Abstract: In order to supply the theoretical basis for the normalized planting of Achyranthes bidentata, a field determination on the leaf area, chlorophyll content of the 2nd leaf, and dynamic parameters of chlorophyll fluorescence, as well as the root yield and plant polysaccharide content of A. bidentata under different planting densities (A: 500 000 plants·hm^-1, B: 330 000 plants·hm^-1, C: 250 000 plants·hm^-1, D: 200 000 plants·hm^-1) was made. The results showed that under different planting densities, the maximum values of leaf area index and chlorophyll content were all appeared at the 45th day of post-emergence, with the order of A>B>C>D and B>C>A>D, respectively. The F_v/F_o,F_v/F_m,Ф_PSⅡ,qp, and ETR of photosystem Ⅱ increased first and decreased then, while the qN kept increasing. At the same growth period, treatment B had the highest F_v/F_o, F_v/F_m, Ф_PSⅡ, qN and ETR, and displayed the least restriction from high light and better performance of photosynthesis. The root yield and plantpolysaccharide content were correlated positively with F_v/F_o, and F_v/F_m, and negatively with qN. At the 55th day of spike bringing forth, the qN was correlated negatively with plant polysaccharide content. It was suggested that treatment B was the most suitable planting density.

Key words: Sinonovacula constricta, Tidal-flat area, Heterotrophic bacteria, Ammonifying bacteria, Denitrifying bacteria, Sulphate reducing bacteria