Benthic nitrogen metabolism in a macrophyte meadow (Vallisneria spiralis L.) under increasing sedimentary organic matter loads
- 633 Downloads
Organic enrichment may deeply affect benthic nitrogen (N) cycling in macrophyte meadows, either promoting N loss or its recycling. This depends upon the plasticity of plants and of the associated microbial communities, as those surrounding the rhizosphere. Rates of denitrification, dissolved inorganic N fluxes and N uptake were measured in sediments vegetated by the submerged macrophyte Vallisneria spiralis L. under increasing organic matter loads. The aim was to investigate how the combined N assimilation and denitrification, which subtract N via temporary retention and permanent removal, respectively, do vary along the gradient. Results showed that V. spiralis meadows act as regulators of benthic N cycling even in organic enriched sediments, with negative feedbacks for eutrophication. A moderate organic load stimulates N uptake and denitrification coupled to nitrification in the rhizosphere. This is due to a combination of weakened competition between macrophytes and N cycling bacteria and enhanced radial oxygen loss by roots. An elevated organic enrichment affects N uptake due to hostile conditions in pore water and plant stress and impairs N mineralisation and its removal via denitrification coupled to nitrification. However, the loss of plant performance is almost completely compensated by increased denitrification of water column nitrate, resulting in a shift between the relative relevance of temporary and permanent N removal processes.
KeywordsOrganic enrichment Vallisneria spiralis Radial oxygen loss N fluxes Denitrification N uptake
ES was supported by a doctoral scholarship within the 25th PhD program in Ecology (2010–2012), University of Parma. The authors would like to thank Fabio Vincenzi (Department of Life Sciences and Biotechnology, University of Ferrara) for helping with laboratory analyses.
- A.P.H.A., A.W.W.A., W.P.C.F. 1981. Standard methods for the examination of water and wastewater. A.P.H.A., WashingtonGoogle Scholar
- Armstrong FAJ, Sterus CR, Strickland JDH (1967) The measurement of upwelling and subsequent biological processes by means of the Technicon AutoAnalyzer and associated equipment. Deep-Sea Res 14:381–389Google Scholar
- Coci M, Nicol GW, Pilloni GN, Schmid M, Kamst–van Agterveld MP, Bodelier PLE, Laanbroek HJ (2010) Quantitative assessment of ammonia–oxidizing bacterial communities in the epiphyton of submerged macrophytes in shallow lakes, Appl Environ Microb 76:1813–1821Google Scholar
- Dalsgaard T, Nielsen LP, Brotas V, Viaroli P, Underwood GJC, Nedwell DB, Sundbäck K, Rysgaard S, Miles A, Bartoli M, Dong L, Thornton DCO, Ottosen LDM, Castaldelli G, Risgaard-Petersen N (2000) Protocol Handbook for NICE–nitrogen cycling in estuaries: a project under the EU research programme. Marine Science and Technology (MAST III). National Environmental Research Institute, Silkeborg, p 62Google Scholar
- Henriksen K, Kemp WM (1988) Nitrification in estuarine and coastal marine sediments: methods, patterns and regulating factors. In: Blackburn TH, Sorensen J (eds) Nitrogen cycling in coastal marine environments. Wiley, New York, pp 207–250Google Scholar
- Holmer H, Wildish D, Hargrave B (2005) Organic enrichment from marine finfish aquaculture and effects on sediment biogeochemical processes. In B Hargrave (ed) Environmental effects of marine finfish aquaculture. Hdb Env Chem Vol. 5, Part M, Springer, Berlin, pp 181–206Google Scholar
- McAuliffe C (1971) Gas Chromatographic determination of solutes by multiple phase equilibrium. Chem Technol 1:46–51Google Scholar
- Nizzoli D, Welsh DT, Longhi D, Viaroli P (2014) Influence of Potamogeton pectinatus and microphytobenthos on benthic metabolism, nutrient fluxes and denitrification in a freshwater littoral sediment in an agricultural landscape: N assimilation versus N removal. Hydrobiologia 737:183–200CrossRefGoogle Scholar
- R Development Core Team (2013) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria, ISBN 3–900051–07–0, URL http://www.R-project.org