Biological Aspects of Nitrogen Mineralization in Humus from a Pine Forest Podsol Incubated under Different Moisture and Temperature Conditions

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Abstract
Fluctuations of soil organism abundance, soil respiration and inorganic N were studied in a laboratory experiment on material taken from the humus layer of a Scotch pine forest and incubated under different moisture and temperature regimes. The experiment was run for 28 wk with samplings every 7 wk. At 28 wk, increases in total movable N (inorganic N + biomass N) were observed in samples incubated at high temperature and/or high moisture content. Most of the N was found in biomass except in incubations at the highest temperatures and moistures. Under those conditions, high abundance of nematodes occurred together with drastically increased amounts of inorganic N. Low values of inorganic N were recorded under conditions common in the field. No obvious relations could be detected between standing crops of bacteria and temperature, moisture or respiration. The number of bacterial-feeding nematodes seemed to be a possible measure of previous bacterial production contributing more information than the standing crop measurements of the bacteria, which varied little despite the direct evidence of substantial bacterial production in some incubation conditions.