Sargassum horneri blooms have been a major issue in East China Sea, the Yellow Sea and Korea since 2015, causing significant damages to seaweed farms in Korea and China. Due to the economic and ecological risks induced by the extensive growth of S. horneri, efforts have been made to utilize the massive biomass of S. horneri by extracting useful bioactive compounds . S. horneri extract’s efficacies such as anti-oxidant, anti-inflammatory, and anti-tumor activities have been demonstrated by several studies . Suaeda maritima and Salicornia herbacea are major s pecies of saltmarsh plant, widely distributed in Korea, and they have been proposed as good candidates to be used in saltmarsh afforestation . Thus, we examined how Sargassum horneri extract (SHE) affects the germination and seedling growth of Su. maritima and Sa. herbacea for 18 days, both at optimal and elevated temperatures.
In the group exposed to SHE treatment, seeds were placed within Petri dishes containing filter papers soaked with approximately 5 - 7 ml of a 0.5% SHE solution diluted with deionized water (DW). In contrast, the control group had filter papers moistened only with DW. The Petri dishes were maintained at a temperature of 25°C, while, for the heat stress condition, an identical set of experimental trials was conducted at 30°C. The light was set at an intensity of 20 μmol photons m -2 s-1 , and the photoperiod followed a 12:12 (L:D).
W e observed a clear enhancement in thermal tolerance in Sa. herbacea due to the application of SHE. In the presence of both heat stress and SHE treatment, the germination percentage (GP) and seedling vigor index (SVI) of Sa. herbacea were 33.3% and 25.8, respectively (Figure 1) . These values were significantly higher compared to those of the untreated group, which recorded 20% for GP and 12.3 for the SVI (P<0.05) . However, in the case of the Su. maritima experiment, there was no observed improvement in thermal tolerance induced by SHE treatment. These findings suggest that the application of Sargassum horneri extract can enhance thermal tolerance in Sa. herbacea, and the effect of SHE for thermal tolerance improvement may be species specific.
Figure 1. Germination percent (Above) and Seedling vigor index (Below) of Suaeda maritima and Salicornia herbacea seeds in optimal and heat stressed temperature.