| In this study Cercis canadensis var. canadensis L. (eastern redbud) and C. canadensis var. mexicana (Rose) M. Hopkins (mexican redbud) were examined for tolerances to high temperature and drought stress. In another study, taxa of Illicium L. (flowering anise) were evaluated for differential tolerances to high irradiance and underlying photosynthetic characteristics of different taxa grown in full-sun and 50% shade.; Eastern redbud and mexican redbud were grown under high temperatures and increasing drought. Although both ecotypes responded similarly, the mexican redbud maintained higher stomatal conductance, photosynthesis, and instantaneous water use efficiency than eastern redbud as the root substrate dried. Additionally, 37°C was the optimum temperature for photosynthesis for both ecotypes and irrigation regimes. Watered plants had greater photosynthesis, and the mexican redbud maintained a higher rate of assimilation than the eastern redbud. Tissue osmotic potential was more negative in the eastern redbud, but was unaffected by drought stress in either ecotype. Soluble carbohydrate concentration was also higher in the eastern ecotype. In both ecotypes, pinitol was the major carbohydrate and its concentration was highest in drought-stressed plants. Both ecotypes proved to be very tolerant of high temperatures and drought.; To investigate how light affects Illicium, 11 taxa were grown in full sun or under 50% shade. Light-tolerance was evaluated by measuring light-saturated photosynthetic capacity (Amax), dark-adapted quantum efficiency of photosystem II (Fv/Fm), and relative chlorophyll concentration. Amax indicated that three of the 11 taxa maintained similar rates of net photosynthesis and Fv/Fm when grown in full-sun as when grown in 50% shade. All other taxa in full-sun experienced a significant reduction in A max. A deeper examination of I. parviflorum ‘Forest Green’ (high-light tolerance) and I. floridanum (low-light tolerance) demonstrated that I. parviflorum ‘Forest Green’ had a considerably higher Amax, higher light saturation point, greater potential photosynthetic capacity, reduced susceptibility to photoinhibition, greater capacity for thermal de-excitation (NPQ), greater apparent electron transport rate (ETR), and higher concentrations of the free-radical scavenger myo-inositol. |
