Performance of Fast Repetition Rate fluorometry based estimates of primary productivity in coastal waters

Abstract

Capturing the variability of primary productivity in highly dynamic coastal ecosystems remains a major challenge to marine scientists. To test the suitability of Fast Repetition Rate fluorometry (FRRf) for rapid assessment of primary productivity in estuarine and coastal locations, we conducted a series of paired analyses estimating 14 C carbon fixation and primary productivity from electron transport rates with a Fast Repetition Rate fluorometer MkII, from waters on the Australian east coast. Samples were collected from two locations with contrasting optical properties and we compared the relative magnitude of photosynthetic traits, such as the maximum rate of photosynthesis (P max ), light utilization efficiency (α) and minimum saturating irradiance (E K ) estimated using both methods. In the case of FRRf, we applied recent algorithm developments that enabled electron transport rates to be determined free from the need for assumed constants, as in most previous studies. Differences in the concentration and relative proportion of optically active substances at the two locations were evident in the contrasting attenuation of PAR (400 -700 nm), blue (431 nm), green (531 nm) and red (669 nm) wavelengths. FRRF-derived estimates of photosynthetic parameters were positively correlated with independent estimates of 14 C carbon fixation (P max : n = 19, R 2 = 0.66; α : n = 21, R 2 = 0.77; E K : n = 19, R 2 = 0.45; all p < 0.05 ), however primary productivity was frequently underestimated by the FRRf method. Up to 81% of the variation in the relationship between FRRf and 14 C estimates was explained by the presence of picocyanobacteria, chlorophyll-a biomass, and the proportion of photoprotective pigments, that appeared to be linked to turbidity. We discuss the potential importance of cyanobacteria in influencing the underestimations of FRRf productivity and steps to overcome this potential limitation.

Variation of the photosynthetic electron transfer rate and electron requirement for daily net carbon fixation in Ariake Bay, Japan

“…Previous comparison studies between ETR and C-uptake clearly show variability of K C was correlated to that of temperature and/or inorganic nutrients rather than light availability in some biogeographic regions (see Lawrenz et al 2013). Such environmental factors also drive large changes in both phytoplankton community structure and physiological status, both of which can drive variance in K C (Debes et al 2008;Kromkamp et al 2008;Suggett et al 2006bSuggett et al , 2009aRobinson et al 2014).…”

Air exposure of coral is a significant source of dimethylsulfide (DMS) to the atmosphere

“…FRRf inductions (0.2 Hz) parameterised the photosynthetic efficiency ( F q ´/ F m ´, dimensionless), effective absorption cross sectional area (σ´, nm2) and electron turnover time (τ´, μs)31.…”

Impact of nitrogen availability upon the electron requirement for carbon fixation in Australian coastal phytoplankton communities

“…FRRf can probe photosynthetic rates in situ near‐instantaneously enabling deployment on a range of platforms and overcoming data‐resolution constraints inherent with conventional incubation‐based MPP measurements. FRRf quantifies photosynthetic rates as an electron transport rate (ETR) through PSII, and not in units of C‐uptake, thus requiring a conversion factor to derive FRRf‐based estimates of C‐fixation (Kolber and Falkowski, , Moore et al , Lawrenz et al ; Robinson et al ). However, this conversion factor, termed the “electron requirement for carbon fixation,” K C appears highly variable, reflecting dynamic processes which regulate the efficiency with which ETR PSII is ultimately incorporated into fixed, organic C (Suggett et al a ).…”

“…These processes provide sinks for excess electrons and simultaneously build proton motive force ( pmf ), which may be used to drive additional ATP generation or play a regulatory role in the activation of non‐photochemical quenching (NPQ) to protect PSII from photodamage (Kanazawa and Kramer, ; see also Nawrocki et al ). Growing evidence also suggests that K C fundamentally varies as a function of the prevailing taxa (Suggett et al a ; Robinson et al ) in addition to environmental conditions (Lawrenz et al ; Schuback et al ; Zhu et al ).…”