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Background: Ziziphus lotus, wild jujube, is a xerophytic shrub of the Rhamnaceae family widely distributed in arid and semi-arid regions of Tunisia, where it occupies most soil types. Phenological patterns of desert plants are strongly affected by the seasonality of water availability and phreatophytes represent a particularly interesting case for studying such relationships.

Aim: This study aims to investigate the relationship between phenological traits and water potential patterns of the wild jujube as a tool for understanding how plants cope with extreme drought.

Methods: Phenophases and predawn (Psi(pd)) and midday (Psi(md)) xylem water potentials of wild jujube were studied monthly (Nov 2007-Oct 2008) at Samaaliate and Oued El Hallouf in southern Tunisia. These sites receive164 mm and 191 mm of annual rainfall, respectively, and differ in slope and soil type.

Results: The Psi(md) decreased progressively and concomitantly with increasing seasonal drought, reaching the lowest values in late summer (down to -3.9 MPa for both sites). Seasonality of Psi(pd) was less pronounced for plants established in Oued El Hallouf (-2.09 MPa) than in Samaaliate (-2.63 MPa) at the end of the dry season. Wild jujube is dormant from October through to March and mature plants flower in May and produce fruits in August.

Conclusions: Our results clearly demonstrate that wild jujube is a drought tolerant species reaching low water potentials during the driest months of summer.