Morphological and physiological responses of some halophytes to salinity stress

Abstract

<p>A pot experiment was conducted to examine whether the morphological and physiological characteristics of some halophytes may be affected by salt stress. For this purpose, a factorial experiment based on randomized complete block design was carried out with three replications. The treatments were some halophytes (<em>Salicornia europaea</em>, <em>Atriplex leucoclada, </em>and <em>Kochia scoparia</em>) and salinity stress levels [Electrical conductivity 0 (Hoagland’s solution), Hoagland’s solution consisting of 100, 200, 300 and 500 mM NaCl]. Among the halophytes tested, <em>Salicornia europaea </em>had significantly higher shoot and root of dry matters compared to the other halophytes in all salt treatments. Salinity stress resulted in an increase in photosynthetic pigments up to 200 mM and thereafter, it decreased in all of the studied plants. Photosynthetic pigments, ranked in a descending order, were high in <em>Kochia scoparia</em>, <em>Salicornia europaea, </em>and <em>Atriplex leucoclada</em>. In addition, salinity stress led to an enhancement in malondialdehyde (MDA) and H2O2. The tolerance of <em>Salicornia europaea </em>under high salinity stress was associated with low MDA and H2O2 contents as well as high contents of photosynthetic pigments. The shoot and root Na+ increased considerably by augmenting the salinity levels in all halophytic plants; however, there was a significant difference among halophytes at higher salinity levels. The shoot K+ decreased by increasing the salinity levels, but K+ partitioning pattern varied among the halophytes. Under saline conditions, the shoot and root Na+/K+ ratio of all halophytes grew. The highest and the lowest of Na+ were observed in <em>Salicornia europaea </em>and <em>Kochia scoparia</em>, respectively. Thus, the Na+/K+ ratio could be considered as an indicator of salt evaluation. Nitrogen, protein content, dry matter digestibility (DMD), and metabolizable energy (ME) were high in <em>Salicornia europaea </em>plants in comparison to other plants at 200–500 mM salinity levels; in contrast, acid detergent fiber (ADF) and netural detergent fiber (NDF) were low. According to the results of this study, the tolerance of halophytes towards NaCl is possibly due to the differences in damage from reactive oxygen species (ROS), especially H2O2, and toxicity to metabolism Na+.</p>