The daily integral of growth by Planktothrix rubescens calculated from growth rate in culture and irradiance in Lake Zürich

Abstract

In Lake Zu$ rich, populations of the cyanobacterium Planktothrix rubescens develop in the metalimnion during the summer and become gradually entrained in the deepening surface mixed layer during the autumn. It had previously been demonstrated that the daily integrals of photosynthetic production accounted for the growth observed in the metalimnion and greatly exceeded the smaller increase during the autumn. We have now determined the relationship between growth rate (µ) and irradiance (I ) in cultures of P. rubescens strain Pla 9316 maintained at 20mC on a 12 : 12 h light : dark cycle : the highest net growth rate averaged over the 24 h (µ h ) was 0.123 d −" , the dark rate (µ D ) was k0.020 d −" , the gross rate (φ m l µ h kµ D ) was 0.144 d −" , the affinity coefficient (α) was 0.0273 (d µmol m −# s −" ) −" and the compensation point (I C ) was 1.76 µmol m −# s −" . Using the corresponding coefficients calculated for the light period (µ Lh l 0.267 d −" , φ Lm l 0.287 d −" and α L l 0.0547 (d µmol m −# s −" ) −" ), instantaneous growth rates could be calculated from the irradiance. Comparison with growth rates at 10mC indicated a Q "! of 1.48. These coefficients were used in a modification of the Smith equation to calculate potential growth rates of Planktothrix from the irradiance and temperature at each time and depth in Lake Zu$ rich. Data on irradiance, vertical light attenuation and temperature were used to calculate the daily integrals of biomass increase over a period of 136 d. These growth integrals gave a closer correspondence to the observed population increase than the photosynthetic integrals calculated previously from measurements made with lakewater samples dominated by Planktothrix. Photosynthetic measurements made with the Planktothrix culture indicated a maximum rate of carbon increase (0.467 d −" ) that exceeds the maximum growth rate, which suggests that other factors limit growth over long periods.

Initial growth phases of two bloom-forming cyanobacteria (Cylindrospermopsis raciborskiiandPlanktothrix agardhii) in monocultures and mixed cultures depending on light and nutrient conditions

“…The highest differences of growth rate (m max ) between P. agardhii and C. raciborski in monocultures, concerned the low light intensity (P < 0.01) and starvation and/or low nutrient concentration (P< 0.001). With regard to light intensity, P. agardhii had a higher m max (0.65 d x1 ) at low light than at 75 mmol photons m x2 .s x1 , which corroborated previous studies (Davis and Walsby, 2002;Oberhaus et al, 2007), and highlighted the high affinity of this species for low irradiance (Mur and Beydorff, 1978;Bright and Walsby, 2000). Consequently, P. agardhii grew faster and outcompeted C. raciborskii with regard to biomass (IVF and biovolumes), especially at day 6 in our study, which are consistent with Bonilla et al (2012) findings, who reported that P. agardhii had a higher capacity for growth than C. raciborskii under low light intensity.…”

Modelling the plankton groups of the deep, peri-alpine Lake Bourget

“…Average surface concentrations of DIP and TP can considered to be very good (r>0.85, Fig.8). The measured DIP concentrations during summer tend to be somewhat higher than the simulations, which might be, to some extent, due to the river uxes that not by internal waves or upwelling events that occur frequently in Lake Bourget (Cuypers et al, 2011), given their low growth rates (Bright and Walsby, 2000) and limited losses imposed by zooplankton (Kurmayer and Jüttner, 1999). On the other hand, their growth at 10-20 m depth (Fig.…”

“…P. rubescens was assigned as a separate algal group because of its distinctive eco-physiology characterized by low-light tolerance (Walsby and Schanz, 2002), slow growth (Bright and Walsby, 2000), and grazing defense (Kurmayer and Jüttner, 1999) as well as the fact that it represented about half of the phytoplankton assemblage in some years ( Fig. 1,3).…”

“…µ∞ Given the average volumes and the taxa of the species involved in these groups (3), rst the µmax values were visually determined from Edwards et al (2012), Fig3C, to be 10 0.1 (=1.1), 10 −0.1 (=0.9) and 10 −0.25 (=0.55) respectively for As, A l , and M (for the reference temperature: 20°C). Maximum growth rates for Apr was determined to be 0.35, considering relatively low growth rates (Bright and Walsby, 2000). Then, µ∞ values were calculated using these µmax, allometrically calculated Qmin and Qmax, and the property µmax = µ∞(1 − Qmin/Qmax).…”

“…Analysis of the longterm changes in individual lakes and inter-comparison between lakes suggest that phosphorus (and nitrogen, see Posch et al, 2012) availability is the primary determinant (Dokulil and Teubner, 2012;Jacquet et al, 2014b;Anneville et al, 2015). P. rubescens is characterized by their slow growth rates (Bright and Walsby, 2000) and tolerance to low light conditions (Walsby and Schanz, 2002). As a result of the latter, it often develops thin and intense layers within the metalimnion during the growing season (eg., Jacquet et al, 2014b), where they are the rst to harvest the nutrients leaking from the nutrient-rich layers beneath the thermocline.…”