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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Inorganic and Organic Nitrogen Uptake by Phytoplankton and Bacteria in Hong Kong Waters
Auteurs :	Xiangcheng Yuan, Auteur ; Patricia M. Glibert, Auteur ; Jie Xu, Auteur ; Hao Liu, Auteur ; Mianrun Chen, Auteur ; Hongbin Liu, Auteur ; Kedong Yin, Auteur ; Paul J. Harrison, Auteur
Type de document :	Article
Dans :	Estuaries and Coasts (35(1) JAN 2012)
Article en page(s) :	325-334
Résumé :	Measurements of uptake rates of inorganic (NO(3)(-) and NH(4)(+)) and organic (urea, glycine, and glutamic acid) N, and indirect estimates of total N uptake by bacteria, were made in four contrasting environments in sub-tropical Hong Kong waters in summer of 2008. In addition, the effects of several days of rain on N uptake rates were studied in eastern waters. Although ambient NO(3)(-) was the dominant form of N in Hong Kong waters, the dominant N form taken up by phytoplankton was usually NH(4)(+) and organic N, including urea and amino acids, rather than NO(3)(-). Hence, because of the low NO(3)(-) uptake, there was a long turnover time for NO(3)(-) (100 days), and most of the NO(3)(-) was apparently transported offshore into deeper shelf waters. In eastern waters where NH(4)(+) was undetectable, NO(3)(-) uptake rates were positively correlated with phytoplankton cell size. In contrast, potential rates of glutamic acid uptake were negatively correlated with phytoplankton size. N uptake rates in the smaller size fraction (0.7-2.8 mu m) were less affected by the rain event, and smaller phytoplankton appeared to outcompete larger cells after several days of rain. The surface (PN)-specific N uptake rates in the >8-mu m fraction decreased from 0.02 to 0.0001 h(-1), while the smaller fraction only exhibited a one-to threefold decrease after the rainfall. In contrast, bacterial production and N uptake were not affected by the rain event, and bacteria N uptake accounted for 10-60% of the total N uptake by phytoplankton.

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