Environmental Behavior And Microbial Response Of DBP In Rhizosphere Interface Of Brassica Chinensis L.

Dibutyl phthalate(DBP)is a class of compounds widely used as industrial plasticizers with endocrine disrupting effects.It does not form tight chemical bonds with plastic products,and easy migration into the soil poses a significant risk to ecological safety.DBP is not easily degraded,and DBP remaining in the soil can be absorbed by the crop and transmitted to the human body through the food chain,which seriously endangers human health.Therefore,exploring the key scientific issues such as the migration and fate of DBP in the rhizosphere multi-media interface is of great significance for the study of plant-contaminant interaction.In this experiment,DBP was used as the target pollutant,and pok choy was used as the tested plant.The adsorption behavior of DBP in the rhizosphere interface of pok choy was investigated.The spatial and temporal variability of DBP at the rhizosphere interface was studied by constructing a multi-layer root box model.The interaction mechanism between root exudates and DBP was elucidated,and the response of rhizosphere microorganisms to DBP pollution was revealed at the molecular level.The main results of this study are as follows:Tolerance of pok choy to DBP at 20 mg·kg-1 was investigated by a pot experiment.pok choy had a strong tolerance to 20 mg·kg-1 DBP.The plant height and root length of pok choy were only slightly inhibited in the first 28 days of the experiment,and then the inhibition was weakened.The microscopic morphology of the roots showed that DBP stress caused the exfoliation of some epidermal cells in the roots and reduced the number of root hairs in the fine roots.The microscopic morphology of the soil showed that DBP and root exudates increased the number of soil aggregates.Through the root bag experiment,the adsorption behavior of DBP in the rhizosphere soil of pok choy was discussed.The adsorption of 50 mg·L-1 DBP in soil reached equilibrium within 12 h,and the maximum adsorption capacity of rhizosphere soil and non-rhizosphere soil was obtained.The adsorption kinetics process was in accordance with the quasi-secondary model,and the adsorption thermodynamic process was in accordance with the Freundlich model,indicating that the adsorption process was multi-layer heterogeneous chemical adsorption.The cultivation of pok choy could change the adsorption capacity of Mollisol to DBP.The adsorption of DBP on rhizosphere Mollisol was much larger than that of non-rhizosphere Mollisol.The KF of rhizosphere soil containing root exudates is 6.6264,which was twice that of non-rhizosphere soil.Through the fluorescence binding test,it was revealed that the root ex udates of pok choy promoted the adsorption of DBP in soil.The main components of root exudates were analyzed by GC-MS to investigate the effects of DBP on soil nutrients and soil structure.The results showed that the root exudates contained hydrocarbons,sulfur compounds and acids.Root exudates could promote the adsorption of DBP on soil by increasing the number of soil aggregates and increasing the content of available phosphorus,organic matter and dissolved organic matter(DOM).The interaction between root exudates and DBP,DOM and DBP was analyzed by three-dimensional excitation emission matrix(3D-EEM),simultaneous fluorescence and Fourier transform infrared spectroscopy(FTIR).Fluorescence spectra showed that the main components of root exudates are protein-like substances,and the main components of DOM are protein-like and humic-like substances.The root exudates,DOM and DBP complexed,and the fluorescence quenching mechanism was static quenching.The-COO in the root exudates and the-CH2 functional group in DOM play a major role in the binding to DBP.By constructing a multi-layer root box model,the temporal and spatial dynamics of DBP in the rhizosphere micro-domain of pok choy were revealed.The reduction rate of DBP in the rhizosphere micro-domain showed a trend of root chamber>near rhizosphere>non-rhizosphere.The DBP reduction rate was the highest at 3 mm from the root system,and the reduction rate on the 45 th day was 91%.The biochemical mechanism of DOM binding to DBP in the rhizosphere microdomain was revealed by 3D-EEM,synchronous fluorescence spectroscopy,two-dimensional correlation spectroscopy(2D-COS)and 2D-FTIR-COS.The results showed that the alkyl ester in DBP first responds with the highest binding strength,followed by the aromatic,hydroxyl and phenolic groups in the DOM-like humic substances,and finally the amide functional groups in the DOM-like proteinaceous material.The response of rhizosphere microorganisms to DBP was investigated by high-throughput sequencing(sampling time was 7,14,21,28,45 days).DBP stress increased the number of Sphingomonas and Pseudarthrobacter in soil,but the ? diversity index of rhizosphere microorganisms was chao1,shannon,PD whole tree and observed species.The decrease indicated that DBP disturbed the metabolic activities and functional diversity of Mollisol microorganisms.The presence of root exudates increased soil microbial abundance and changed soil microbial community structure,alleviated DBP stress on rhizosphere microorganisms,increased soil microbial alpha diversity and increased actinobacteria in rhizosphere soil and the number of bacteria of Acidobacteria.The ?-diversity index of the non-rhizosphere soil farther from the root system was higher than DBP after the 14 th day,but still lower than the rhizosphere soil,indicating that the rhizosphere secretion could gradually spread from the rhizosphere soil over time and promote the growth of microorganisms in the nearby soil.The presence of root exudates could also aggregate unique bacterial degradation DBP such as Alsobacter,Lacibacter,Myceligenerans,Schrenkiella parvula and Undibacterium.