C₄ photosynthesis, atmospheric CO₂, and climate

Area of Science:

• Plant Ecology
• Evolutionary Biology
• Biogeography

Background:

• C4 photosynthesis offers advantages in low CO2 and high temperatures.
• Understanding C3/C4 plant distribution impacts ecosystems and food webs.
• C4 plants are disproportionately common in monocots compared to dicots.

Purpose of the Study:

• Review factors influencing C4 plant distribution (ecological, geographical, palaeoecological).
• Propose a model for C4 plant distribution based on temperature and CO2.
• Explain the rarity of C4 photosynthesis in dicots versus monocots.

Main Methods:

• Literature synthesis of 16 studies on C4 monocot distribution and 7 on C4 dicot distribution.
• Analysis of temperature and aridity correlations with C4 plant types.
• Modeling of C3 and C4 light-use efficiencies under varying CO2 and temperature.
• Review of palaeocarbonate and fossil data for C4 ecosystem expansion.

Main Results:

• C4 monocot distribution strongly correlates with growing season temperature.
• C4 dicot distribution is better described by aridity.
• Light-use efficiency differences explain C3/C4 monocot distribution.
• C4 ecosystems globally expanded near the Miocene boundary and during glacial periods.
• C4 monocots generally exhibit higher light-use efficiency than C4 dicots.

Conclusions:

• C4 plant distribution is strongly influenced by temperature, CO2, and plant type.
• Leaf venation may contribute to higher light-use efficiency in C4 monocots.
• C4 dicots, with lower light-use efficiency, may be restricted to warmer, saline, or disturbed habitats.
• C4 plants, especially monocots, have a significant advantage in low CO2 environments and expanded during glacial periods.