ISSN:
1573-5117
Keywords:
primary production
;
phytoplankton
;
factorial analysis
;
laboratory incubations
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract An array of factors simultaneously controls phytoplankton photosynthesis and hence the primary production process. Because their relative importance shifts both with depth and with season, the significance of individual factors cannot be resolved by in situ incubations, even if all relevant environmental and biotic variables are measured. Here a procedure is described by which in addition to in situ measurements, photosynthesis is simultaneously assessed in identical subsamples under constant temperature (10 °C) and light (0.66 mol m−2 h−1 PAR conditions, ‘in vitro’). By calculating photosynthesis per unit of chlorophyll, effects of shifting biomass on photosynthesis can be eliminated but seasonal variations of light-saturated photosynthesis generated by temperature, and vertical changes of light-requirements (e.g. by light-shade adaptation) remain obscure. Quotients of in situ photosynthetic rates divided by in vitro rates allow the quantification of light-mediated changes. Provided that photosynthesis measured in vitro is light-saturated, quotients in situ: in vitro rates should never exceed unity. They are a measure for the degree of light-limitation. In vitro rates normalized to chlorophyll give information on temporal changes caused by variations in photosynthetic capacity. In Lake Constance, mean cell size appears to control light-saturated assimilation numbers.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00015523
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