Unveiling Fungal Contributions to Agricultural Soil Nitrogen Cycling Following Application of Organic And Inorganic Fertilizers
0" 1" 5" 9" 15" 22" 30"
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.
Figure 1. Revised soil nitrogen cycle
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
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
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
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
5. Higher inhibition of fungal N2 production was found in
the soil mesocosms treated with either tetracycline or
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.
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.
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
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
July 29, 2015