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Applied and Environmental Microbiology, January 2008, p. 216-224, Vol. 74, No. 1
0099-2240/08/$08.00+0     doi:10.1128/AEM.01355-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Effects of Wildfire and Harvest Disturbances on Forest Soil Bacterial Communities{triangledown} ,{dagger}

Nancy R. Smith,1 Barbara E. Kishchuk,2 and William W. Mohn1*

Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada,1 Northern Forestry Centre, Canadian Forest Service, 5320-122nd Street, Edmonton, Alberta T6H 3S5, Canada2

Received 18 June 2007/ Accepted 2 November 2007

Wildfires and harvesting are important disturbances to forest ecosystems, but their effects on soil microbial communities are not well characterized and have not previously been compared directly. This study was conducted at sites with similar soil, climatic, and other properties in a spruce-dominated boreal forest near Chisholm, Alberta, Canada. Soil microbial communities were assessed following four treatments: control, harvest, burn, and burn plus timber salvage (burn-salvage). Burn treatments were at sites affected by a large wildfire in May 2001, and the communities were sampled 1 year after the fire. Microbial biomass carbon decreased 18%, 74%, and 53% in the harvest, burn, and burn-salvage treatments, respectively. Microbial biomass nitrogen decreased 25% in the harvest treatment, but increased in the burn treatments, probably because of microbial assimilation of the increased amounts of available NH4+ and NO3– due to burning. Bacterial community composition was analyzed by nonparametric ordination of molecular fingerprint data of 119 samples from both ribosomal intergenic spacer analysis (RISA) and rRNA gene denaturing gradient gel electrophoresis. On the basis of multiresponse permutation procedures, community composition was significantly different among all treatments, with the greatest differences between the two burned treatments versus the two unburned treatments. The sequencing of DNA bands from RISA fingerprints revealed distinct distributions of bacterial divisions among the treatments. Gamma- and Alphaproteobacteria were highly characteristic of the unburned treatments, while Betaproteobacteria and members of Bacillus were highly characteristic of the burned treatments. Wildfire had distinct and more pronounced effects on the soil microbial community than did harvesting.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada. Phone: (604) 822-4285. Fax: (604) 822-6041. E-mail: wmohn{at}interchange.ubc.ca

{triangledown} Published ahead of print on 16 November 2007.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, January 2008, p. 216-224, Vol. 74, No. 1
0099-2240/08/$08.00+0     doi:10.1128/AEM.01355-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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