Is atmospheric CO₂ a selective agent on model C₃ annuals?

Area of Science:

• Plant Science
• Evolutionary Biology
• Climate Change Research

Background:

• Atmospheric CO₂ partial pressure (pCO₂) fluctuated historically and is projected to rise significantly.
• Previous research on C₃ plant responses to pCO₂ changes often overlooked evolutionary adaptation.
• Understanding plant evolution under varying pCO₂ is key for predicting future carbon sequestration and past plant function.

Purpose of the Study:

• To investigate the evolutionary responses of C₃ annuals to past (Pleistocene) and future projected atmospheric CO₂ levels.
• To determine if CO₂ acts as a selective agent influencing fitness components like seed number, biomass, and development rate.
• To predict the potential for evolutionary adaptation in C₃ plants under different CO₂ scenarios.

Main Methods:

• A selection experiment using *Arabidopsis thaliana* to select for high seed number at low (20 Pa) and high (70 Pa) pCO₂.
• Growth and reciprocal transplant experiments to assess the impact of selection on biomass, development rate, and reproductive success.
• Analysis of changes in life cycle duration, flowering time, and senescence patterns.

Main Results:

• *Arabidopsis thaliana* showed significant adaptation to selection for high seed number under both low and high pCO₂.
• Plants selected under low CO₂ exhibited enhanced performance and increased biomass (35% average) compared to controls when grown at low pCO₂.
• Selection at high CO₂ led to developmental changes, including earlier flowering and senescence, but did not significantly increase seed production or biomass.
• Low CO₂ acted as a selective agent, favoring individuals with traits suited to lower atmospheric carbon conditions.

Conclusions:

• C₃ annuals may have achieved greater biomass under low Pleistocene pCO₂ than previously estimated due to evolutionary adaptation.
• Evolutionary responses to future high pCO₂ may involve developmental shifts rather than enhanced biomass production.
• CO₂ can act as a significant selective pressure on C₃ annuals, driving evolutionary changes in development and carbon accumulation that single-generation studies cannot predict.