Seasonal variation of radial oxygen loss in Vallisneria spiralis L.: An adaptive response to sediment redox?

In temperate shallow aquatic bodies large seasonal variations in water temperature result in a wide range of benthic respiration rates which are coupled to changes of pore water redox. To cope with such sediment modifications, we hypothesize that rooted macrophytes vary the oxygen amount released by roots. To this purpose, we reinterpreted published data on seasonal oxygen and inorganic carbon fluxes measured in vegetated (Vallisneria spiralis L.) sediments by combining them with the outcomes from laboratory incubations of apical tips and intact plants. Results suggest that V. spiralis transfers progressively higher amounts of oxygen to roots in the shift winter-summer. Maximum radial oxygen loss occurs in early autumn and probably overlaps with the lowest sediment redox. At the end of the summer, the exhaustion of energy yielding electron acceptor pools is in fact coupled to input of labile organic matter from senescent meadows, further exacerbating the demand of oxidized compounds to support degradation processes. The oxygen released by roots measured in hydroponic conditions corresponds to similar to 7% of the plant gross production in the light; a small amount of oxygen is leaked also in darkness. We speculate that the oxygen injected in the pore water by a V. spiralis meadow can significantly affect the sediment biogeochemistry of eutrophic sites, representing up to similar to 20% of the daily benthic oxygen consumption. (c) 2012 Elsevier B.V. All rights reserved.