enrichment Capacity Of Cultivars Of Willow Seedlings To Copper Pollution

With the rapid development of polluting heavy industries and chemical agriculture,Cu p ollution is becoming increasingly serious.Compared to physical-chemical methods of remedi ation,phytoremediation has the advantages of lower cost,less secondary pollution to the envir onment and longer duration of remediation effects.The discovery of super-accumulator plants has opened up more possibilities for the practical application of phytoremediation,but due to the limitations of the application of super-accumulator plants,the use of woody plants with hi gh biomass,high biological rates and short rotation periods has become a viable alternative fo r pollution remediation.In this study,eight willow cultivars:Salix matsudana’Shidi1’（breed ing code:A42）,Salix Matsudana’Shidi2’（breeding code:A52）,Salix matsudana’Hanxiong2’（breeding code:A57）,Salix Matsudana’Luliu1’（breeding code:A57）B28),Salix matsudana’Luliu2’（breeding code B39）and Salix Matsudana’Luliu3’（breeding code B39）.B95),Salix m atsudana’Luliu6’（Breeding code B99）,Salix psammophila’Huangpi1’（breeding code A94）w ere used in a hydroponic approach to investigate the effects of Cu stress on willow growth and the physiological and biochemical responses,and to explore the uptake and enrichment patter ns of Cu²⁺by willows.Growth indicators included the determination of biomass;physiologica l indicators included the determination of net photosynthetic rate,intercellular CO₂concentrat ion,stomatal conductance and transpiration rate;biochemical indicators included the determin ation of root vigour,superoxide dismutase activity,peroxidase activity,catalase activity,chlor ophyll content,free proline content,malondialdehyde amount and soluble protein content.Th e new willow cultivars that can be used for phytoremediation of copper pollution were screen ed to provide a theoretical basis for cultivation techniques to improve copper uptake and accu mulation in willows,and to provide a reference value for the use of willow to remediate and i mprove heavy metal contaminated soils and water bodies.The results showed that:（1）Effects of different concentrations of Cu stress on the growth and physiological and bioch emical indicators of willowWith the increase of Cu²⁺concentration,the growth of all cultivars of willow was signifi cantly inhibited,and the biomass showed a gradual decrease with the increase of Cu2+conce ntration.When the Cu²⁺concentration was 300μmol-L-1,the biomass of A94,A52,A57,A42,B28,B39,B95 and B99 decreased by 75.4%,76.9%,76.7%,78.3%,78%,78.3%,75.5%a nd 81.9%,respectively,compared with the control.Cu stress also inhibited photosynthesis in willow,as evidenced by a significant decrease in chlorophyll content and light and parameters with increasing Cu²⁺concentration,indicating that Cu stress caused damage to chloroplast str ucture and inhibited chloroplast synthesis.The effects of Cu stress on the protective enzymes i n the leaves of eight cultivars of willow showed an increase in SOD,POD and CAT activities at low concentrations and a significant decrease at high concentrations.The malondialdehyde content in the leaves of all willow cultivars showed a gradual increase with increasing Cu²⁺c oncentration,indicating that Cu stress increased the level of reactive oxygen cultivars in willo w leaves.Proline content showed a trend of increasing and then decreasing with increasing Cu concentration,while soluble protein showed a trend of gradually decreasing with increasing c oncentration.The high level of proline under stress conditions helped to maintain the osmotic pressure inside and outside the cells and keep the cells stable.（2）Changes in biochemical indicators of willow seedlings under low concentrations of Cu in r esponse to time spanUnder Cu2+concentration of 100μmol-L^-1stress in eight varieties of willow,chlorophyl l content and soluble protein content in leaves showed a trend of decreasing and then increasin g with time;proline content and malondialdehyde content showed a trend of increasing and th en decreasing;SOD activity showed a trend of decreasing and then gradually increasing,and all SOD activities in leaves were higher than the control after 35 d;A94,A52,B39,B95,B99and POD activities showed a trend of first decreasing and then gradually increasing,A42 and B28 POD activities showed a trend of first sharply increasing and then gradually decreasing,A57 showed a different trend from other cultivars of willow,POD activities showed a signifi cant increase and then decreasing and then increasing trend.With the extension of stress time,CAT activity in A94,A52,B28,B39 and B99 showed a significant increase followed by a de crease and then an increase,while CAT activity in A57,A42 and B95 leaves showed a signifi cant increase followed by a decrease.In summary,all cultivars of willow can mitigate the tox ic effects of Cu stress through the combined effects of their own antioxidant enzyme systems and non-enzymatic substances,and all have some ability to adapt when faced with low concen trations of Cu stress.（3）Enrichment pattern of Cu2 in different organs of seedlingsAll cultivars of willow showed a similar pattern of Cu²⁺distribution,i.e.accumulation mainly in the roots.The Cu concentration accumulated in roots could reach tens of times the Cu concentration accumulated in stems and leaves,and the Cu accumulation concentration wa s root>leaf>stem.With the increase of Cu²⁺treatment concentration,the accumulation conc entration of Cu²⁺in leaves,stems and roots of each cultivars of willow showed a significant i ncrease.At a Cu²⁺concentration of 100μmol-L^-1,each cultivars of willow was able to mainta in a high transfer coefficient.As the concentration of Cu treatment increased,the transfer capa city of eight willow cultivars for Cu²⁺gradually decreased.（4）Screening of good asexual lines by principal component analysis based on growth and phy siological and biochemical indicatorsFrom the principal component scores and overall scores,the higher scores of principal co mponent Y1 were A52,B99 and B28,indicating that these three willow cultivars maintained a high growth rate while maintaining a high Cu enrichment capacity;while the scores of B39,B95 and A42 were all negative,indicating that Cu stress severely inhibited the growth of thes e three willow cultivars.The higher scores for principal component Y2 were B28,A94 and B39,indicating that these three cultivars of willow had a strong ability to decompose H₂O₂and maintain cellular osmotic pressure and stability in the face of Cu stress.The four cultivars B28,A52,B99 and A94 have higher overall scores and are more suitable for Cu-contaminated phytoremediation to some extent.