Continuous photoperiod of the Artic summer stimulates the photosynthetic response of some marine macrophytes

Abstract

Subarctic macrophytes are predicted to expand in the Arctic as a result of on-going global climate change. This will expose them to 24 hours of light during the Arctic summer while pCO2 levels are predicted to rise globally. Here, we tested the photosynthetic activity of two brown macroalgae (Ascophyllum nodosum, Fucus vesiculosus) and one seagrass (Zostera marina) from subarctic Greenland, measuring their relative maximum electron transport rate (rETRmax), photosynthetic efficiency (a) and saturating irradiance (Ik) after 3 days of incubation at different photoperiods (12:12h, 15:09h, 18:06h, 21:03h and 24:00h, light:dark) with ambient values of pCO2 (200 ppm, characteristic of current subarctic surface waters) and increased pCO2 (400 and 1000 ppm). The photosynthetic parameters rETRmax and Ik increased significantly with longer photoperiods and increased, however insignificantly, with increased pCO2. Responses differed between species. A. nodosum and Z. marina showed the highest increase of rETRmax and Ik from 12 h to 24 h while the increase of F. vesiculosus was smaller. Our results suggest that as subarctic macrophytes expand in the Arctic in response to retracting sea ice, the long summer days will stimulate the productivity of the species tested here, while the effect of high-CO2 environment needs further research. Highlights• Long photoperiods increase the photosynthetic activity of certain subarctic macrophytes • Increased CO2 had no effect on tested macrophytes • Highest increases of photosynthetic activity of Ascophyllum nodosum and Zostera marina at long day lengths; smaller increase for Fucus vesiculosus • Subarctic macrophytes, expanding as sea ice retreats, will benefit from long summer days Keywords Macrophytes; subarctic; electron transport rate; continuous photoperiod and carbon dioxide. IntroductionThe presence of macroalgae assemblages in the Arctic is often limited by extended sea-ice cover that reduces submarine light penetration (Krause-Jensen et al., 2012;Krause-Jensen and Duarte, 2014;Wulff et al., 2009). However, an Arctic largely free of sea ice in summer, as predicted by the year 2037 (IPCC Panel, 2014;Wang and Overland, 2009), may favour the entrance of new species into the Arctic and the expansion of existing Arctic vegetation (Krause-Jensen and Duarte, 2014). Indeed, the northward extension range of macroalgae, mainly Phaeophyta, but also Chlorophyta and Rhodophyta has been observed around 78 ºN in Svalbard (Fredriksen et al., 2014). An increase of macrophyte biomass has also been detected together with the upward movement of sublittoral algal species to the littoral zone and a biodiversity increase in this Arctic region, likely related to climate warming (Weslawski et al., 2010). Arctic warming has already led to the reappearance of the blue mussel, Mytilus edulis, in Svalbard after 1,000 year absence (Berge et al., 2005) as well as an increase of the Arctic cod fishery due to the poleward expansion of cod habitat (Kjesbu et al., 2014). At a global scale, 75 % of the range shifts st...

Mutual impacts and interactions of antibiotic resistance genes, microcystin synthetase genes, graphene oxide, and Microcystis aeruginosa in synthetic wastewater

“…From another perspective, the higher the Fv/Fm and ETRmax values would indicate the less stressed conditions in growth environment of M. aeruginosa. The lower the Fv/Fm and ETRmax values would indicate the more stressed conditions in growth environment and the worse photosynthetic performance (Sanz-Martín et al 2019). Photosynthetic performance, the growth rate in M. aeruginosa increased under 0.01 mg/L GO-exposure and decreased under 10 mg/L GO-exposure (Fig.…”

Productivity of Mixed Kelp Communities in an Arctic Fjord Exhibit Tolerance to a Future Climate

“…One potential factor thought to potentially support macrophyte expansion in the Arctic are long photoperiods (Sanz-Martín et al, 2019). The daily production determined from this study found that despite the potential for nearly day-long saturating irradiance (~ 1.5 mol photons m − 2 d − 1 derived from the model in this study), the mixed kelp assemblages maintained a natural biorhythm, or at least a decrease in production as the day evolved.…”

Mutual Impacts and Interactions of Antibiotic Resistance Genes, Microcystin Synthetase Genes, Graphene Oxide, and Microcystis Aeruginosa in Synthetic Wastewater

“…From another perspective, the higher the Fv/Fm and ETRmax values would indicate the less stressed conditions in growth environment of M. aeruginosa. The lower the Fv/Fm and ETRmax values would indicate the more stressed conditions in growth environment and the worse photosynthetic performance (Sanz-Martín et al 2019). Photosynthetic performance, the growth rate in M. aeruginosa increased under 0.01 mg/L GO-exposure and decreased under mg/L GO-exposure (Fig.…”