Ha. Gallego et al., LEAF WATER POTENTIAL AND STOMATAL CONDUCTANCE IN QUERCUS-PYRENAICA WILLD FOREST - VERTICAL GRADIENTS AND RESPONSE TO ENVIRONMENTAL-FACTORS, Tree physiology, 14(7-9), 1994, pp. 1039-1047
Two permanent sampling sites were selected at the two extremes of a ra
infall gradient in natural forests of Quercus pyrenaica Willd. located
in the Sierra de Gata (Salamanca Province, Spain). During 1991 and 19
92, diurnal courses of transpiration rate (E), stomatal conductance (g
(s)) and leaf water potential (PSI1) were studied at different levels
in the tree canopy. Leaf water potential fell from a high value in the
early morning to a minimum at midday and then increased again in the
afternoon. Values of PSI1 in the early morning and at midday were lowe
r at Fuenteguinaldo (dry site) than at Navasfrias (wet site) and were
related to soil water availability. Stomatal conductance increased dur
ing the morning and maximum g(s) occurred about 3 h before PSI1 was at
its lowest value. The highest values of g(s) were found at Navasfrias
during July. The lowest PSI1 values were found in the upper parts of
the canopy and differences among canopy levels were greatest when soil
water availability was low. In August, minimum values of Ti differed
among canopy levels by 1.0 MPa at Navasfrias and by 0.8 MPa at Fuenteg
uinaldo. The maximum difference in g(s) among canopy levels was about
150 mmol m-2 s-1 at Navasfrias and about 300 mmol m-2 s-1 at Fuentegui
naldo. The results indicate a nonconservative pattern of water use in
Quercus pyrenaica.