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Effects of CO2 supply on growth and photosynthetic ability of young sporophytes of the economic seaweed Sargassum fusiforme (Sargassaceae, Phaeophyta)

Jiang, Heng, Zou, Dinghui, Lou, Wenyong, Gong, Jingyu
Journal of applied phycology 2019 v.31 no.1 pp. 615-624
Sargassum fusiforme, carbon dioxide, climate change, commercial farms, macroalgae, pH, photons, photosynthetic electron transport, photosystem II, seawater, sporophytes, temperature
Young sporophytes of Sargassum fusiforme were cultured at decreased CO₂ (20 μatm), ambient CO₂ (400 μatm), and high CO₂ (1000 μatm), and then the quantum efficiency of open photosystem II (Fᵥ′/Fₘ′), initial slope of the rapid light curves (α), and relative maximum photosynthetic electron transport rate (rETRₘ) of the algae under different temperatures and light levels were measured. The study aimed to investigate how the decreased CO₂ and high CO₂ supply affected the growth and photosynthetic functions of S. fusiforme young sporophytes. While both lowered and increased CO₂ supply significantly reduced the growth rates of the alga, greater declines were observed under decreased CO₂. The Fᵥ′/Fₘ′, α, and rETRₘ of alga remained stable after short-term (120 min) exposures to 18, 22, and 26 °C, as well as to highlight (300 μmol photons m⁻² s⁻¹), with no significant difference among the three CO₂ supply treatments. Hence, neither decreased nor increased CO₂ affected the photosynthetic responses of S. fusiforme young sporophytes to temperature and high light. However, the Fᵥ′/Fₘ′ of the three CO₂ treatments declined by 72% under 60 μmol photons m⁻² s⁻¹, suggesting its sensitivity to short-term low light. These observations are crucial for the improved management of S. fusiforme for commercial farming, while ensuring its sustainable production and supply amid seawater pH shifts brought about by global climate change.