Diurnal dynamics of CO₂ gas exchange in coastal photoautotrophs Honckenya peploides and Fucus vesiculosus of the Barents Sea

The ongoing climate changes heighten the interest in studying the patterns of carbon-containing gas exchange between the atmosphere and the underlying surface at various scale levels. Using two photoautotrophic species, Fucus vesiculosus and Honckenya peploides, which differ markedly in taxonomic position, morpho-functional organization, and habitat conditions, CO₂ gas exchange parameters have been examined in the coastal zone of Zelenetskaya Bay in the Barents Sea. The macroalga inhabits the littoral zone and photosynthesizes across the entire surface of its thallus, whereas the vascular plant occurs in the supralittoral zone and absorbs atmospheric CO₂ via the stomatal apparatus. The study was conducted using the chamber method in two configurations: transparent chambers were used to measure net ecosystem exchange (NEE), while dark chambers were used to measure ecosystem respiration (R_eco). Gross primary production (GEE) was calculated indirectly. The mean daily flux values (mg C m⁻² h⁻¹) differed between H. peploides and F. vesiculosus. NEE was −44.84 and −20.34, and R_eco was 19.59 and 33.05. No significant differences were observed in GEE. The amplitude of the NEE, Reco, and GEE oscillations of the photoautotrophs during the day was significant and reflected diurnal changes in environmental conditions and the physiological reactions of the organisms themselves. Relationships between CO₂ gas exchange parameters and environmental factors were identified. The primary factors influencing carbon dioxide fluxes were light intensity and temperature, while the tidal cycle additionally affected the gas exchange parameters of the macroalga.

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