Rapid Response by the Ectomycorrhizal (ECM) Community of a Lodgepole Pine Forest to Diesel Application as Indicated by Laccase Gene Fragment Diversity

Abstract

A combination of field baiting and molecular methods was used to identify basidiomycete fungi that are able to withstand conditions within diesel contamination in a pine forest soil. Diesel was applied to 3, 1 meter x 1 meter blocks, which penetrated to a depth of 4 cm. After two weeks fungi that exhibited positive growth responses were identified by amplifying laccase (phenol oxidase) gene fragments using primers specific to basidiomycete laccase genes. The internal transcribed spacer (ITS) region of the nuclear ribosomal DNA (nrDNA) gene repeat was amplified as well to provide a broad community screen, to indicate the pool of basidiomycete fungi that could respond to diesel application. Results indicated that ectomycorrhizal (ECM) fungi in the genera Russula, Piloderma and the ECM species Tricholoma saponaceum (rather than wood-rotting basidiomycetes) responded rapidly to diesel application. These results support recent hypotheses regarding the ecological role of ECM fungi in carbon cycling via exploitation of short chain phenolic carbon compounds. Further the ECM fungi that responded correspond roughly to classification of ECM exploration type, a criterion that describes ECM fungi on the basis of their hyphal growth patterns and potential for enzymatic activity. Finally, because it is apparent that these ECM fungi can survive and express laccase genes under conditions created by diesel contamination, these data provide new models for phytoremediation and site restoration strategies that utilize ECM fungi and pines.