Combined effect of salinity and hypoxia in seedlings of two varieties of Panicum coloratum: Morphology, root system architecture, oxidative damage and antioxidant response

The effect of the combination of salinity and waterlogging may be additive, or alternatively, more or less detrimental than effects of them separately. Our objective was to evaluate the effects of waterlogging, salinity and the combination of both on seedlings of Panicum coloratum, a subtropical forage grass. Seedlings of cultivars Kapivera INTA (KA) and Klein (KL) were exposed to treatments in a controlled hydroponic experiment and several morphological and physiological variables evaluated. The effect of hypoxia was almost null when the plants were already in salinity. KA showed lower reduction than KL in shoot biomass. Both varieties showed synergistic effect of stresses, indicating that biomass production was less affected under the combined treatment than predicted from them separately. Root length, tips, forks and volume were reduced by saline exposure, while no differences in root architecture was noticeable between cultivars. Plants of KA increased leaf temperature in salinity. Nonenzymatic oxidative response and the activity of antioxidant enzymes increased in saline conditions and were lower in KA than in KL. Oxidative damage was equivalent between cultivars and among stress conditions. Proline content was comparable to control in hypoxia but increased significantly in saline conditions, with a higher response in KL than in KA. Increases in Na+ (over 900%) and decreases in K+ (50%) tissue concentration in salinity occurred only in KA. In general, P. coloratum proved more tolerant to hypoxia than to salinity or their combination, KA being more tolerant than KL. Findings provide basis to deepen research into tolerance mechanisms.