Effect Of Cadmium Contaminated Soil On Physiological And Biochemical Characteristics Of Brassica Rapa Var. Chinensis And Its Blocking And Control Study With Biochar

In high-intensity production systems of facility agriculture,excessive fertilization leads to heavy metals accumulation and acidification of soil,which in turn increases accumulation of heavy metals in vegetables.As the heavy metal element with the highest over-standard rate in arable soil,Cd is highly toxic.Vegetables have a strong ability to absorb and accumulate soil Cd.Cd enters human body through food chain and seriously threatens human health.Therefore,it is urgent to reduce the content of Cd in vegetables and ensure the safe production of vegetables.This paper is intended for the study of greenhouse vegetable soil in Yan’an area.Through fixed-point sampling analysis and the research methods of pot experiment,the Yan’an soil heavy metal pollution status quo and characteristics of Brassica Chinensis to absorb Cd accumulation characteristics,and the sunlight greenhouse soil Cd contamination resistance control research have been carried out.The main results are as follows:（1）In four facilities agricultural bases in Yan’an area,Soil Cd content was0.42,0.93,0.62 and 0.77 mg·kg^-1,Cr content was 61.42,53.46,42.32 and 5 4.76 mg·kg^-1,respectively;Ni contents were 33.21,26.87,25.74 and 26.45 mg·kg^-1,and Pb contents were23.68,44.78,33.06,47.34 mg·kg^-1,respectively.The single factor pollution index of Cr,Pb and Ni contents was less than 1,which belonged to the level of no pollution.Mild pollution of heavy metal Cd;The comprehensive factor evaluation showed that the average value of greenhouse soil pollution index in Yan’an city was 0.99,which was at the warning level.Compared with the background value of Shaanxi Province,the single factor ecological risk coefficient of Cd in Yan’an greenhouse soil reached a high level.The evaluation result of potential ecological index showed that the ecological risk index of greenhouse soil in Yan’an city reached medium hazard level.（2）Under Cd stress,with the increase of soil Cd concentration,the absorption of Cd and the transport coefficient of Cd showed an upward trend,while the enrichment coefficient showed a downward trend;With the increase of growth period,the content of Cd increased gradually,but the cumulative efficiency of Cd decreased continuously.The concentration of Cd was higher at peak growth period and decreased at mature period.The content of Cd in the root of Brassica chinensis was higher than that in the aboveground part.Under the treatment of Cd,the concentration of Cd in the old leaves of Brassica chinensis was higher than that in the new leaves.（3）Cd stress had an inhibitory effect on the growth of Brassica chinensis.With the increase of soil Cd treatment concentration,the growth indexes of Brassica chinensis declined markedly,and the plant height,root length,fresh weight and dry weight of Brassica chinensis decreased significantly.Furthermore,Cd stress significantly weakened photosynthesis.The contents of malondialdehyde（MDA）,hydrogen peroxide（H₂O₂）and superoxide anion free radical（superoxide anion）,antioxidant enzyme activity and non-enzymatic antioxidant substance content of Brassica chinensis increased firstly and then decreased.（4）Pot experiment showed that with the increase of biochar addition level,the Cd content in small cabbage tissue had a decreasing trend,and decreased the Cd enrichment coefficient and transport coefficient of Brassica chinensis.For instance,3%biochar application remarkably reduced the Cd content in small cabbage tissue.What’s more,Biochar can promote the growth of Brassica chinensis.Applying biochar can significantly improve the biomass of Brassica chinensis under Cd stress,enhance the photosynthetic characteristics of Brassica chinensis,and greatly improve the net photosynthetic rate,intercellular CO₂ concentration,transpiration rate and stomatal conductance of Brassica chinensis.Meanwhile,application of biochar increased the activity of antioxidant enzyme in small cabbage under cadmium stress.Therefore,the soil of facility vegetable production base with more than 10 years of age is prone to Cd pollution.Cd inhibited the growth of Brassica chinensis,leading to a significant decrease in plant height,root length,fresh weight and dry weight,weakened photosynthesis,and increased antioxidant enzymes and non-enzymatic antioxidant substances content of Brassica chinensis.The addition of biochar can reduce the toxicity of Cd to Brassica chinensis,effectively alleviate the stress of Cd on the growth of Brassica chinensis,reduce the accumulation of Cd in the plant body,and improve the safety of Brassica chinensis.