Effects of Hydrothermal Conditions and Salinity Stress on the Seed Germination of the Threatened Arid Zone Samphire Tecticornia lylei (Amaranthaceae: Salicornioideae)

ABSTRACT

Seed germination of species in arid zones is shaped by climatic extremes, which include high temperatures, prolonged drought and episodic rainfall. Halophytic plants, such as samphires, face additional pressure from fluctuating salinity. It is anticipated that current physiological thresholds will be surpassed for many species because of climate change, resulting in disrupted plant recruitment patterns as seed germination windows narrow or shift. Our study aimed to determine the timing of germination opportunities for the threatened samphire Tecticornia lylei and understand the effects that climate change may have on future recruitment. We assessed the germination responses of seeds to light, temperature, water and salinity stress. The comparative effects of salinity and water stress under increasing temperatures were also observed, as were responses to freshwater exposure characteristic of episodic rainfall. We found seeds removed from fruits commenced germination more rapidly, but other treatments assessed had minimal effect on final germination percentages. Tecticornia lylei germinated optimally in cooler conditions under constant darkness, but also had capacity for strong germination in fluctuating light/dark photoperiods. Low numbers were observed to germinate at higher temperatures, and under water stress which caused greater delays than salinity stress, with increasing temperatures exacerbating these effects. However, ungerminated seeds responded rapidly to freshwater treatment, even after exposure to stress levels that surpassed thresholds for germination, this being suggestive of the action of a priming effect. While Tecticornia lylei has a broad thermal window for germination in very low stress environments, it narrows substantially as osmotic stress increases. High rainfall events during cooler seasons are therefore critical to reduce salinity and increase soil moisture for sufficient time for seeds to germinate in high numbers.