How Do The Differences In Stomatal Density And Morphology Between The Adaxial And Abaxial Surfaces Of Leaves In C3 And C4 Plants Influence Their Respective Photosynthetic Water-use Efficiencies Under Conditions Of High Temperature And Drought Stress?

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Under high temperature and drought stress, the differences in stomatal density and morphology between the adaxial and abaxial surfaces of leaves in C3 and C4 plants significantly influence their photosynthetic water-use efficiency (WUE). Here's a structured summary of the key points:

  1. C4 vs. C3 Plants:

    • C4 Plants: These plants, such as corn and sugarcane, exhibit higher drought tolerance and thermal efficiency. They often have lower stomatal density overall, which may contribute to reduced water loss. Their stomatal distribution may favor the abaxial surface, allowing efficient gas exchange while conserving water.
    • C3 Plants: These plants, like wheat and rice, typically have higher stomatal density. While this can enhance CO2 uptake, it may lead to greater water loss, especially under stress, potentially reducing WUE.

  2. Stomatal Distribution and Morphology:

    • C4 Plants: They may have fewer stomata but more efficient ones, possibly with morphology that allows rapid adjustment to environmental changes. This efficiency helps maintain CO2 intake while minimizing water loss, enhancing WUE.
    • C3 Plants: Higher stomatal density might lead to increased transpiration without proportional carbon gain, especially under drought, resulting in lower WUE compared to C4 plants.

  3. Photosynthetic Efficiency and WUE:

    • C4 Plants: Their photosynthetic pathway allows efficient CO2 use, maintaining higher WUE under stress. Even with fewer stomata, they can manage gas exchange effectively.
    • C3 Plants: Despite higher stomatal density, water loss may outweigh carbon gain, leading to lower WUE under stress conditions.

  4. Environmental Adaptations:

    • Drought and Heat: C4 plants' stomatal efficiency and distribution likely contribute to better WUE, while C3 plants may struggle with water conservation, affecting their WUE negatively.

In conclusion, C4 plants' stomatal adaptations, including lower density and possibly more efficient morphology, enable them to maintain higher WUE under high temperature and drought stress compared to C3 plants.