Aerobic emissions of N2O and N2 from soil cores : factors influencing production from 13N-labelled NO3- and NH4+

Abstract Gas-stripping procedures, with air as the stripping and carrying gas, were used to investigate the effects of amendments on production in soil cores of N 2 O and N 2 arising from 13 N-labelled NO 3 − (denitrification) or NH 4 + (nitrification). These cores had been used previously to investigate ambient gas emission rates; the rates after amendment were compared with these “natural” emission results. Using 13 NO 3 − , the results of amendment with H 2 O, glucose, NO 3 − or glucose + NO 3 − , several hours before the experiment, were usually explicable in terms of effects on microbial numbers and soil O 2 status. However, results obtained immediately after amendments were made, before de novo enzyme synthesis or change of O 2 status would have occurred, were generally difficult to interpret. Amendments which included NO 3 − gave spuriously low N 2 O and N 2 emission rates, probably due to isotopic dilution. The immediate effect of amendments may vary from time to time and depend upon soil conditions at the time of sampling. Only glucose consistently stimulated gas emissions, presumably because it enhanced activity of the existing denitrifying population. Using 13 NH 4 + , amendment with H 2 O increased production of N 2 , but not N 2 O, and amendment with glucose reduced emissions of both gases. The advantages and disadvantages of this 13 N method for investigating the influence on N 2 O and N 2 production of various soil amendments, and the relationships of these results with those of more conventional studies, are discussed.