Phosphorus utilization by phytoplankton in the Yellow Sea during spring bloom: Cell surface adsorption and intracellular accumulation

摘要

Phosphorus (P) is frequently considered the limiting nutrient for marine phytoplankton growth and primary production in oceans. To explore P utilization by phytoplankton during spring blooms, field observations and incubation experiments were conducted during a cruise in the Yellow Sea (YS). In particular, phytoplankton cell-associated P pools were identified as intracellular P pool (P-intracellular) and cell surface-adsorbed P pool (P-surface). Both P-intracellular and P-surface varied in a wide range of 9.0-125.7 and 0.5-93.3 mu mol g(-1), respectively, in the YS. Pintracellular was frequently dominant in the total cellular P pool (contributing to 46-96%). Variation in the cell-associated P content was observed at different bloom stages, probably depending on phytoplankton species and seawater parameters. Cell-associated P enrichment was associated with a decrease in phosphate and increase in chlorophyll a, suggesting that the phytoplankton assimilated phosphate from the seawater and stored P in both cell interior and surface. This process supported the rapid biomass accumulation during the spring blooms. Incubation experiments further indicated that the accumulation rate of P-intracellular and P-surface was positively correlated with the phosphate removal rate in the seawater. Phytoplankton luxury P consumption could enhance both P-intracellular and P-surface mass content. P-surface, as a bioavailable P pool on the cell surface, could be internalized by the phytoplankton during active growth. Our study on the P assimilation mechanism involved in cell surface adsorption and intracellular accumulation enhanced the understanding of the dynamics of spring bloom.