Abstract
Nitrogen fixation can be a substantial flux of new biologically available nitrogen (N) into some aquatic ecosystems. The most commonly used method for measuring N2-fixation is the acetylene reduction method, which measures nitrogenase activity. This method requires the assumption of a theoretical ratio of ethylene produced to N2-fixed unless the estimates are calibrated using 15N2 as a tracer. We measured N2-fixation using both the acetylene reduction method and 15N2 uptake methods to examine the ratio of ethylene produced to N2-fixed (C2H4:N2), estimate controls on variation in this ratio, and quantify the immediate release of N2-fixed as dissolved N. We estimated N2-fixation for benthic biofilms and separated Nostoc in four streams in Wyoming, Little Laramie River, Ditch Creek, Spread Creek, and Polecat Creek. Estimates of the C2H4:N2 ratio for any one stream and date ranged from 1.6 to 7.1 with a group-level mean of 3.8. Immediate release of N2-fixed as dissolved organic and inorganic N was < 1% of N2-fixation. Ethylene production increased 1.8 times faster than N2-fixation as temperature increased showing strong control of temperature in the C2H4:N2 ratio. Temperature contributed substantially to the variability in ratios of ethylene produced to N2-fixed. Slight differences in the C2H4:N2 ratio can considerably alter N2-fixation estimates particularly in N2-fixation dominated stream biofilms, thus when calibrating using a range of temperatures may be essential.
| Original language | English |
|---|---|
| Pages (from-to) | 269-282 |
| Number of pages | 14 |
| Journal | Biogeochemistry |
| Volume | 166 |
| Issue number | 3 |
| DOIs | |
| State | Published - 2023 |
Funding
We thank Kurt Chowanski for his quick attention to data management support. Kady Hogeland, Angela Ostrander, Jenny Carpenter, Paul Newman, Trista Neikum, Brittany Donovan, and Amy Krist helped in the field and laboratory. Patricia Colberg for use of her GC, Norbert Swoboda for setting up the GC at a remote field station, Hank Harlow for support at the UW-NPS field station, Fred Lindzey for access to the Little Laramie River, and Sue O’Ney at Grand Teton National Park for permitting and support. This work was funded by the Wyoming Water Development Commission and USGS, University of Wyoming, NSF Grant DEB 0111410, NSF EPSCoR small grants, NSF GK-12 Science Posse. We thank Kurt Chowanski for his quick attention to data management support. Kady Hogeland, Angela Ostrander, Jenny Carpenter, Paul Newman, Trista Neikum, Brittany Donovan, and Amy Krist helped in the field and laboratory. Patricia Colberg for use of her GC, Norbert Swoboda for setting up the GC at a remote field station, Hank Harlow for support at the UW-NPS field station, Fred Lindzey for access to the Little Laramie River, and Sue O’Ney at Grand Teton National Park for permitting and support. This work was funded by the Wyoming Water Development Commission and USGS, University of Wyoming, NSF Grant DEB 0111410, NSF EPSCoR small grants, NSF GK-12 Science Posse.
| Funders | Funder number |
|---|---|
| DEB 0111410 | |
| University of Wyoming |
Keywords
- Acetylene reduction
- Biofilms
- Calibration
- Conversion factor
- N uptake
- Nitrogen fixation
- Nostoc
- Streams