Effect of Acetylene on Nitric Oxide Production in Soil under Denitrifying Conditions

Abstract

Acetylene inhibition of N2O reduction to N2 is traditionally used to estimate denitrification. Although NO is also produced in the denitrification process, the effect of C2H2 on NO production in denitrification has not previously been examined, mainly because C 2 H 2 interferes with chemiluminescent analysis of NO. We used a gas-flow system to study the effect of C2H2 on NO and N2O production in soil columns under denitrifying conditions and developed a method to avoid C2H2 interference of NO analysis. Nitric oxide, N 2 O, and C 2 H 2 were measured in NO 3 - -amended Brookston clay loam (fine-loamy, mixed, mesic Typic Argiaquoll) and Fox sandy loam (fine-loamy over sandy or sandy-skeletal, mixed, mesic Typic Hapludalf) with various moisture contents with and without added glucose during 50-h anaerobic incubations. In glucose-amended Brookston soil with =8% C 2 H 2 added to the N2 carrier gas, net NO production rates were increasingly inhibited after the first 24 h, and by 50 h were only 2 to 7% of the rates obtained in the absence of C 2 H 2 . Without glucose amendment and with C 2 H 2 , net NO production rates decreased by 24 to 62% in the Brookston soil. In the Fox soil inhibition occurred almost immediately on C2H2 addition and net NO production during 50 h was reduced by 36 to 62% with glucose amendment, and by 65 to 76% without glucose amendment. In most cases, net N 2 O production rates were decreased by C2H2 due to the decrease in production of its precursor, NO, and in some cases, increased due to inhibition of N 2 O reduction to N 2 . Our data suggest that the C2H2 inhibition method may underestimate total denitrification rates under low water contents or high levels of C substrate.