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Title:Intact soil core experiments reveal that temperature and depth influence microbial community function and impact the fate of nitrogenous fertilizer amendments
Author(s):Napieralski, Stephanie A
Advisor(s):Sanford, Robert A.
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Nitrogen cycling
dissimilatory nitrate reduction to ammonium (DNRA)
Nitrous oxide (N2O)
Cytochrome c nitrite reductase (nrfA)
nitrous oxide reductase gene (nosZ)
Ammonia Monooxygenase (amoA)
Abstract:The application of nitrogenous fertilizer to agricultural soil has potentially large impacts on environmental quality, including large scale emission of the potent greenhouse gas nitrous oxide and runoff of nitrates. Through their metabolic activities, including nitrification, denitrification and dissimilatory nitrate reduction to ammonium (DNRA), soil microbial communities play an active role in determining the fate of nitrogenous species, thus thorough knowledge of microbial community structure and function is important to understanding ecosystem scale N-fluxes. While much work has been done to understand the role of microbes in soil N-cycling, rarely are such communities studied in ecological context of depth and temperature combined and we hypothesize that diurnal temperature variation, large in surface soils and more narrow at depth, will result in a differential response to N-input. To investigate both the fate of exogenous N-inputs and microbial community and functional response, intact soil cores (0-10 cm and 10-30 cm depth) taken from an agricultural field site in Havana, IL were imbibed with 15N labelled NH4Cl and KNO3 to simulate fertilizer input. The unsaturated cores were then incubated under a summer diurnal temperature regime reflective of natural temperature profiles observed at specified depths (20-35°C shallow, 22-24°C deep). At nine time points over 21 days, replicate cores were deconstructively sampled for pH, NO3-, NH4+, and 15N isotopic analyses. Stable isotope pool dilution was used to calculate gross transformation rates and microbial community structure and function were assessed by T-RFLP and qPCR, respectively. Comparison of 16S rRNA based T-RFLP total community profiles revealed a distinct temporal succession across soil depths, with shifts in community structure corresponding to changes in soil NO3- and NH4+ concentration. While no significant difference in 16 rRNA based communities was evident between depths, a large temporal shift in nitrous oxide reductase gene (nosZ) based denitrifier community structure of was evident after 7 days, resulting in denitrifier communities that were significantly distinct. Additionally, qPCR analysis of relevant functional gene transcripts reveals differential trends in gene expression between depths. These results suggest that while diurnal temperature variation and depth may not significantly alter overall community structure, the functional response of community members to N-input is a function of temperature and these functional differences between soil communities has a direct impact on not only rates of transformation, but also for the timing and magnitude of N2O fluxes.
Issue Date:2015-07-21
Rights Information:Copyright 2015 Stephanie Napieralski
Date Available in IDEALS:2015-09-29
Date Deposited:August 201

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