The physiological response of seven strains of picophytoplankton to light, and its representation in a dynamic photosynthesis model

Abstract

Picophytoplankton dominate the phytoplankton community in wide ocean areas and are considered efficient in the acquisition of light compared to other phytoplankton groups. To quantify their photophysiological parameters we use three strains of picoprokaryotes and four strains of picoeukaryotes. We measure the acclimated response of the exponential growth rates and chlorophyll a (Chl a) to carbon ratios, as well as the instantaneous response of photosynthesis rates at 5-7 light intensities. We then use a dynamic photosynthesis model (Geider et al. 1997) and extend it with a photoinhibition term. We derive five photophysiological parameters: the maximum rate of photosynthesis (P C m ), the affinity to light (a chl ), the photoinhibition term (b chl ), the respiration rate (resp), and the maximum Chl a to carbon ratio (h max ). We show that P C m is significantly lower for picoprokaryotes than for picoeukaryotes and increases significantly with increasing cell size. In turn, a chl decreases significantly with increasing maximum growth rate (l max ). The latter finding is contrary to a previously reported relationship for phytoplankton, but agrees with theoretical assumptions based on size. The higher efficiency in light acquisition gives picoprokaryotes an advantage in light limited environments at the expense of their maximum growth rate. In addition, our results indicate that the accumulation of long-term damage through photoinhibition during acclimation is not well represented by the dynamic photosynthesis model. Hence, we would recommend to distinguish between the effects of irreversible damage (on a time scale of days) on growth rates and of reversible damage (on a time scale of minutes) on photosynthesis rates.

Are temperature sensitivities of Prochlorococcus and Synechococcus impacted by nutrient availability in the subtropical northwest Pacific?

“…In comparison, Synechococcus are more plastic in their thermal adaption and have higher optima than Prochlorococcus in the study region. Our results are in line with previous studies on laboratory cultures, demonstrating that the optimal temperatures of many Prochlorococcus strains were lower than the Synechococcus isolated from similar latitudinal ranges (Stawiarski et al 2016). Therefore, without considering other factors, we speculate that the projected rising temperature might have a stronger and more deleterious effect on Prochlorococcus but be more favorable to Synechococcus in the subtropical waters.…”

“…Thus, the across-population E a estimated from meta-analysis was lower than the emergent E a estimated from the short-term experiments. The high emergent E a values were consistent with the estimates for many Prochlorococcus and Synechococcus strains in laboratory experiments (Stawiarski et al 2016;Chen and Laws 2017;Barton and Yvon-Durocher 2019). Moreover, the high E a could also arise from stress reactions of Prochlorococcus and Synechococcus to the abrupt temperature changes in such temperature manipulated experiments at short-term scales, which could be alleviated by acclimation and long-term adaptation.…”

“…The phytoplankton communities in the oligotrophic subtropical northwest Pacific are dominated by the marine cyanobacteria Prochlorococcus and Synechococcus (Endo and Suzuki 2019) which are the most abundant phytoplankton and the major contributors to primary productivity in the oligotrophic ocean (Buitenhuis et al 2012). Their temperature sensitivities have recently been explored in laboratory and field studies (Johnson et al 2006;Chen et al 2014;Stawiarski et al 2016), yet few studies evaluated their thermal response under the influence of nutrient availability. We conducted short-term temperature manipulated dilution experiments to estimate the temperature sensitivity of Prochlorococcus and Synechococcus growth rates under two nutrient scenarios.…”

Quantifying photosynthetic performance of phytoplankton based on photosynthesis–irradiance response models

“…To describe the entire range of light levels of phytoplankton, Platt et al [20,21] proposed another empirical model with a photoinhibition function (model 2 in this study). Superficially, the P n -I curves fitted by model 2 seem to be perfect as other studies [42,43], but the value of P s among the fitted results was notably higher than the value of P nmax in seven phytoplankton species, specially, for I. galbana, M. aeruginosa and S. obliquus when β > 0 (Table 4). To calculate P nmax , Eq.…”

“…However, the Kok effect was widespread observed in phytoplankton [33]. Currently, most researchers ignore these problems when they use model 2 to investigate and fit the P n -I curves of phytoplankton [1,[43][44][45]. Therefore, model 2 may be treated carefully in explaining biological implication of P s and estimating photosynthetic parameters.…”