Spatial heterogeneity of leaf gas exchange

Abstract

Spatial heterogeneity of cuticular conductance gc for water may induce stomata-specific response towards air humidity, non-uniformity of stomatal conductance gs (stomatal patchiness, SP) and depressions in the leaf CO2 fixation A. We present 2 novel approaches indicating that (i) gc of the solid phase of stomatous cuticles is heterogeneous and (ii) that the level of SP fluctuates during oscillations of the mean gs in proportion to mesophyll carboxylation capacity (CC). Material and methods Diffusion of 3H2O across isolated stomatous and astomatous cuticles of Hedera helix was measured in helium and nitrogen in order to distinguish the flux of water in the gas phase form the solid phas of the poreous cuticles. Sensitivity of net photosynthesis to gs, ¶ A¶ gs, rises with stomatal patchiness and falls at depression of carboxylation capacity. We investigated this variable in ABA-fed sunflower plants using LI-6400. Results and conclusions Water flux through the solid phase of stomatous cuticles was higher than the flux through astomatous cuticles by a factor of 20. The difference in diffusivity was not due to different barrier properties of cuticular waxes between stomatous and astomatous leaf sides. Thus, we conclude that stomatous cuticles are characterized by a pronounced lateral heterogeneity of gc. A and gs oscillated in the ABA treated plants when exposed to dry atmosphere. When compared with the pre-ABA leaf A was reduced at particular substomatal CO2 concentration during the oscillations. The sensitivity ¶ PN/¶ gs tended to keep its original pre-ABA values. We conclude that SP and the leaf CC vary in proportion during the oscillations. The mesophyll effect on stomata is considered.