Anu S~ober1, Kr~o~ot Aasamaa2, Eve Eensalu1

1University of Tartu, Institute of Ecology and Earth Sciences, Tartu, Estonia
2University of Life Sciences, Institute of Eorestry, Tartu, Estonia

Previous analyses of stomatal mechanics have demonstraed, that the turgor - generated force of the epidermal cells dominates that of the guard cells in determining stomatal aperture (DeMichele, Sharpe, 1973, 1974, Sharpe and Wu, 1978, 1979). It was interpreted based upon geometric relationships calculated from anatomical dimensions of guard and epidermal cells (Wu et al. 1984).
Domination of epidermal cells was seen as transient increase in stomatal conductance in our experiments with rapid desiccation of leaves and occurred in wide range of deciduous tree species. These transients in stomatal conductance were different in different species, as it was expected from different cell dimensions, measured for these species (Aasamaa, S~ober, 2001). In general, transient stomatal opening during leaf desiccation was more pronounced in shade tolerant tree species (with bigger values of leaf hydraulic resistance) than in pioneer species with smaller hydraulic resistance of leaves. However, these transients in stomatal conductance also widely varied in one species (dependently on leaf position in canopy light gradient and initial transpiration rate).
We used a simple mathematical model to analyse transient changes of gs in desiccation experiments.
The mechanical advantage of epidermal cells over guard cells