HR: 0800h
AN: B21D-0905    [Abstracts]
TI: A new method of quantifying contributions from nitrification and denitrification. Tree species effects on soil sources of N$_{2}$O.
AU: * Menyailo, O V
EM: menyailo@hotmail.com
AF: Institute of Forest SB RAS, Akademgorodok, Krasnoyarsk, 660036 Russian Federation
AU: Hungate, B A
EM: bah@nau.edu
AF: Dept. of Biological Sciences and Merriam Powell Center for Environmental Research, Northern Arizona Iniversity, Beaverstreet,30, Flagstaff, AZ 86001 United States
AB: Soil microorganisms produce N$_{2}$O through denitrification and nitrification. Here we propose the new method to accurately distinguish contributions of nitrification or denitrification to the N$_{2}$O production. This method is based on the application of the NH$_{4}$NO$_{3}$ (substrate for both processes) with low level of oxygen isotopes enrichment (ca. 1.6 atom excess, %). During nitrification, the first atom of oxygen in nitrous oxide derives from atmospheric O$_{2}$ and the second from H$_{2}$O, while in denitrification, all oxygen atoms of the formed N$_{2}$O originate from oxygen of NO$_{3}$$^{-}$. Thus applying enriched $^{18}$O-NO$_{3}$$^{-}$ and measuring $^{18}$O-N$_{2}$O thereafter it is possible to distinguish the two processes. We used the Siberian afforestation experiment with six dominant in Siberia tree species grown artificially for about 30 y on initially homogeneous soil. The soil samples from all species were incubated at the two moisture levels to test whether the isotopic signatures of oxygen in N$_{2}$O will be more enriched at high moisture level due to increase of denitrifier-derived N$_{2}$O. Overall, both tree species and soil moisture strongly affected not only the N$_{2}$O production but also $^{18}$O-N$_{2}$O with significant interaction between the two factors. This indicates that the role of denitrification and nitrification is different under different tree species and grassland as well as that with increase of soil moisture the part of denitrification is increasing not uniformly but species-dependent. We have shown that at low soil moisture (30% of WHC), the N$_{2}$O efflux is very low but nitrification contributes to 62-92% of the all N$_{2}$O formed. At high moisture (90% of WHC), the efflux is increasing by 10-100 times and the contribution of nitrification is declining to 10-25% and denitrification is responsible for most of the flux.
DE: 4805 Biogeochemical cycles (1615)
DE: 4840 Microbiology
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting