Response of microbial activity in the rhizosphere of maize seedlings (Zea mays L.) to pyrene contamination

A soil-cultivating test,with rhizobag technique,was used to quantify the responses of microbial biomass carbon and quotient,metabolic quotient,and soil enzyme activity in rhizosphere and non-rhizosphere soil under three concentration levels of pyrene(50,200,and 800 mg·kg-1,denoted by T1,T2,and T3,respectively)after 45 days phytoremediation by maize seedlings(Zea mays L.).The growth of maize seedlings was slightly stimulated at lower pyrene concentration,while inhibited at higher pyrene concentration,and the effect increased with initial pyrene concentration.In addition,the effect of pyrene on maize root was more obvious than that on shoot.Maize seedlings significantly promoted pyrene dissipation in the soil.During the experimental period,56.67%-76.18% and 32.64%-70.44% of spiked pyrene disappeared from the rhizosphere and non-rhizosphere soils respectively.The average removal rate of pyrene in rhizosphere soils was 16.06% higher than that in non-rhizoshpere soils.In the same treatment,the concentration of pyrene in rhizosphere was significantly lower than that in non-rhizosphere,but the removal rate was on the contrary,and their differences were positively affected by increasing initial pyrene concentration in soil.The microbial biomass carbon and quotient,polyphenol oxidase,dehydrogenase,and phosphatase activities were higher in rhizosphere than those in non-rhizosphere.The metabolic quotients were lower in rhizosphere than that in non-rhizosphere and the corresponding differences increased with increasing pyrene concentration in soil.Under different concentrations of pyrene,the microbial biomass carbons and quotients and dehydrogenase activities in rhizosphere and non-rhizosphere were T1T2T3,while the metabolic quotients were T3T2T1.The polyphenol oxidase activities were T2T1T3 and T1T2T3 in rhizosphere and non-rhizosphere,respectively.The phosphatase activities were T3T1T2 and T1T2T3 in rhizosphere and non-rhizosphere,respectively.Significantly negative correlations were found between pyrene concentrations and the soil microbial biomass carbon and quotient,polyphenol oxidase,dehydrogenase,and phosphatase activity.There were significantly positive correlations between pyrene concentrations and the metabolic quotient.