As leaves age, their stomatal conductance to CO2 (gsc) significantly decreases.
Older leaves generally exhibit a reduced capacity for gas exchange through their stomata compared to younger leaves. This decline in stomatal conductance (gsc) is a key factor contributing to the overall reduction in photosynthetic rate observed in aging leaves. Specifically:
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Reduced Stomatal Conductance (gsc): The ability of stomata to open and close effectively diminishes with age, leading to lower gsc values. This restricts the intake of CO2, a critical ingredient for photosynthesis.
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Impact on Photosynthesis: The reduced gsc directly impacts the rate of photosynthesis. With less CO2 available, the plant's ability to convert light energy into chemical energy is compromised.
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Mesophyll Conductance (gm): Along with stomatal conductance, mesophyll conductance (gm), which refers to the efficiency of CO2 diffusion from the substomatal cavity to the chloroplasts within the mesophyll cells, also decreases with leaf age. This further limits CO2 availability for photosynthesis.
Therefore, leaf age negatively affects stomata by reducing their conductance to CO2, ultimately hindering the photosynthetic process.
