Phytoplankton transcriptomic and physiological responses to fixed nitrogen in the California current system

Area of Science:

• Marine microbial ecology
• Oceanography
• Biogeochemistry

Background:

• Marine phytoplankton drive global photosynthesis but require essential nutrients like nitrogen (N).
• Nitrogen is scarce in many ocean regions, impacting phytoplankton productivity.
• Phytoplankton species exhibit diverse nutrient preferences and requirements.

Purpose of the Study:

• To investigate transcriptomic responses of phytoplankton communities to nutrient additions in the California Current System (CCS) transition zone.
• To understand how different nitrogen (N) substrates and iron (Fe) affect phytoplankton gene expression and nutrient stress.
• To elucidate competitive dynamics and nutrient utilization strategies among phytoplankton groups.

Main Methods:

• Utilized the MicroTOOLs high-resolution environmental microarray for transcriptomic analysis.
• Applied additions of urea, ammonium, nitrate, and iron (Fe) to phytoplankton communities.
• Analyzed gene expression related to photosynthesis, carbon fixation, and nutrient stress.

Main Results:

• Nitrogen limitation was relieved in Prochlorococcus, Synechococcus, and eukaryotic phytoplankton, indicated by changes in photosynthetic and carbon fixation genes.
• Prochlorococcus showed decreased N stress gene expression and significant growth with urea and ammonium, outcompeting others.
• Diatoms responded to Fe addition with increased carbon fixation gene expression, but not when N was also added, suggesting N-Fe co-limitation.

Conclusions:

• Co-existing phytoplankton strains in the CCS transition zone experience distinct nutrient stresses.
• Prochlorococcus demonstrates a competitive advantage with readily available N sources like urea and ammonium.
• Variability in N utilization exists even within closely related phytoplankton strains, highlighting complex ecological interactions.