EXCRETION OF ORGANIC CARBON AS FUNCTION OF NUTRIENT STRESS
A. JENSEN
Institute of Marine Biochemistry, University of Trondheim,
N-7034 Trondheim, NTH, Norway
INTRODUCTION
For half a century aquatic biologists have studied and debated how
planktonic algae contribute to the pool of dissolved organic matter in
culture media and in natural waters. Krogh took up this topic already
in 1934 (Krogh, 1934) and the debate seemed to culiminate with Sharp's
contribution in 1977 immediately followed by Fogg's comments (Sharp,
1977; Fogg, 1977) and by the duel between Aaronson and Sharp in 1978
Aaronson, 1978; Sharp, 1978). Several reviews have covered the development of the field (Fogg, 1971; Hellebust, 1974; Wangersky, 1978;
Sharp, 1977), and more recent publications have clarified some of the
discrepancies (Nalewajko, 1977; Mague et af., 1980; Larsson and Hagstrom, 1979, 1982).
There is a general agreement that algal cells will deliver dissolved organic compounds to the surrounding water when the cells die
or are disrupted in some way, e. g. through grazing (" sloppy feeding").
The major dispute has been concerned with the release of extracellular
material by living cells which is the real excretion or exudation.
Sharp (1977) concluded that evidence of excessive excretion of organic
material by "healthy" phytoplankton was not good, and he maintained
(Sharp, 1978) that undisturbed phytoplankton would only excrete negligible quantities of material in nature. By "healthy" cells he meant
exponentially growing cells.
It seems to be generally accepted that exponentially growing cells
excrete less material than cells in other growth phases do (see p. ex.
Wangersky, 1978; Guillard and Wangersky, 1958; Myklestad and Haug, 1972;
Haug and Myklestad, 1976; Myklestad, 1977). However, since phytoplankton populations normally go through several growth phases in addition
A. JENSEN
Institute of Marine Biochemistry, University of Trondheim,
N-7034 Trondheim, NTH, Norway
INTRODUCTION
For half a century aquatic biologists have studied and debated how
planktonic algae contribute to the pool of dissolved organic matter in
culture media and in natural waters. Krogh took up this topic already
in 1934 (Krogh, 1934) and the debate seemed to culiminate with Sharp's
contribution in 1977 immediately followed by Fogg's comments (Sharp,
1977; Fogg, 1977) and by the duel between Aaronson and Sharp in 1978
Aaronson, 1978; Sharp, 1978). Several reviews have covered the development of the field (Fogg, 1971; Hellebust, 1974; Wangersky, 1978;
Sharp, 1977), and more recent publications have clarified some of the
discrepancies (Nalewajko, 1977; Mague et af., 1980; Larsson and Hagstrom, 1979, 1982).
There is a general agreement that algal cells will deliver dissolved organic compounds to the surrounding water when the cells die
or are disrupted in some way, e. g. through grazing (" sloppy feeding").
The major dispute has been concerned with the release of extracellular
material by living cells which is the real excretion or exudation.
Sharp (1977) concluded that evidence of excessive excretion of organic
material by "healthy" phytoplankton was not good, and he maintained
(Sharp, 1978) that undisturbed phytoplankton would only excrete negligible quantities of material in nature. By "healthy" cells he meant
exponentially growing cells.
It seems to be generally accepted that exponentially growing cells
excrete less material than cells in other growth phases do (see p. ex.
Wangersky, 1978; Guillard and Wangersky, 1958; Myklestad and Haug, 1972;
Haug and Myklestad, 1976; Myklestad, 1977). However, since phytoplankton populations normally go through several growth phases in addition