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<p>Despite extensive knowledge of light-dependent growth in the green tide alga <i>Ulva prolifera</i>, the metabolic basis of its dark-period productivity and environmental adaptive significance in variable coastal habitats remain largely unexplored. This study investigated the dark-period metabolic plasticity of <i>U. prolifera</i> germlings cultured at 22&#xa0;°C under 100&#xa0;µmol photons m⁻<sup>2</sup>&#xa0;s⁻<sup>1</sup> to elucidate its environmental adaptation strategy. The results showed that 1) <i>U. prolifera</i> maintained equivalent growth rates in darkness (1.9% h⁻<sup>1</sup>) and light period (1.8% h⁻<sup>1</sup>). 2) Photosynthates (soluble sugars, starch), pigments (chlorophyll <i>a</i>, chlorophyll <i>b</i> and carotenoids) accumulated during light periods, which incurred significant oxidative costs as evidenced by elevated reactive oxygen species (O<sub>2</sub>·<sup>−</sup>, H<sub>2</sub>O<sub>2</sub>), lipid peroxidation (MDA) and antioxidant enzyme activity (SOD, CAT). 3) Nitrogen assimilation (higher soluble protein) predominated at ZT23 (Zeitgeber Time). 4) Transcriptomic analysis showed carbon fixation and starch synthesis related genes peaked at dark to light transition (ZT23 and ZT1), whereas TCA cycle and fatty acid degradation related genes were up-regulated during darkness (ZT13). However, carbon budget analysis further revealed that starch and soluble sugar reserves accounted for only a minor fraction of the nocturnal carbon demand, indicating that additional carbon sources supporting nighttime growth remain to be identified. These findings suggest that dark-period metabolism makes a critical contribution to overall growth and may serve as a complementary ecological strategy for its adaptation to the dynamic coastal environments, while acknowledging that the exact mechanisms underlying nighttime carbon supply warrant further investigation.</p>

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Nighttime growth in the green tide alga Ulva prolifera: metabolic basis and ecological implications

  • 期刊论文

  • 发表日期：

    2026年7月31日

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  • Han Xu,
  • Mingzi Lin,
  • Jiaying Bian,
  • Dongyi Yang,
  • Jianan Jiang,
  • Shenyuan Liang,
  • Hao Zhang,
  • Wenrong Zhu,
  • Nianjun Xu,
  • Yahe Li

摘要

Despite extensive knowledge of light-dependent growth in the green tide alga Ulva prolifera, the metabolic basis of its dark-period productivity and environmental adaptive significance in variable coastal habitats remain largely unexplored. This study investigated the dark-period metabolic plasticity of U. prolifera germlings cultured at 22 °C under 100 µmol photons m⁻2 s⁻1 to elucidate its environmental adaptation strategy. The results showed that 1) U. prolifera maintained equivalent growth rates in darkness (1.9% h⁻1) and light period (1.8% h⁻1). 2) Photosynthates (soluble sugars, starch), pigments (chlorophyll a, chlorophyll b and carotenoids) accumulated during light periods, which incurred significant oxidative costs as evidenced by elevated reactive oxygen species (O2·−, H2O2), lipid peroxidation (MDA) and antioxidant enzyme activity (SOD, CAT). 3) Nitrogen assimilation (higher soluble protein) predominated at ZT23 (Zeitgeber Time). 4) Transcriptomic analysis showed carbon fixation and starch synthesis related genes peaked at dark to light transition (ZT23 and ZT1), whereas TCA cycle and fatty acid degradation related genes were up-regulated during darkness (ZT13). However, carbon budget analysis further revealed that starch and soluble sugar reserves accounted for only a minor fraction of the nocturnal carbon demand, indicating that additional carbon sources supporting nighttime growth remain to be identified. These findings suggest that dark-period metabolism makes a critical contribution to overall growth and may serve as a complementary ecological strategy for its adaptation to the dynamic coastal environments, while acknowledging that the exact mechanisms underlying nighttime carbon supply warrant further investigation.