Future CO₂-induced seawater acidification mediates the physiological performance of a green alga Ulva linza in different photoperiods

Abstract

Photoperiods have an important impact on macroalgae living in the intertidal zone. Ocean acidification also influences the physiology of macroalgae. However, little is known about the interaction between ocean acidification and photoperiod on macroalgae. In this study, a green alga Ulva linza was cultured under three different photoperiods (L: D = 8:16, 12:12, 16:8) and two different CO2 levels (LC, 400 ppm; HC, 1,000 ppm) to investigate their responses. The results showed that relative growth rate of U. linza increased with extended light periods under LC but decreased at HC when exposed to the longest light period of 16 h compared to 12 h. Higher CO2 levels enhanced the relative growth rate at a L: D of 8:16, had no effect at 12:12 but reduced RGR at 16:8. At LC, the L: D of 16:8 significantly stimulated maximum quantum yield (Yield). Higher CO2 levels enhanced Yield at L: D of 12:12 and 8:16, had negative effect at 16:8. Non-photochemical quenching (NPQ) increased with increasing light period. High CO2 levels did not affect respiration rate during shorter light periods but enhanced it at a light period of 16 h. Longer light periods had negative effects on Chl a and Chl b content, and high CO2 level also inhibited the synthesis of these pigments. Our data demonstrate the interactive effects of CO2 and photoperiod on the physiological characteristics of the green tide macroalga Ulva linza and indicate that future ocean acidification may hinder the stimulatory effect of long light periods on growth of Ulva species.

Physiological responses of <i>Skeletonema</i> <i>costatum</i> to the interactions of seawater acidification and combination of photoperiod and temperature

“…neutral effects of higher pCO2 were observed. However, different patterns were reported for other species, such as E. huxleyi and the macroalgae Ulva linza (Bretherton et al, 2019;Yue et al, 2019). For these two species, reduced growth rate at elevated pCO2 were found when the daylength was longest.…”

“…For these two species, reduced growth rate at elevated pCO2 were found when the daylength was longest. High temperature might accelerate nutrient uptake and metabolic rates, which may alleviate the negative effects of longer daylength under higher pCO2 environment (Bretherton et al, 2019;Yue et al, 2019). Maximum photosynthetic rate increased significantly under higher pCO2 in spring condition.…”

“…Cells were filtered and resuspended in 2 ml of extracting medium (50 mM Tris-HCl, pH 7.6, 5.0 mM MgCl2, 10 mM NaCl, 0.4 M sucrose, and 0.1 % BSA) according to Ma et al (2019). After cell disruption and centrifugation, supernatant liquid was used to measured chlorophyll concentration according to Arnon (1949): C = D 652 × 1000 ÷ 34.5 × T, where C represents total chlorophyll concentration, D652 represents absorption value in 652 nm, T represents dilution ratio, 1000 and 34.5 are constants.…”

“…For diatoms, a mounting body of studies has pay attention to the effect of interactions of ocean acidification and other environmental factors such as light intensity, UV, temperature, nutrient limitation, salinity or photoperiod (Gao et al, 2012;Yue et al, 2019), and the results showed positive, negative or neutral effects (Xu et al, 2014c;Li et al, 2017). However, few studies combined elevated pCO2 with seasonal changes in seawater physical and chemical characters on marine diatoms.…”

Effects of ocean acidification and eutrophication on the growth and photosynthetic performances of a green tide alga Ulva prolifera

“…Ocean acidification also affected the photosynthetic pigment contents of Ulva spp. The chlorophyll a and chlorophyll b synthesis of U. lactuca and U. linza were inhibited under high CO 2 level and long photoperiods (Olischläger et al, 2013;Yue et al, 2019), and the carotenoid content of U. prolifera was significantly reduced under a high CO 2 level (Sun et al, 2021).…”