Abstract
Human intervention in nature, especially fertilization, greatly increased the amount of N(2)O emission. While nitrogen fertilizer is used to improve nitrogen availability and thus plant growth, one negative side effect is the increased emission of N(2)O. Successful regulation and optimization strategies require detailed knowledge of the processes producing N(2)O in soil. Nitrification and denitrification, the main processes responsible for N(2)O emissions, can be differentiated using isotopic analysis of N(2)O. The interplay between these processes is complex, and studies to unravel the different contributions require isotopic cross-labeling and analytical techniques that enable tracking of the labeled compounds. Fiber-enhanced Raman spectroscopy (FERS) was exploited for sensitive quantification of N(2)O isotopomers alongside N(2), O(2), and CO(2) in multigas compositions and in cross-labeling experiments. FERS enabled the selective and sensitive detection of specific molecular vibrations that could be assigned to various isotopomer peaks. The isotopomers (14)N(15)N(16)O (2177 cm(-1)) and (15)N(14)N(16)O (2202 cm(-1)) could be clearly distinguished, allowing site-specific measurements. Also, isotopomers containing different oxygen isotopes, such as (14)N(14)N(17)O, (14)N(14)N(18)O, (15)N(15)N(16)O, and (15)N(14)N(18)O could be identified. A cross-labeling showed the capability of FERS to disentangle the contributions of nitrification and denitrification to the total N(2)O fluxes while quantifying the total sample headspace composition. Overall, the presented results indicate the potential of FERS for isotopic studies of N(2)O, which could provide a deeper understanding of the different pathways of the nitrogen cycle.