PARENT SESSION
Oral Session # 6: Fire Ecology I: Structure and Demographics
Presiding: R Parmenter
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 105.

Wildfire effects on soil microbial activity and community-level physiological profiles in a ponderosa pine ecosystem.

Newman, Gregory^*,1, Hart, Stephen¹, Guido, Daniel¹, Overby, Steven², ¹ School of Forestry and Merriam-Powell Center for Environmental Research, Flagstaff, AZ² Rocky Mountain Research Station, Flagstaff, AZ

ABSTRACT- Forests of the western United States have received increasing incidence and extent of wildfire during the past decade as a result of increased tree densities and buildup of forest floor fuels due to fire suppression policies. Evidence of the direct effects of wildfire on soil microbial activity and composition is scarce and these effects may have a greater influence than prescribed burns due to the greater intensity of disturbance. Ponderosa pine plots in New Mexico associated with the national Fire - Fire Surrogate network were burned by wildfire in September 2002 following pretreatment measurements and prior to the initiation of treatments. We resampled these plots one month following the wildfire and one year following pretreatment measurements, removing any seasonal influence on soil activity. Wildfire homogenized bacterial community-level physiological profiles (CLPPs) and had the opposite effect on fungal populations. The bacterial CLPP plate activity doubled following wildfire while there was no effect on fungal plate activity. Conversely, basal and substrate-induced respiration were substantially lower than in a nearby unburned stand which was similar to the wildfire stand based on pretreatment measurements. Although -glucosidase activity declined following wildfire, galactase, xylosidase, cellobiohydrolase, alkaline phosphatase, and sulfatase activites all increased significantly, consistent with the amplified bacterial metabolism observed in CLPPs. Wildfire and subsequent microbial activity resulted in 23x increase in net N mineralization, an 80% decline in net nitrification, and nearly 2x and 19x increases in soil available NO3- and NH4+ pools, respectively. Altered soil microclimate and organic matter transformations, as well as the removal of plant competition, following wildfire create a more favorable environment for microbial populations, which may facilitate the regeneration of forest stands through increased mineralization of plant available nutrients.

Key words: fire, Biolog, microbial ecology, nitrogen