Effects of Sodium Chloride and Sodium Sulfate on Haloxylon ammodendron Seed Germination

Haloxylon ammodendron adapts to desert environments through seed polymorphism during diaspore germination and seedling establishment

Introduction

Seed polymorphism, defined as the production of two or more types of diaspores with distinct morphology and ecological function within a species, represents a bet-hedging strategy that enables plants to cope with unpredictable spatiotemporal environmental variability. Previous studies have mainly focused on annual plants; therefore, little is known about in perennial species, particularly in desert constructive plants.

Methods

This study investigated seed polymorphism in Haloxylon ammodendron, a foundational desert shrub critical for maintaining the stability of fragile arid ecosystems. Field surveys, morphological characterization, phytohormone quantification, germination assays, and seedling growth analyses were conducted to elucidate the ecological significance of seed polymorphism in this species.

Results and discussion

Seed polymorphism was prevalent across natural populations within the study region, with different plants producing three distinctly colored diaspores: YY (yellow fruit-wing perianth and yellow pericarp), YP (yellow fruit-wing perianth and pink pericarp), and PP (pink fruit-wing perianth and pink pericarp). The fruit/diaspore biomass and gibberellic acid/abscisic acid ratio were the lowest in YY (0.611 and 0.64, respectively) and the highest in YP (0.684 and 1.56). YY plants exhibited grater drought resistant and produced fewer but more robust seedlings, ensuring population persistence. YP seeds have a higher germination percentage, germination rate, and emergence percentage, facilitating rapid population expansion under favorable conditions. PP seeds showed reduced germination under salt stress, suggesting a potential role as a persistent soil seed bank. These results indicate that H. ammodendron employs seed polymorphism to adapt to unpredictable desert environment during diaspore germination and seedling establishment. This study enhances the theoretical understanding of the bionomic strategies underpinning plant adaptation to extreme environments, with implications for population persistence and regeneration dynamics, while also providing diversified germplasm resources for desertification prevention.

Effect of Salinity and Temperature on the Seed Germination and Seedling Growth of Desert Forage Grass Lasiurus scindicus Henr

Lasiurus scindicus Henr. is one of the most important forage grass species of the Arabian deserts. Temperature and soil salinity are well known to influence the germination and seedling development of various forage species. Therefore, in the current study, the effect of temperature and salinity and their interaction on the germination parameters, seedling growth, and physiological parameters of L. scindicus were evaluated. For this reason, L. scindicus seeds were treated with five salinity concentrations (i.e., 0, 50, 100, 150, and 200 mM NaCl) and incubated at two temperature levels (T1 = 25/20 °C, D/N and T2 = 35/30 °C, D/N). The results indicated that the salinity and temperature significantly affected the germination indices, seedling growth parameters, chlorophyll, and proline content. The highest germination percentage (GP; 90%) was recorded in the non-saline-treated seeds incubated at T1. The seeds at T2 under the non-saline treatment exhibited an increased germination rate (GR = 17.5%). The interactive effect of salinity and temperature on germination and growth parameters was significant, indicating that the germination response to salinity depends on temperature. The germination of seeds treated with 200 mM NaCl was completely inhibited at both temperatures T1 and T2. However, the ungerminated seeds at both T1 (85%) and T2 (78%) restored their germination abilities after they were transferred to distilled water. Also, the seed vigor index (SVI) constantly showed a decline with the increasing salinity levels especially at T2, which was lowest when seeds were treated with 150 mM salinity. Growth parameters (i.e., aRL, aSL, RDW, SDW, SB, and SLA) and the chlorophyll content showed a similar pattern as that of germination. However, the proline content (shoot proline and root proline) showed a progressive increase with increasing salinity and temperature. All of these characteristics indicate that L. scindicus seeds were not able to germinate under extreme salinity and temperature conditions but remained viable in a state of enforced dormancy. This is most likely an important adaptive strategy of this species for survival in the high-saline changing habitats of the arid region of Saudi Arabia, and thus, it can be an excellent choice for restoring degraded rangelands and salinity-inflicted abundant farmlands for forage agriculture.