Aeluropus littoralis maintains adequate gas exchange, pigment composition and phenolic contents under combined effects of salinity and phosphorus deficiency

Salinity and phosphorus (P) deficiency are important environmental factors that decrease plant growth and productivity throughout the world. These two stresses frequently coexist in calcareous salt-affected soils. To better understand how plants adapt to these combined stresses, we investigated the interactive effects of salinity and P availability on photosynthetic activity, leaf pigment, phenolic compounds content and antioxidant activity in Aeluropus littoralis (Gouan)Parl., a promising C4 monocotyledonous halophyte that usually grows in dry salty areas or marshes. Plants were grown hydroponically under low or sufficient P supply (5 or 180µM KH2PO4 respectively), with or without 400mM NaCl. When individually applied, salinity and P deficiency stresses significantly restricted shoot and root relative growth rate, with a more marked effect of the former stress. However, the effects of the two stresses combined were non-additive on plant growth. Our results showed that salinity and P deficiency stresses applied individually or combined have no significant effect on CO2 assimilation rate, instantaneous water-use efficiency (WUEi), and leaf malondialdehyde content. Chlorophyll, carotoneoids, anthocyanins and phenolics content increased significantly under both P shortage and salt stresses applied individually or combined. Furthermore, a strong correlation was found between both total antioxidant capacity and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity and shoot phenolics and carotenoids contents. These results suggest that the ability of A. littoralis to cope with both P deficiency and high salt stresses is a result of several mechanisms mainly involved in the conservation of the integrity of the photosynthetic apparatus. Secondary metabolites – mainly phenolic compounds and carotenoids – play an important role in the protection of A. littoralis plants against oxidative damage under combined high salinity and P deficiency stresses.