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Abstract Denitrification in soil microenvironments is difficult to study by conventional techniques. By use of O 2 and N 2 O microsensors, it was possible to study the spatial distribution of oxygen respiration and denitrification in soil aggregates kept at field capacity. Aggregates with diameters of 20 to 25 mm often contained anaerobic centers but exhibited only low rates of denitrification due to a limiting availability of electron donors. Addition of organic matter such as clover leaves or tryptone to the surface of the aggregates greatly stimulated respiratory activity and caused anoxia and high rates of denitrifying activity within the organic hot‐spot and in the underlying soil. Due to imbalance between N 2 O production and N 2 O reductase activity, the creation of a hot‐spot led to an initial accumulation of N 2 O even when acetylene was absent. Denitrification within the center of a hot‐spot rapidly became limited by the diffusional supply of NO − 3 , even when the underlying soil contained 5 m M NO − 3 , and such hot‐spot centers depleted of NO − 3 served as sinks for N 2 O while N 2 O concentrations of up to 400 µ M were building up immediately below. The bulk N 2 O production rate of the soil was thus the result of a net production in some microenvironments and simultaneous net consumption in other microenvironments.
Højberg et al. (Tue,) studied this question.