Water stress impact on young seedling growth of Acacia arabica

Drought is the major constraint in arid regions throughout the world and identification of drought-resistant plants is therefore of crucial importance. Since young seedling stage is especially sensitive to water stress, the present work analyzed the physiological behavior of seedling from Acacia arabica issued from a dry area, grown under controlled environmental conditions and subjected to progressive soil drying. Although soil gravimetric water content (g H2O g(-1) soil dry weight) dropped from 80 % to less than 35 %, most plants remained alive until the end of the water stress. Seedlings were able to efficiently close their stomata to reduce water losses and accumulated high amounts of proline. Despite osmotic adjustment, turgor pressure decreased in stressed plants and could explain the stress-induced inhibition of plant growth. Decrease in net photosynthesis was related to stress-induced decrease in stomatal conductance and not to any impact on chlorophyll concentration or fluorescence-related parameter: both PSII efficiency and photochemical quenching remained unaffected by water stress while drought-induced increase in non-photochemical quenching should be regarded as a strategy to avoid over-energisation of the photosynthetic apparatus. Instantaneous water use efficiency increased in stressed plants comparative to controls. Oxidative stress estimated by malondialdehyde concentration was recorded only at the end of the treatment, suggesting that stressed plants remained able to cope with reactive oxygen species. Water stress induced an increase in anthocyanins, while aglycone flavonols decreased. Those compounds were not involved in the management of oxidative stress. It is concluded that A. arabica is a promising drought-resistant plant species for rehabilitation of dry areas.