Relative Contribution of nirK- and nirS- Bacterial Denitrifiers as Well as Fungal Denitrifiers to Nitrous Oxide Production from Dairy Manure Compost
Maeda, Koki | Toyoda, Sakae | Philippot, Laurent | Hattori, Shohei | Nakajima, Keiichi | Itō, Yumi | Yoshida, Naohiro
The relative contribution of fungi, bacteria, and nirS and nirK denirifiers to nitrous oxide (N₂O) emission with unknown isotopic signature from dairy manure compost was examined by selective inhibition techniques. Chloramphenicol (CHP), cycloheximide (CYH), and diethyl dithiocarbamate (DDTC) were used to suppress the activity of bacteria, fungi, and nirK-possessing denitrifiers, respectively. Produced N₂O were surveyed to isotopocule analysis, and its ¹⁵N site preference (SP) and δ¹⁸O values were compared. Bacteria, fungi, nirS, and nirK gene abundances were compared by qPCR. The results showed that N₂O production was strongly inhibited by CHP addition in surface pile samples (82.2%) as well as in nitrite-amended core samples (98.4%), while CYH addition did not inhibit the N₂O production. N₂O with unknown isotopic signature (SP = 15.3–16.2‰), accompanied by δ¹⁸O (19.0–26.8‰) values which were close to bacterial denitrification, was also suppressed by CHP and DDTC addition (95.3%) indicating that nirK denitrifiers were responsible for this N₂O production despite being less abundant than nirS denitrifiers. Altogether, our results suggest that bacteria are important for N₂O production with different SP values both from compost surface and pile core. However, further work is required to decipher whether N₂O with unknown isotopic signature is mostly due to nirK denitrifiers that are taxonomically different from the SP-characterized strains and therefore have different SP values rather than also being interwoven with the contribution of the NO-detoxifying pathway and/or of co-denitrification.
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