Mechanism Of Cystamine Modified Biochar Alleviating Cadmium Stress In Lettuce(L Actuca Sativa L.)

With the continuous acceleration of industrialization and urbanization process in China,the quality and safety of the facility vegetables.has been seriously affected.In this study,surface-modified biochar with polydentate binding sites were synthesized by surface modification to improve the specific adsorption on cadmium.The possible alleviate mechanism of cystamine-modified biochar for lettuce?Lactuca sativa L.?under cadmium stress were investigated through'Flandria'lettuce pot experiments in order to provide theoretical guidance for the safe planting of vegetables in the soil contaminated by heavy metals.The main results as follows:1.The average content of metals is higher than the background value except lead of the surface soil in 8 vegetable production areas and the average content of cadmium is 2.78 times as much as the background value.The heavy metal content in the soil increased with the increasing of greenhouse age;The heavy metal content of deep soil is lower than that of surface soil.Further,the heavy metal pollution situation in Shandong province was evaluated through the Nemerow's synthetical pollution index?Pn?and Potential ecological risk index?RI?.2 areas were clean soils,2 areas reached alert levels,and 4 areas were lightly polluted soils of the 8 surveyed areas;Cadmium contributes the most to environmental ecological risks of 6 heavy metals,accounting for 53.7%of the total ecological risks.2.Through a variety of characterization methods to verify that cystamine was successfully modified to the surface of biochar.Among different types of modified biochar,the type of C_0.75 with the best adsorption performance to cadmium.The adsorption kinetics study indicated that the modified biochar belong to a monolayer adsorption and there were saturated adsorption sites on the surface of biochar,cystamine-modified biochar could specific adsorption of cadmium ions through ion exchange,electrostatic interaction and coordination of multi-affinity sites on the surface;The cystamine-modification method could improve the selectivity and adsorption capacity of biochar to cadmium,the adsorption capacity for cadmium is 48.87 mg g^-1,and the enrichment factor is 7.0.Besides,the modified biochar with good stability which could be applied in practice.3.The addition of modified biochar could alleviate the toxicity of cadmium to lettuce and promote the growth of lettuce,the fresh weight of the shoot and root of lettuce increased by 40.54%⁴4.95%and 37.54%⁴7.44%than cadmium stress treatment,respectively;The addition of modified biochar could promote the development of lettuce root,increase the root length,rootsurface area,total root volume,root diameter and number of root tips of lettuce;After the addition of modified biochar,photosynthesis pigment and photosynthesis parameters of lettuce were significantly improved,the chlorophyll content,net photosynthetic rate,stomatal conductance,and transpiration rate were increased by 39.31%⁹1.02%,14.09%³7.93%,13.69%³4.77%,and 13.69%³4.77%compared to the cadmium-stressed treatment groups,respectively;The addition of modified biochar could significantly reduce the content of oxidative stress markers in each part of the lettuce,the malondialdehyde and hydrogen peroxide content in the root of the lettuce were significantly reduced by 55.28%and56.52%,respectively;The addition of modified biochar significantly increased the activity of the antioxidant system of shoot and root of lettuce,the activities of SOD,POD and CAT increased by 73.83%and 99.39%,64.37%and 70.42%,86.30%,and 71.52%,respectively;The addition of modified biochar could promote the ascorbate-glutathione cycle.The content of GSH and cysteine increased by 1.30 and 13.85 times than blank control.The glutathione reductase activity in the shoot and root of the lettuce was increased by 67.17%and 70.42%compared to the cadmium-treated group.4.Cysteamine-modified biochar could significantly reduce the exchangeable cadmium content in the soil and convert the exchangeable and reducible cadmium to the residue state to reduce the biological toxicity of cadmium;The raw biochar could reduce soil available cadmium content by increasing soil pH,while the modified biochar could reduce soil available cadmium content by increasing soil cation exchange amount;The modified biochar could reduce the absorption rate of cadmium in the root of lettuce and inhibit the transfer of cadmium from the shoot to the root of lettuce.5.The addition of raw biochar and modified biochar could significantly increase the microbial diversity of cadmium-contaminated soil,while the effect of modified-biochar on cadmium-contaminated soil microbial diversity is more significant.After the addition of modified biochar,the Shannon index,Chao1 index and ACE index increased by 12.81%,14.48%and 17.15%,respectively.The microbial diversity was significantly different under different treatments.At different levels of bacteria classification,the abundance of Nitropirae-Nitrospira-Nitrospirates-Nitrospiraceae-Nitrospiraceae in modified biochar groups was significantly higher than other groups.In addition,it was found that the addition of modified biochar can significantly reduce the relative abundance of harmful Leptosphaeria in cadmium-contaminated soil.