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. 2023 Aug 22;99(9):fiad088.
doi: 10.1093/femsec/fiad088.

Adaptation versus plastic responses to temperature, light, and nitrate availability in cultured snow algal strains

Emily L M Broadwell  1 , Rachel E Pickford  1 , Rupert G Perkins  2 , Fotis Sgouridis  1 , Christopher J Williamson  1
Affiliations

Adaptation versus plastic responses to temperature, light, and nitrate availability in cultured snow algal strains

Emily L M Broadwell et al. FEMS Microbiol Ecol. .

Abstract

Snow algal blooms are widespread, dominating low temperature, high light, and oligotrophic melting snowpacks. Here, we assessed the photophysiological and cellular stoichiometric responses of snow algal genera Chloromonas spp. and Microglena spp. in their vegetative life stage isolated from the Arctic and Antarctic to gradients in temperature (5 - 15°C), nitrate availability (1 - 10 µmol L-1), and light (50 and 500 µmol photons m-2 s-1). When grown under gradients in temperature, measured snow algal strains displayed Fv/Fm values increased by ∼115% and electron transport rates decreased by ∼50% at 5°C compared to 10 and 15°C, demonstrating how low temperatures can mimic high light impacts to photophysiology. When using carrying capacity as opposed to growth rate as a metric for determining the temperature optima, these snow algal strains can be defined as psychrophilic, with carrying capacities ∼90% higher at 5°C than warmer temperatures. All strains approached Redfield C:N stoichiometry when cultured under nutrient replete conditions regardless of temperature (5.7 ± 0.4 across all strains), whereas significant increases in C:N were apparent when strains were cultured under nitrate concentrations that reflected in situ conditions (17.8 ± 5.9). Intra-specific responses in photophysiology were apparent under high light with Chloromonas spp. more capable of acclimating to higher light intensities. These findings suggest that in situ conditions are not optimal for the studied snow algal strains, but they are able to dynamically adjust both their photochemistry and stoichiometry to acclimate to these conditions.

Keywords: photophysiology; psychrophile; snow algae; stoichiometry.

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Conflict of interest statement

None declared.

Figures

Figure 1.
Figure 1.
Growth parameters for the temperature incubations. All panels show mean ± SE, N = 4. Lower case letters indicate homogenous subsets determined through a two-way ANOVA analysis of respective parameters in relation to temperature and strain. Upper case letters indicate homogenous subsets determined through one-way ANOVA analysis in relation to strain only. (A) Biomass carrying capacity — K (lc: F6,35 = 1.77, UC: F3,35 = 13.45, P < .05). (B) Cell count carrying capacity — K (lc: F6,36 = 3.87, UC: F3,36 = 13.52, both P < .05). (C) Biomass specific growth rate during exponential phase — µ (lc: F6,36 = 0.90, UC: F3,36 = 0.16). (D) Cell count specific growth rate during exponential phase — µ (lc: F6,36 = 0.69, UC: F3,36 = 0.79).
Figure 2.
Figure 2.
Photophysiology and stoichiometry parameters for the exponential phase of the temperature incubations. All panels show mean ± SE, N = 4. Lower case letters indicate homogenous subsets determined through a two-way ANOVA analysis of respective parameters in relation to temperature and strain. Upper case letters indicate homogenous subsets determined through one-way ANOVA analysis in relation to strain only. (A) Proxy for algal stress — Fv/Fm (lc: F6,36 = 9.14, UC: F3,36 = 4.56, P < .05). (B) Electron transport rate — rETR max (lc: F6,34 = 5.89, P < .05, UC: F3,34 = 2). (C) Efficiency of light use — alpha (lc: F6,34 = 1.69, UC: F3,34 = 3.91, P < .05). (D) Light saturation coefficient — Ek (lc: F6,34 = 1.93, UC: F3,34 = 3.91, P < .05). (E) NPQ at Ek (lc: F6,33 = 3.40, UC: F3,33 = 5.15, both P < .05). (F) Cellular C:N ratio (lc: F6,36 = 0.87, UC: F3,36 = 0.84).
Figure 3.
Figure 3.
Growth parameters for the nitrate and light incubations. All panels show mean ± SE, N = 4. Lower case letters indicate homogenous subsets determined through a two-way ANOVA analysis of respective parameters in relation to strain and nitrate within light treatments. Upper case letters indicate homogenous subsets determined through a three-way ANOVA analysis in relation nitrate, light, and strain. (A) Biomass carrying capacity — K (lowercase: low light: F6,35 = 2.43; high light: F6,29 = 2.21; both P < .05), (uppercase: F3,64 = 27.23, P < .05). (B) Cell count carrying capacity — K (lowercase: low light: F6,36 = 3.17; P < .05; high light: F6,32 = 0.52), (uppercase: F3,68 = 11.53, P < .05). (C) Biomass specific growth rate during exponential phase — µ (lowercase: low light: F6,35 = 1.33; high light: F6,35 = 2.56; P < .05), (uppercase: F3,70 = 7.04, P < .05). (D) Cell count specific growth rate during exponential phase — µ (lowercase: low light: F6,36 = 3.46; high light: F6,35 = 3.62; both P < .05), (uppercase: F3,71 = 3.71, P < .05).
Figure 4.
Figure 4.
Photophysiology and stoichiometry parameters for the exponential phase of the nitrate and light incubations. All panels show mean ± SE, N = 12. Lower case letters indicate homogenous subsets determined through a two-way ANOVA analysis of respective parameters in relation to light intensity and strain. (A) Proxy for algal stress — Fv/Fm (F3,87 = 41.51, P < .05). (B) Electron transport rate — rETR max (F3,86 = 10.09, P < .05). (C) Efficiency of light use — alpha (F3,87 = 17.16, P < .05). (D) Light saturation coefficient — Ek (F3,86 = 0.86). (E) NPQ at Ek (F3,78 = 0.43). (F) Cellular C:N ratio (F3,88 = 9.15, P < .05).
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