Abstract: Biocycle of potassium in a subtropical evergreen broad-leaved forest dominated by Cyclobalanopsis glauca growing on red soil in Zhejiang was elucidated in this paper. The concentration of K in most representative species were 0.2~0.4%. The order of them in various layers were Liana and herb> Understory> Tree and Subtree, and that in various organs were leaf> branch, root> trunk. The Sequences of the concentrations of K in C. gleuca were understory> tree> Subtree, young and assimilation> old and nonassimilation organs, reproductive> vegetative organs. K was resorbed before litter senesced and fallen. The standing crop of K in the community was 431.64kg/hm², that in the litter layer was 25.88kg/hm², and in the soil(A0 B) was 64298kg/hm². Retention of K was 53.83kg/hm²·a. Return of it was 51.89 kg/hm²·a, in which via throughfall occupied 70%. Uptake of K was 105-72kg/hm².a. Annual input of K through incident precipitation was 7-10kg/hm². Comparing with other forest types, cycling rate and use efficiency of K in this ecosystem was reflected to the environmental condition in the corresponding region.

Key words: Cycloblanopsis glauca, Evergreen broad-leaved forest, Ecosystem, Potassium, Biocycle