Short-term variations in photosynthetic parameters of Nannochloropsis cultures grown in two types of outdoor mass cultivation systems

Abstract

The present study evaluated productivity under different operational (optical) conditions using the unicellular alga Nannochloropsis sp. (Eustigmatophyta). This alga is often grown in mass algal cultures because it contains high contents of the polyunsaturated fatty acid, eicosapentaenoic acid (EPA, 20:5ω3). We followed biomass, photosynthetic activities and physiological parameters in a 3 d experiment using various photosynthesis techniques in 2 outdoor cultivation systems: a flat panel photobioreactor (FPP) and a high rate algal pond (HRAP). We aimed to detect acclimation behaviour to the different optical conditions, with the FPP having a short light path and the HRAP having a long light path. Both algae cultures showed an afternoon depression of photosynthetic activity, which was more pronounced in the FPP. Therefore, the HRAP culture showed 'classical' shade adaptation behaviour, whereas the FPP algae was high-light acclimated. The FPP showed diurnal changes in the potential rates of photosynthesis and respiration. High temperatures (41°C) on Day 3 in the FPP caused a large reduction in the maximum Photosystem II (PSII) efficiency (F v /F m ) and an over-reduction of the PSII acceptors, which did not recover during the light period. Chlorophyll fluorescence measurements with and without dark adaptation suggested that the decreased photosynthetic activity was due to both chronic and dynamic downregulation. Photodamage was higher in the FPP, but most was recovered during the evening. A comparison between the quantum efficiencies for PSII charge separation and oxygen evolution revealed a close coupling between the 2 processes. We also concluded that the optical absorption cross section of PSII equalled 75% of the total absorption cross section.

Photosynthesis monitoring to optimize growth of microalgal mass cultures: application of chlorophyll fluorescence techniques

“…Vonshak et al 1994, Torzillo et al 1996, Masojídek et al 1999, 2011b, Oxborough et al 2000, Baker 2008, Kromkamp et al 2009). Environmental conditions that impact the photosynthetic apparatus, especially PSII, directly or indirectly influence the measures of chl a fluorescence yield.…”

“…The fiber optics of the fluorometer was protected by a glass tube and placed directly, 3 mm deep into the suspension using solar irradiance as actinic light (at an angle of about 60°) Photosynthetic efficiency measured by fluorescence was found to be related to quantum yields of other photosynthetic processes, such as O 2 evolution and CO 2 uptake (Genty et al 1989, Flameling & Kromkamp 1998. The relationship between ETR and gross photosynthesis (as oxygen evolution) has been studied in microalgae (see reviews of Flameling & Kromkamp 1998, Gilbert et al 2000, Kromkamp et al 2009, Suggett et al 2009). …”

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

“…These devices present different characteristics according to the quality of actinic lamps (halogen, red or blue light emitted diodes), sensitivity and measuring units (cuvettes versus fiber). On the other hand, measurements of in vivo chlorophyll fluorescence in algal mass cultures in open or closed photobioreactors are still scarce (Vonshack et al, 1994;Torzillo et al, 1996;Masojídek et al, 1999Masojídek et al, , 2011Kromkamp et al, 2009).…”

Monitoring of Microalgal Processes

“…This is substantially lower than the intensity of direct sunlight (full sun plus sky), which yields up to 2000 µE/m 2 /s [55]. PAR constitutes energetically (in W/m 2 ) about 40 % of the visible sunlight [56].…”

“…The standard method for estimating the biomass concentration online is measurement of the optical density (OD) of the microalgal suspension at various wavelengths and calculating the biomass concentration through calibration by offline dry weight determination or microscopic cell counts [48,55,[101][102][103]. The selection of measurement wavelength is important because the absorption of light by pigments and organelles can significantly affect the measured extinction [104], and accurate biomass concentration estimation requires that extinction should reflect only light scattering and not absorption [17].…”