ISSN:
1573-5117
Keywords:
14C uptake
;
14C loss
;
productivity
;
assimilation number
;
oligotrophic water
;
phytoplankton
;
bacteria
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Measurements of the uptake and loss of 4C in the light and in the dark in the Tasman and Coral Seas have revealed methodological problems with the estimation of productivity in these waters. Rates of productivity estimated without replication, time series incubations and dark controls frequently overestimated the true rates of autotrophic production. The data showed unexpectedly high rates of both uptake and loss in the dark in oligotrophic waters. In oligotrophic oceanic waters, dark incorporation of 14C sometimes equalled the uptake of 14C in the light bottle. Rapid uptake of isotope in the dark controls appeared to be the result of rapid bacterial growth and metabolism. This problem was exacerbated by agitation of the sample before or during the incubation. Tropical samples were particularly susceptible to problems arising from the agitation of the samples. Latitudinal gradients of dark uptake and loss were revealed in these incubations. The loss of label during 8–12 hours in the dark (after 12 hr in the light) was as high as 50% in subtropical waters. The loss was frequently unmeasurable (〈 10%) in temperate waters. The time course of 14C uptake indicated active grazing in the bottles and suggested that most of the nighttime losses of label were due to grazing by microheterotrophs. Respiratory losses appeared to be small. Calculated values of the assimilation number (or photosynthetic capacity) which did not correct for dark 14C uptake were too high to be biochemically realistic. The errors were due to the heterotrophic uptake of label and the lack of dark controls. Rapid release of 14C in the dark after incubation in the light meant that the estimate of ‘productivity’ was dependant on the trophic state of the sample and on the period of incubation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00015519
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