Carbon monoxide as an inhibitor of N2ase activity(C2H2) in control measurements of endogenous formation of ethylene by forest soils

Two problems with the recently suggested method to measure endogenous formation of C₂H₄ in an atmosphere enriched with C₂H₂ and CO in studies of N₂ase activity (C₂H₂) in forest soils were analysed, namely the effect of consumption of CO during incubation and the effect of water-saturated conditions.After an initial addition of 100 ml C₂H₂ and 20 ml CO 1^?1 to soil incubation vessels, CO was gradually consumed and followed by a recovery of N₂ase activity when the concentration of CO was lower than about 10 ml 1^?1. The shortest period within which this concentration was achieved was 1 day when incubating fresh soil cores at 15°C, and it was concluded that longer incubations should be avoided.The inhibition of N₂ase activity by CO was strongly suppressed when all soil pores were filled with water. Dissolved inorganic N (0.1% of dry mass soil) was much more efficient in inhibiting N₂ase activity under such conditions.