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Influence of the submersed plant, Potamogeton perfoliatus, on nitrogen cycling in estuarine sediments
Journal article   Peer reviewed

Influence of the submersed plant, Potamogeton perfoliatus, on nitrogen cycling in estuarine sediments

Jane M. Caffrey and W. Michael Kemp
Limnology and Oceanography, Vol.37, pp.1483-1495
37
1992
DOI: https://doi.org/10.4319/lo.1992.37.7.1483
Web of Science ID: WOS:A1992KM34100010

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Abstract

Effects of Potamogeton perfoliatus on N transformations in sediments were examined with ¹⁵N isotope techniques. Rates of ammonification, nitrification, denitrification, and plant uptake of nitrogen were measured in intact sediments with and without P. perfoliatus twice during the growing season (May and July). Sediments were injected with ¹⁵NH₄+ and the appearance of ¹⁵N over time in overlying water, pore water, and plant tissues was measured. Most of the ¹⁵N added was recovered. Rates of bacterial NH₄+ utilization (including NH₄+ assimilation and nitrification) were similar to gross ammonification rates in vegetated and bare sediments, although rates were highly variable. Root (and rhizome) uptake represented -90% of total N uptake by the plants in May, but only 20% in July. Tissue-specific (root or shoot) uptake rates were similar in May and July, although shoot (leaves plus stems) biomass increased faster than root biomass from May to July. Between 70 and 75% of the N taken up by roots was translocated to shoots. Denitrification rates, calculated from the appearance of ¹⁵N-N₂ in the overlying and pore water, were significantly greater in vegetated than in bare sediments in July. Nitrification and denitrification were closely coupled, and denitrification in the root zone represented - 16% of total denitrification. In vegetated sediments, - 75% of the ¹⁵N lost from sediments was denitrified, and 25% was taken up by the plants. P. perfoliatus had a significant influence on sediment N cycling by direct uptake of NH₄ and NO₃ and by indirect mechanisms leading to enhanced nitrification and denitrification.

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