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Long‐term 15 N‐nitrogen retention in tidal freshwater marsh sediment: Elucidating the microbial contribution
Author(s) -
Gribsholt Britta,
Veuger Bart,
Tramper Anton,
Middelburg Jack J.,
Boschker Henricus T. S.
Publication year - 2009
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.2009.54.1.0013
Subject(s) - sediment , phragmites , organic matter , environmental chemistry , estuary , marsh , nitrogen , chemistry , biota , ammonium , nitrogen cycle , environmental science , ecology , wetland , biology , paleontology , organic chemistry
The long‐term retention of nitrogen in sediment of a tidal freshwater marsh in the Scheldt estuary (Belgium) was investigated by an in situ 15 N‐labeling experiment. Sediment of an unvegetated creek bank and sediment vegetated by common reed ( Phragmites australis ) were labeled with 15 NN‐enriched NH 4 + after which 15 N was traced into pore‐water dissolved NH 4 + , NO 3 − , and N 2 ; plant roots and leaves; and bulk sediment over a 1‐yr period. Label retention in the sediment organic matter was further characterized by analyzing KCl‐extracted sediment and hydrolyzable amino acids (including the bacterial biomarker D‐alanine). Within weeks all added 15 NH 4 + was transformed and/or assimilated by the biota. Between 42% and 48% of the added label was recovered in plants, root, and sediment (collectively) after 3‐6 months, whereas 24% remained after 1 yr. Transfer to plants and roots was rapid and although retention in leaves was transient, the 15 N assimilated by roots was retained for the entire 1‐yr period. Root assimilation could account for 12‐23% of the 15 N retained in vegetated plots. The majority of 15 N was retained in the organic matter pool within the sediment (represented by 15 N in the KCl extracted sediment and total hydrolyzable amino acids), primarily through efficient recycling of the 15 N within the microbial community. 15 N incorporation into D‐alanine confirmed that bacteria were the major group of microorganisms responsible for the strong retention of 15 N. This study shows the strong potential of reed roots and especially bacteria to retain nitrogen in tidal freshwater sediment over longer periods of time.