Seasonal courses of maximum hydraulic conductance in shoots of six temperate deciduous tree species

The seasonal course of maximum hydraulic conductance of leaf laminae (Klamina) of shoots correlated strongly with the seasonal course of the maximum hydraulic conductance of leaf laminae of HgCl2-treated shoots (Klamina(HgCl2)), and with the seasonal course of the difference (dKlamina) between Klamina and Klamina(HgCl2). However, it did not correlate strongly with the seasonal course of the hydraulic conductance of stem and petioles of the shoot (Kstpt) in six temperate deciduous tree species. The species ranked according to Klamina as follows: Populus tremula L. > Salix caprea L. > Padus avium Mill. > Quercus robur L. > Tilia cordata Mill. > Acer platanoides L. The species-specific maxima of Klamina correlated positively with the simultaneous values of Klamina(HgCl2), dKlamina and Kstpt; the correlation was strongest with Klamina(HgCl2). It was concluded that the seasonal dynamics of maximum hydraulic conductance of leaf laminae was determined almost equally by the seasonal dynamics of the hydraulic conductance of foliar protoplasts and apoplast, but the inter-specific differences in Klamina were mainly caused by the different apoplastic hydraulic conductance in leaves of these species. The relative contribution of dKlamina (in Klamina) was highest in slow-growing species (~55% in A. platanoides) and the lowest in fast-growers (~30% in S. caprea).