Shrub seedlings were grown in 0.5 kg pots in a greenhouse
under controlled conditions (18–24 C, with a 18/6 light/dark
period and 50% of relative humidity). A photoperiod of 16 h at a
photosynthetic photon flux density (PPFD) of 400–700mmol m2
s1 as measured with a light meter (model LI-188B; Licor Inc.,
Lincoln, NE, USA) was maintained during the experiment by
supplementary light to compensate natural illumination. Water
was supplied daily to maintain constant soil water close to field
capacity (17% volumetric soil moisture) during 2 weeks after
transplanting. After this time, and during a period of 1 year, these
plants were allowed to dry until soil water content was 50% of field
capacity. However, during the 24-h period comprised between
each re-watering the soil water content was progressively
decreasing until a minimum value of 30% of field capacity. Soil
moisture was measured with an ML2 X ThetaProbe (AT Delta-T
Devides Ltd., Cambridge, UK), which measures volumetric soil
moisture content by responding to changes in the apparent
dielectric constant of moisture (Roth et al., 1992). This volumetric
soil moisture is considered to be a normal environmental condition
in dry Mediterranean areas. A completely random experimental
design was adopted.