Abstract: The contents, pool amounts and yearly dynamics of C, H and N elements were studied in 55-year-old Bruguiera sexangula (Lour.) Poir. mangrove forest in Dongzhai harbour of Hainan Island, China. The results showed that C, H and N contents in various fractions of B. sescangula were: C 46.82%–53.04%, H 4.61%–5.85% and N 0. 18%0-1.55%. The atom rato was C (1), H (1.16–1.36), N (0. 003–0. 028). In standing crop of the community, the pool amounts of C, Hand N were 20330.9g· m- 2. 2139.7 g·m- 2 and 233.5 g·m- 2, respectively. The yearly dynamics of C, H and N for the community were: annual net fixing C1473.4 g·m-2, net binding H166.1 g·m- 2 and absorbing N 23.3 g·m-2. among which the annual retention was: C 786.6 g · m- 2, H83.8 g·m- 2. N 10.3 g· m- 2 and the annual litter fall export was: C 686.8 g· m- 2 H 82.3 g · m-2, N 13. 0 g· m-2, The yearly net energy production was about 57622 k J·m- 2 and net O2 giving out was about 3929 g·m- 2.

Key words: Mangrove, Bruguiera sexangula, C, H and N dynamic