Acclimation traits determine the macromolecular basis of harmful dinoflagellate Alexandrium minutum in response to changing climate conditions.

• Combined temperature and p CO 2 elevation, were investigated at a different transitional period of A. minutum for its acclimation. • This is the first study to consider depicting conditions of ocean warming and acidification on the element storage and related functional processes modification in A. minutum. • Combined temperature and p CO 2 elevation induced luxurious nitrogen and phosphate contents during the acclimation process. • Both nitrogen and phosphate molecules have unique functions to promote efficient growth and proliferation of A. minutum in the future ocean conditions. Ocean warming and acidification are expected to have profound impacts on the marine ecosystem, although the dinoflagellate Alexandrium minutum is reported to be acclimated to such conditions. However, it is unknown on the transition time scale how this species physiologically adjusts their element accumulation and associated resource allocation for this process. We designed a set of experiments to examine how different culture generations (1st, 5th, and 10th) change their cell physiology, cellular quotas and macromolecular cellular contents related to functional processes in A. minutum grown with future (p CO 2 , 1000 ppm; 25°C) and present (p CO 2 , 400 ppm; 21°C) ocean conditions. The differing cell sizes and storage capacity at different generations confirmed that compared to ancestors (1st generation), acclimation cells (10th generation) gained increases in quota carbon (Q C ; 55%; [ p < 0.05]) and quota phosphate (Q P ; 23% [ p < 0.05]). This variation in C:P and N:P influences was transition-specific and largely determined by phosphate-based molecules. It was observed that A. minutum was initially dependent on P molecules, which help cells act as alternative lipids for quick acclimation until N molecules resume carbon-based lipids for their long-term acclimation. Our study demonstrated that rising temperature and p CO 2 concentrations in ocean may increase A. minutum based on the comprehensive analysis of different physiological modifications, including its growth, element accumulation, transformation, and functional allocation. [ABSTRACT FROM AUTHOR]