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 (K-lamina(HgCl2)), and with the seasonal course of the difference (dK(lamina)) between Klamina and K-lamina(HgCl2). However, it did not correlate strongly with the seasonal course of the hydraulic conductance of stem and petioles of the shoot (K-stpt) in six temperate deciduous tree species. The species ranked according to K-lamina 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 K-lamina correlated positively with the simultaneous values of K-lamina(HgCl2), dK(lamina) and K-stpt; the correlation was strongest with K-lamina(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 K-lamina were mainly caused by the different apoplastic hydraulic conductance in leaves of these species. The relative contribution of dK(lamina) (in K-lamina) was highest in slow-growing species (similar to 55% in A. platanoides) and the lowest in fast-growers (similar to 30% in S. caprea).