ABSTRACT: The common reed (Phragmites australis) is a clonal wetland grass with high genetic variability. Clone-specific differences are reflected in morphological and physiological traits, and hence in the ability to cope with environmental stress. The responses to progressively increasing salinity of fifteen distinct Phragmites australis clones reveal genotype-related strategies of salt avoidance and exclusion. The salinity-induced inhibition in shoot elongation rate and photosynthesis varies widely between clones. The differences can be partially attributed to their geographic range, but not correlated to ploidy level. Thus, the genetic background is a major factor influencing the salinity tolerance of distinct Phragmites australis clones. Different clones of the wetland grass Phragmites australis differ in their morphology and physiology, and hence in their ability to cope with environmental stress. We analysed the responses of 15 P. australis clones with distinct ploidy levels (PLs) (4n, 6n, 8n, 10n, 12n) and geographic origins (Romania, Russia, Japan, Czech Republic, Australia) to step-wise increased salinity (8, 16, 24, 32, 40, 56 and 72 ppt). Shoot elongation rate, photosynthesis and plant part-specific ion accumulation were studied in order to assess if traits associated with salinity tolerance can be related to the genetic background and the geographic origin of the clones. Salt stress affected all clones, but at different rates. The maximum height was reduced from 1860 mm in control plants to 660 mm at 40 ppt salinity. The shoot elongation rate of salt-exposed plants varied significantly between clones until 40 ppt salinity. The light-saturated photosynthesis rate (Pmax) was stimulated by a salinity of 8 ppt, but decreased significantly at higher salinities. The stomatal conductance (gs) and the transpiration rate (E) decreased with increasing salinity. Only three clones survived at 72 ppt salinity, although their rates of photosynthesis were strongly inhibited. The roots and basal leaves of the salt-exposed plants accumulated high concentrations of water-extractable Na+ (1646 and 1004 µmol g?1 dry mass (DM), respectively) and Cl? (1876 and 1400 µmol g?1 DM, respectively). The concentrations of water-extractable Mg2+ and Ca2+ were reduced in salt-exposed plants compared with controls. The variation of all the measured parameters was higher among clones than among PLs. We conclude that the salinity tolerance of distinct P. australis clones varies widely and can be partially attributed to their longitudinal geographic origin, but not to PL. Further investigation will help in improving the understanding of this species' salt tolerance mechanisms and their connection to genetic factors.
