Estimating phytoplankton photosynthesis by active fluorescence

Conference · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7034128

Falkowski, P G; Kolber, Z

Photosynthesis can be described by target theory, At low photon flux densities, photosynthesis is a linear function of irradiance (I), The number of reaction centers (n), their effective absorption capture cross section {sigma}, and a quantum yield {phi}. As photosynthesis becomes increasingly light saturated, an increased fraction of reaction centers close. At light saturation the maximum photosynthetic rate is given as the product of the number of reaction centers (n) and their maximum electron transport rate (I/{tau}). Using active fluorometry it is possible to measure non-destructively and in real time the fraction of open or closed reaction centers under ambient irradiance conditions in situ, as well as {sigma} and {phi} {tau} can be readily, calculated from knowledge of the light saturation parameter, I{sub k} (which can be deduced by in situ by active fluorescence measurements) and {sigma}. We built a pump and probe fluorometer, which is interfaced with a CTD. The instrument measures the fluorescence yield of a weak probe flash preceding (f{sub 0}) and succeeding (f{sub 0}) a saturating pump flash. Profiles of the these fluorescence yields are used to derive the instantaneous rate of gross photosynthesis in natural phytoplankton communities without any incubation. Correlations with short-term simulated in situ radiocarbon measurements are extremely high. The average slope between photosynthesis derived from fluorescence and that measured by radiocarbon is 1.15 and corresponds to the average photosynthetic quotient. The intercept is about 15% of the maximum radiocarbon uptake and corresponds to the average net community respiration. Profiles of photosynthesis and sections showing the variability in its composite parameters reveal a significant effect of nutrient availability on biomass specific rates of photosynthesis in the ocean.

• Research Organization: Brookhaven National Lab., Upton, NY (United States)
• Sponsoring Organization: USDOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 7034128
• Report Number(s): BNL-47937; CONF-9204164-2; ON: DE93000369
• Resource Relation: Conference: International symposium on the measurement of primary production from the molecular to global scale, La Rochelle (France), 19-26 Apr 1992
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CARBON CYCLE
GLOBAL ASPECTS
FLUORIMETERS
PERFORMANCE TESTING
PHYTOPLANKTON
FLUORESCENCE SPECTROSCOPY
CLIMATIC CHANGE
PHOTOSYNTHESIS
AQUATIC ORGANISMS
CHEMICAL REACTIONS
EMISSION SPECTROSCOPY
MEASURING INSTRUMENTS
PHOTOCHEMICAL REACTIONS
PLANKTON
PLANTS
SPECTROSCOPY
SYNTHESIS
TESTING
540310* - Environment
Aquatic- Basic Studies- (1990-)