Chara is usually found in hard and alkaline waters with low level of phosphorus (P) concentration. Calcite encrustation with P co-precipitation is very important for the growth of Chara and the maintenance of a low nutrient state in aquatic ecosystems. However, the effects and mechanisms of elevated P content in water on the growth, uptake and allocation of P in Chara are not well understood. This study performed an experiment to clarify how Chara vulgaris Linn, a common and widely distributed macroalga, allocated the P it uptake at different P availability. The results indicated that the growth rate of C. vulgaris in low P treatments (LP, less than 6 μg P /L) was 0.8 times higher than that in high P treatments (HP, more than 100 μg P /L), and the growth rate was significantly increased when C. vulgaris were transferred from the water with high P content to water with low P content, indicating that high P contents in water inhibited the growth of C. vulgaris. The increase of P content in water resulted in a fourfold increase in inorganic P (IP) content, while only 0.2-fold increase in organic P (OP) content, making the stoichiometric homeostasis index (1/H) of IP 7.9 times that of OP. More than 70% of the total P (TP) accumulated in Chara in LP was used for biomass growth, while more than 60% of the TP in C. vulgaris in HP was precipitated into calcite encrustation. This study highlighted that C. vulgaris had high growth rate under low P environment, and the inhibiting effect of high P to C. vulgaris was reversible, which may be a special P competition mechanism for this species in low P water. However, in high P condition, the Ca-P co-precipitation may limit the apparent P availability and be expressed as an inhibition of growth. [ABSTRACT FROM AUTHOR]