Urea decomposition by a freshwater red tide phytoplankton in Lake Biwa
Mitamura, O.
Memoirs of Osaka Kyoiku University Series III Natural Science and Applied Science 41(1): 25-33
1992
Accession: 009699958
This study was undertaken to clarify the ability of urea decomposition by a freshwater red tide phytoplankton in Lake Biwa. To measure the decomposition rate of urea by Uroglena americana, sample waters from euphotic layer at three stations in the north basin of Lake Biwa were softly separated by sieving the water. The decomposition rate of urea by unit colony of U. americana was 104 to 301 f mol urea cntdot colony-1 cntdot hr-1 in the light and 17 to 100 f mol urea cntdot colony-1 cntdot hr-1 in the dark condition. The major part of urea decomposition was the phase of CO-2 liberation. Four to 19% of the urea decomposition was incorporated into the cell of U. americana in the light, but this was much lower in the dark. The ratio of urea carbon decomposition rate to photosynthetic carbon assimilation rate was 0.7 to 2.7%. The contribution of urea carbon in the carbon source of U. americana was negligible. The present results indicate that a freshwater red tide phytoplankton, U. americana, has a ability of the urea decomposing activity and effectively decomposes urea in the euphotic layer of Lake Biwa.