JOURNAL OF PLANKTON RESEARCH | VOLUME 9 | NUMBER 3 | PAGES 513-524 | 1987
© Oxford University Press
research-article |
Diel changes of uptake of inorganic carbon and nitrogen by phytoplankton, and the relationship between inorganic carbon and nitrogen uptake in Lake Nakanuma, Japan
Institute of Biological Sciences, The University of Tsukuba Sakura-mura, Ibaraki 305, Japan
Received on June 23, 1986; accepted on February 16, 1987 Diel changes of uptake of inorganic carbon and nitrogen were examined in a small freshwater lake, Lake Nakanuma, Japan, by the 13C and 15N method. Experiments were earned out in spring, summer and autumn in 1984. Carbon and nitrogen uptake in the light incubation showed maxima around noon at the three seasons. Carbon uptake ceased at night, but ammonium uptake was fairly large at night. In the dark incubation carbon uptake did not occur. Ammonium uptake showed a maximum at dusk in the dark experiments. Diel changes of nitrate uptake were less clear than those of ammonium uptake. These results indicate that nitrogen uptake partly depended on the carbon uptake. Then, we tried to explain the diel changes of nitrogen uptake, assuming that the nitrogen uptake partly depends on stored carbohydrate. The diel changes may be elucidated by the sum of three terms: one is the term of decay of stored carbohydrate, the second is the term which indicates cumulative increase of stored carbohydrate and the third is the term which directly depends on light.