Functional Traits for Carbon Access in Macrophytes.

Area of Science:

• Marine biology
• Evolutionary ecology
• Phycology

Background:

• Marine macrophytes utilize dissolved inorganic carbon (DIC) for photosynthesis, accessing both CO2 and bicarbonate (HCO3-).
• Carbon concentrating mechanisms (CCMs) are crucial for efficient carbon uptake in marine environments where CO2 is scarce.
• Understanding the distribution and evolution of CCMs is vital for predicting responses to environmental change.

Purpose of the Study:

• To investigate the presence and phylogenetic distribution of CCMs in Northeast Pacific rocky intertidal macrophytes.
• To determine the evolutionary history and conservation patterns of CCMs within red algae (Rhodophyta) and brown algae (Ochrophyta).
• To assess the role of macrophytes in altering seawater Total Alkalinity (TA) and its implications for carbon availability.

Main Methods:

• Surveyed 40 macrophyte species for the presence and functionality of CCMs.
• Utilized ancestral state reconstructions and stochastic character mapping to infer evolutionary patterns of CCMs.
• Analyzed changes in Total Alkalinity (TA) associated with carbon uptake in 23 species.

Main Results:

• 32 out of 40 surveyed species exhibited CCMs, actively transporting CO2 and HCO3-.
• CCMs showed significant phylogenetic signal in red algae but were highly labile, indicating divergent evolutionary paths.
• CCMs were universally present and conserved across surveyed brown algal families.
• Fifteen species altered seawater TA, potentially influencing local carbon availability.

Conclusions:

• CCM presence is a conserved trait in brown algae but a labile trait in red algae.
• Macrophyte-induced changes in TA can modify the seawater carbonate system, affecting carbon availability for photosynthesis.
• Phylogenetic and physiological understanding of CCMs is key to predicting marine ecosystem responses to climate change.