Abstract: From September 2004 to September 2005, the effects of waterlogging on the seedlings growth and physiological characteristics of Bruguiera gymnorrhiza were studied in the diurnal tide region of Yingluo Bay in Guangxi.Eight tidal flat altitude (TFA) treatments were installed, with the surface plane of seedlings substrates ranged from 320 to 390 cm and a 10 cm difference between each other. The growth characteristics and some physiological parameters of the seedlings were measured, and the results showed that both the lower and the higher TFA treatments promoted the longitudinal development of stem significantly, while moderate TFA treatments did not. The seedlings in moderate TFA treatments had fewer knots on the stems. The leaf number, leaf area and leaf conservation rate presented congruously a rapid decline as the TFA fell. A slight promotion to the chlorophyll contents was found in lower TFA habitats, while a stronger promotion occurred in the higher ones. The Chl-a /Chl-b ratio in lower TFA treatments was higher than that under higher TFAs, while the SOD and POD activities in leaves and roots were both promoted significantly in lower TFAs. At the same TFA, the activities of SOD and POD in roots were several times higher than those in leaves. Higher TFA habitats were more beneficial to the biomass accumulation of the seedlings, especially for their leaves. The biomass partition tended to transfer from leaf to stem with increasing degree of waterlogging stress. Seedlings death occurred in all treatments, but the survival rate decreased from 73.6% to 35.0% as the TFA lowered. It was suggested that the critical tidal level for B. gymnorrhiza in terms of forestation with hypocotyls directly in Beibu Gulf region was 21 cm higher than the altitude of local mean sea level.

Key words: Oryza sativa, Allelopathy, Terpenoids, Allelochemicals