Effects Of Aged Biochar On Growth Of Pakchoi And Properties Of Black Soil Under DEHP Stress

PAEs is the most commonly used plasticizer in the world,it is widely used in plastic films.DEHP belongs to one of PAEs and its structure is complex,more toxic and difficult to degrade.Because of extensive use,it has become one of the most widely used pollutants and it exists in various environmental media.DEHP can accumulate through plant absorption into the food chain,which will cause serious health risks.Biochar has a large specific surface area and abundant functional groups,which can effectively adsorb pollutants in the soil so as to achieve the purpose of remediation of contaminated soil.But biochar applied to the environment will gradually age,how is the remediation effect of aged biochar on pollutants? How to affect the effectiveness of pollutants? The relevant reports are less.In this experiment,corn straw was used as raw material to prepare fresh biochar and carry out spontaneous aging and freeze-thaw cycles aging.Aged biochar was characterized by scanning electron microscopy(SEM),fourier infrared spectrometer(FTIR),element analyzer and so on.And the effects of aged biochar on soil physical and chemical properties,soil enzyme activity,DEHP bioavailability,physiological and biochemical characteristics and growth of pakchoi were investigated and analyzed by pot experiment with pakchoi as indicative plant.The main conclusions are as follows:(1)Aging changes the properties of biochar.By scanning electron microscopy(SEM),more pores appeared on the surface of spontaneous aging biochar and severe fragmentation appeared on the surface of freeze-thaw cycles aging biochar,which significantly increased the surface area.After biochar aging,the C content decreased,the O content increased,the O/C ratio increased,and the surface oxygen-containing functional groups changed significantly by elemental analyzer and fourier infrared spectroscopy(FTIR).The change of freeze-thaw cycles aging is obviously higher than that of spontaneous aging.(2)Aged biochar enhanced the adsorption capacity to DEHP and the adsorption rate of freeze-thaw cycles aging biochar to DEHP was the largest.Applying to 3% freeze-thaw cycles aging biochar to the soil,DEHP was almost no residue around 14 days(0.00011mg/kg).(3)Biochar significantly reduced DEHP bioavailability.Under DEHP single stress,the accumulation of DEHP in different organs of pakchoi was as follows: root > stem > leaf.The application of fresh and aged biochar reduced DEHP bioavailability in the soil and effectively alleviated the stress pressure of DEHP on pakchoi.After the application of fresh biochar and aged biochar,the contents of chlorophyll,Vc,soluble protein increased,but the growth and physiological and biochemical indexes of pakchoi in the treatment group of aged biochar were relatively good.(4)Aged biochar can effectively improve the physical and chemical properties of soil under DEHP pollution stress.With the increase of additive amount of spontaneous aging and freeze-thaw cycles aging biochar in the soil,the contents of organic matter,available phosphorus and alkalihydrolyzed nitrogen of soil were increasing.The available phosphorus of soil reached a maximum of 123.44mg/kg when applied to 3% spontaneous aging biochar,organic matter and alkalihydrolyzed nitrogen were the highest when applied to 2% freeze-thaw cycles aging biochar,which were 3.90%,187.08 mg/kg,respectively.(5)Invertase activity and catalase activity were activated in the soil under DEHP contamination stress and the enzyme activity was increased.Aged biochar can reduce the fluctuation of enzyme activity of soil.The stability ability of biochar to enzyme activity of soil is as follows: freeze-thaw cycles aging biochar > spontaneous aging biochar > fresh biochar.The application of straw-based biochar to agricultural soil can not only effectively reduce the bioavailability of PAEs,but also greatly improve the soil quality.This effect is long-lasting and will not reduce with the aging of biochar.On the contrary,the contribution of aged biochar to the agricultural soil environment may be greater and more lasting,which will provide scientific basis and practical basis for the treatment of organic pollution in the agricultural soil.