Effects Of Water Hyacinth Biochar On Cadmium Enrichment In Lettuce

Heavy metal pollution in cultivated soil is seriously affecting food security in China.Biochar,as a soil conditioner,has been proved to be an effective method for the prevention and control of soil heavy metal pollution,but its treatment effect is highly correlated with the properties of raw materials.Water hyacinth contains a large number of functional groups such as cellulose,carboxyl group and hydroxyl group,which has strong adsorption capacity for heavy metals.If water hyacinth can be prepared as biochar and applied to heavy metal contaminated soil,on the one hand,it is helpful for the resource utilization of alien invasive organisms,on the other hand,it also provides a new idea for the prevention and control of heavy metal contaminated farmland.Therefore,in this study,the effect of biochar prepared by water hyacinth on cadmium absorption of cd-polluted cultivated lettuce was investigated.Firstly,the effects of biochar preparation on cadmium enrichment in lettuce were investigated.When 1% water hyacinth biochar was applied,the fresh weight of lettuce increased by 32.31% compared with the control,and also increased by 11.75% and 16.69%compared with rice straw and corn straw.Under the same carbon application rate(1%),rice straw,corn straw and water hyacinth biochar can effectively reduce the content of cadmium in lettuce plants and roots.However,when water hyacinth biochar was applied,it could reduce cadmium in all organs of lettuce more effectively,and plant and root decreased by14.46% and 8.14%,respectively,compared with the control.FTIR results showed that water hyacinth biochar had better adsorption effect on heavy metals due to its more functional groups such as carboxyl and hydroxyl groups.Secondly,the effects of water hyacinth biochar prepared under different conditions on cadmium enrichment in lettuce were investigated.The experimental results show that biochar has stronger cadmium resistance with increasing carbonization temperature and time.When the preparation condition of water hyacinth biochar was 700℃-2 h and the amount of carbon applied was 3%,the cadmium content of lettuce plants and roots decreased by 73.64%and 38.13%,respectively,compared with the control.The main reason why the biochar prepared under different conditions resulted in different cadmium absorption of Pakchoi was that the available cadmium in soil was changed,and the content of available cadmium in soil was proportional to the uptake of plant.The results of FTIR and SEM showed that water hyacinth biochar could reduce the content of available heavy metal cadmium in soil,inhibit the accumulation of available heavy metal cadmium from soil to lettuce,and reduce the content of heavy metal cadmium in various organs of lettuce.Finally,the 16 s RNA results showed that the application of biochar could greatly change the diversity and abundance of soil microorganisms,and enhance the ability of soil resistance to pests and diseases.Finally,the effect of potassium permanganate modified water hyacinth biochar on cadmium enrichment in lettuce was investigated.When the carbon application amount was1%,the highest fresh weight of lettuce modified with k Mno4 was 18.10 g,which was 44.11%and 21.39% higher than that of the control and water hyacinth biochar lettuce,respectively.The yield of lettuce would decrease with the increase of biochar application.Potassium permanganate modification significantly reduced the cadmium uptake of lettuce,which was22.44% lower than that of unmodified biochar,and 4.94% lower than that of unmodified biochar in root system.With the increase of application amount of modified biochar,the cadmium uptake of lettuce decreased significantly.The results of FTIR and SEM-EDS showed that potassium permanganate modification resulted in the increase of Mn-O covalent bond,and the ability of cadmium adsorption was obviously stronger,which was the fundamental reason why potassium permanganate modified biochar could reduce the cadmium absorption of lettuce.