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Tetracycline+treatment+
nmoles+N
2O2N
++g21+ h21+
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nmoles+N
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μmol%N
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Day%a0er%treatment%applica7on%
Control" Tetracycline"Manure" Manure"+"Tetracycline"
Methods
Results
Acknowledgements This research is funded by the AFRI program of National Institute of Food and Agriculture.
Figure 2. Rates of N2 (A) and N2O (B) productions measured in soil slurry incubations with the samples collected from a North Dakota grassland. Different concentrations of tetracycline were used to test antibiotic inhibition on N2 and N2O production. Water was added to the controls. Columns represent mean ± SE.
Figure 5. Percent inhibition of cycloheximide (fungal inhibitor) on N2 production in the soil samples collected at the end of the mesocosm experiment . % inhibition =[( N2 production without cycloheximide – N2 production with cycloheximide)/ N2 production without cycloheximide] x 100.
N2 or N2O
Anammox/Codenitrifica4on
Figure 1. Revised soil nitrogen cycle
A
North Dakota Soil Sampling (16 cores)
Soil Laboratory Experiments (1 week)
An?bio?c Treatments Tetracycline 0.1 – 1000 mg Kg-‐1 soil
-‐ N2 and N2O poten?al rates (soil slurry incuba?ons with 15NO3
-‐)
Soil Mesocosm Experiment (1 month)
No an?bio?c
-‐ N2O fluxes measurements -‐ N2 poten?al rates (soil slurry incuba?ons with 15NO3
-‐)
Tetracycline Manure Manure + tetracycline
B
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Figure 3. N2O fluxes measured in the soil mesocosm experiments with manure and antibiotic treatments. Tetracycline (2 mg Kg-1) was applied for the antibiotic treatment. Markers represent mean ± SE.
Figure 4. Rates of N2 production in soil slurry incubations with the samples collected at the end of the mesocosm experiment. Columns represent mean ± SE.
Summary 1. Antibiotic inhibition of soil N2 production was dose-
dependent, reaching 25 and 80% inhibition in the samples treated with 0.5 mg Kg-1 and 1,000 mg Kg-1 of tetracycline, respectively.
2. N2O production was enhanced 8 times in the soils treated with high concentration of tetracycline, but no effect on N2O production was observed at lower doses of tetracycline.
3. Higher N2O fluxes were generally measured in the soil mesocosms treated with manure plus tetracycline until day 15. However, N2O fluxes in each mesocosm decreased during the incubation period.
4. Inhibition of N2 production was only observed in the soil mesocosms treated with tetracycline but not with manure.
5. Higher inhibition of fungal N2 production was found in the soil mesocosms treated with either tetracycline or manure.
Impact 1. Agricultural producers, industry advisors, and
government program officials will be advised of the potential consequences of antibiotic carryover from livestock manures to field soils.
2. This will encourage development and enable selection of appropriate livestock production and nutrient management planning schemes to minimize agricultural N2O emission.
Relevance Environmental impacts of nitrogen (N) fertilization are well documented, including contributions to the increasing concentration of atmospheric nitrous oxide (N2O), a powerful greenhouse gas. While denitrification and nitrification are the primary pathways leading to N2O emission in the soils, there is uncertainty regarding the organisms responsible for N2O production. Previously, bacteria were considered the only microbial N2O source. Current studies, however, indicate that fungi also produce N2O by denitrification. While bacteria can produce N2O or N2 as an end product of denitrification, fungal denitrification produces only N2O. Higher N2O emissions are likely to occur when most of the denitrification is due to fungal rather than bacterial activity. One potential factor influencing soil N2O emissions is the application of animal manures to agricultural fields. Antibiotics targeting mostly bacteria can pass through to animal manure as a result of antibiotic use in the livestock industry. Antibiotic contaminated manures may have significant impacts on soil communities, which could lead to higher contributions of fungi to N2O emissions. Thus, we investigate the importance and contribution of fungal denitrification to N2O production under variable fertilizer practices. We expect to identify the primary microbial N2O sources in grasslands fertilized with manure. This information will yield data to support potential N2O mitigation strategies.
Objectives 1. Examine the effects of antibiotic on microbial communities
responsible for N2 and N2O production in grassland soils 2. Determine the effects of organic fertilization on bacterial and
fungal N2 and N2O in grassland soil communities. 3. Examine the effects of organic fertilization and antibiotic on
N2O emission in grassland fields. 4. Identify the major microbial pathway producing N2O and N2
under different scenario of fertilization and antibiotic at grasslands.
Unveiling fungal contributions to agricultural soil nitrogen cycling following application of organic and inorganic fertilizers
Miguel Semedo1*, Bongkeun Song1, Tavis Sparrer1, Carl Crozier2, Craig Tobias3, and Rebecca Phillips4 1Department of Biological Sciences, Virginia Institute of Marine Science, College of William & Mary
2Department of Soil Science, North Carolina State University 3Department of Marine Sciences, University of Connecticut, 4Ecological Insights Corporation
Miguel Semedo [email protected]
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July 29, 2015
