231 INTRODUCTION Studies of the functional mechanisms and behavior of plants are needed, in order to use phytogenetic re- sources in the rehabilitation and restoration programs of degraded ecosystems. Indeed, given the scale of disturbance affecting the arid and saharan ecosystems of Tunisia, attempts to improve and restore the ecological balance are deemed necessary (Aronson et al., 1993). However, the success of such operations can only be guaran- teed by the use of native species (Chaieb et al., 1992; Ourcival et al., 1994). Several studies have been car- ried out in the Tunisian arid zones on the water use dynamics of various perennial species (Floret & Pon- tanier, 1978; Le Houérou, 1984) such as Cenchrus cil- iaris, Stipa lagascae, Plantago albicans, Argyrolobium uniflorum. In addition to their pastoral qualities, these species are suitable for sand stabilization and com- bating desertification (Le Houérou, 1995). Further- more, they improve the soil water balance by reducing soil aridity (Floret & Pontanier, 1984). Our contribu- tion towards the process of even partial restoration of the ecological balance in the North African environ- ment in general and in Tunisia in particular, consists an ecophysiological study of one key species of Tuni- sian arid zones. Cenchrus ciliaris L. is a perennial buffel grass and C 4 plant, in the grass family (Poaceae), invading arid tropical habitats around the globe. It is one of the candidate species for ecological restoration of de- Net photosynthesis and leaf water potential of buffel grass (Cenchrus ciliaris L.) accessions, growing in the arid zone of Tunisia Lobna MNIF * and Mohamed CHAIEB Department of Biology, Faculty of Sciences, U.R. of Biology & Ecophysiology of Arid Ecosystems, Sfax, Tunisia Received: 4 August 2009 Accepted after revision: 12 January 2010 Four local Cenchrus ciliaris L. accessions (P1: Bou Hedma, P2: Tozeur, P3: Raâs Jedir, and P4: Sidi Toui) were planted in a common garden experiment in Tunisia in autumn 2002. Net photo- synthesis (Pn), stomatal conductance (gs) and leaf water potential (æ) were measured between September 2003 and September 2004. All accessions showed two distinct periods of growth, in- terspersed by summer and winter dormancy periods. Initiation of the cycle occurred in autumn and appeared to be associated with soil water availability. There were significant differences (p < 0.001) between seasonal measures of net photosynthesis (Pn) and stomatal conductance (gs) of each accession. The highest value was observed for accession P3 (42 Ìmol m –2 s –1 ). P1 and P4 showed the same value of Pn (35 Ìmol m –2 s –1 ) in spring. Photosynthetic rate (Pn) of all acces- sions decreased with decreased stomatal conductance (gs). The annual course of predawn water potential (æ pd ) and minimum water potential (æ md ) observed during the year, showed that lower water potentials were observed at the end of spring (–3.0 MPa). As would be expected, higher water potentials (–1.0 MPa) were observed during winter, due to the high level of rainfall during that season. It has been observed that seasonal water availability and air temperature influence the seasonal dynamics of photosynthesis and leaf water potential. Cenchrus ciliaris accessions originated from different regions of Tunisia, and growing under the same conditions did not differ in their net photosynthesis and water status. Key words: gas exchange, arid bioclimate. * Corresponding author: tel.: +21 698488250, fax: +21 674274437, e-mail: mniflobna@yahoo.fr Journal of Biological Research-Thessaloniki 14: 231 – 238, 2010 J. Biol. Res.-Thessalon. is available online at http://www.jbr.gr Indexed in: WoS (Web of Science, ISI Thomson), SCOPUS, CAS (Chemical Abstracts Service) and DOAJ (Directory of Open Access Journals)