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Nitrogen emissions associated with nutrient management practices: measurements, modeling, and microbial communities Julie Zilles 1 , Sotiria Koloutsou-Vakakis 1 , Angela Kent 2 , Yanjun Ma 1 , Mary Foltz 1 , & Timothy Alston 1 1 Department of Civil and Environmental Engineering; 2 Department of Natural Resources and Environmental Sciences University of Illinois at Urbana-Champaign 1. Introduction § Agriculture is an important source of reactive nitrogen (N r ), which negatively affects human health and the environment. § For management strategies designed to control aquatic N r losses, the impacts on atmospheric Nr emissions are not well-characterized. § Many terrestrial N transformations are microbially meditated. § It is not clear whether the composition of microbial functional groups has a significant impact on N transformations in the environment. In situ N 2 O emissions were low across managements. 5. Acknowledgements § This material is based upon work that was supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award numbers 2015-67019-23584 and 2011-6703-30343. § We thank Adam Davis, Jeffrey Warren, and Chris Greer for supplying management information and coordinating field operations with us. § We thank Lais Marques for assistance with the field work, as part of her National Great Rivers Research and Education Center’s summer internship, and Dora Cohen for training on selected protocols. 3. Approach 4. Preliminary Results Biochemical pathways and functional genes catalyzing microbial N r transformations. Gray boxes of N 2 O and NH 3 indicated Nr gas emissions. DNRA: Dissimilatory nitrate reduction to ammonium. § Measure potential for microbial N transformations. § Characterize microbial groups involved in N transformations. In situ N 2 O flux in left panel from chisel plow plots, comparing with and without fertilizer and cover cropping. Right panel is from no till plots and compared in row and between rows. The no till plots were fertilized and did not have a cover crop. Error bars represent standard deviation of measurements in triplicate plots. Concentration of NO 3 - (left) and NH 4 + (right) in plots with chisel plow. Error bars represent standard deviation of measurements in four replicate plots. 2. Long term objectives NO 3 - NH 4 + nifH NO 2 - NH 2 OH NO 2 - amoA Ammonia monooxygenase Nitrite reductase nrfA NO 2 - N 2 NO 2 - NO N 2 O N 2 NH 3 Denitrification DNRA Nitrification Nitrate reductase Nitrite reductase dNir Nitric oxide reductase p450Nor NO N 2 O Nitrite reductase nirS/nirK Nitric oxide reductase norB Nitrous oxide reductase nosZ atypical nosZ Bacteria Fungi Nitrate reductase N 2 O N 2 O § Model nitrogen cycling using the DNDC model. Simplified schematic of the DNDC model structure Measured values Literature values 0 5 10 15 20 25 30 0 100 200 300 N2O-N flux (gN/ha/d) Day N2O-N flux plant/harvest fertilization irrigation § Eight functional genes (bacterial amoA, archaeal amoA, nrfA, nirK, nirS, norB, nifH, and nosZ) were quantified using high-throughput qPCR on a Fluidigm ® Biomark HD system in bulk and rhizosphere soil samples collected from an agricultural field with different crop rotations, with and without fertilization. § In most cases, no significant differences were observed in gene abundance across crop rotations and between with and without fertilizer plots. § Improve our understanding of the relation- ships between microbial functional group composition and N r transformations. § Model aquatic and atmospheric N r emissions from different management practices. § Integrate the N r model with a farmer decision making model to evaluate the effects of nutrient management policies. Management Measurements NH 4 + amoA Nitrification NO 2 - Target Genes nifH NO 2 - nrfA N 2 DNRA NH 4 + NO 2 - N 2 NO 2 - NO N 2 O Bacteria dNir p450Nor NO N 2 O nirS, nirK norB nosZ, Atyp. nosZ Nitrogen fixation NH 4 + Fungi Abundance (High-throughput qPCR) Composition (High-throughput sequencing) Denitrification: Modeling Fields are in a corn-soy rotation, with measurements conducted in corn plots. Chisel Plow No Till Soil inorganic N was affected by fertilization and cover cropping. Nitrate Ammonium Denitrification potential showed no significant differences across managements. § Total denitrification potential ranged from 107 to 541 ng N 2 O-N g -1 dry soil h -1 . Analysis of microbial groups involved in N transformations is ongoing. Nitrification potential Denitrification potential N 2 O consumption N 2 O production Total denitrification (Use C 2 H 2 to block reduction of N 2 O) No inhibitors Bacterial inhibitor Fungal inhibitor NH 4 + NO 2 - NO 3 - /NO 2 - N 2 O NO 3 - N 2 O+N 2 N 2 O N 2 Nitrate reductase dNar/nap dNar/nap aNar/ dNar+UQFdh § Measure N 2 O and NH 3 emission fluxes in situ. Construct gas sampling chamber Analyze samples on GC y = 0.0122x + 0.1529 R² = 0.94746 0 0.2 0.4 0.6 0.8 1 0 20 40 60 80 concentration (ppm) time (min) Calculate flux by linear regression
