Seasonal regulation of nitrification in a rooted macrophyte (Vallisneria spiralis L.) meadow under eutrophic conditions

Variable oxygen release from the root of macrophytes growing in ammonium-rich organic substrates can stimulate the process of nitrification. To verify this hypothesis, we performed seasonal measurements of potential nitrification activity in sediments with and without the perennial submersed plant Vallisneria spiralis L. (Hydrocharitaceae). Pore water and sediment features were simultaneously considered in order to provide insights into the regulation of the process. Results demonstrated a significant effect of season and plant presence on potential nitrification activity, with higher rates in winter and lower rates in summer. Vegetated sediment displayed lower pore water ammonium, but always higher potential nitrification activity compared to the unvegetated substrate, regardless the season. Nitrification activity was strongly correlated with pore water redox status, which were affected by both season and plant presence. Along its annual cycle V. spiralis promoted more oxidized condit...