Salt Tolerance of Sea Flax (Linum maritimum L.), a Rare Species with Conservation Interest in Eastern Spain

Abstract

Seldom found in saltmarshes, Linum maritimum is a halophyte of great conservation interest in the eastern Iberian Peninsula. Although the species has been reported in different plant communities, there is no information on its range of salinity tolerance or mechanisms of response to environmental stress factors. In this study, L. maritimum plants were subjected to increasing salt concentrations in controlled conditions in a greenhouse. After six months of watering with salt solutions, only plants from the control, 50 mM and 100 mM NaCl treatment groups survived, but seeds were produced only in the first two. Significant differences were found between the plants from the various treatment groups in terms of their growth parameters, such as plant height, fresh weight, and the quantity of flowers and fruits. The main mechanism of salt tolerance is probably related to the species' ability to activate K⁺ uptake and transport to shoots to partly counteract the accumulation of toxic Na⁺ ions. A biochemical analysis showed significant increases in glycine betaine, flavonoids and total phenolic compounds, highlighting the importance of osmotic regulation and antioxidant compounds in the salt tolerance of Linum maritimum. These findings have implications for the conservation of the species, especially under changing climatic conditions that may lead to increased soil salinity in its Mediterranean distribution area.

Keywords: biochemical parameters; biodiversity; conservation programmes; halophytes; plant growth analysis; salt stress; soil analysis.

Figure 1

Length (a), fresh weight (b) and water content (c) of the roots and shoots of Linum maritimum after six months of salt treatments. Values show means ± SE (n = 5). The same letters indicate homogeneous groups between treatments for roots and for shoots, respectively, according to the Tukey test (p < 0.05).

Figure 2

Evolution of flowering (a) and fruit set (b) showing the mean number of flowers and fruits per plant during the salt stress treatments in the spring and summer of 2022.

Figure 3

Mean seed length (SL), seed width (SWI) and seed weight (SWE) of seeds produced by control and 50 mM-NaCl-treated plants. Values shown are means per plate ± SE; n = 5. Different lowercase letters indicate significant differences between treatments for each determined variable, according to the Tukey test (p < 0.05).

Figure 4

The unilateral effect of the source of seeds (origin), the conditions of germination (treatment) (b), and the combined effect of the two factors for parameters that showed significant interaction with the two factors: germination percentages (a), mean radicle length (b), and mean seedling length (c). Significant differences between means are illustrated within each treatment with different letters, according to the Tukey test (p < 0.05). Abbreviations: S0, seeds produced by control plants grown without salt; S50, seeds produced by plants treated with 50 mM NaCl for six months; T0, germination in distilled water; and T50, germination in 50 mM NaCl solution.

Figure 5

Effect of stress treatments on the root and shoot contents of ions: (a) sodium; (b) potassium; (c) calcium; and (d) chloride. Values shown are means ± SE; n = 5. The same letters indicate homogeneous groups between treatments for roots and for shoots, respectively, according to the Tukey test (p < 0.05).