Evaluation of direct and transgenerational influences of salinity on germination and early seedling growth in an edible halophyte, Crithmum maritimum

Abstract

Background and aims: Crithmum maritimum is a wild, edible halophyte with large potential as a cash crop for salinized soils. However, its tolerance during seed germination appears to be highly site-specific and contradictory, whereas little is known on salinity tolerance during early seedling growth. This study aimed to characterize variation in the responses of germination and early seedling growth in diverse C. maritimum populations along the southwest Iberian coast. Specifically, we sought to distinguish between direct salinity effects and those influenced by the salinity of maternal environments.

Methods: Physicochemical properties, including salinity of maternal environments, were assessed across diverse habitats. A total of 3480 seeds from 58 mother plants were utilized. Seeds were subjected to germination assays under various salinity treatments (0-500 mM NaCl), with subsequent monitoring of germination parameters. Non-germinated seeds were tested for recovery germination, and viability was assessed using a tetrazolium test. Of germinated seeds, 1160 seedlings were monitored for survival and early growth metrics. General Linear Models were used to analyse the effects of salinity and maternal environmental influence on germination and early growth.

Key results: Despite reduced and delayed germination under salinity, seeds showed remarkable tolerance up to 150 mM, surpassing prior reports, with consistent viability up to 500 mM, indicating substantial salinity-induced dormancy. Seedling growth was more sensitive to continued treatment; no plants survived above 150 mM. The salinity experienced by maternal plants had only a marginal effect on germination but significantly contributed to reduce seedling biomass production, both above and below ground.

Conclusions: This study highlights the significance of maternal salinity on early growth in C. maritimum, emphasizing the species' resilience to salt stress during germination and recovery. These insights are crucial for optimizing cultivation techniques and informing research on other halophytes in saline environments.

Keywords: Sea fennel; halophytic response; maternal effects; salinity tolerance; seed growth; soil salinity.

Fig. 1.

Map showing the location of study populations on the southern Iberian coast.

Fig. 2.

Topsoil conductivity (0–30 cm depth) measured at 10–20 cm from the projected canopy of each C. maritimum plant from sampled populations. Dashed lines represent the threshold values used to categorize maternal salinity: low salinity (<100 mS cm⁻¹), intermediate salinity (101–200 mS cm⁻¹), high salinity (201–450 mS cm⁻¹) and hypersalinity soils (>450 mS cm⁻¹).

Fig. 3.

Germination parameters and viability of C. maritimum seeds in different salinity treatments (50–500 mM) and non-saline solution (0 mM NaCl). (A) Final germination percentage at the end of the experiment (104 d). (B) Lag time (d). (C) Mean germination time (d). (D) Germination index. (E) Reciprocal of the time to 50 % of the final germination percentage (1/T₅₀). (F) Percentage of total viable seeds (including seeds that germinated in saline solutions, seeds that recovered and germinated after being transferred to distilled water, and seeds that were viable according to the tetrazolium test). (G) Percentage of seeds germinated in distilled water following exposure to saline conditions (recovery). (H) Percentage of viable seed according to the tetrazolium test. Different letters indicate significant differences (P < 0.05). Data represent mean and standard error of 58 independent replicates. N/A, not applicable.

Fig. 4.

Responses of different parameters related to early growth and plant water status depending on the salinity treatments where they germinated (50–500 mM NaCl or non-saline solution). (A) Relative growth rate (g g^–1 d^–1). (B) Below-ground biomass (g dry weight per plant). (C) Above-ground biomass (g dry weight per plant). (D) Maximum vegetative height (cm). (E) Relative water content (%). Different letters indicate significant differences (P < 0.05). Data represent means and standard errors of 201–264 independent replicates.

Fig. 5.

Maternal effects on the germination and viability of C. maritimum seeds assessed based on the maternal salinity (<100, 100–200, 201–450, > 450 mS cm⁻¹). (A) Final germination percentage at the end of the experiment (104 d). (B) Lag time (d). (C) Mean germination time (d). (D) Germination index. (E) Reciprocal of the time to 50 % of the final germination percentage (1/T₅₀). (F) Percentage of total viable seeds (including seeds that germinated in saline solutions, seeds that recovered and germinated after being transferred to distilled water, and seeds that were viable according to the tetrazolium test). (G) Percentage of seeds germinated in distilled water following exposure to saline conditions (recovery). (H) Percentage of viable seed according to the tetrazolium test. Different letters indicate significant differences (P < 0.05). Data represent mean and standard error of 78–90 independent replicates.

Fig. 6.

Maternal effects on different parameters related to early seedling growth and plant water status in C. maritimum. (A) Relative growth rate (g DW g^–1 d^–1). (B) Below-ground biomass (g dry weight per plant). (C) Above-ground biomass (g dry weight per plant). (D) Maximum vegetative height (cm). (E) Relative water content (%). Different letters indicate significant differences (P < 0.05). *Marginally significant effects. Data represent mean and standard error of 222–259 independent replicates.