Fig. 7. Denitrification limiting factors in the upper soil horizon (0–25 cm) of the topohydrosequence. Seasons and sites have been pooled together (means and standard errors, n = 36). ANA, denitrification activity of soil samples incubated with acetylene under N₂ atmosphere alone. ANAC, denitrification activity of soil samples amended with carbon (4 g glucose kg^-1 fresh soil) and incubated with acetylene under N₂ atmosphere. ANAN, denitrification activity of soil samples amended with nitrate (10 mg NO₃–N kg^-1 fresh soil) and incubated with acetylene under N₂ atmosphere.