A greenhouse investigation of responses to different water stress regimes of Laurus nobilis trees from two climatic regions

Plants from two populations of Laurus nobilis (Tunisia issued from a semi-arid inland site and Algeria originating from a coastal sub-humid area) were exposed during three months under similar controlled conditions to two stress intensities of permanent stress (60% (S1) and 20% (S2) of field capacity) or to cyclic water stress, plants being re-watered when the soil moisture dropped to 60% (S11) or 20% (S22) of field capacity. One-year old plants displayed contrasting physiological strategies to cope with water stress. Algeria exhibited a higher decrease in osmotic potential (Ψs) in relation to stress-induced proline accumulation. Glycinebetaine accumulated in response to drought in response to permanent stress (Algeria) or cyclic stress (Tunisia). The two populations had similar net photosynthesis (A) but Algeria exhibited higher water use efficiency (WUE) than Tunisia. A drought-induced increase in the apoplastic water content (AWC) was noticed in response to mild stress intensities (S1 and S11) in Tunisia and in response to higher stress intensities (S2 and S22) in Algeria in relation to a stress-induced accumulation of pectin and proportion of arabinose within the pectic fraction. Bulk modulus of elasticity (ɛ) increased in Tunisia in response to permanent drought and in Algeria in response to cyclic stress, as a result of a stress-induced increase in cellulose (Algeria) or hemicellulose (Tunisia). It is concluded that water stress tolerance could be achieved by both osmotic and elastic adjustment in the coastal population which did not exhibit a prodigal water use comparatively to the inland population. Differences between populations are strongly influenced by the kinetics of water stress application.