Crassulacean acid metabolism: a continuous or discrete trait?

Area of Science:

• Plant Physiology
• Biochemistry
• Evolutionary Biology

Background:

• Crassulacean acid metabolism (CAM) is a water-saving carbon assimilation pathway.
• CAM involves nocturnal CO2 fixation and processing via Rubisco during the day.
• The extent of CAM activity varies significantly among species, ontogeny, and environments.

Purpose of the Study:

• To investigate the variability in CAM plant phenotypes.
• To understand the distribution of carbon fixation strategies in plants.
• To explore the evolutionary transition from C3 photosynthesis to CAM.

Main Methods:

• Analysis of carbon-isotope ratios in large-scale plant surveys.
• Identification of species exhibiting low-level CAM activity.
• Investigating genetic architecture and gene expression in CAM-transitioning species.

Main Results:

• Carbon-isotope surveys reveal a bimodal distribution, with few intermediate values.
• Many species with low-level CAM activity exhibit C3-type isotope signatures.
• The adaptive significance of low-level CAM requires further investigation.

Conclusions:

• Plants with low-level CAM are valuable models for studying the C3 to CAM evolutionary transition.
• Understanding genetic changes associated with low-level CAM can illuminate evolutionary pathways.
• Further research is needed to determine the adaptive advantages of nocturnal CO2 fixation in certain species.