Leaf hydraulic conductance and mesophyll conductance are not closely related within a single species.

Stomata represent one resistor in a series of resistances for carbon and water exchange between the leaf and the atmosphere; the remaining resistors occurring within the leaf, commonly represented as mesophyll conductance to CO , g , and leaf hydraulic conductance, k . Recent studies have proposed that g and k may be coordinated across species because of shared pathways. We assessed the correlation between g and k within cotton, under growth CO partial pressure and irradiance treatments and also with short-term variation in irradiance and humidity. g was estimated using two isotopic techniques that allowed partitioning of total g (Δ C-g ) into cell wall plus plasma membrane conductance (Δ O-g ) and chloroplast membrane conductance (g ). A weak correlation was found between Δ C-g and k only when measured under growth conditions. However, Δ O-g was related to k under both short-term environmental variation and growth conditions. Partitioning g showed that g was not affected by short-term changes in irradiance or correlated with k , but was strongly reduced at high growth CO partial pressure. Thus, simultaneous measurements of g , k and g suggest independent regulation of carbon and water transport across the chloroplast membrane with limited coordinated regulation across the cell wall and plasma membrane.