Abstract: The accumulation of phenolic acids in soil is one of the main hindrances to continuous peanut cropping. Although laccases secreted by fungi can efficiently transform phenolic acids, the application of laccases in the bioremediation of continuously cropped soil has not been investigated. Therefore, a pot experiment was carried out to study the effect of adding different concentrations of laccase rLACB3 on a continuously cropped peanut soil. After 30 days, the 500 U·kg^-1 laccase treatment was superior to those with the 20 and 100 U·kg^-1 treatments in soil bioremediation. The populations of bacteria, fungi and Azotobacter in the rhizospheric soil of the 500 U·kg^-1 treatment increased by 33.0%, 37.7% and 30.2% respectively, compared with the control. The rhizospheric soil microbial community was analyzed by denaturing gradient gel electrophoresis (DGGE), showing that the Shannon’s indexes of culturable bacteria, diazotrophic bacteria and azotobacter of the 500 U·kg^-1 treatment increased by 9.0%, 17.3% and 14.8%, respectively compared with the control. The 500 U·kg^-1 laccase treatment also had 41.2%, 43.8% and 35.9% lower levels of the phenolic acids, coumaric acid, 4hydroxybenzoic acid and vanillic acid, respectively compared with the control. The biomass and the number of nodules of the 500 U·kg^-1 treatment increased by 17.9% and 17.4%, respectively compared with the control. These results indicated that rLACB3 was a potential candidate for the remediation of the continuously cropped peanut soil.

Key words: infiltration, dye tracing, piston flow, Loess Tableland, apple orchard, root