© 2007 Heron Publishing—Victoria, Canada
Water relations of seedlings of three Quercus species: variations across and within species grown in contrasting light and water regimes
Pilar Castro-Díez (1, 2) and Javier Navarro (1)
1. Departamento de Ecología, Facultad de Ciencias, Universidad de Alcalá. Ctra. Madrid-Barcelona, km 33.6, E-28871 Alcalá de
Henares, Madrid, Spain / 2. Corresponding author (mpilar.castro@uah.es) / Received July 14, 2006; accepted October 7, 2006; published online April 2, 2007
Summary
We compared seedling water relations of three Mediterranean Quercus species (the evergreen shrub Q. coccifera L., the evergreen tree Q. ilex L. subsp. ballota (Desf.) Samp. and the deciduous or marcescent tree Q. faginea L.). We also explored seedling potential for acclimation to contrasting growing conditions. In March, 1-year-old seedlings
of the three species were planted in pots and grown outdoors in a factorial combination of two irrigation regimes (daily (HW)
and alternate day watering (LW)) and two irradiances (43 and 100% of full sunlight). At the end of July, predawn and midday
water potentials (Ψpd, Ψmd) were measured, and pressure–volume (P–V) curves were obtained for mature current-year shoots. Species exhibited similar
Ψpd and Ψmd values, but differed in leaf morphology and water relations. The evergreens possessed larger leaf mass per area (LMA) and
were able to maintain positive turgor pressure at lower water potentials than the deciduous species because of their lower
osmotic potential at full turgor. However, the three species had similar relative water contents at the turgor loss point
because Q. faginea compensated for its higher osmotic potential with greater cell wall elasticity. Values of Ψpd had a mean of –1.12 MPa in LW and –0.63 MPa in HW, and Ψmd had a mean of –1.13 MPa in full sunlight and –1.64 MPa in shade, where seedlings exhibited lower LMA. However, the P–V curve
traits were unaffected by the treatments. Our results suggest that Q. faginea seedlings combine the water-use characteristics of mesic deciduous oak and the drought-tolerance of xeric evergreen oak.
The ability of Q. coccifera to colonize drier sites than Q. ilex was not a result of higher drought tolerance, but rather may be associated with other dehydration postponement mechanisms
including drought-induced leaf shedding. The lack of treatment effects may reflect a relatively low contrast between treatment
regimes, or a low inherent responsiveness of these traits in the study species, or both.
Keywords:
modulus of elasticity, osmotic adjustment, pressure-volume curves, shade, water stress.
