Gross photosynthesis and lake community metabolism during the spring phytoplankton bloom

Abstract

Daily productivity determinations of linear photosynthetic electron transfer and of net and gross inorganic CO 2 uptake were determined in situ throughout a 6-week sampling period of the spring phytoplankton bloom in Esthwaite Water in the English Lake District. Photosynthetic electron transfer rates, expressed as gross O 2 evolution, were determined from fast repetition rate (FRR) fluorometry and discrete laboratory measurements of the photosynthetic unit size. These gross O 2 evolution determinations were also made free from contemporaneous dark-adapted FRR measurements and the need for sample blanks. Net and gross CO 2 uptake was determined from changes in total inorganic carbon calculated from in situ pH measurements. Two phases to the bloom were observed. An initial bloom was dominated by the diatom Asterionella formosa, while a secondary phase was characterized by an increase in flagellates and cyanobacteria. For both phases, daily FRR-based gross O 2 evolution and pH-based gross CO 2 uptake were tightly coupled, suggesting that daily gross O 2 production was driving daily changes in CO 2 assimilation and thus in community metabolism. This is the first investigation to show closely related rates of gross O 2 production and CO 2 uptake measured in situ.

Modeling the irradiance dependency of the quantum efficiency of photosynthesis

“…At each irradiance, six measures of f PSII were averaged into a single composite value. Background fluorescence was determined by measuring sample filtrate (filtered through a Whatman GF/F filter) in the FAST act and subtracted from all fluorescence measurements following Suggett et al (2006).…”

Interpretation of fast repetition rate (FRR) fluorescence: signatures of phytoplankton community structure versus physiological state

“…This maximum PSII photochemical efficiency typically decreases when autotrophs experience 'stressful' growth conditions, such as nutrient starvation or excessive light (Kolber et al 1988, Geider et al 1993b. It is this concept that has led to use of chlorophyll a fluorescence measurements for ascertaining the photosynthetic 'condition' of entire phytoplankton communities across large temporal (Suggett et al 2006a) and spatial (Behrenfeld et al 1996, Suzuki et al 2002, Moore et al 2005,b, Suggett et al 2006b) scales approaching those of oceanic ecosystems (Behrenfeld & Kolber 1999, Behrenfeld et al 2006). …”

Diurnal variation in the coupling of photosynthetic electron transport and carbon fixation in iron-limited phytoplankton in the NE subarctic Pacific

“…Our results show that the conversion factor K c /n PSII , derived for in situ irradiances at 5 m depth, varied significantly (by a factor of 3.4) over the diurnal cycle, with most of the variability attributable to changes in K c . Unless both carbon fixation and ETR RCII are measured and integrated over a whole diurnal cycle (e.g., Suggett et al, 2006), diurnal variability in K c /n PSII should thus be considered, along with phytoplankton taxonomy and nutrient status (Lawrenz et al, 2013), when deriving regional conversion factors between ETR RCII and carbon fixation. Building on previously published results (Schuback et al, 2015), we show that the magnitude and variability of K c /n PSII can be correlated to FRRF-based measurements of nonphotochemical quenching (NPQ NSV ).…”