© 2003 Heron Publishing—Victoria, Canada
Stomatal responses to drought at a Mediterranean site: a comparative study of co-occurring woody species differing in leaf
longevity
Sonia Mediavilla (1, 2) and Alfonso Escudero (1)
1. Departamento de Ecologia, Facultad de Biologia, Universidad de Salamanca, 37071 Salamanca, Spain / 2. Author to whom correspondence should be addressed (ecomedv@usal.es) / Received December 3, 2002; accepted March 8, 2003; published online September 1, 2003
Summary
We studied stomatal responses to decreasing predawn water potential (Ψpd) and increasing leaf-to-air water vapor pressure difference (VPD) of co-occurring woody Mediterranean species with contrasting
leaf habits and growth form. The species included two evergreen oaks (Quercus ilex subsp. ballota (Desf.) Samp. and Q. suber L.), two deciduous oaks (Q. faginea Lam. and Q. pyrenaica Willd.) and two deciduous shrubs (Pyrus bourgaeana Decne. and Crataegus monogyna Jacq.). Our main objective was to determine if stomatal sensitivity is related to differences in leaf life span and leaf
habit.
The deciduous shrubs had the least conservative water-use characteristics, with relatively high stomatal conductance and low
stomatal sensitivity to soil and atmospheric drought. As a result, Ψpd decreased greatly in both species during the growing season, resulting in early leaf abscission in the summer. The deciduous
oaks showed intermediate water-use characteristics, having maximum stomatal conductances and CO2 assimilation rates similar to or even higher than those of the deciduous shrubs. However, they had greater stomatal sensitivity
to soil drying and showed less negative Ψpd values than the deciduous shrubs. The evergreen oaks, and especially the species with the greatest leaf longevity, Q. ilex, exhibited the most conservative water-use behavior, having lower maximum stomatal conductances and greater sensitivity to
VPD than the deciduous species. As a result, Ψpd decreased less during the growing season in the evergreens than in the deciduous species, which may contribute to greater
leaf longevity by avoiding irreversible damage during the summer drought. However, the combination of low maximum CO2 assimilation rates and high stomatal sensitivity to drought must have a negative impact on the final carbon budget of leaves
with a long life span.
Keywords:
deciduous species, evergreen species, predawn water potential, stomatal conductance, vapor pressure difference.
