Effects of enhanced hydraulic supply for foliage on stomatal responses in little-leaf linden (Tilia cordata Mill.)

Abstract

Responses of leaf conductance (g L ) to variation in environmental and plant hydraulic factors were examined on intact and detached shoots of little-leaf linden (Tilia cordata Mill.) with respect to branch position in the crown. Using detached shoots, we manipulated leaf water supply and light availability in order to separate the effects of insufficient hydraulic supply and low irradiance. The intact upper-crown leaves demonstrated 2.0-2.2 times higher (P < 0.001) daily maxima of g L compared to the lower-crown leaves growing in the shadow of upper branches. Mean soil-to-leaf conductance (G T ) was 1.9 times higher (P < 0.001) for the upper-crown foliage compared to that of the lower crown. The total hydraulic resistance was distributed: soil to distal shoots-41-51%, 25-cm distal shoots-10-15% and leaves-39-44%. In lower branches, g L was constrained by both low light availability and limited water supply; in upper branches, only by irradiance. Artificial reduction of hydraulic constraints raised bulk leaf water potential (W L ) and made g L less sensitive to changes in both atmospheric and plant factors. Stomatal responses to leaf-to-air vapour pressure difference (VPD) were significantly modified by leaf water status: high W L seemingly inverted the g L versus VPD relationship. Enhanced water supply increased g L and transpiration rate (E) in the lower-crown foliage, but not in the upper-crown foliage. The results support the idea that leaves in the lower canopy are hydraulically more constrained than those in the upper canopy.Abbreviations DBH: Diameter at breast height (cm) AE E: Transpiration rate (mmol m -2 s À1 ) AE g L : Leaf conductance to water vapour (mmol m À2 s À1 ) AE G L : Leaf hydraulic conductance (mmol m À2 s À1 MPa À1 ) AE G S : Shoot hydraulic conductance (mmol m À2 s À1 MPa À1 ) AE G T : Soil-to-leaf hydraulic conductance (mmol m À2 s À1 MPa À1 ) AE HV: Sapwood area to leaf area ratio (cm 2 m À2 ) AE Q P : Photosynthetic photon flux density (lmol m À2 s À1

Leaf water status and stem xylem flux in relation to soil drought in five temperate broad-leaved tree species with contrasting water use strategies

“…They found mean maximum g L between 100 and 300 mmol m −2 s −1 in a four-year period with the lowest values reported during the dry year 2003. For T. cordata, our diurnal mean maximum g L values agree with the measurements reported by Niinemets et al (1999), and Sellin and Kupper (2007).…”

Distribution of vessel size, vessel density and xylem conducting efficiency within a crown of silver birch (Betula pendula)

“…Leaves account for a majority (50-90%) of the hydraulic resistance to water flow through shoots of trees (Yang and Tyree 1994;Nardini and Salleo 2000;Nardini 2001), and thus form a substantial part of the whole resistance of the water transport pathway from soil to leaves (Sack et al 2003;Sack and Holbrook 2006;Sellin and Kupper 2007a). However, not in all cases, majority of the total hydraulic resistance occurs at the leaf level (Gyenge et al 2005).…”

“…Opposite patterns of hydraulic capacity have often been revealed within crowns of both coniferous and broad-leaved trees: specific hydraulic conductivity of branches (Protz et al 2000;Lemoine et al 2002;Jerez et al 2004;Burgess et al 2006) or shoot hydraulic conductance increased with branch height in the crown (Aasamaa et al 2004). Also apparent soil-to-leaf hydraulic conductance (G T ), defined as a current transpiration rate divided by water potential drop from soil to leaves (Meinzer et al 1995;Wullschleger et al 1998), has been shown to increase from basal to top branches (Sellin and Kupper 2004, 2005a, 2007a. Thus, qualitatively different phenomena can be observed within a crown.…”

Morphological traits and water use strategies in seedlings of Mediterranean coexisting species

“…Species with greater K As displayed greater leaf gas exchange values consistent with previously reported correlations (Bond and Kavanagh 1999;Sperry et al 2002;Hernández et al 2009). High photosynthetic rates and the correspondingly high stomatal conductance must be supported by high hydraulic conductance (Mencuccini and Comstock 1999;Hubbard et al 2001;Sellin and Kupper 2007). Under optimal soil water supply, high K As allows more efficient water transport from stems into photosynthetic organs to compensate leaf water loss and consequently maintain daily water potential high (Ackerly 2004;Jacobsen et al 2007b).…”