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PHOTOSYNTHESIS AND PHOTOSYNTHESIS‐COUPLED RESPIRATION IN NATURAL BIOFILMS QUANTIFIED WITH OXYGEN MICROSENSORS 1
Author(s) -
Glud Ronnie Nøhr,
Ramsing Niels Birger,
Revsbech Niels Peter
Publication year - 1992
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.0022-3646.1992.00051.x
Subject(s) - photosynthesis , photorespiration , respiration , photic zone , biology , oxygen , respiration rate , botany , ecology , chemistry , phytoplankton , organic chemistry , nutrient
ABSTRACT Photosynthesis and respiration were analyzed in natural biofilms by use of O 2 microsensors. Depth profiles of gross photosynthesis were obtained from the rate of decrease in O 2 concentration during the first few seconds following extinction of light, and net photosynthesis of the photic zone was calculated from O 2 concentration gradients measured at steady state. Respiration within the photic zone was calculated as the difference between gross and net photosynthesis. Two types of biofilms were investigated: one dominated by diatoms, and one dominated by cyanobacteria. High O 2 /CO 2 ratios caused increased respiration especially within the diatom biofilm, which could indicate that photorespiration was a dominant O 2 ‐consuming process. The rate of respiration was constant within both biofilms during the first 4.6 s following extinction of light, even when respiration was stimulated by high O 2 /CO 2 ratio. The assumption of a constant rate of respiration during the dark period is an essential one for the determination of gross photosynthetic activity by use of O 2 microsensors. We here present the first evidence to substantiate this assumption. The results strongly suggest that gross photosynthesis as measured by use of O 2 microsensors may include carbon equivalents that are subsequently lost through photorespiration. Computer modeling of photosynthesis profiles measured after 1.1, 1.6, and 2.6 s of dark incubation illustrated how the actual photosynthesis profile could have appeared if it had been possible to do the determination at time 0. Diffusion of O 2 during the up to 4.6‐s long dark incubations did not affect gross photosynthetic rate when integrated over all depths, but the apparent vertical distribution of the photosynthetic activity was strongly affected.