Jp. Montoya et Jj. Mccarthy, ISOTOPIC FRACTIONATION DURING NITRATE UPTAKE BY PHYTOPLANKTON GROWN IN CONTINUOUS-CULTURE, Journal of plankton research, 17(3), 1995, pp. 439-464
The isotopic fractionation associated with uptake of NO3- by six speci
es of phytoplankton (two diatoms, one cryptophyte, one chlorophyte and
two haptophytes) was measured at a variety of steady-state growth rat
es in nitrogen-limited continuous culture. The magnitude of the isotop
ic fractionation factor (alpha) declined with growth rate in the diato
m Thalassiosira weissflogii, but did not vary consistently with growth
rate in the other species. In combination with data from earlier stud
ies, these results suggest that the net isotopic fractionation during
growth on NO3- is insensitive to growth rate, but may vary significant
ly with photon flux density. The six species studied fell into two dis
tinct groups: the two diatoms showed mean isotopic fractionation facto
rs of 1.0090 and 1.0121, which was significantly different from the va
lues of alpha measured for the four flagellate species (mean alpha = 1
.0009-1.0032). These results imply that the isotopic perturbation asso
ciated with phytoplankton blooms will be greatest when diatoms are the
dominant bloom species. Such isotopic perturbations may provide a use
ful tool for studying the dynamics of nitrogen movement through plankt
onic food webs.