Effects of light intensity on the photosynthetic responses ofSargassum fusiformeseedlings to future CO₂rising

Abstract

Mariculture of the economically important seaweed will likely be affected by the combined conditions of ocean acidification that resulting from increasing CO 2 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 CO 2 levels. Under low light conditions, elevated CO 2 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 CO 2 level predicted for the end of the century. K E Y W O R D Sclimate change, light, mariculture, ocean acidification, photosynthesis, Sargassum fusiforme

Quantifying photosynthetic performance of phytoplankton based on photosynthesis–irradiance response models

“…Although classical P-I models have been widely used to fit the P n -I curve for estimating photosynthetic performance and responses to environment changes for phytoplankton [18][19][20][21][22], many of them were not built based on the photosynthetic mechanism. The exponential model established by Webb et al [18] and model 1 are still applied extensively for phytoplankton [37][38][39][40][41] even though they lack photoinhibition function. For example, Ma et al [40] indicated that the P nmax calculated by model 1 for M. aeruginosa FACHB-905 and M. aeruginosa FACHB-469 were 253.92 ± 6.79 and 231.32 ± 6.40 μmol O 2 mg −1 Chl a h −1 , respectively, at 25 °C, yet the corresponding I sat were only 92.71 ± 7.86 and 88.61 ± 3.22 μmol photons m −2 s −1 , respectively.…”

Differences of photosynthesis and nutrient utilization in Sargassum fusiforme and its main epiphyte, Ulva lactuca

“…lactuca ) have higher and faster photosynthetic oxygen release rates while the same weight of thick algae (such as S . fusiforme ) show the opposite trend (Chen, Lin, et al, 2019; Chen et al, 2015; Chen, Zou, et al, 2019; Xu et al, 2022). However, when they have the same surface area, thick algae have the higher and faster photosynthetic oxygen release rates (Johansson & Snoeijs, 2002).…”

“…The photosynthesis of S. fusiforme is affected by many factors in its growth environment, including temperature, salinity, CO 2 concentration, light intensity, heavy metals, other abiotic factors and harmful organisms such as red tide microalgae (Chen, Zou, et al, 2019; Hong et al, 2021; Jiang et al, 2019; Li et al, 2019; Shang et al, 2020; Zhang et al, 2020). Furthermore, the internal biological factors of seaweeds, including their morphology, ontogeny and circadian rhythm also affect photosynthesis (Hurd et al, 2014).…”

The effects of desiccation and salinity gradients on the PSII photochemical efficiency of an intertidal brown alga, Sargassum fusiforme from Kagoshima, Japan

“…2006, 2011, 2012; Chen et al . 2019). For instance, a pioneering study by Yokohama (1973) on the manometric measurement of photosynthesis of this species revealed that the optimum temperature for photosynthesis was higher in summer samples than in winter samples, suggesting the possibility of long‐term acclimation to environmental temperature or adaptation by the perennial thallus (e.g.…”