Growing status rather than temperature was more associated with phytoplankton stoichiometry

Abstract

Phytoplankton growth is regulated primarily by temperature and nutrient availability. Due to the increasing trend of global warming and eutrophication, it is important to unravel the responses of phytoplankton to varying temperatures and nutrients. This study investigated the interactive effects of temperature (15 °C vs 25 °C) and nitrogen/phosphorus availability (N/P ratios: 13–77) on phytoplankton stoichiometry and community assembly in subtropical reservoir communities. We assumed that (1) Temperature effect on stoichiometry would intensify under nutrient limitation due to altered metabolic demands. Phosphorus limitation would dominate at higher temperatures through growth rate-mediated utilization; (2) Stoichiometric homeostasis would primarily reflect growth phase rather than thermal regime. Results demonstrated that temperature-nutrient interactions shape cellular stoichiometry through growth dynamics. Biomass increased with warming and nutrient enrichment, particularly under P-repleted conditions. Alkaline phosphatase, acting as a strategy for P-limitation, showed temperature-dependent, phase-specific patterns. Cellular elemental contents exhibited greater thermal sensitivity during the exponential growth, aligning with ribosomal investment demands. The homeostasis of phytoplankton was growth-phase dependent, with stationary-phase communities showing plasticity at 25 °C and stability at 15 °C. Temperature affected the stoichiometry indirectly by adjusting the growth rate and metabolism which changes the nutrient demand and resource allocation within cells. Cyanobacteria dominated warmer treatments through enhanced P-use efficiency. This study highlighted temperature-mediated shifts in nutrient limitation thresholds and homeostasis strategies, which provides evidences for predicting bloom dynamic under eutrophication and climate change in this region.