(1978) Acetylene Inhibition Method for Short-term Measurement of Soil ...

Published July, 1978

The Acetylene Inhibition Method for Short-term Measurement of Soil Denitrification and its Evaluation Using Nitrogen-131 M. SCOTT SMITH, MARY K. FIRESTONE, AND JAMES M. TiEDJE2 ABSTRACT Acetylene was found to effectively inhibit the reduction of N2O by

soils are lacking. Due to limited sensitivity, previous «*&«* extensive amendment of soils and/or

methods have

anaerobic soils. With concentrations of C2H2 above 0.1 atm, added

lon

NO3- was quantitatively converted to N2O, and added N2O was reduced at an insignificant rate. Experiments with I3N demonstrated that at low soil nitrate concentrations at least 0.1 atm C2H2 was

cidated the basic controlling factors, the dynamics of denitrification and the quantitative effects of environmental or management parameters on natural soils are largely

required for effective inhibition. Denitrification rates determined by

unknown.

N and by C2H2 inhibition methods correlated well, as did determinations of NjO/(N2 + N2O). The methods also revealed that an

The inhibition of N2O reductase by acetylene in pure culture was reported by Yoshinari and Knowles (1976) and

acceleration in denitrification rate occurred within a few hours after soil was exposed to anaerobic conditions. The acetylene method was generally used to measure denitrification rates in soils incubated as .. . . . • . .. . . . . , „ ,, ., anaerobic slurries, but was also used to determine rates for field moist aggregrates incubated anaerobically and aerobically. When assayed as anaerobic slurries, initial denitrification rates ranged from 0.1 to

by Balderston,

et al. (1976). It is now widely accepted that and probably freely diffusable . . ,. . • .T , .. -c .. ./ ,n intermediate in the demtnfication pathway (Payne, irm 1973; ir>-.-rs T^. r St John and Hollocher, 1977). Therefore, one would ex ect the P quantity of N2O produced by C2H2-inhlblted

denitrification rate in aerobic aggregrates was approximately 1,000

N produced without inhibition. If N2O is the sole de-

times less, showing the strong inhibitory effect of O2 on the indigenous denitrifying enzymes. Additional Index Words: nitrous oxide, nitrogen losses, nitrogen transformations.

nitrification product, analysis is greatly simplified since N2O, unlike N 2 , is a minor atmospheric constituent (approximately 300 ppb) and can be assayed by sensitive gas chromatographic detectors. The successful application of mis memocj to soi j denitrification studies has been reported

Smith, M. Scott, Mary K. Firestone, and James M. Tiedje. 1978. The acetylene inhibition method for short-term measurement of soil denitrification and its evaluation using nitrogen-13. Soil Sci. Soc. Am. J.

by Yoshinari, et al. (1977). T th; nanpr ,,,, i™/p iisoH trac rhrnmatnoranhv and ,, ln tnlS PaPer We nave used gas CnromatOgrapny and

I3

0.7 nmoles N gas • soir1 • min"1 for the mineral soils examined. The

42:611-615.

________________ HE INCREASED COST OF FIXED nitrogen and the posTsibility that soil-evolved N O may contribute to at2

mospheric ozone depletion (McElroy et al., 1976) have caused renewed interest in the process of denitrification. Despite a considerable mass of research on denitrification, reliable values for rates of N2 and N2O production in field

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'Contribution from the Dept of Crop and Sod Sciences and Dept. of Microbiology and Public Health, Michigan State Univ., East Lansmg, MI 48824. Journal article no. 8280. of The Michigan Agric. Expt. Stn. Received 3 Oct. 1977. Approved 6 Mar. 1978. 2 Research Assistants and Associate Professor, respectively.

S

term

N Q js

incubation. Although these methods have elu-

an

obligatorV)

microorganisms to be a direct measure of the total gaseous

'"NOs" to evaluate the acetylene inhibition technique in soils and have identified the conditions and soil types for which this method is valid and for which blockage of N2O reductase is complete. The radioactive isotope, 13N, provi