Hydraulic and stomatal adjustment of Norway spruce trees to environmental stress
Arne Sellin (1)
1. Department of Botany and Ecology, University of Tartu, Lai 40, 51005 Tartu, Estonia () / Received March 15, 2000
Summary
A study of how the water conducting systems of 30–50-year-old Norway spruce (Picea abies (L.) Karst.) trees growing at three sites adjust to shade and waterlogging indicated that water relations characteristics
varied with the life histories of the trees. Xylem was more efficient at conducting water and stomata were more sensitive
to atmospheric evaporative demand in trees subjected to favorable growth conditions (control trees) than in trees growing
in shade or waterlogged conditions. At the same soil water availability, shade-grown trees suffered more severely from water
deficit than control trees. Under conditions of high atmospheric vapor pressure deficit, foliage of shade-grown trees exhibited
low water potentials, as a result of low hydraulic conductance of the vascular system and inefficient stomatal control. Because
of the increased internal resistance to water flow, more negative leaf water potentials (Ψx) must be reached to provide an adequate water supply to the foliage. It is concluded that dynamic water stress is one of
the main causes of the continuing growth retardation in suppressed Norway spruce trees after their release from the overstory.
Trees growing in waterlogged soil (bog-grown trees) were characterized by weak stomatal control, resulting in large water
losses from the foliage. Although bog-grown trees exhibited uneconomical water use, they possessed mechanisms (e.g., osmotic
adjustment) that allowed leaves to tolerate low Ψx while stomata remained open. Under conditions of sufficient soil water availability and moderate atmospheric vapor pressure
deficit, soil-to-leaf conductance was highest in bog-grown trees (1.45 ± 0.06 mmol m–2 s–1 MPa–1), followed by control and shade-grown trees (1.04 ± 0.04 and 0.77 ± 0.05 mmol m–2 s–1 MPa–1, respectively). The lowest soil-to-leaf conductance (0.45 ± 0.04 mmol m–2 s–1 MPa–1) was recorded in control trees at high atmospheric evaporative demand, and was probably caused by tracheid cavitation.
