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Temperature affects the ratio of ethylene produced to N2-fixed more than immediate release of fixed N in streams
Ist Teil von
Biogeochemistry, 2023-12, Vol.166 (3), p.269-282
Ort / Verlag
Cham: Springer International Publishing
Erscheinungsjahr
2023
Quelle
SpringerLink
Beschreibungen/Notizen
Nitrogen fixation can be a substantial flux of new biologically available nitrogen (N) into some aquatic ecosystems. The most commonly used method for measuring N
2
-fixation is the acetylene reduction method, which measures nitrogenase activity. This method requires the assumption of a theoretical ratio of ethylene produced to N
2
-fixed unless the estimates are calibrated using
15
N
2
as a tracer. We measured N
2
-fixation using both the acetylene reduction method and
15
N
2
uptake methods to examine the ratio of ethylene produced to N
2
-fixed (C
2
H
4
:N
2
), estimate controls on variation in this ratio, and quantify the immediate release of N
2
-fixed as dissolved N. We estimated N
2
-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 C
2
H
4
:N
2
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 N
2
-fixed as dissolved organic and inorganic N was < 1% of N
2
-fixation. Ethylene production increased 1.8 times faster than N
2
-fixation as temperature increased showing strong control of temperature in the C
2
H
4
:N
2
ratio. Temperature contributed substantially to the variability in ratios of ethylene produced to N
2
-fixed. Slight differences in the C
2
H
4
:N
2
ratio can considerably alter N
2
-fixation estimates particularly in N
2
-fixation dominated stream biofilms, thus when calibrating using a range of temperatures may be essential.