Direct and indirect measurements of nitrification and denitrification in the rhizosphere of aquatic macrophytes

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 19:81-91 (1999) - doi:10.3354/ame019081 Direct and indirect measurements of nitrification and denitrification in the rhizosphere of aquatic macrophytes Lars Ditlev Mørck Ottosen*, Nils Risgaard-Petersen, Lars Peter Nielsen Institute of Biological Sciences, Department of Microbial Ecology, University of Aarhus, Ny Munkegade, 8000 Aarhus C, Denmark *E-mail: lars.ottosen@biology.aau.dk ABSTRACT: Coupled nitrification-denitrification rates in the rhizosphere of 4 different aquatic macrophytes, Zostera marina, Lobelia dortmanna, Littorella uniflora and Potamogeton pectinatus, were measured by means of both an indirect and a direct 15N technique. Using the indirect technique we estimated the fraction of O2, excreted by plant roots in the rhizosphere, that was used by coupled nitrification-denitrification. Incubations were carried out in 15NH4+ amended oxic slurries. This fraction was multiplied with values for root O2 excretion reported in the literature. The indirect technique allowed us to quantify both the oxidation of NH4+ to NO3- , and the reduction of NO3- to NH4+ compared to denitrification. Using the direct technique we estimated coupled nitrification-denitrification from the amount of 15N2 labeled gas that accumulated in intact sediment-plant systems. The 2 techniques recorded similar trends. In these cores 15NH4+ was added homogeneously to the rhizosphere by perfusion. Denitrification activity in the rhizosphere of Z. marina and P. pectinatus was low (1.5 to 5 μmol N m-2 h-1) compared to the activity measured in L. dortmanna and L. uniflora vegetated sediments (24 and 30 μmol N m-2 h-1). The variability in denitrification activity was due to differences in the ability of the plants to oxidize the rhizosphere, and difference in the character of sediment O2 and NO3- consumption. This study attempts to clarify how rooted aquatic vegetation affects the sediment nitrogen cycle via oxygen excretion from the roots. Rhizosphere associated nitrogen transformations (coupled nitrification-denitrification) are central to the understanding of nutrient cycling in shallow aquatic ecosystems. KEY WORDS: Rooted macrophytes · Rhizosphere · O2 excretion · Coupled nitrification-denitrification Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 19, No. 1. Publication date: September 06, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.