Dynamics of change in stomatal response and water status of Picea abies during a persistent drought period: a contribution to the traditional view of plant water relations

Abstract

Four experiments on the simulation of a persistent drought period were carried out with cloned Picea abies (L.) Karst. trees: two in the field under varying weather conditions and two in a climate chamber under variously manipulated humidity conditions. Patterns of diurnal dynamics in gas exchange rates and water potential were monitored and analyzed. The first phase of the drought was characterized by relatively high daily maxima for photosynthesis and transpiration. With decreasing humidity during the day, the values dropped steeply, and the declines were larger and occurred earlier on each passing day of the drought period. When soil water potential was lower than -2000 hPa, maximum stomatal aperture was greatly reduced despite a humid atmosphere. Under these conditions, rates of photosynthesis and transpiration decreased less steeply from the daily maxima and differences between maxima and minima were small. In the field, the daily sums of transpiration and photosynthesis were more dependent on atmospheric conditions than on soil water potential. In the growth chamber experiments, the daily sums of transpiration and photosynthesis decreased continuously as the soil dried, at first steeply until a soil water potential of -2000 hPa was reached, then slowly. Predawn water potential values fluctuated under field conditions, but tended to decrease with time, whereas needle osmotic potential increased slightly. Because relative humidities did not reach 100% in the growth chamber, predawn water potentials of plants in the growth chamber were never higher than -1.0 MPa although the soil was saturated. In the experiment with a high average air humidity during the daily stress period, relatively high predawn water potentials were maintained until lower soil water potentials of -8000 hPa were reached. Results were used to assess the importance of evaporative demand versus soil drying on stomatal responses within the context of current concepts of plant water relations. The observed trends in diurnal dynamics can be explained solely by the interdependency of leaf conductance and water potential. Stomata react directly to the ratio of water supply to demand. The central role of peristomatal transpiration in this system is emphasized.

Predawn plant water potential does not necessarily equilibrate with soil water potential under well-watered conditions

“…The soil-leaf hydraulic conductance and the rate of nighttime transpiration can interact to affect the magnitude of predawn disequilibrium, particularly for tall trees (Hinckley et al 1978a;Ourcival et al 1994;Richter 1997;Maier-Maercker 1998). In P. abies and V. myrtillus, where maximal Ψ p can occur up to 2 h after dawn, nighttime transpiration and low hydraulic conductivity lead to both predawn Ψ p and base Ψ p more negative than soil Ψ w (Sellin 1996(Sellin , 1999.…”

“…Although substantial nighttime transpiration is an unexpected phenomenon for non-CAM plants, it has also been reported or inferred for other species: Abies sp., Betula pendula, Eucalyptus grandis, Larrea tridentata, Picea abies, Pseudotsuga menziesii, Rosa sp., and Vaccinium myrtillus (Hinckley and Ritchie 1973; Klepper et al 1973, 2 Ritchie and Hinckley 1975, 3 Berger et al 1996, 4 Le Roux and Bariac 1998, 5 Hinckley et al 1978a, 6 Bréda et al 1995, 7 Gallego et al 1994, 8 Cermák et al 1980, 9 Garnier and Berger 1987, 10 Lu et al 1995, 11 Sellin 1999, 12 Schmidhalter 1997, 13 Schmidhalter et al 1998 Améglio et al 1999, 15 Donovan et al 1999 Jordan and Ritchie 1971, 17 Sala et al 1981, 18 Elfving et al 1972, 19 Cohen et al 1983, 20 Ourcival et al 1994, 21 Sobrado 1986 Maier-Maercker 1998, 23 Fahey and Young 1984, 24 Nnyamah et al 1978, 25 Lassoie et al 1983, 26 Meinzer et al 1988, 27 Franco et al 1994, 28 Nilsen et al 1983, 29 Küppers et al 1987, 30 Donovan et al 1996, 31 Hinckley et al 1978b, 32 Ourcival and Berger 1995 Difference between predawn plant Ψ w or Ψ p and soil Ψ w <0. Blake and Ferrell 1977;Hinckley et al 1978b;Meinzer et al 1988;Wieser and Havranek 1993;Matyssek et al 1995;Assaf and Zieslin 1996;Maier-Maercker 1998;…”

Temperature and humidity effects on branchlet gas-exchange in white spruce: an explanation for the increase in transpiration with branchlet temperature

“…The fact that tree mortality from xylem dysfunction is relatively rare (e.g. Kavanagh and Zaerr 1997) would indicate that mechanisms regulating stomatal aperture are highly sensitive to the balance between water supply and loss (Meinzer and Grantz 1991;Jones 1998;Maier-Maercker 1998).…”

Regulation of Water Use in the Southernmost European Fir (Abies pinsapo Boiss.): Drought Avoidance Matters

“…This type of elemental stoichiometric change has been associated with shifts in the plant metabolome, indicating growth rather than drought resistance [62]. A similar pattern of osmotic potential decline (toward positive values) during shoot growth has been observed in species such as Picea abies [26]or Nothofagus menziesii [63]. According to these authors, this indicates higher sensitivity/susceptibility of the new shoots to drought.…”

“…The same procedure was used to measure the xylem water potential; the twigs were cut with a razor blade. Each measure was replicated three times per tree [26]. After each measurement, the twigs were placed in a plastic bag to obtain the surface area, dry weight and foliar nutrient content in the laboratory.…”