L. Dendooven et al., DENITRIFICATION POTENTIAL AND REDUCTION ENZYMES DYNAMICS IN A NORWAY SPRUCE PLANTATION, Soil biology & biochemistry, 28(2), 1996, pp. 151-157
As part of a programme aimed at understanding controls of the N cycle
and possible effects of increased N depositions in a soil under a Norw
ay spruce plantation, the denitrification potential and the kinetics o
f NO3-, NO2, N2O and N-2 were investigated. Intact soil cores were con
ditioned for 14 days at 25 degrees C, sieved and amended with 20 mg NO
3--N kg(-1). Treatments were with or without C2H2 and with or without
chloramphenicol (found to inhibit de novo synthesis of reduction enzym
es). Samples were purged of O-2 and anaerobically incubated at 25 degr
ees C for 96 h while CO2 and N2O production and NO3- and NO2- concentr
ations were monitored. Chloramphenicol did not affect the CO2 producti
on which decreased by nearly 50% under anaerobic conditions. Differenc
es in NO3- concentrations between chloramphenicol and unamended soil w
ere only detectable after 48 h while differences in NO2- concentration
s were only measurable after 70 h. Nitrous oxide production in the chl
oramphenicol-amended and unamended soils was comparable, 1.3 and 2.6 m
g N kg(-1), respectively, for the first 38 h while no N-2 was produced
in either treatment over the first 15 h. The production of Nz was onl
y 0.6 mg N kg(-1) after 96 h in the chloramphenicol-amended soil but i
t was the sole gaseous product of denitrification after 70 h in the un
amended soil. The kinetics of NO3-, NO2- N2O and N-2 were satisfactori
ly described with a model, DETRAN, assuming a competitive Michaelis-Me
nten kinetic and an uptake of NO3- by micro organisms that was not dir
ectly matched by a reduction of NO3-. The uptake of NO3- was higher (c
a. 2 mg NO3--N kg(-1)) than they release of reduction products NO2- an
d N2O for the entire incubation in the chloramphenicol-amended soil bu
t only for the first 70 h in the unamended soil. Concentrations of NO3
-, NO2- and N2O reductase appeared to increase by 4-fold between 20 an
d 30 h after the onset of anaerobiosis when;he affinity for NO3- was s
et at 1 and the affinity for NO2- was between 120 and 160 and for N2O
between 1.2 and 2.6. Several factors of C and N dynamics in these expe
riments are compared with those made in soil from a poorly drained pas
ture. It is concluded that the microbial community in the well-drained
forest soil described here was not well pre-adapted to periodic anaer
obiosis.