Combined effects of carbon and phosphorus levels on the invasive cyanobacterium, Cylindrospermopsis raciborskii

Abstract

The invasive cyanobacterium, Cylindrospermopsis raciborskii, was cultured semicontinuously for 18 days at different carbon and phosphorus levels. Growth and photosynthesis were measured to study the combined effects of CO 2 and phosphorus availabilities. The results showed that enrichment of CO 2 or inorganic phosphorus (Pi) levels in the culture medium significantly increased specific growth rate (m), light-saturated photosynthesis (P m ) and photosynthetic efficiency (a), but tended to decrease dark respiratory rate (R d ), saturating irradiance for photosynthesis (E k ) and the light compensation point (E c ). However, photosynthetic responses to inorganic carbon concentration in C. raciborskii were affected by interactions between CO 2 and Pi. At high Pi concentration, elevated CO 2 significantly increased the inorganic carbon-saturated photosynthesis rate (V max ) and substrate concentration giving half-maximal photosynthetic rate [K 0.5 (DIC)], whereas at low Pi levels, elevated CO 2 slightly decreased the values of V max and K 0.5 (DIC). Additionally, enrichment with Pi significantly increased K 0.5 (DIC) and V max regardless of the CO 2 level, suggesting that Pi plays a role in photosynthetic carbon fixation in C. raciborskii. Furthermore, when C. raciborskii was batch cultured in different carbon and phosphorus concentrations for 72 h, the uptake rate of nitrogen increased with enrichment of both CO 2 and Pi, while the uptake rate of phosphorus was enhanced only by increases in Pi concentration. The results suggest that the availability of CO 2 and phosphorus have combined and independent effects on photosynthesis and nutrient uptake in C. raciborskii, reflecting that changes in environmental factors could influence the dominance of this invasive cyanobacterium. These combined effects need to be considered when generalizing this species response to changing CO 2 levels.

Dryland biological soil crust cyanobacteria show unexpected decreases in abundance under long‐term elevated CO2

“…A growing number of species reportedly do not grow more rapidly nor achieve higher cell densities in culture when CO2 concentrations are above ambient Czerny et al, 2009). Explanations range from CO2 saturation surrounding the carboxysome (even when environmental CO2 concentrations are low) via CO2concentrating mechanisms that are nearly ubiquitous among cyanobacteria, to growth limitations imposed by other nutrients or environmental factors (Beardall et al, 2009a;Czerny et al, 2009;Wu et al, 2012). Both of these mechanisms are pertinent to biocrusts in natural settings.…”

Photo-acclimation to low light—Changes from growth to antenna size in the cyanobacterium Cylindrospermopsis raciborskii

“…For instance, the parameter E k , which indicates the onset of light saturated photosynthesis, has been measured to occur between 40 and 240 mmol photons (PAR) m À2 s À1 among different C. raciborskii strains and experimental conditions (Wu et al, 2009(Wu et al, , 2012Pierangelini et al, 2014b,c). Analysis of the photosynthetic apparatus also showed that an Australian strain of C. raciborskii (CS506) can potentially tolerate up to 425 mmol photons (PAR) m À2 s À1 (Pierangelini et al, 2014c) and Chinese strains between 900 and 1200 mmol photons (PAR) m À2 s À1 (Wu et al, 2009(Wu et al, , 2012Bai et al, 2014).…”

Strong effects of elevated CO2 on freshwater microalgae and ecosystem chemistry

“…Microalgal growth response included stimulations to bloom‐forming species when consumers were excluded (Fig. S6), with observed increases in biomass, cell abundance, population densities, and chlorophyll a in bloom‐forming Microcystis aeruginosa (Qiu and Gao ; Sandrini et al , b ), and increases in cell division rate, biovolume, growth rate, and chlorophyll a in bloom‐forming Cylindrospermopsis raciborskii under elevated CO 2 conditions (Wu et al ; Pierangelini et al ). Elevated CO 2 may thus worsen the impacts of algal blooms, although it is difficult to extend the results from the lab to the field.…”