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Transport of gases into leaves
Author(s) -
CSIRO R. LEUNING
Publication year - 1983
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11587617
Subject(s) - water vapor , knudsen number , chemistry , conductance , isothermal process , flux (metallurgy) , thermodynamics , diffusion , vapor pressure , mole fraction , porous medium , porosity , physics , organic chemistry , condensed matter physics
. Transport of gases between the intercellular spaces of plant leaves and the surrounding air is analysed in terms of multicomponent collision processes through an isothermal, porous septum. Interaction of diffusing species with each other and with the pore walls is described using a modified Stefan–Maxwell equation and an equation relating the pressure gradient to the sum of the diffusive fluxes, weighted by their appropriate Knudsen diffusivities. Viscous How arising from an excess pressure within the leaf is also considered. Equations are derived which describe the flux densities of water vapour and CO 2 through the stomata. The analysis is general and is applicable to trace gases other than CO 2 . A simple conductance is defined for water vapour to relate the flux and mol fraction difference across the stomata, viz. N w =− g w , δ x w / x a . A simple conductance cannot be defined for CO 2 because the flux of water vapour has a significant influence on the CO 2 gradient. The equation derived for the intercellular mol fraction of CO 2 is in terms of the fluxes of CO 2 and water vapour and represents a ‘large‐pore’ ( d > μm) approximation which requires no information about stomalal geometry. Analogous equations are developed for transfer of gases through the leaf boundary layer. Sample calculations are presented to illustrate the effect of neglecting the interaction of water vapour and CO 2 on the calculated intercellular and surface concentrations of CO 2 . Equations for computing water vapour and CO 2 flux densities from leaf chamber measurements are also presented.