| Due to the huge traffic volume in the artificial wetland in the high-speed service area,a third of the lead particles emitted from the vehicle exhaust will settle into the wetland environment,causing lead pollution.Lead is not only difficult to degrade,but also toxic to the environment.In view of the difficulty in removing heavy metals in constructed wetlands,the key is to find simple and effective biosorption and bioenrichment methods of scholars.Hedychium coronarium,Vetiveria zizanioides,Nerium indicum and Thalia dealbata are four relatively common type of wet plants.Each has a very good viewing effect and significant ecological benefits,and has a wide application prospect in the wetland environment.In this paper,these four plant materials were selected to study their resistance physiology under lead-ion stress,reveal their resistance mechanisms and construct their lead-tolerant evaluation system,which provides relevant theoretical basis for selecting lead-free wet plants.The experimental analysis results are as follows:1.The plant height,biomass change,root and leaf damage of the four plants were different under different lead concentrations.The height inhibition of Thalia dealbata was the smallest among the four plants.The growth height of Hedychium coronarium and Nerium indicum decreased by 84.89%,64.22% and 60.82% compared with CK group.And the height change of Nerium indicum was the most gradual during the whole test period.The lightest damage to the leaves and roots was Vetiveria zizanioides,only in the lead concentration of 300mg/L appeared more serious black and yellow growth stagnation.The stems dry weight of the plants was significantly lower than that of the roots and leaves.The leaves dry weight of Nerium indicum decreased by 78.96% compared with CK.The lead stress concentration of Thalia dealbata was the significant correlation with the dry weight of plants.The correlation coefficient between dry weight of whole plant and concentration was-0.807,P<0.01.Vetiveria zizanioides is the only plant species in which the dry weight of all four plants exceeds CK at all lead stress concentrations.It can be considered that Vetiveria zizanioides has strong resistance to lead stress..2.Low concentration of lead ions promoted the synthesis of chlorophyll content in Vetiveria zizanioides and Thalia dealbata,and the concentration was too high to inhibit.The chlorophyll change trend of Vetiveria zizanioides is relatively stable,indicating that it has strong resistance.The chlorophyll content of Hedychium coronarium was not only negatively correlated with the time of lead stress,but also affected by the high and medium concentration of lead stress.The chlorophyll content decreased rapidly from the concentration of 100 mg/L.The chlorophyll content of Nerium indicum reached the maximum in all plant treatments at 35 days of high lead concentration treatment.However,at this time,the Nerium indicum leaves showed severe shrinkage and wilting,indicating that the increase of chlorophyll content of plants was closely related to dehydration.The conductivity of the four plants was peaked in the late stage of lead treatment,except that the conductivity of Thalia dealbata was decreased during the experiment.On the 28 th day,the conductivity of the Thalia dealbata was 78.92% of the CK,and the other three plants reached the maximum at 300mg/L concentration.The electrical conductivity of Hedychium coronarium,Vetiveria zizanioides and Nerium indicum was 112.39%,105.47% and116.40% of the CK,indicating that the Thalia dealbata has strong defense mechanism under lead stress and is highly adaptable.The other three plants reacted fiercely to medium to high concentrations of lead stress and eventually showed a positive correlation.In addition,the stress of Vetiveria zizanioides at low lead concentration is less than the high lead concentration.3.The plant antioxidant enzymes SOD and POD showed different performance under the lead stress of four plants.The overall SOD activity of Nerium indicum was relatively stable,and the activity of SOD was constant,which was almost unaffected by lead stress.The SOD activity of Vetiveria zizanioides maintained a steady rise,The activity is positively correlated with the treatment concentration.The correlation coefficient is 0.550,P<0.01,and it has a excellent adaptability.The SOD activity of Thalia dealbata was slightly increased under low concentration stress,but it dropped sharply when the lead concentration was 300 mg/L.The POD activity of Thalia dealbata was significantly higher than that of the other three plants,and the correlation with lead treatment concentration was not high,and the overall trend was first to increase and then decrease;while the POD activity of Thalia dealbata was the lowest overall,which was related to the concentration of lead treatment.The coefficient r =-0.613,P < 0.01.The POD activity of Hedychium coronarium was mainly affected by the time of lead treatment,and the correlation between POD activity and treatment time was-0.573,P<0.01.The correlation between POD activity and lead treatment concentration and treatment time of Nerium indicum was low.However,the POD activity of Nerium indicum was gradually increased under the lead concentration of medium and high concentration(200mg/L,300mg/L).And on the 35 th day,the POD activity of Nerium indicum at 300 mg/L lead concentration was also greater than CK,which was 123.99% of the CK.Hedychium coronarium reached the maximum POD at 50mg/L concentration,while Vetiveria zizanioides and Thalia dealbata reached the maximum at 10mg/L,indicating that the three plants were very sensitive to lead stress.4.The lead content and lead enrichment of the roots,stems and leaves of the four plants showed root>stem>leaf,and all were significantly larger than CK,and the enrichment efficiency of roots was the strongest.The lead content of the roots of the four plants changed greatly at 100 mg/L,indicating that the lead concentration of 100 mg/L can be used as a reference guideline for plant lead tolerance standards.The lead content ofleaves and stems was positively correlated with the concentration of lead treatment.The lead content of the three components of Nerium indicum is the lowest among the four plants.The reason is speculated that Nerium indicum is a typical woody plant.The ion transport driven by plant water metabolism and transpiration is not as intense as aquatic plants.In addition,the transport coefficient of Thalia dealbata was positively correlated with the lead treatment concentration,and the lead enrichment ability of the aboveground organs was enhanced.The lead content in stems and leaves of Hedychium coronarium was directly proportional to the concentration of lead treatment,but decreased at 300 mg/L,indicating that the lead ion absorption in roots of Hedychium coronarium reached saturation,and the absorption of leaves and roots of Vetiveria zizanioides was very similar to that of Hedychium coronarium.The amount of lead enrichment in stem and leaf of Thalia dealbata was completely positively correlated with the concentration,but reached the maximum at 300 mg/L.Moreover,the transport coefficient of re-flowering was also positively correlated with the concentration of lead treatment,indicating that the lead enrichment ability of Thalia dealbata leaves and stems were the strongest. |
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