Influence of stomatal conductance on the efficiency of internal pressurisation in Typha domingensis

Since the pores connecting the lacunae (the site of pressurisation in emerg ent macrophytes) with the atmosphere include the stomatal aperture, it was hypothesised that stomata may influence the effectivity of pressurisation i n Typha domingensis. To investigate this, stomatal conductance and effectiv ity were measured over the diel period. The relative mean pore diameter was predicted using a derivative of the Poiseuille-Hagen equation, and also re lated to effectivity. Both the stomatal conductance and the relative mean p ore diameter were found to be correlated to effectivity (r(2) = 0.95 and 0. 93, respectively) suggesting stomatal conductance did influence the ability to pressurise. As the baseline effectivity (e.g., when the stomata were fu lly open) was 1.4% it is suggested that while the stomatal aperture is the primary tissue involved in the ability to pressurise (contributing up to ca . 30% to the effectivity), other tissues between the lacunae and the atmosp here aid the process. (C) 2000 Elsevier Science B.V. All rights reserved.