AB 5:1-11 (2009)  -  DOI: https://doi.org/10.3354/ab00141

ABSTRACT: We examined the influence of environmental calcium on phosphorus biokinetics and regulation in Daphnia magna. When the Ca concentration in culturing media increased from 0.5 to 200 mg l^–1, the specific P content of D. magna feeding on P-sufficient algae decreased significantly from 1.43 to 1.05% of dry weight. There was a negative significant relationship between the specific Ca and P contents (% dry wt) of daphnids. However, measured biokinetic parameters, including the assimilation efficiency (AE) of dietary P, the weight-specific ingestion rate (IR), the uptake of inorganic P from water, and the efflux rate constant (k_e) of P, were similar over the wide range of Ca concentrations, with some exceptions at the lowest Ca level (0.5 mg l^–1). Diet was the dominant source of P for daphnids, and only 1 to 2% of P was incorporated from water, based on the biokinetic calculation. With the elevation of the Ca level from 0.5 to 200 mg l^–1, the proportion of P lost through molting by D. magna feeding on P-sufficient diets increased 2.5-fold, whereas the dissolved release decreased 1.9-fold. P released into the dissolved phase is readily re-utilized by primary producers, while P contained within the shed molts sinks out of the epilimnion and becomes at least temporarily unavailable to primary producers; thus, the effects of Ca on molting and dissolved release have significant implications for P cycling in freshwater lakes. Our results suggest that the availability of P to primary producers can be reduced by sedimentation of P-rich daphnid molts in high-Ca lakes, and Ca concentration in the water needs to be considered in studying the stoichiometric regulation of P in freshwater cladocerans.

KEY WORDS: Phosphorus regulation · Phosphorus cycling · Phosphorus biokinetics · Effects of calcium · Daphnia magna

Full text in pdf format Information about this Feature Article

Cite this article as: Tan QG, Wang WX (2009) Calcium influence on phosphorus regulation in Daphnia magna: implications for phosphorus cycling. Aquat Biol 5:1-11. https://doi.org/10.3354/ab00141 Export citation Share:    Facebook - - linkedIn