土壌の脱窒過程で生成されるN₂Oの濃度に及ぼす細菌類と真菌類の影響

抄録

The relative contributions of bacteria and fungi to N₂O production by denitrification in acidic tea soils amended with farmyard manure or chemical fertilizer, were studied with laboratory experiments using selective inhibitors. The pHs of these soils were kept at 4.8 and 5.5 in situ, respectively. Fungal denitrification accounted for about 30% and 15% of the total denitrification in the farmyard manure-amended soil and chemical fertilizeramended, respectively. The main final product by bacterial denitrification was N₂ and the concentration of N₂O as intermediate increased in the denitrification process from nitrate rather than from nitrite. On the other hand, the final product of fungal denitrification was N₂O independent of pH values and kinds of substrates. The increases of N₂O concentration by denitrification in acidic soils were due to the decrease of N₂O reduction activities by bacteria and the increase of fungal denitrification. Bacteria had an important role in reducing N₂O produced by fungi in natural environment. These results suggest that the agricultural soils acidified by the excessive use of nitrogen fertilizer may be one of the major sources of N₂0 in natural system and the use of farmyard manure increases both bacterial and fungal denitrifications.