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Effects of light intensity on the photosynthetic responses of Sargassum fusiforme seedlings to future CO2 rising

Chen, Binbin, Zou, Dinghui, Ma, Zengling, Yu, Ping, Wu, Mingjiang
Aquaculture research 2019 v.50 no.1 pp. 116-125
Sargassum fusiforme, absorption, acclimation, biomass production, carbohydrates, carbon dioxide, carbon dioxide enrichment, dissolved inorganic carbon, energy, light intensity, macroalgae, mariculture, ocean acidification, photosynthetic electron transport, seawater, seedlings
Mariculture of the economically important seaweed will likely be affected by the combined conditions of ocean acidification that resulting from increasing CO₂ rising and decreased light levels, especially under high culture intensity and high biomass accumulation. To examine this coupling effect on the photosynthetic performance of Sargassum fusiforme seedlings, we cultured seedlings of this alga under different light and CO₂ levels. Under low light conditions, elevated CO₂ significantly decreased the photosynthesis of S. fusiforme seedlings, including a decreased photosynthetic electron transport rate. Seedlings grown under the low light intensity exhibited higher photosynthetic rates and compensation irradiance, and displayed higher photosynthetic pigment contents and light absorption than seedlings grown under high light intensity, providing strong evidence of photosynthetic acclimation to low light. However, the captured light and energy were insufficient to support photosynthesis in acidified seawater regardless of increased dissolved inorganic carbon, resulting in declined carbohydrate and biomass accumulation. This indicated that S. fusiforme photosynthesis was more sensitive to acidified seawater in its early growth stage, and strongly affected by light intensity. Future research should evaluate the practical manipulation of biomass accumulation and mariculture densities during the early culture period at the CO₂ level predicted for the end of the century.