Enzymatic strategies for phosphorus utilization in periphyton: A study of alkaline phosphatase kinetics in...

Alkaline phosphatase (AP) plays an important role in phosphorus (P) cycling in aquatic ecosystems, particularly under nutrient limitation. In post-mining lakes of Czechia, periphyton forms extensive mats despite chronic P deficiency, suggesting dissolved organic P (DOP) may serve as a key P source. This study examines periphyton's ability to hydrolyze DOP via AP in three post-mining lakes in Czechia, assessing enzyme kinetic models, seasonal variation, and P-acquisition strategies. Seasonal shifts of apparent alkaline phosphatase catalytic efficiency (APCE) in periphyton, determined as the ratio of maximum hydrolysis velocity to Michaelis constant, have indicated that periphyton dynamically adjusts its enzyme activity. Periphyton exhibited rapid DOP turnover (tenths to tens of seconds) but had significantly lower APCE than phytoplankton. This suggests fundamental differences in P-acquisition strategies: Although phytoplankton relies on ambient DOP, periphyton retains and recycles P within its matrix. Retained P can be distributed throughout the periphyton taxa, supporting an idea of metabolic commensalism in periphyton assemblage. Our results underscored the adaptive role of periphyton community in buffering P availability through internal recycling, which, alongside P uptake from the lake water, supports persistence of periphyton in fluctuating P conditions. By sequestering and recycling P internally, periphyton alters lake-wide P dynamics, reduces P availability for phytoplankton, and potentially influences ecosystem productivity. Furthermore, this research has highlighted the limitations of applying simple Michaelis-Menten kinetics to describe complex enzymatic processes in natural ecosystems, emphasizing the need for models that better capture enzymatic heterogeneity and environmental interactions.