Why do C3 plants have lower photosynthesis under higher temperatures? A. Stomata

Question

Why do C3 plants have lower photosynthesis under higher temperatures?

A. Stomata close to limit water loss as the VPD (vapor pressure deficit)
increases with air temperature

B. Photorespiration is increased relative to carboxylation

C. Photosynthetic damage may occur as the chloroplast membranes may be
damaged in part due breakdown of the membranes

D. All of the above are reasonable

A. Stomata close to limit water loss as the VPD (vapor pressure deficit)
increases with air temperature

B. Photorespiration is increased relative to carboxylation

C. Photosynthetic damage may occur as the chloroplast membranes may be
damaged in part due breakdown of the membranes

D. All of the above are reasonable

Explanation / Answer

It has been observed that when photosynthetic rate is plotted as function of temperature in a leaf with C4 photosynthesis either C3 or C4 leaf under ambient CO2 concentration, the curve shows a bell-shaped which clearly demarcates a temperature dependent stimulation of enzymatic activities

As a matter of fact, temperature affects all biochemical reactions of photosynthesis as well as membrane integrity in chloroplasts, so it is not surprising that the responses to temperature are complex. moreover, at ambient CO2 concentrations, photosynthesis is limited by the activity of RUBISCO, and a result two conflicting events come into action: an increase in carboxylation rate and a decrease in the affinity of RUBISCO for CO2 as the temperature rises.

It is evident that the RUBISCO activity decreases at high temperature because of temperature effect on RUBISCO activate and thus causes lower photosynthesis in the case of C3 plants under high temperature.

Moreover, photorespiration is favoured to avoid photooxidative damage is such case.

So, all of the above is right.

(Reference: Taiz and Zeiger)

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