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Nitrification and denitrification in the rhizosphere of the aquatic macrophyte Lobelia dortmanna L.
Author(s) -
Petersen Nils Risgaard,
Jensen Kim
Publication year - 1997
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1997.42.3.0529
Subject(s) - nitrification , denitrification , sediment , rhizosphere , environmental chemistry , macrophyte , nitrogen cycle , chemistry , botany , nitrogen , ecology , geology , biology , geomorphology , organic chemistry , bacteria , paleontology
Nitrogen and O 2 transformations were studied in sediments covered by Lobelia dortmanna L.; a combination of 15 N isotope pairing and microsensor (O 2 , NO 3 − , and NH 4 + ) techniques were used. Transformation rates and microprofiles were compared with data obtained in bare sediments. The two types of sediment were incubated in doublecompartment chambers connected to a continuous flow‐through system. The presence of L. dortmanna profoundly influenced both the nitrification‐denitrification activity and porewater profiles of O 2 , NO 3 − , and NH 4 + within the sediment. The rate of coupled nitrification‐denitrification was greater than sixfold higher in L. dortmnanna ‐vegetated sediment than in bare sediment throughout the light–dark cycle. Illumination of the Lobelia sediment reduced denitrification activity by ∼30%. In contrast, this process was unaffected by light–dark shifts in the bare sediment. Oxygen microprofiles showed that O 2 was released from the L. dortmanna roots to the surrounding sediment both during illumination and in darkness. This release of O 2 expanded the oxic sediment volume and stimulated nitrification, shown by the high concentrations of NO 3 − (∼30 µM) that accumulated within the rhizosphere. Both 15 N 2 isotope and microsensor data showed that the root‐associated nitrification site was surrounded by two sites of denitrification above and below, and this led to a more efficient coupling between nitrification and denitrification in the Lobelia sediment than in the bare sediment.