Changes in photosynthetic properties measured by oxygen evolution and variable chlorophyll fluorescence in a simulated entrainment experiment with the cyanobacterium Planktothrix rubescens

Abstract

The metalimnion of lake Zürich is dominated by the red coloured cyanobacterium Planktotrix rubescens, where it lives in an extremely low light environment. Photosynthesis of the organism was studied using oxygen evolution and variable fluorescence. After transfer to 2 m depth in the epilimnion, simulating an entrainment event that normally occurs in late summer, photoacclimation was followed.The metalimnetic population had a very high photosynthetic efficiency, and the minimum quantum requirement varied between 7 -12 photons (mol O 2 ) -1 . Upon transfer to high light the quantum requirement increased, which was interpreted as inactivation of a number of photosystem II (PSII) units. At the first entrainment we observed only inactivation of PSII, causing a decrease in the slope of the photosynthesis light curve (both for oxygen evolution and photosynthetic electron transport by PSII (ETR)), without affecting the maximal rate of oxygen evolution (P B max ), suggesting no effect on CO 2 -fixation. During the 2 nd entrainment experiment we observed both an inactivation of the number of PSII as well as a decrease in P B max . In both cases the ETRbased estimates of oxygen evolution (P B ) overestimated the measured rate of P B , indicating the operation of alternative electron sinks. Especially at high light respiratory processes were seemingly stimulated.

Use of in vivo chlorophyll fluorescence to estimate photosynthetic activity and biomass productivity in microalgae grown in different culture systems

“…Cell weight/number cells (mg DW10 6 cells -1 ), cell weight/culture volume (mg DW L -1 ),electron transport rate (ETR, µmol e -m -2 s -1 ), average measured (mBP) and average estimated (eBP) biomass productivity expressed as g DW m -2 day -1 , photosynthetic efficiency as mBP per mol photons absorbed (%) and specific absorption coefficient (Kc, m 2 mg Chl-a Photosynthetic efficiency (%) 2.11 ± 0.35 1.63 ± 0.18 overestimation is rather constant, despite considerable changes in phytoplankton composition. Spectral correction of fluorescence data caused a reduction of 30% or an increase of 44% in the estimated Cfixation, depending how C-fixation was estimated (Kromkamp et al, 2001). In this study with C. fusca, less deviation among estimated and measured biomass yield than that between carbon fixation and ETR reported by Kromkamp et al (2001) in other species was found.…”

“…Spectral correction of fluorescence data caused a reduction of 30% or an increase of 44% in the estimated Cfixation, depending how C-fixation was estimated (Kromkamp et al, 2001). In this study with C. fusca, less deviation among estimated and measured biomass yield than that between carbon fixation and ETR reported by Kromkamp et al (2001) in other species was found. Linear relation between estimated and measured biomass productivity has been determined in Chlorella sp.…”

Application of fast repetition rate fluorometry to phytoplankton photosynthetic parameters in freshwaters

“…These values most probably underestimate the efficiency of PS II. As Kromkamp et al (2001) point out, thylakoids of cyanobacteria are also used for respiration and phycobilisomes produce fluorescence both leading to underestimations of F v /F m . The functional absorption cross section (r PSII ) was higher during stratification and also showed a distinct vertical pattern.…”

Photosynthetic efficiency as a function of thermal stratification and phytoplankton size structure in an oligotrophic alpine lake

“…In the metalimnion (10-12 m) where P. rubescens by far dominates the phytoplankton assemblage in summer, F v /F m was 0.39-0.44. These values most probably underestimate the efficiency of PSII because of alternative electron sinks: (1) thylakoids of cyanobacteria are also used for respiration, and (2) phycobilisomes can produce fluorescence (Kromkamp et al, 2001).…”