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Comparison of Growth and Alkalinity-induced Responses in Two Cultivars of Hibiscus (Hibiscus rosa-sinensis L.)

2006; American Society for Horticultural Science; Volume: 41; Issue: 7 Linguagem: Inglês

10.21273/hortsci.41.7.1704

2327-9834

Luis Alonso Valdez‐Aguilar, David William Reed,

Plant Physiology and Cultivation Studies

Response to alkalinity was evaluated in two hibiscus cultivars, Bimini Breeze and Carolina Breeze, grown in a soilless growing medium and in hydroponic culture. For soilless growing medium, plants were potted in a sphagnum peat–perlite-based substrate and irrigated with solutions containing 0 to 10 m m NaHCO 3 for 12 weeks. In hydroponic culture, bare-rooted plants were transferred to a 9-L tray containing a Hoagland's nutrient solution prepared with NaHCO 3 at the concentrations previously indicated. In soilless growing medium, shoot dry weight was minimally affected by NaHCO 3 concentration for `Bimini Breeze', but `Carolina Breeze' exhibited a significant decrease in shoot mass with increasing NaHCO 3 concentration. In hydroponic culture, increasing concentration of NaHCO 3 induced a decrease in shoot and root mass in both cultivars, but root mass decrease was more pronounced in `Bimini Breeze'. In soilless growing medium, increasing the concentration of NaHCO 3 caused an increase in growing medium pH. The pH increase was less pronounced for `Bimini Breeze' than for `Carolina Breeze', indicating a higher capacity for root zone acidification by `Bimini Breeze'. Newly developed leaves of both cultivars showed increasing chlorosis with increasing NaHCO 3 concentration. However, `Bimini Breeze' was more tolerant because, according to regression models, 5.7 m m NaHCO 3 would be required to reduce chlorophyll levels by 10%, compared with 2.2 m m for `Carolina Breeze', when grown in soilless medium. Fe reductase activity decreased when `Carolina Breeze' plants were grown in 5 m m NaHCO 3 . However, in `Bimini Breeze', Fe reductase activity was enhanced. These observations indicate that the increased tolerance of `Bimini Breeze' to increasing alkalinity is the result of enhanced Fe reductase activity and increased acidification of the root zone.