Daily dynamics of leaf and soil-to-branch hydraulic conductance in silver birch (Betula pendula) measured in situ

Daily dynamics of leaf (K-L) and soil-to-branch hydraulic conductance (KS-B) was investigated in silver birch (Betula pendula Roth.) using evaporative flux method in situ: water potential drop was measured with a pressure chamber and evaporative flux was estimated as sap flux density measured with sap flow gauges. Canopy position had a significant (P < 0.001) effect on both K-L and KS-B. Upper-canopy leaves exhibited 1.7 and soil-to-branch pathway 2.3 times higher hydraulic efficiency than those for lower-canopy. K-L varied significantly with time of day: K-L for both upper- and lower-canopy leaves was lowest in the morning and rose gradually achieving maximal values in late afternoon (4.75 and 3.38 mmol m(-2) s(-1) MPa-1, respectively). Relevant environmental factors affecting K-L were photosynthetic photon flux density (Q(P)), air relative humidity (RH) and air temperature (TA). KS-B started rising in the morning and reached maximum in the lower canopy (1.44 mmol m(-2) s(-1) MPa-1) at 1300 h and in the upper canopy (2.52 mmol m(-2) s(-1) at 1500 h, decreasing afterwards. Environmental factors controlling KS-B were Psi(S) and Q(P). The diurnal patterns of K-L reflect a combination of environmental factors and endogenous rhythms. The temporal pattern of KS-B refers to daily up- and down-regulation of hydraulic conductance of water transport pathway from soil root interface to leaves with respect to changing irradiance. (C) 2013 Elsevier Masson SAS. All rights reserved.