Abstract
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 μm) 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-μm 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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Acknowledgments
This research was supported by grants from NSFC (41106107) and Hong Kong UGC AoE project (UGC AoE/P-04/04-1). We also acknowledge the support from the CAS/SAFEA International Partnership Program for Creative Research Teams (KZCX2-YW-T001), LMEB201001, NSFC (40806050), and Hong Kong RGC (HKUST6478/05 M, HKUST6505/06 M). This is contribution number 4545 from the University of Maryland Center for Environmental Science. We thank the staff in the Environmental Central Facility at HKUST for their excellent service. Thanks to Y. K. Tam for her assistance with general technical support.
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Yuan, X., Glibert, P.M., Xu, J. et al. Inorganic and Organic Nitrogen Uptake by Phytoplankton and Bacteria in Hong Kong Waters. Estuaries and Coasts 35, 325–334 (2012). https://doi.org/10.1007/s12237-011-9433-3
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DOI: https://doi.org/10.1007/s12237-011-9433-3