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Effects of wildfire and harvest disturbances on forest soil bacterial communities Smith, Nancy Rosalee

Abstract

Little attention has been paid to the effects of wildfires on soil bacterial communities. The opposite is true for the effects of harvest treatments on soil bacterial communities. This scarcity of microbiological research post wildfire may be because of the unpredictability of such events or because of a focus on other fire-induced changes such as soil chemistry. In this study, Boreal forest soil bacterial communities were assessed post disturbance in four treatments: control, harvest, burn and burn-salvage. The burn treatments were areas affected by the wildfire near Chisholm, Alberta in May, 2001. Changes in these microbial communities occurred as a consequence of the wildfire or harvest treatment disturbance, with greater effects in the burn treatments. Significant decreases in microbial biomass carbon (C[sub mic]) were seen as a result of the burn or harvest treatments. Microbial biomass nitrogen (N[sub mic]) decreased 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. The C[sub mic]:N[sub mic] decreased in the harvest, burn and burn-salvage treatments, indicating a probable decrease in fungal biomass. Nonparametric ordination of molecular fingerprint data (ribosomal intergenic spacer analysis and rRNA gene denaturing-gradient gel electrophoresis) of 119 samples indicated clear distinctions between community composition in the burned and unburned treatments. Differences between control versus harvest and between burn versus burn-salvage treatments were less obvious, but multi-response permutation procedures demonstrated statistically significant separations between the two. Sequencing of bands from fingerprints uncovered interesting patterns of bacterial divisions specific to treatment type, y- and α-Proteobacteria were highly characteristic of the unburned treatments, while β-Proteobacteria and members of Bacillus were highly characteristic of the burned treatments. Biomass determinations confirmed general trends observed in past literature, while relatively new molecular methods unveiled new and interesting effects to bacterial communities in Boreal forest soils impacted by human and natural disturbances.

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