Phenolic accumulation and related antioxidant capacity in stems and roots of the Tunisian extremophile Sulla carnosa as influenced by potassium application under salinity stress

Abstract

Salinity and potassium deficiency are major abiotic constraints affecting plant growth, productivity, and metabolism. The present work was conducted to check whether salinity alleviates, aggravates, or does not affect the effects of potassium deficiency on Sulla carnosa, a salt-tolerant legume common in diverse saline soils. We investigated the changes in plant growth, phenolic compound composition, and antioxidant activity in stems and roots of this species grown hydroponically under different conditions: C, control (complete nutrient solution containing 6 mM K+ and not added with NaCl); KD, K+ deficiency (K+-deficient nutrient solution (60 μM K+) not added with NaCl); C + S, salt treatment (control nutrient solution containing 6 mM K+ and added with 100 mM NaCl); and KD + S, combined treatment between salinity and K+ deficiency (K+-deficient nutrient solution (60 μM K+) added with 100 mM NaCl). Results showed that all treatments applied led to a significant decrease of root and stem growth, with a more marked reduction in plants exposed to the combined stresses, suggesting synergistic effects of salinity and K+ deficiency. In addition, results indicated that both stresses either applied alone or in combination quantitatively or qualitatively modulated phenolic compound accumulation and their antioxidant activities. But a predominance of K+ deficiency effect was noticed, which may be considered as a suitable manipulation for the production of antioxidants compared to the other treatments.