Effects of short-term exposure to different salinity levels on Myriophyllum spicatum and Ceratophyllum demersum and suitability of biomarkers to evaluate macrophyte responses to salinity stress

Sea-level rise caused by global warming is leading to increased freshwater salinization, which causes significant stress on aquatic ecosystems and species, including macrophytes. To form a better understanding of the responses of macrophytes to salinity stress, we assessed biochemical, pigmentation and growth responses of Myriophyllum spicatum L. and Ceratophyllum demersum L. exposed to different salinity levels (0, 1.5, 2.5, 5.0, and 10 ppt). For both species, elongation rates decreased, and levels of photosynthetic pigments (chlorophyll a and chlorophyll b) increased at higher salinities (5 ppt and 10 ppt). Anthocyanin and H2O2 concentrations increased in M. spicatum but decreased in C. demersum with the increase in salinity. The activities of antioxidant enzymes (guaiacol peroxidase, catalase, and ascorbate peroxidase) were different between two species and fluctuated along the salinity gradient. M. spicatum and C. demersum exhibit species-specific salinity sensitivities, reaching different physiological statuses at each salinity level. Elongation rates were significantly correlated with several biochemical parameters in a species-specific manner. These correlations can be used in evaluating the expected responses of these two species to salinity changes. The species-specific responses of most parameters measured in the present study suggests the inapplicability of common biochemical responses across species.