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MEPS 713:39-53 (2023)  -  DOI:

Temperature-light shapes the nutritional strategy of a mixotrophic green alga, Picochlorum sp. GLMF1 (Trebouxiophyceae)

Mengwen Pang1, Kailin Liu2, Zuyuan Gao1, Chang-Keun Kang3, Hongbin Liu1,4,*

1Department of Ocean Science, Hong Kong University of Science and Technology, Clear Water Bay Road, Kowloon 999077, Hong Kong SAR, China
2College of the Environmental & Ecology, Xiamen University, Xiamen 361102, China
3School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, ROK
4Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511400, China
*Corresponding author:

ABSTRACT: Constitutive mixotrophs (CM), combining phagotrophy with inherent phototrophy, are critical primary producers and consumers in marine pelagic food webs. However, how mixotrophs, especially obligate CM, balance phototrophy and phagotrophy in response to changing environmental conditions remains equivocal. Here, we examined the growth performance, photosynthesis traits, and phagotrophic activities of a mixotrophic green alga, Picochlorum sp. GLMF1, over a wide range of temperature-irradiance combinations. The growth of Picochlorum sp. exhibited a unimodal thermal response under all the experimental light intensities. The optimal growth temperature decreased dramatically when the irradiance exceeded 80 μmol m-2 s-1, whereas the maximum growth rate kept a relatively constant and high value (around 1.1 d-1). This might be attributed to the trade-off between photosynthesis and ingestion under various light and temperature conditions. We found that the photosynthetic electron transport rate (ETR) and chlorophyll a specific inorganic carbon uptake rate increased with increasing irradiance. The maximum ETR decreased from 22.26 ± 1.93 μmol e m-2 s-1 at 22°C to 8.96 ± 0.42 μmol e m-2 s-1 at 31°C, suggesting a significant constraint of photosynthesis at high temperature. By contrast, ingestion increased with increasing temperature in most cases, and was significantly lower under high irradiance conditions. Combining the contributions of phototrophic and phagotrophic processes to total carbon acquisition, Picochlorum sp. showed a flexible nutritional strategy in response to temperature and light. Increasing light favors photosynthesis, whereas warming stimulates phagotrophy. Such complementation allows them to flourish under a wide range of temperature and irradiance. Our study adds knowledge to the nutritional strategy of mixotrophic green algae, with significant implications for their ecological role in marine food webs under projected climate change.

KEY WORDS: Mixotrophic green alga · Phototrophy · Phagotrophy · Nutritional strategy · Temperature · Light intensity

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Cite this article as: Pang M, Liu K, Gao Z, Kang CK, Liu H (2023) Temperature-light shapes the nutritional strategy of a mixotrophic green alga, Picochlorum sp. GLMF1 (Trebouxiophyceae). Mar Ecol Prog Ser 713:39-53.

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