Arranging marine plankton into several functional groups based on their trophic modes when studying the ecological processes provides approaches to link individual or group-specific behaviors to ecosystem feedback. Temperature-dependent planktonic metabolism is crucial for determining marine primary production and the structure of planktonic food webs in the projected global warming. However, our understanding of the thermal response of marine plankton with different trophic modes remains limited, especially under the influence of other environmental factors. To gain a more comprehensive understanding, in this thesis, we first studied the effects of light intensity on the thermal response of a constitutive mixotrophic green alga. Increasing light promoted photosynthesis and lowered the...[ Read more ]

Arranging marine plankton into several functional groups based on their trophic modes when studying the ecological processes provides approaches to link individual or group-specific behaviors to ecosystem feedback. Temperature-dependent planktonic metabolism is crucial for determining marine primary production and the structure of planktonic food webs in the projected global warming. However, our understanding of the thermal response of marine plankton with different trophic modes remains limited, especially under the influence of other environmental factors. To gain a more comprehensive understanding, in this thesis, we first studied the effects of light intensity on the thermal response of a constitutive mixotrophic green alga. Increasing light promoted photosynthesis and lowered the optimal growth temperature (T_opt), while the growth maxima (μ_max) remained consistently high. In contrast, rising temperature favored phago-heterotrophy. This work explains how temperature and irradiance modulate the nutritional strategy of mixotrophic green algae, with implications for their ecological roles under global change. Subsequently, we tested the nutrient effects on the thermal performance of marine diatoms. By combining the in situ manipulation experiments with a 20-year historical dataset, we found that nutrient limitation not only constrained diatom growth rates but also suppressed their T_opt and μ_max. In contrast, abundant nutrients, can alleviated thermal stress on marine diatoms and enhanced their capacity to cope with ocean warming. Our finding highlights the importance of considering nutrient effects on phytoplankton thermal response. Finally, we investigated how long-term warming affects the thermal performance of a cosmopolitan heterotrophic nanoflagellate Cafeteria burkhardae, with a focus on its thermal adaptation capability and the underlying molecular mechanisms. Our results showed that after a 700-day warming selection, C. burkhardae adapted well to a high temperature, as evidenced by the significantly increased T_opt and μ_max. Changes in gene expression supported the physiological response, where warming adaptation mitigated high temperature- induced oxidative stress, revealing a trade-off between oxidative stress and cell proliferation. This thesis deepens our understanding of the plastic thermal response of plankton with different trophic modes in a changing ocean, providing insights into accurately forecasting primary production and ecosystem functioning under global warming.