Impact We will gain a better understanding of the critical soil conditions and microbial factors that uncouple or couple nitrification from the other NH4+ consuming sinks. This will enable us to refine nitrogen models and field based management strategies that prevent excessive and/or untimely losses of soil and fertilizer N. This will reduce economic losses to farmers and reduce the potential for off-site damage to environmental quality.

1. Summary of NIFA funded
research on soil nitrification at
Oregon State University

2. Topics of Research
• 1) Temperature response of AOA and AOB
contributions to soil nitrification
• 2) Impact of uncoupling nitrification on N2O
production
• 3) Response of soil AOB and AOA nitrification to applications
of different N forms
• 4) Quorum sensing among nitrifiers

3. Publications relevant to this research
Use of aliphatic n-alkynes to discriminate soil nitrification activities of
ammonia-oxidizing thaumarchaea and bacteria. Taylor, A.E. N. Vajrala, A.T.
Giguere, A.T., Gitelman, A.I., Myrold, D.D., Sayavedra-Soto, L., and P. J. Bottomley.
2013. Applied and Environmental Microbiology, 79: 6944-6951.
Uncoupling of ammonia oxidation from nitrite oxidation: impact upon
nitrous oxide production in non-cropped Oregon soils. Giguere, A.T., Taylor,
A.E., Suwa, Y., Myrold D.D., and P. J. Bottomley. 2016. Soil Biol Biochem. In Press.
Modeling of soil nitrification response to temperature reveals
thermodynamic differences between ammonia oxidizing activity of
bacteria and archaea. Taylor, A.E., Giguere, A.T., Zoebelein, C., Myrold, D.D., and
P.J. Bottomley. ISMEJ. 2016. In Press.

4. Cropped and noncropped soils at four locations in
Oregon
Pendleton
Madras
Klamath
Falls
Corvallis

5. Soil Nitrification Responses to
Temperature (4-42C) in cropped and non-
cropped soils

6. Model parameters differed between AOA and AOB
driven nitrification

7. Conclusions from temperature study
• Topt of AOA and AOB were significantly different
• ToptAOA 36.4±5.1oC and ToptAOB 22.6±3.8oC.
• Heat capacity (ΔCP
‡) was correlated with Topt.
• ΔCP
‡ of AOB was more negative (-4 to -12 kJ/mol/K) than of AOA activity (-2 to -7
kJ/mol/K).
• Different thermodynamic parameters suggest that the process of NH3
oxidation is different in AOA and AOB.
• Model predicted and experiment verified a lower Tmin for AOB than for
AOA, and a higher Tmax for AOA than for AOB.
Evidence was obtained for AOA subgroups with different Tmin, no
evidence found for multiple Tmin within the AOB.

8. Uncoupling of Soil Nitrification
• Nitrite accumulation in soils
• Impact on nitrifier-driven N2O production

9. Persistent and substantial NO2
-
accumulation
• Both AOA and AOB contributed to
NO2
- accumulation.
• NO2
- accumulated in all soils for ≥48h
when both AOA and AOB were active,
and when AOA alone were active.
• NO2
- accumulation accounted for 10-
100% of total NO2
-+NO3
-.
• NO2
- accumulation was inhibited by
acetylene.
NO2
-
(molg
-1
soil)
0.00
0.05
0.10
0.15
0.20
NO3
-
(molg
-1
soil)
0.0
0.5
1.0
1.5
2.0
NO2
-
NO3
-
6h 24h 6h 24h
AOA+AOB
-Octyne
48h48h
A
B
C
a
b
c
A
B
C
a
c
b
AOA
+Octyne
Pendleton

10. Roles of NH4+ and NO2- in nitrifier
dependent N2O formation
Addition of NO2
- stimulated N2O
production in all soils.
The combination of NO2
- and NH4
+
further stimulated N2O production.
All N2O production was acetylene
inhibited and did not occur in sterile
soils.
N2
O(nmolg
-1
soil)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-NH4
+
+NH4
+
- Octyne + Octyne
Pendleton
a
b
a
b
A a
a
b
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
- Oc
aA
B
A
B
a A
B
B
A
A
N
o
adde
N
O
N
o
added
N
O
2-
+N
O
2-
N
o
added
N
O
2-
+N
O
2-

11. Percentage of NH4
+ oxidized to N2O is increased by presence
of NO2-
Total AOA AOB
No
added
NO2
-
No
added
NO2
-
No
added
NO2
-
Pendleton 0.04 0.28 0.03 0.40 0.06 0.16
Klamath 0.06 0.39 0.08 0.22 0.05 0.30
Madras 0.06 0.16 0.06 0.09 0.06 0.28
Mean 0.053 0.28 0.06 0.23 0.06 0.25

12. Removal of NO2- stops N2O production

13. Relationship between the magnitude of
NO2
- accumulation and N2O production
• Regression analysis revealed a
positive, non-linear relationship
between NO2
- accumulation and
N2O production by both AOA
plus AOB and by AOA alone.
• Values of Vmax ranged 12-fold
from 0.05-0.62 nmol N2O g-1 soil
d-1.
• Predicted Km values for NO2
-
ranged 15-fold from 0.02-0.30
µmol NO2
- g-1 soil.

14. Conclusions about NO2
- dependent N2O
production
NO2
- accumulation was driven by “under capacity” of soil
NO2
- oxidizing activity compared to NH4
+ oxidizing activity.
Regression analysis revealed a positive, non-linear
relationship between NO2
- concentration and rate of N2O
formation.
Vmax rates of N2O formation correlated with maximum
nitrification rates among the soils.
Different Km NO2
- values were obtained for AOA and AOB
driven N2O formation.