Journal of Forestry Research (2014) 25(1): 155-161 DOI 10.1007/s11676-014-0441-6 Morphogenetic responses of Populus alba L. under salt stress Mejda Abassi  Khaled Mguis  Zoubeir Béjaoui  Ali Albouchi Received: 2012-06-16 Accepted: 2012-10-25 © Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2014 Abstract: The morphogenetic responses to salt stress of Tunisian Popu- lus alba clones were studied in order to promote their plantation in dam- aged saline areas. One year-old plants of three P. alba clones (MA-104, MA-195 and OG) were subjected to progressive salt stress by irrigation during two consecutive years. The plants were grown in a nursery, inside plastic receptacles containing sandy soil and were irrigated with tap water (control) or 3–6 g/l NaCl solution. During this study, leaf epinasty, elongation rate, vigor, internode length, plant architecture, and number of buds were evaluated. Test clone response was highly dependent on the applied treatment and degree of accommodation. The most pronounced alterations were induced under 6g/l of NaCl treatment including leaf epinasty, leaf elongation rate delay, vigor decrease, internode length shortening, and morphogenetic modifications. These responses were less noticeable in the MA-104 clone with respect to the two other clones. The salt effect induced a delay in the leaf elongation rate on the MA-195 and OG clones leading to an early leaf maturity. The vigour and internode length of the MA-104 clone was less affected than the other clones. The OG clone was the most salt-sensitive thus, it developed shorter branches and more buds number than MA-195 and MA-104. The effect of long-term salt stress was to induce early flowering of the P. alba clones which suggests that mechanism of salt accommodation could be devel- oped. Keywords: Poplar, salinity, leaf elongation, vigor, internode length, floral bud Introduction In Tunisia, the lack of summer rainfall, high evaporative demand, and high salinity of irrigation water has caused salt to accumulate in the soil. Such accumulation has been increased in some areas, the result of inadequate irrigation practices and lack of suitable The online version is available at http://link.springer.com Mejda Abassi †  Khaled Mguis ( ) †  Zoubeir Béjaoui Ali Albouchi Unit of Agrosulvopastoralisme, INRGREF, Hedi El Karray Street, 2080 Ariana, Tunisia † First and second authors contributed equally in this work E-mail: k_guigis@yahoo.fr ; Tel.: 21697680666; Fax: 21671717951 Corresponding editor: Chai Ruihai leaching, which raised water levels bringing salts to the soil sur- face. Saline and waterlogged areas covered respectively 12% (Mashali et al. 2005) and 10% of the country total area (Béjaoui et al. 2008), making rehabilitation of these areas complex and expensive (FAO 2005). Using fast-growing woody species such as Populus sp., which is known to tolerate salinity (Marcar et al. 1993) and has higher water consumption, might be an opportu- nity to phytoremediate such areas and, in the mean time, could decrease water levels. The genus Populus is widespread in the Mediterranean, Cen- tral Europe, and the Middle East. By comparing the response of different P. alba and P. nigra clones to increasing levels of salin- ity, Abassi et al. (2004) showed encouraging tolerance degree of P. alba but with great variability among the clones. Furthermore, Sixto et al. (2005) pointed out that Spanish genotypes of P. alba showed an intermediate degree of tolerance to salinity between the one displayed by Populus euphratica, known as the most tolerant poplar species (Chen et al. 2003), and the one displayed by an hybrid of P. euramericana and P.deltoides × P. alba clones. Given the high variability of P. alba clones, a better understand- ing of morphological responses to salt stress is required before their utilization in degraded saline sites. Plants growing in saline soils encounter osmotic stress and ion imbalance or disturbance in ion homeostasis and toxicity (Hu et al. 2005). Changes in water status can lead to reduce initial growth and limit plant productivity (Parida and Das 2005). The immediate response to salt stress is the moderate reduction to cessation of leaf surface expansion as salt concentration rises (Wang and Nil 2000) and petiole epinasty (El Iklil et al. 2000). After longer period of salt stress, detrimental effects are induced at the plant morphology, such as shortening internode length (Gucci et al. 1997; Barhoumi et al. 2007) and plant stunting (Takemura et al. 2002). Moreover, studies show that abiotic stress induced early-flowering of a Populus genotype (Meilan et al. 2004). The overall goal of this study is to define the adaptive mecha- nisms developed by Tunisian P. alba clones in response to long-term salt stress through induced morphogenetic modifica- tions. Three clones, different in terms of their tolerance to salin- ity, were compared by measurement of leaf expansion rate and epinasty, as well as, morphogenetic traits. ORIGINAL PAPER