title: Daily dynamics of leaf and soil-to-branch hydraulic conductance in silver birch (Betula pendula) measured in situ.
abstract: 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 K(S-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 (T(A)). K(S-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 MPa⁻¹) at 1500 h, decreasing afterwards. Environmental factors controlling K(S-B) were Ψ(S) and Q(P). The diurnal patterns of K(L) reflect a combination of environmental factors and endogenous rhythms. The temporal pattern of K(S-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.
authors.affiliation: Institute of Ecology and Earth Sciences, University of Tartu, Vanemuise 21, 51014 Tartu, Estonia. eele.ounapuu@ut.ee
authors.forename: Eele
authors.initials: E
authors.lastname: Õunapuu
authors.forename: Arne
authors.initials: A
authors.lastname: Sellin
mesh_terms: D029662:Betula / Q000378:metabolism / Q000502:physiology*; D002940:Circadian Rhythm; D015536:Down-Regulation; D004777:Environment; D008027:Light; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology*; D012987:Soil; D013696:Temperature; D014867:Water / Q000378:metabolism
chemical_list: D012987:Soil; D014867:Water