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Marine Ecology Progress Series

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MEPS 327:95-106 (2006)  -  doi:10.3354/meps327095

Phosphorus stress of phytoplankton in the Taiwan Strait determined by bulk and single-cell alkaline phosphatase activity assays

Linjian Ou1, Bangqin Huang1,*, Lizhen Lin1, Huasheng Hong1, Fang Zhang2, Zhaozhang Chen1

1State Key Laboratory of Marine Environmental Science and Environmental Science Research Center, Xiamen University, 361005 Xiamen, Fujian, PR China
2Fujian Institute of Oceanography, 361012 Xiamen, Fujian, PR China
*Corresponding author. Email:

ABSTRACT: Phosphorus stress of marine phytoplankton was determined by using both bulk and single-cell alkaline phosphatase activity (APA) assays during the summer (July to August 2004) and winter (March 2005) along 2 transects (A and B) in the Taiwan Strait. During the summer of 2004, time-series variations in APA were monitored on a daily basis for 6 d along a third transect (F). Results showed that surface APA along Transects A and B ranged between 1.14 and 7.30 nmol l–1 h–1, respectively with a mean of 4.43 nmol l–1 h–1. High soluble APA contribution indicated that phytoplankton in this area suffered long-term phosphorus (P) stress. Percentages of enzyme-labeled fluorescence (ELF-labeled) representative phytoplankton increased with bulk APA during the time-series investigation and compared favorably with phosphate concentration. Dinoflagellates had high percentages of ELF labeling during both seasons, suggesting that they were under severe P-stress. The predominant dinoflagellates were Skeletonema costatum, Chaetoceros spp., Asterionellopsis glacialis, Thalassionema nitzschioides and Pseudo-nitzschia spp. During the summer, A. glacialis, T. nitzschioides and Pseudo-nitzschia spp. were labeled with ELF, which meant they were also P-stressed during that time of year. Percentages of algal cells labeled with ELF were lower during the winter, suggesting that the relatively high, soluble reactive phosphorus supply softened phytoplankton P-stress in this period. Species such as Rhizosolenia spp. and T. nitzschioides were for some reason still P-stressed during the winter. Both field and lab data suggested that bulk and single-cell APA should be used together to provide comprehensive assessment of phytoplankton P-stress from the community level to the individual taxon level in natural phytoplankton communities.

KEY WORDS: Phytoplankton · Phosphorus stress · Alkaline phosphatase · Enzyme-labeled fluorescence · Taiwan Strait

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