Trifolium spp. are native plants in Iran exhibiting good ground cover po- tential. Salinity is a major environmental stress and today, 20% of the world cultivated areas and nearly half of all irrigated lands are affected by salinity. The main aim of this research was to study morphological and physiological adaptations of these native species under different salinity levels for urban landscape usage. For this purpose a factorial experiment based on completely randomized design (CRD) with 4 replicates was conducted. Plants of Trifolium repens and two Trifolium pratense species (native and commercial) were submitted to salinity stress in a pot experiment with 4 different salinity levels (0, 75, 150, 225 mM NaCl) during the experiment period. Leaf area, LRWC (leaf relative water content), electrolyte leakage, root and shoot length and root and shoot fresh and dry weight were measured. Results showed significant dif- ferences within salinity treatments in all 3 species studied. Highest values measured for traits in cultivars were observed in T. pratense commercial followed by T. pratense native and T. repens except electrolyte leakage and root fresh weight. But salinity effect on these species increased along with severity, linearly. Leaf area was most affected and decreased to 40.21 mm2 (225 mM) from 184.14 mm2 in control. Generally Trifolium species showed sensitivity to salinity stress, especially in higher levels. This study should help understand some physiological and morphological responses of Trifolium species to salinity stress for urban landscape projects, parks and xeriscapes in Iran.

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