Stomatal response to VPD in C₄ plants with different biochemical sub-pathways

Area of Science:

• Plant physiology
• Photosynthesis research
• Ecology

Background:

• C4 photosynthesis exhibits subtypes: NAD-malic enzyme (NAD-ME) and NADP-malic enzyme (NADP-ME).
• NAD-ME species are found in drier regions, suggesting different drought responses compared to NADP-ME species.
• The physiological basis for these geographical distribution differences remains unclear.

Purpose of the Study:

• To investigate gas exchange patterns explaining the distribution differences between NAD-ME and NADP-ME C4 subtypes.
• To compare the responses of leaf gas exchange to vapor pressure deficit (VPD) and CO2 in closely related species of both C4 subtypes.

Main Methods:

• Leaf gas exchange was measured using a Li-Cor 6400 system.
• Responses to varying VPD and CO2 concentrations were analyzed.
• Six distinct C4 clades with related NAD-ME and NADP-ME species were studied.

Main Results:

• NAD-ME species demonstrated a more significant reduction in stomatal conductance (gs) as VPD increased, compared to NADP-ME species.
• No consistent differences were found in C4 cycle activity between the subtypes, based on the initial slope of the assimilation (A) response to intercellular CO2 concentration.
• The greater stomatal response to VPD in NAD-ME species was highlighted.

Conclusions:

• The enhanced stomatal conductance regulation in response to VPD may provide a survival advantage for NAD-ME plants in arid conditions.
• This physiological difference could explain the prevalence of NAD-ME C4 species in hot, dry environments.
• Further research into C4 subtype adaptations to water-deficit stress is warranted.