Source of Nitrous Oxide Emissions during the Cow Manure Composting Process as Revealed by Isotopomer Analysis of and amoA Abundance in Betaproteobacterial Ammonia-Oxidizing Bacteria

Abstract

ABSTRACT A molecular analysis of betaproteobacterial ammonia oxidizers and a N 2 O isotopomer analysis were conducted to study the sources of N 2 O emissions during the cow manure composting process. Much NO 2 − -N and NO 3 − -N and the Nitrosomonas europaea -like amoA gene were detected at the surface, especially at the top of the composting pile, suggesting that these ammonia-oxidizing bacteria (AOB) significantly contribute to the nitrification which occurs at the surface layer of compost piles. However, the 15 N site preference within the asymmetric N 2 O molecule (SP = δ 15 N α − δ 15 N β , where 15 N α and 15 N β represent the 15 N/ 14 N ratios at the center and end sites of the nitrogen atoms, respectively) indicated that the source of N 2 O emissions just after the compost was turned originated mainly from the denitrification process. Based on these results, the reduction of accumulated NO 2 − -N or NO 3 − -N after turning was identified as the main source of N 2 O emissions. The site preference and bulk δ 15 N results also indicate that the rate of N 2 O reduction was relatively low, and an increased value for the site preference indicates that the nitrification which occurred mainly in the surface layer of the pile partially contributed to N 2 O emissions between the turnings.