MORPHOLOGICAL AND PHYSIOLOGICAL RESPONSES OF HAWAIIAN HIBISCUS TILIACEUS POPULATIONS TO LIGHT AND SALINITY

Louis S. Santiago,¹ Tina S. Lau, Peter J. Melcher,² O. Colin Steele, and Guillermo Goldstein

Department of Botany, University of Hawaii, 3190 Maile Way, Honolulu, Hawaii 96822, U.S.A.

Manuscript received May 1999; revised manuscript received September 1999.

Hibiscus tiliaceus (Hau) is a pantropical mangrove associate that usually occurs in coastal ecosystems where substrate salinity is relatively high, but it also inhabits upland habitats in Hawaii. Cuttings from three populations on the island of Oahu, Hawaii, were collected and grown in the glasshouse under two levels of substrate salinity (0 and 335 mOsm kg^-1) and three light treatments (0%, 50%, and 90% shade). Photosynthetic gas exchange, biomass allocation, and accumulation were studied in relation to salinity and light. Salinity reduced net CO₂ assimilation in the upland population but had no effect or stimulated photosynthesis in the coastal populations, whereas increasing salinity decreased stomatal conductance in all populations and therefore increased water-use efficiency. The degree to which photosynthesis was inhibited by salinity was inversely proportional to the salinity of the source population, indicating a loss of salinity tolerance in upland plants. Light had a stronger effect on leaf area ratio (LAR) and leaf mass per area (LMA), whereas salinity had a stronger effect on leaf water content, internode length, and plant biomass. Salinity reduced total new biomass by 58%, 50%, and 34% in full sun, 50% shade, and 90% shade, respectively, but this response did not differ between populations. Salinity reduced the photosynthesis, but not growth, of upland plants because increased allocation to photosynthetic tissue increased LAR to compensate for inhibition of photosynthesis by salinity.

¹ Author for correspondence. Current address: Department of Botany, University of Florida, 220 Bartram Hall, P.O. Box 118526, Gainesville, Florida 32611-8526, U.S.A. Telephone 352-392-1894; fax 352-392-3993; e-mail santiago@botany.ufl.edu.
² Current address: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, U.S.A.