Type of Document Dissertation Author Ely, Damon Thomas URN etd-05072010-214046 Title Stress-induced alterations in ecosystem function: the role of acidification in lotic metabolism and biogeochemistry Degree PhD Department Biology Advisory Committee
Advisor Name Title Valett, H. Maurice Committee Chair Jones, Robert H. Committee Co-Chair Burger, James A. Committee Member Daniels, Walter Lee Committee Member Webster, Jackson R. Committee Member Keywords
- aquatic fungi
- nitrogen uptake
- chlorophyll a
- stream metabolism
Date of Defense 2010-03-31 Availability unrestricted Abstract
I investigated how anthropogenic acidification influences stream metabolism and nitrogen (N) cycling by considering the stress response of microbial compartments responsible for these ecosystem processes. Microcosm incubations of leaf biofilms from streams of differing pH revealed greater rates of fungal biomass-specific respiration (i.e. the stress metric qCO2) and biomass-specific N uptake (i.e. qN) with increasing acidity. The positive relationship between qCO2 and qN indicated alternate fates for N other than structural biomass, possibly related to increased exoenzyme production as part of the stress response.
Whole-stream 15N experiments and measurements of respiration and fungal standing crop across the pH gradient resulted in similar patterns in qCO2 and qN found in microcosm experiments, supporting qCO2 as an ecosystem-level stress indicator and providing insight towards controls over N cycling across the pH gradient. Fungal biomass and ecosystem respiration declined with increasing acidity while N uptake metrics were not related to pH, which suggested qN in acid streams was sufficiently high to counteract declines in fungal abundance.
During spring, chlorophyll a standing crops were higher in more acidic streams despite lower nutrient concentrations. However, N uptake rates and gross primary production differed little between acid and circumneutral streams. Reduced heterotrophy in acid streams was apparent in lower whole-stream respiration rates, less ability to process organic carbon, and little response of N uptake to added carbon resources. Overall, acid-induced stress in streams was found to impair decomposer activity and caused a decoupling of carbon and nitrogen cycles in these systems.
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