Abstract:

The response and feedback of phytoplankton elemental stoichiometry to their ambient available nutrients is a vital approach to understand the relationship between structure and function of aquatic ecosystems. The change of silicon (Si) to carbon (C) stoichiometric ratio in water can reflect the coupling of Si-C biogeochemical cycles to some extent; however, the pattern of phytoplankton Si∶C ratio interacting with the ambient dissolved silicon (DSi) and CO₂ and the underlying mechanisms are still unclear yet. Here, we found that phytoplankton Si∶C molar ratio converged towards the DSi∶CO₂ molar ratio with years (i.e., Si-C stoichiometric convergence), and this convergence was driven by phytoplankton community succession in lakes. The large-scale survey across different inland waters (including rivers, lakes, reservoirs, and wetlands) showed that there was significant spatial difference in phytoplankton Si∶C and DSi∶CO₂ molar ratios, and most of them deviated greatly from the Redfield ratio. Random forest analysis indicated that the relative abundance of diatoms, water temperature, and dissolved inorganic nitrogen were important predictive factors for phytoplankton Si∶C ratio. Metatranscriptomic evidence suggested that phytoplankton community succession and its matched protein turnover in response to the changing DSi∶CO₂ ratio resulted in a Si-C stoichiometric convergence in water. The study will provide some new insights into phytoplankton stoichiometry, and the Si-C stoichiometric convergence could characterize the interaction between the lithosphere, hydrosphere, and biosphere in surface-earth system to some extent and provide a quantitative pattern for describing the structure and function of aquatic ecosystems in response to environmental changes.

Key words: aquatic ecosystems, phytoplankton, stoichiometric ratio, community composition, metatranscriptome