© 2003 Heron Publishing—Victoria, Canada
Sap flow of three co-occurring Mediterranean woody species under varying atmospheric and soil water conditions
Jordi Martínez-Vilalta (1, 2, 3), Marta Mangirón (4), Romà Ogaya (4), Miquel Sauret (2), Lydia Serrano (4), Josep Peñuelas (4) and Josep Piñol (2)
1. Ecology and Resource Management, School of Earth, Environmental & Geographical Sciences, University of Edinburgh, Darwin
Building, King’s Buildings, Edinburgh EH9 3JU, U.K. / 2. CREAF, Facultat de Ciències, Universitat Autònoma de Barcelona, Bellaterra-08193 (Barcelona), Spain / 3. Author to whom correspondence should be addressed (Jordi.Martinez-Vilalta@ed.ac.uk) / 4. Unitat Ecofisiologia, CSIC-CREAF, CREAF, Facultat de Ciències, Universitat Autònoma de Barcelona, Bellaterra-08193 (Barcelona),
Spain / Received December 19, 2001; accepted January 24, 2003; published online July 1, 2003
Summary
We studied the seasonal patterns of water use in three woody species co-occurring in a holm oak forest in northeastern Spain.
The three species studied, Quercus ilex L., Phillyrea latifolia L. and Arbutus unedo L., constitute more than 99% of the total basal area of the forest. The study period included the dry seasons of 1999 and
2000. Water use was estimated with Granier-type sap flux sensors. Standard meteorological variables, soil water content and
leaf water potentials were also monitored. All monitored individuals reduced leaf-related sap flow (Ql) during the summer, concurrent with an increase in soil moisture deficit (SMD). Despite similar maximum Ql between species, the decline in Ql with increasing SMD was species-dependent. The average reduction in Ql between early summer and the peak of the drought was 74% for A. unedo (n = 3), 58% for P. latifolia (n = 3) and 87% for Q. ilex (n = 1). The relationship between canopy stomatal conductance (Gs) and vapor pressure deficit (D) changed during the course of the drought, with progressively lower Gs for any given D. Summertime reductions of Ql and Gs were associated with between-species differences in vulnerability to xylem embolism, and with the corresponding degree of
native embolism (lowest in P. latifolia and highest in Q. ilex). Our results, combined with previous studies in the same area, outlined differences among the species studied in manner
of responding to water shortage, with P. latifolia able to maintain water transport at much lower water potentials than the other two species. In an accompanying experiment,
A. unedo responded to an experimental reduction in water availability by reducing Ql during the summer. This species also modified its water use between years according to the different seasonal patterns of
precipitation. These results are discussed in relation to the possible impacts that climate change will have on Q. ilex-dominated forests.
Keywords:
Arbutus unedo, drought, Phillyrea latifolia, Quercus ilex, sap flux, water use.
