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EAFES Special Symposium EX04-3

Tropical peat soil turns into a potent source of N2O emission after inappropriate management of reclaimed peatland

HASHIDOKO, Yasuyuki. Hokkaido University, Japan

Tropical peat swampy forests, distributed throughout Southeast Asia, precipitate a large mass of carbon as woody peat soil. This peatland ecosystem with a thick peat layer (2-10 m) is relatively stable ecosystem as long as it is forest, but once the forest was reclaimed and drained ground water there, it became a potent N2O efflux source. We searched for vertical distribution of N2O emitting bacteria using a soil microbiota-culturing assay. In the 10-year-period of oil palm plantation, shallow soils less than 50 cm showed active N2O emission. In contrast, deeper soils (100-400 cm) were more active in 2-year-old oil palm plantation, suggesting that the N2O emitters in the shallow soil newly emerged in the ecosystem after the reclamation. Our microbial investigation revealed that major N2O emitting bacteria in the reclaimed tropical peat soils are eubacteria in subdivision of β-Proteobacteria, genera of Burkholderia and Janthinobacterium. As their conversion rates of NO3 into N2O were extremely high (maximum 50%), it was speculated that the active N2O emitters are missing nitrous oxide reductase (N2OR) gene. Both an acetylene inhibition assay for denitrificaion of the N2O emitters and PCR amplification of N2OR large subunit (nosZ) gene supported our speculation that nosZ was missing in them. In this presentation, we answer to the question why these denitrifiers emit N2O actively.


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