Seed Germination in <i>Phragmites australis</i> and <i>P. mauritianus</i> : Effects of Salinity and Thermoperiod

Understanding species-specific salt and heat tolerance mechanisms provides valuable insights into colonization and zonation patterns in saline environments. To explore these mechanisms, this study investigated the effects of selected salinity and thermoperiod on seed germination in the African haplotypes of the common reeds, <i>P. australis</i> and <i>P. mauritianus</i>. The effect of salinity was determined by germinating seeds in 0%, 5%, 10%, 20%, and 50% seawater at alternating night/day temperatures of 15°C/25°C and 20°C/30°C for 21 days. In both species, the highest germination, seedling vigor, root length, and number of leaves were obtained in the non-saline control treatment. In <i>P. australis,</i> there was 100% seed germination in the non-saline controls in both thermoperiods, while in <i>P. mauritianus</i>, germination was 36% and 45% lower, respectively. Salinity did not affect the germination of <i>P. australis</i> at 15°C/25°C, but at 20°C/30°C, germination decreased. In <i>P. mauritianus</i>, seed germination decreased significantly with an increase in salinity in both thermoperiods. Salinity and 20°C/30°C thermoperiod significantly reduced biomass, leaf production, culm height, and root elongation in both species. <i>Phragmites australis</i> was more salt-tolerant than <i>P. mauritianus</i>, as germination percentage, biomass, root length, and seedling vigor index were higher in both thermoperiods. Neither species germinated at 5°C and 35°C/40°C thermoperiods; however, <i>P. australis</i> seeds exhibited higher viability as indicated by a greater germination recovery percentage compared to <i>P. mauritianus</i>. <i>Phragmites australis</i> seeds are lighter, fluffier, more viable, disperse easily, and may contribute to its ability to colonize a greater diversity of habitats compared to <i>P. mauritianus</i>.