Study On The Influence Of Heavy Metal Pb On The Growth Of Calendula Officinalis And Its Remediation Of Polluted Land

The increasing severity of heavy metal pollution of soils has already had grave impacts on the ecology and environment.Pb pollution is a particularly serious issue.The presence and continuous increase of Pb in soils will adversely affect the metabolism of plants,and will eventually be transferred into animals through the food chain,thus increasing the scope of harm.Recent studies have shown that Calendula officinalis has a certain enrichment effect on Pb,which therefore raises the following research questions:Whether the presence of Pb²⁺affects the germination of Calendula officinalis seeds?After growing seedlings,does the increasing Pb²⁺concentration affect the growth and enrichment ability of plants?How does the addition of a chemical enhancer affect the enrichment and tolerance?In order to solve these problems,the following experiments were conducted with Calendula officinalis as the target plant.First of all,to determine the effects of Pb²⁺on seed germination,a germination test was performed,where the seed was subjected to different Pb²⁺concentration stress.Pot experiment was also conducted to study the effects of different concentrations of Pb²⁺on the growth and enrichment ability of Calendula officinalis.Lastly,changes of the enrichment ability of Calendula officinalis caused by the addition of SDS and EDTA were studied.The main results show that:?1?In the germination test,with the Pb²⁺concentration of 20mg/L as the boundary,the relatively low concentration of Pb²⁺stress significantly promoted the germination rate,germination potential and germination index of Calendula officinalis seeds?P<0.05?.Under the stress of this concentration,the germination rate,germination potential and germination index reached the highest value,and the germination rate was 90.67%.After the concentration being increased beyond 20mg/L,Pb²⁺'s promoting effect gradually decreased.At each concentration of Pb²⁺stress,the root length of Calendula officinalis did not change significantly?P>0.05?,and Pb²⁺stress also had a certain inhibitory effect on root cross-sectional area.?2?In the pot experiment,with the increase of Pb²⁺concentration,the plant height and biomass of Calendula officinalis increased initially and then decreased.When the concentration of Pb²⁺was 20mg/L,the plant height and biomass reached the maximum value.After that,the plant height and biomass began to decrease,and the accumulation of Pb²⁺in the aerial part and root increased significantly with the increase of concentration?P<0.05?.At 100mg/L,each of the Calendula officinalis could enrich 649.9ug of Pb.Under the whole concentration treatment of this experiment,the transfer coefficient of Calendula officinalis was less than 1,and the enrichment factor was greater than 1.As the concentration increased,the enrichment factor became larger,and the tolerance coefficient was the largest when the Pb²⁺concentration was 20mg/L.The value was1.33 and then started to decrease.?3?The results showed that under the two concentrations of Pb²⁺,single SDS could significantly increase the plant height and biomass of Calendula officinalis?P<0.05?,and also significantly increased the enrichment of Pb²⁺in Calendula officinalis?P<0.05?.The optimal SDS concentration was 1mmol/L;after adding EDTA,the plant height and other related indicators were also significantly higher than CK?P<0.05?.Under the combined treatment,the plant height,biomass and total accumulation value of Calendula officinalis were significantly higher than that of other treatments and CK?P<0.05?when the concentration of SDS was 1mmol/L and the concentration of EDTA was 1mmol/L.In summary,exogenous Pb²⁺does have a certain effect on the germination,seedling growth and plant enrichment characteristics of Calendula officinalis,the overall tendency proves to be promotion in low concentration and decreased promotion in high concentration;when the Pb²⁺concentration is 20mg/L,the germination rate of the seeds of Calendula officinalis is the highest,and the seedlings grow best.Both EDTA and SDS can enhance the enrichment ability of Calendula officinalis and there is a synergistic effect.When the concentration of SDS is 1mmol/L and the concentration of EDTA is 1mmol/L,their promotion effect on the growth of Calendula officinalis and its enrichment ability of Pb²⁺proves to be the strongest.