Jae Jung Ahn’s scientific contributions

Betula platyphylla var. japonica, a member of the Betulaceae family, is a temperate landscape tree species with significant industrial value. This study investigated the effects of short-term dry-cold treatment periods that ranged from 0 to 60 days on the germination success of B. platyphylla var. japonica seeds and their post-germination growth and physiological characteristics. The short-term dry-cold treatment periods were 0 (control), 15, 30, 45, and 60 days. The results revealed that seeds subjected to a 30-day dry-cold treatment period exhibited the highest germination percentage, seedling survival rate, and germination energy, whereas relatively longer dry-cold treatment periods significantly decreased these parameters. Furthermore, the control without any dry-cold treatment exhibited a more pronounced decrease in these parameters. In contrast, the 15-day dry-cold treatment period was observed to be most beneficial in regard to enhancing the size and biomass of B. platyphylla var. japonica seedlings. Analysis of the remote sensing vegetation indices and chlorophyll fluorescence responses used to assess the physiological characteristics of seedlings indicated that a dry-cold treatment period of 0-15 days was the most appropriate. Therefore, when the primary objective is to maximize germination success and seedling survival rates, a 30-day dry-cold treatment period is optimal. Conversely, if the goal is to enhance rapid seedling growth and improve physiological characteristics, a 15-day short-term dry-cold treatment period is the most suitable. These findings offer valuable guidance for selecting appropriate short-term dry-cold treatment periods to maximize germination success, post-germination growth, and physiological performance of B. platyphylla var. japonica seeds.

This study investigated the suitable shading levels for Peperomia species and cultivars, a genus within the Piperaceae family known for its ornamental value as an indoor plant. We examined the effects of four different shading levels (45, 60, 75, and 99 %) using polyethylene (PE) shading films on four Peperomia species and cultivars, namely: P. obtusifolia (L.) A.Dietr., P. quadrangularis (J.V.Thomps.) A.Dietr., P. caperata Yunck. ‘Eden Rosso’, and P. caperata ‘Napoli Nights’. After an eight-week cultivation period, we assessed plant sizes, biomass (i.e. fresh and dry weight), leaf color, chlorophyll content (SPAD units), and five chlorophyll fluorescence parameters (Fv/Fm, ΦDo, ABS/RC, DIo/RC, and PIABS) in Peperomia species and cultivars. The results indicated that P. obtusifolia and ‘Eden Rosso’ exhibited the best growth performance within the 45-75 % shading range, whereas P. quadrangularis and ‘Napoli Nights’ showed optimal performance at the 45 and 60 % shading levels, respectively. All species and cultivars demonstrated reduced growth and biomass under the 99 % shading level, hypothesized to be due to restricted CO2 assimilation under low-light conditions. Leaf color, measured by CIE76 color-difference (ΔE* ab) analysis based on the Commission Internationale de l'Eclairage Lab (CIELAB) color space, remained relatively constant across four different shading levels. Analyses of chlorophyll content and chlorophyll fluorescence revealed that high shading levels might deactivate some reaction centers, although the overall photosynthetic efficiency appeared largely unaffected. The performance index (PIABS) suggested that except for P. quadrangularis, which peaked at the 60 % shading level, P. obtusifolia, ‘Eden Rosso’, and ‘Napoli Nights’ generally performed well under the 45- 75 % shading levels. Therefore, Peperomia plants are capable of tolerating broad shading conditions, except for excessively high shading (99 % shading level). These results indicate that providing suitable shading levels is effective in improving the growth and photosynthetic activity of those several Peperomia species and cultivars.