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Aquatic Microbial Ecology

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AME 39:193-203 (2005)  -  doi:10.3354/ame039193

Presence of dissolved nucleotides in the North Pacific Subtropical Gyre and their role in cycling of dissolved organic phosphorus

Karin M. Björkman*, David M. Karl

Department of Oceanography, SOEST, University of Hawaii, Honolulu, Hawaii 96 822, USA

ABSTRACT: Dissolved and particulate nucleotide triphosphate (NTP) concentrations were measured in the upper 1000 m of the water column during 3 summer and 3 winter months at Stn ALOHA (22.75°N, 158°W) in the oligotrophic North Pacific Subtropical Gyre. In the euphotic zone (0 to 175 m) particulate adenosine-5’-triphosphate (P-ATP) and dissolved ATP (D-ATP) concentrations were positively correlated in summer (0 to 175 m; r2 = 0.61, p < 0.001, n = 24), but not in winter (r2 =0.02, n = 24). D-ATP comprised >65% of the total ATP (T-ATP) pool in the summer, and ~50% in winter. Dissolved guanosine-5’-triphosphate (D-GTP) inventories were 5- to 6-fold greater in July and August than those observed in mid-June (1.1 ± 0.1 vs. 8.0 ± 0.6 and 6.5 ± 0.3 µmol D-GTP m–2, respectively) and winter concentrations were on average lower than the mean summer concentrations. The particulate GTP (P-GTP) inventories were almost twice those measured in winter (mean 1.1 ± 0.4 in summer vs. 0.6 ± 0.1 µmol P-GTP m–2 in winter, n = 3). These results are consistent with higher microbial growth rates in summer. Uptake of D-ATP showed multi-phasic kinetic patterns. The halfsaturation constants (Kt) ranged from 1 to 26 nM at D-ATP concentrations of 0.2 to 30 nM, and Vmax ranged from 0.3 to 1.4 nM d–1. At concentrations >30 nM, Kt exceeded 100 nM and Vmax was 10.4 nM d–1. The calculated net production rates of D-ATP ranged from 40 to 150 pM d–1, and the turnover time of the ambient D-ATP pool was estimated to be 1 to 2 d. The P flux through the D-ATP pool could potentially be 5 times faster than that of the bulk DOP pool, implying that P derived from nucleotides may be an important pathway in the P cycle of oligotrophic oceans.

KEY WORDS: North Pacific · ATP · GTP · Nucleotides · DOM · Microbial ecology

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