Growth, Chl a content, photosynthesis, and elemental composition in polar and temperate microalgae

Abstract

Polar microalgae live under extreme environmental conditions: permanently low temperatures (−1.7°C to +5°C) and extreme variations in irradiance and day length. These conditions may have led to various specific adaptations allowing Arctic phytoplankton to become specialists under these conditions. The goal of this study is to derive, for polar microalgae, empirical relationships between key physiological parameters (growth rate, photosynthesis–irradiance curve parameters, Chl a : C, and N : C ratios) and growth temperature and irradiance in nutrient replete cultures. Ecophysiological characteristics of polar and temperate microalgae were also compared in order to highlight some strategies that are specific to the polar environment. Most of the polar species are psychrophilic. Polar microalgae have low light‐saturated growth rates (μm) and very low light saturation parameters for growth (KE) but similar initial slopes of their growth–irradiance curve (αµ = μm/KE). Low temperatures probably account for low μm and KE in polar species. The C : Chl a ratios (θ) of polar species are similar to those of temperate species although they have much lower growth rates, which implies major differences in energy allocation. Polar microalgae also exhibit very unique photosynthetic properties [low light saturation parameters for photosynthesis (EK), low maximum photosynthetic rates ( PmC), decreasing PmC and decreasing initial slope of the photosynthesis vs. irradiance curve (α*) with increasing irradiance] and have lower C : N ratios than their temperate cousins, which may be related to a much higher protein content. Some of the implications of these findings in terms of adaptation/acclimation to the environment in which polar species evolve are discussed.

Increased temperature benefits growth and photosynthetic performance of the sea ice diatom Nitzschia cf. neglecta (Bacillariophyceae) isolated from saroma lagoon, Hokkaido, Japan

“…Indeed, the fastest specific growth rate of around 0.65 was found in cells grown in HL at 10°C, and was higher than that previously reported for sea ice diatom communities in situ, as well as the reported maximum growth rates under optimal temperatures (Lacour et al 2017). However, although growth rates were comparable to those of temperate diatom species grown at similar temperatures, they were still much lower than the maximum growth rates of those temperate species (McMinn et al 2005, Coello-Camba et al 2015, Lacour et al 2017. Considering that the water temperature of Saroma Lagoon may rise up to around 20°C in summer, this result suggests that despite being isolated from an ice core, the species we used here can tolerate a wide range of temperatures and can continue its growth throughout the year.…”

“…Indeed, the fastest specific growth rate of around 0.65 was found in cells grown in HL at 10°C, and was higher than that previously reported for sea ice diatom communities in situ, as well as the reported maximum growth rates under optimal temperatures (Lacour et al. ). However, although growth rates were comparable to those of temperate diatom species grown at similar temperatures, they were still much lower than the maximum growth rates of those temperate species (McMinn et al.…”

“…, Lacour et al. ). Considering that the water temperature of Saroma Lagoon may rise up to around 20°C in summer, this result suggests that despite being isolated from an ice core, the species we used here can tolerate a wide range of temperatures and can continue its growth throughout the year.…”

Increased intrusion of warming Atlantic water leads to rapid expansion of temperate phytoplankton in the Arctic

“…Indeed, maximum growth rates in the 2−5°C temperature range are on the order of 0.1 per day and then jump to 0.5 per day at 6°C, beyond which growth rates increases as a power function of temperature (Fielding, ). Polar diatoms and other cold‐water adapted phytoplankton have typical growth rates above 0.5 per day in the −1 to 5°C range, thus outcompeting E. huxleyi in cold waters (Lacour, Larivière, & Babin, ). Compared to bottom‐up processes, top‐down control of E. huxleyi blooms is thought to be of limited importance as it has been shown that calcification is an effective strategy to reduce grazer growth by creating indigestion or prolonging digestion time, resulting in net growth of E. huxleyi (Harvey, Bidle, & Johnson, ; Kolb & Strom, ; Monteiro et al., ).…”

Growth and Elemental Stoichiometry of the Ecologically-Relevant Arctic Diatom Chaetoceros gelidus: A Mix of Polar and Temperate

“…While previous studies focused solely on the effects of light intensity or temperature on Arctic diatom species (see references in Lacour et al, 2017), a comprehensive understanding of how phytoplankton will respond to changes in the generally strongly N-limited waters of the Arctic can be gained by considering N form as an additional variable. To our knowledge, this study provides the first investigation of the physiological and compositional response of a widespread diatom that qualifies as a long-term resident of the Arctic and a likely survivor of future change.…”