Negative effects of long-term exposure to salinity, drought, and combined stresses on halophyte Halogeton glomeratus

Plants are subjected to salt and drought stresses concurrently but our knowledge about the effects of combined stress on plants is limited, especially on halophytes. We aim to study if some diverse drought and salt tolerance traits in halophyte may explain their tolerance to salinity and drought stresses, individual and in combination, and identify key traits that influence growth under such stress conditions. Here, the halophyte Halogeton glomeratus was grown under control, single or combinations of 60 days drought and salt treatments, and morphophysiological responses were tested. Our results showed that drought, salinity, and combination of these two stressors decreased plant growth (shoot height, root length, and biomass), leaf photosynthetic pigments content (chlorophyll a, b, a + b and carotenoids), gas exchange parameters (Net photosynthesis rate [P-N], transpiration rate [E], stomatal conductance [g(s)]), and water potential (psi(w)), and the decreases were more prominent under combined drought and salinity treatment compared with these two stressors individually performed. Similarly, combined drought and salinity treatment induced more severe oxidative stress as indicated by more hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulated. Nevertheless, H. glomeratus is equipped with specific mechanisms to protect itself against drought and salt stresses, including upregulation of superoxide dismutases (SOD; EC 1.15.1.1) and catalase (CAT; EC 1.11.1.6) activities and accumulation of osmoprotectants (Na+, Cl-, and soluble sugar). Our results indicated that photosynthetic pigments content, gas exchange parameters, water potential, APX activity, CAT activity, soluble sugar, H2O2, and MDA are valuable screening criteria for drought and salt, alone or combined, and provide the tolerant assessment of H. glomeratus.

Automated summary

Halophyte plant Halogeton glomeratus shows specific morphophysiological responses under drought and salt treatments, with a more significant impact observed under combined stress. The plant has mechanisms to protect itself from drought and salt stresses through upregulation of antioxidant enzymes and accumulation of osmoprotectants. Valuable screening criteria for drought and salt tolerance include photosynthetic pigments content, gas exchange parameters, and oxidative stress indicators.