Interpreting factors of the variations in leaf conductance of Salix matsudana

The variations in leaf conductance of Salix matsudana koidz. were analyzed through pot experiments and field measurements. The results of non-linear regression analyses showed that diurnal variances of field samples were well-accounted for by two meteorological factors, that is, photon flux density and vapor pressure deficit. Through the whole course of soil moisture depletion in the pot experiment, whole plant hydraulic resistance increased. In the first step, the midday leaf water potential slightly decreased. In the second step, although midday water potential was stable, leaf conductance and pre-dawn water potential declined. In the third step, the midday water potential also declined. The decline of leaf conductance was accompanied by decreases in soil moisture content and predawn water potential in severe stressed conditions. In the field conditions, leaf conductance on the sand dune was about half of that on the moist meadow. Because the pre-dawn water potential was similar, it suggested that stomatal response on the sand dune had been acclimated to a lesser soil moisture condition, and the manners of responses to stresses were different among growing sites.