PARENT SESSION
Contributed Oral Session 153: Forest Soils and Nutrient Cycling
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 514 A, Level 5, Palais des congrès de Montréal
Fire, fertilization and rhizosphere effects on extracellular enzyme activity in boreal forest soil.
Gartner, Tracy*,1, 2, Treseder, Kathleen1, Malcolm, Glenna2, Sinsabaugh, Robert3, 1 University of California-Irvine, Irvine, CA2 Pennsylvania State University, University Park, PA3 University of New Mexico, Albuquerque, NM
ABSTRACT- Increasing fire frequency and anthropogenic N deposition are expected to affect carbon stocks in boreal forest soils. Decomposition is facilitated by enzymes that target structural components and recover nutrients from organic material. The production of these enzymes is usually attributed to saprotrophic fungi. However, plant roots and mycorrhizal fungi also can produce degrading enzymes. We examined extracellular enzyme production associated with mycorrhizal plant species along a fire successional gradient. We tested the hypotheses that (1) enzyme activity will vary with mycorrhizal type, and (2) activity of enzymes that target specific nutrients will decrease when limitation by that nutrient is alleviated by succession or fertilization. Three Alaskan sites were chosen to represent different successional stages following severe forest fire. Each site had been exposed for two years to nitrogen and phosphorus fertilization in a factorial design, with four plots per treatment. We collected soil from the rhizospheres of ericoid, ecto-, and arbuscular- mycorrhizal plants from each plot. Using flourimetric and spectrophotometric methods, soils were analyzed for enzymes that target compounds containing nitrogen (beta-N-acetylglucosunidase (NAG), leucine-amino-peptidase (LAP)), phosphorus (phosphatase (phos)), and carbon (beta-1,4-glucosidase (BG), peroxidase). Production of enzymes differed with succession for most enzymes (P<0.001); activity doubled between the youngest and oldest site for BG, NAG, and phos, while LAP activity peaked at the intermediate site. As expected, N fertilization decreased the activity of nitrogen-targeting enzymes (NAG P<0.001, LAP P=0.057), but increased the activity of enzymes targeting carbon (BG P=0.001) and phosphorus (phos P=0.010). Phosphorus fertilization marginally decreased the activity of phosphatase (P=0.054), but had no significant effect on other enzymes. Enzyme activity also varied among the soils beneath different mycorrhizal plants (P<0.014). Our findings indicate that fire, fertilization, and mycorrhizal plants all have the potential to influence the degradation of organic matter in boreal forest soil.
Key words: extracellular enzyme activity, decomposition, nitrogen deposition, carbon storage