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

Topics of Research• 1) Temperature response of AOA and AOBcontributions to soil nitrification

• 2) Impact of uncoupling nitrification on N2Oproduction

• 3) Response of soil AOB and AOA nitrification to applications of different N forms

• 4) Quorum sensing among nitrifiers

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.

Cropped and noncropped soils at four locations in Oregon

Pendleton

Madras

Klamath Falls

Corvallis

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

Model parameters differed between AOA and AOB driven nitrification

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.

Uncoupling of Soil Nitrification

• Nitrite accumulation in soils

• Impact on nitrifier-driven N2O production

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.

NO

2- (m

ol g

-1 s

oil)

0.00

0.05

0.10

0.15

0.20

NO

3 - ( mol g

-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

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.

N2O

(nm

ol g

-1 s

oil)

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

ab

a

b

A a

a

b

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8Madras

- Octyne + Octyne

a

b

a

b

aa

a

b

Col 21

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Klamath

- Octyne + Octyne

No add

ed

NO 2- +N

O 2-

No add

ed

NO 2- +N

O 2-

aa

a

b

aa

a

b

A

B

A

B

A

B

A

B

A

B

A

B

a A

B

B

A

A

B

B

A

A

A

B

A B C

No add

ed

NO 2- +N

O 2-

No add

ed

NO 2- +N

O 2-

No add

ed

NO 2- +N

O 2-

No add

ed

NO 2- +N

O 2-

Percentage of NH4+ oxidized to N2O is

increased by presence of NO2-

  Total AOA AOB

  No added

NO2- No

addedNO2

- No added

NO2-

Pendleton 0.04 0.28 0.03 0.40 0.06 0.16Klamath 0.06 0.39 0.08 0.22 0.05 0.30Madras 0.06 0.16 0.06 0.09 0.06 0.28Mean 0.053 0.28 0.06 0.23 0.06 0.25

Removal of NO2- stops N2O production

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.

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.