Urea metabolism and its significance in the nitrogen cycle in the euphotic layer of lake biwa japan iii. influence of the environmental parameters on the response of nitrogen assimilation

Mitamura, O.

Archiv fur Hydrobiologie 107(3): 281-300


ISSN/ISBN: 0003-9136
Accession: 006871789

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The present study was undertaken to clarify the influence of environmental parameters on the response of nitrogen assimilation by phytoplankton in Lake Biwa. The assimilation rate of urea, ammonia and nitrate nitrogen and the decomposition rate of urea carbon increased with increasing light intensity up to some asymptotic value. The half-saturation constant (KI) for light was approximately 2 klux for urea and ammonia nitrogen assimilation, whereas that for nitrate showed much higher values. An optimum curve, with the optimum temperature of around 30.degree. C , was obtained between the nitrogen assimilation or the urea decomposition and the temperature. A Q10 factor for the nitrogen assimilation of three compounds was calculated as 1.7 to 2.2. The preference of phytoplankton for urea nitrogen was intermediate between that for ammonia and nitrate. The assimilation rate of urea and nitrate nitrogen was suppressed at approximately 1 .mu.g-at. N .cntdot. l-1 of ammonia concentration.