Growth and physiological responses of two mangrove species (Bruguiera gymnorrhiza and Kandelia candel) to waterlogging

Effects of duration of waterlogging on growth and physiological responses of two mangrove species, Bruguiera gymnorrhiza and Kandelia candel, were investigated. The relative growth rate of B. gymnorrhiza decreased significantly with waterlogged time, with the highest value found for drained plants and the lowest in plants under 12 weeks waterlogging. On the contrary, no significant difference was found between waterlogged and drained K. candel plants. The shoot to root biomass ratio of K. candel increased when subjected to 8 or 12 weeks waterlogging but little change was recorded in B. gymnorrhiza, indicating a shift in biomass allocation from roots to shoots in K. candel under prolonged waterlogging but not in B. gymnorrhiza. These different growth responses between the two mangrove species supported the hypothesis that K. candel is more tolerant to waterlogging than B. gymnorrhiza. Under 12 weeks waterlogged treatment, root oxidase activity significantly decreased in B. gymnorrhiza but increased in K. candel. Chlorophyll contents of K. candel increased more rapidly in response to waterlogging than B. gymnorrhiza. Activities of both peroxidase and superoxide dismutase increased significantly in leaves of K. candel when the waterlogging period was longer than 8 weeks, while only the peroxidase activity of B. gymnorrhiza showed a significant increase, indicating that K. candel had stronger resistance to the oxidant damage resulting from waterlogging. These physiological indicators further supported the hypothesis that K. candel is more tolerant to waterlogging than B. gymnorrhiza. © 2002 Elsevier Science B.V. All rights reserved.