Cuticular water permeance of European trees and
shrubs grown in polluted and unpolluted atmospheres, and its relation
to stomatal response to humidity in beech (Fagus sylvatica
L.)
Abstract
Cuticular water permeance (P) of astomatous adaxial surfaces of
intact leaves was determined in Acer pseudoplatanus L.,
Betula pubescens Ehrh., Corylus avellana L., Fagus
sylvatica L. and Prunus avium L. Water evaporating
from the stomata-bearing abaxial leaf surface could not reach
the moisture analyzer. Therefore, the values of P presented here
are free from errors that often arise from unintentional inclusion
of residual stomatal transpiration. Plants were exposed from before
bud-break for several months to 20-50 ppb SO2 (Fagus),
a combination of 50-60 ppb SO2 and 50-60 ppb NO2
(Betula), 300-400 ppb NO (Acer, Corylus,
Fagus), regular ozone episodes of up to 120 ppb (Fagus,
Prunus), or an elevated level of CO2 (600 ppm
for two years; Acer, Fagus). Permeances ranged from
0.6-2.9x105 m s1 and
were unaffected by most treatments. In Prunus, P increased
slightly but significantly in the NO treatment. In Corylus
and Fagus, P was sometimes found to be reduced by fumigation
with NO, but not always. Betula leaves grown under elevated
SO2 and NO2 showed higher values of P
only if they were visibly damaged. Minimum conductances (gmin
) estimated from water loss rates of both sides of detached
hypostomatous leaves were higher than P, and were more strongly
affected by treatments. In these cases, the most probable explanation
is some damage to stomatal function resulting in a reduced ability
to close after leaf excision. Effects of growing conditions and
time of year on P were found, which allowed a hypothetical interaction
between P and stomatal sensitivity to air humidity to be tested
in beech. No unambiguous indication of such a relationship was
found.
© 1995 Cambridge University Press