Dhief, A., Abdellaoui, R., Tarhouni, M., Belgacem, A. O., Smiti, S. A. and Neffati, M. 2011. Root and aboveground growth of rhizotron-grown seedlings of three Tunisian Desert Calligonum species under water deficit. Can. J. Soil Sci. 91: 15-27. In southern Tunisia, plants are subjected to severe drought and many human disturbances, causing the degradation of soils and plants. The study of wild plants and their response to water deficit can facilitate their conservation and help in ecosystem rehabilitation. In this context, the adaptive responses to water deficit of three desert Calligonum species (C. comosum L'Herit, C. azel Maire and C. arich Le Houerou), differing in their topographic location, were studied in rhizotrons under two water regimes. The objectives were to correlate the adaptive ability of these species, with several developmental traits, such as root architecture and growth, aerial growth and height, with environmental and soil properties, and to define which of the three Calligonum species is best adapted to water stress. Water deficit was applied when plants formed two green branches, and measurements were carried out over 8 mo. Under water deficit, all species increased their cumulative root length. In deeper soil layers, only treated C. arich plants developed secondary roots. Under drought, C. azel and C. arich increased their biomass production during the experiment. It seems that C. arich has adapted better to water deficit by developing a deep root system and the greatest root and aboveground biomass. Hence, C. arich is suggested as the best species for early dune stabilization and biomass production.