Nitrogen uptake by phytoplankton and bacteria during an induced Phaeocystis pouchetii bloom, measured using size fractionation and flow cytometric sorting

Aquatic Microbial Ecology

A. F. Sazhin¹  D. A. Bronk¹  M. E. Frischer¹  M. P. Sanderson¹  P. B. Bradley¹  P. G. Verity¹  †¹  L. Campbell¹  L. M. Killberg-Thoreson¹  J. C. Nejstgaard¹ 

关键词: Nitrogen uptake;    Mesocosm experiments;    Phaeocystis;    Phytoplankton;    Bacteria;    Flow cytometry;   

DOI  :  10.3354/ame01414

学科分类：生物科学（综合）

来源: Inter-Research

【 摘 要 】

ABSTRACT: Uptake of inorganic and organic nitrogen (N) by phytoplankton and bacteria was investigated during a mesocosm study conducted in Raunefjord, Norway in April 2005. One mesocosm was fertilized with nitrate and phosphate at a ratio of 16:1 and maintained in the light, while one unamended light mesocosm served as a control. Dissolved nutrients, phytoplankton and bacterial biomass, and phytoplankton community composition were monitored throughout the 26 d experiment. Uptake of ¹⁵N-labeled ammonium and nitrate, and dual-labeled (¹⁵N and ¹³C) urea and dissolved free amino acids (DFAA) was measured for phytoplankton and bacteria using 2 methods: size fractionation into 0.2–0.8 and >0.8 µm size classes, and flow cytometric sorting based on chlorophyll autofluorescence. Prior to fertilization, dissolved inorganic N concentrations were low and comprised ~5% of total dissolved N. Added nitrate was completely utilized in the amended mesocosm within 10 d, stimulating a large bloom of colonial Phaeocystis pouchetii. Ammonium contributed over half of total measured N uptake by phytoplankton and bacteria in both enclosures, while nitrate and urea each supplied roughly 10 to 25%. Overall, DFAA were a negligible N source to phytoplankton but contributed 11% to total bacterial N uptake. Bacterial uptake represented a significant portion of total uptake of all N forms, especially urea and DFAA. Comparison of the 2 methods for measuring phytoplankton versus bacterial uptake demonstrates how the use of 0.8 µm filters can lead to significant overestimation of phytoplankton N uptake due to the retention of bacterial biomass.

【 授权许可】

Unknown