Low Specific Phosphorus Uptake Affinity of Epilithon in Three Oligo- to Mesotrophic Post-mining Lakes.

Epilithon contributes to phosphorus (P) cycling in lakes, but its P uptake traits have been rarely studied. We measured the chemical composition of epilithon and its inorganic P uptake kinetics using isotope ³³ P in three deep oligo- to mesotrophic post-mining lakes in April, July, and October 2019. Over the sampling period, epilithon biomass doubled, while the P content in biomass dropped to 60% of the April values, and the seasonal changes in P content expressed per epilithon area were only marginal and statistically not significant. High epilithic C:P molar ratios (677 on average) suggested strong P deficiency in all investigated lakes. Regarding the kinetic parameters of phosphorus uptake, maximum uptake velocity ( V _max , seasonal range 1.9-129 mg P g OM ^-1 h ^-1 ) decreased by an order of magnitude from April to October, while half-saturation constant ( K _S , seasonal range 3.9-135 mg P L ^-1 ) did not show any consistent temporal trend. Values of epilithic specific P uptake affinity ( SPUA _E , seasonal range 0.08-3.1 L g OM ^-1 h ^-1 ) decreased from spring to autumn and were two to four orders of magnitude lower than the corresponding values for seston ( SPUA _sest ), which showed an opposite trend. Considering our results, we suggest a possible mechanism underlying a stable coexistence of planktonic and epilithic microorganisms, with plankton prospering mostly in summer and autumn and epilithon in winter and spring season. Additionally, a phenomenon of reversible abiotic P adsorption on epilithon was observed.
Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
(Copyright © 2021 Konopáčová, Nedoma, Čapková, Čapek, Znachor, Pouzar, Říha and Řeháková.)