This paper is a part of studies of the mangrove forests in Dongzhai harbour of Hainan island, China. It deals mainly with the accumulation and biological cycle of K and Na elements of 55-year-old Bruguiera sexangula community.
The main results of the measurements are as follows:
1. The amounts of K and Na elements in standing crop of this community were 669.9kg/ha and 2591.3kg/ha in which the amounts of two elements in aerial part of biomass were 425.6 for K and 908.9 for Na (kg/ha), and that of below ground biomass were 244.3 for K and 2042.4 for Na(kg/ha) respectively.
2. In biological cycle of K and Na of this stand, the annual value of vegetation mineral uptake were 89.6 for K and 204.4 for Na(kg/ha), of its return were 49.0 for K and 99.8 for Na(kg/ha) and of its retention were 40.6 for K and 104.6 for Na(kg/ha), respectively.
3. The turnover period of K (14 yrs.) is faster than that of Na (30 yrs .)
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