Effects Of Bamboo Charcoal Addition On The Phytoremediation Of Heavy Metals Contaminated Soil

Many woody plants have strong tolerance and accumulation of heavy metals.Biochar,represented by bamboo charcoal(abbreviation is BB),can improve soil quality and change the bioaviliability of heavy metals.However,,the effect of BB amendmenton phyremediation of soil contaminated by heavy metal using trees are rarely studied.In the current study,we investigated the plant growth and remediation efficiency of willow grown in Cd,Pb,Cu and Zn contaminated soil amended with with BB.We selected S.psammophila as target tree species according to its growth and metal accumulation among the four typical water-tolerant species,i.e.,Salix interga ‘Weishanhu',S.psammophila,Nyssa aquatica,and Taxodium mucronatum,which grown in metals contaminated land.Then,a series trials with the S.psammophila treated with different mass fractions(0?1%?3%?5%?7%),different particle size(P1 < 0.149 mm?0.149 mm < P2 <0.25 mm?0.25 mm< P3 <0.5 mm)of BB,and soil flooding with BB were conducted.We aimed to explore the effects of BB addition on the phytoremediation efficiency of willow on heavy metals,thus we examined the soil quality,plant growth,heavy metals accumulation and distribution in plant tissues.Salix interga ‘Weishanhu',S.psammophila,Nyssa aquatica,and Taxodium mucronatum can maintain normal growth under conditions that heavy pollution of Cd,moderate pollution of Zn,and mild pollution of Pb,respectively,suggested the high tolerance to heavy metals.Meanwhile,the heavy metal accumulation ability differed among tree species.S.interga ‘Weishanhu' has the maximum total accumulation of Cd,Zn and Cu(462.58,4 341.32,261.86 mg·plant-1),followed by S.psammophila(202.39 ? 3 709.95 ? 232.57 mg·plant-1).S.psammophila has the maximum total accumulation of Pb(106.97 mg·plant-1).S.interga ‘Weishanhu'has stronger remediation ability than S.psammophila on Cd pollution,while S.psammophila was stronger with 106.97 mg·plant-1 than S.interga ‘Weishanhu' with 82.19 mg·plant-1 in Pb remediation.In contrast to the S.interga ‘Weishanhu' as a shrub,salt-tolerant arbor tree(S.psammophila)was more suitable for the treatment of heavy metal pollution in the short-rotation mode.The addition of BB(BB 0?1%?3%?5%?7%)increased the contents of organic matter and available potassium in soil,which increased by 75% and 192% in BB-7% treatment than that inthe control group.The growth traits of S.psammophila such as plant height,diameter of breast height and total biomass were influenced by many factors,and they did not show obvious differences with the addition of bamboo charcoal.S.psammophila increased the transport coefficient of heavy metals as the amount of bamboo charcoal increased,and increased by 20%,28%,116%,and 92% for Cd,Zn,Cu,and Pb in BB-7% treatment,in comparison with thecontrol group.The accumulation amount of Cd?Zn?Cu increased by 37%,31% and 27% with BB-3% treatment compared with CK group.The particle size of BB had insignificant effect on soil properties,while showing a significant effect on the concentration and transport of heavy metal accumulation in S.psammophila.BB with P1 size inhibited the growth of S.psammophila,whil promoting the heavy metal transport coefficient from root to shoot of S.psammophila.BB with P2 size stimiluated the growth of S.psammophila and increased the heavy metal accumulation amount in the roots of S.psammophila.The content of Cd,Zn,and Pb in plant increased 52.41%,25.55%,and 14.83% compared with control group.BB in P3 size treatments showed a small decrease in Cu and Pb accumulation compared to the control group.Soil flooding decreased the proportion of available Cd,Cu and Pb in the soil,and the plant height and biomass of S.psammophila were also inhibited.Due to the flooding,the K concentration in all parts of plant increased.Flooding increaseded the concentration of mineral elements in roots significantly and had little effect on the aboveground.Flooding treatment reduced the concentration of heavy metals Cd?Zn and Cu in the aboveground while increased the concentration in the roots.BB amendment during soil flooding elevaled soil p H,organic matter content,available potassium content,and the activities of major soil enzymes.BB addition reduced the proportion of accumulated heavy metals in the aboveground part,but still increased the content in shoots and roots in flooding treatment.In a word,the BB addition ratio,BB particle size,and flooding with BB could affect the accumulation of heavy metals by S.psammophila.The BB 3% with P2 size can promote the plant growth and heavy metal accumulation?...