CO2 availability influences hydraulic function of C3 and C4 grass leaves

Area of Science:

• Plant Physiology
• Ecology
• Climate Change Biology

Background:

• Atmospheric CO2 concentrations have risen since the last glacial period.
• This rise enhances photosynthetic water use efficiency and plant productivity.
• C4 photosynthesis evolved at low CO2, conferring a stomatal conductance advantage that may be diminished by rising CO2.

Purpose of the Study:

• To investigate the impact of increasing atmospheric CO2 on C4 plants compared to C3 plants.
• To determine how rising CO2 affects water use efficiency and gas exchange in C4 and C3 grasses.

Main Methods:

• Controlled environment experiments were conducted using four C3 and four C4 annual grasses.
• Leaf gas exchange and leaf mass per area (LMA) were measured at glacial, ambient, and super-ambient CO2 levels.
• Leaf hydraulic conductance (Kleaf) and osmotic potential were analyzed.

Main Results:

• C4 plants exhibited lower stomatal conductance (gs), leading to a water use efficiency advantage across all CO2 levels.
• At glacial CO2, C3 plants had lower net CO2 assimilation and LMA than C4 plants.
• C4 leaves showed distinct hydraulic adjustments, including decreased osmotic potential at turgor loss, under lower CO2 conditions.

Conclusions:

• C4 grasses maintain a water use efficiency advantage over C3 grasses due to lower stomatal conductance and sensitivity.
• These advantages are amplified at current and projected future atmospheric CO2 concentrations.
• Understanding these responses is crucial for predicting plant community dynamics under climate change.