INORGANIC CARBON ACQUISITION BY CHRYSOPHYTES(1)

Area of Science:

• * Aquatic Botany
• * Phycology
• * Biogeochemistry

Background:

• * Chrysophytes are diverse algae with varied ecological roles.
• * Understanding their inorganic carbon uptake is crucial for aquatic ecosystem studies.
• * Previous research on chrysophyte carbon acquisition is limited.

Purpose of the Study:

• * To determine the inorganic carbon uptake capabilities of twelve chrysophyte species.
• * To investigate the role of carbon-concentrating mechanisms (CCMs) and bicarbonate utilization in chrysophytes.
• * To assess the influence of environmental factors like pH, alkalinity, and oxygen on carbon uptake.

Main Methods:

• * pH-drift technique to measure CO2 compensation points.
• * Membrane inlet mass spectrometry (MIMS) to analyze CO2 and HCO3- uptake kinetics.
• * Testing under varying oxygen partial pressures and in the presence/absence of acetazolamide.

Main Results:

• * CO2 compensation points were generally low (mean 5 μmol·L−1), indicating efficient CO2 use.
• * Neither pH nor alkalinity significantly affected CO2 compensation points.
• * MIMS data suggested minimal external carbonic anhydrase activity and negligible net bicarbonate uptake.

Conclusions:

• * Chrysophytes, as a group, appear to lack a functional CCM.
• * They exhibit limited ability to utilize bicarbonate as an inorganic carbon source.
• * These findings have implications for chrysophyte ecological roles and evolution in aquatic environments.