If overnight the stomata are closed and the process of cellular respiration is continuous, which of the structure is responsible for the release of CO2 into the atmosphere, considering the low permeability gas exchange of epidermal cells?
My feeling is that peristomatal diffusion or diffusion through the epidermis is enough to allow the release. The diffusion of CO2 is proporational to the concentration gradient between leaves and the atmosphere. If the stomatal are closed CO2 concentration will build up in the leaf and might be sufficient for the transport. I am, however, not sure if this has been proven formally.
Correct. Leaf CO2 is loss by surface diffusion following a concentration gradient. Although stomata are closed, stomatal leakness at night contributes largely to this diffusion. the magnitude of the nighttime stomatal leakiness is currently an active area of research, particularly for understanding ecosystem water fluxes.
The stomata of many (both C3 and C4) species remained open during night, which enabled transpiration. Therefore, during measurements of dark respiration of a leaf, you can still detect a small flux of transpiration. So I would guess the main path for CO2 release during night is through stomata. Please check this paper : Caird et al. 2007. Nighttime Stomatal Conductance and Transpiration in C3 and C4 Plants. Plant Physiology
Dear Doctors Frank, Miquel and Xiao Ying.
I greatly appreciate your contributions in solving my doubt. The answers are relevant and scientifically-informed. My question arose when I read an article that mentioned that the CO2 released by respiration during the night could be stored in mesophyll and partially used in photosynthesis, while the stomata were closed. In this case the oxygen produced would be used in breathing. The opening of stomata at night could result in great loss of water, considering the difference between the moisture inside the leaf and the atmosphere, which will always be lower. The recommended article is very interesting and enlightening. Thank you so much.
One clarification, O2 and CO2 are gases and can diffuse through the epidermis as such following concentration gradients. Gas "barriers", as the one in the bundle sheath cells of C4 plants are needed to increase the diffusion resistance to a given gas. In cells, CO2 can be "stored" in organic acids or other forms, and O2 will likely leave the tissue following concentrations gradients (not keeping O2 around is beneficial to prevent high rates of photorespiration).
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