Nutrient Utilization Strategies of Algae and Bacteria after the Termination of Nutrient Amendment with Different Phosphorus Dosage: A Mesocosm Case

ABSTRACT

The impacts of nutrient amendment termination on the growth strategies of algae and bacteria were conducted in experimentally designed mesocosm in which two different phosphorus (P) dosages were treated. The algal community composition did not change greatly in Group A (low phosphorus) and Group B (high phosphorus). In Group A, the secretion of bacterial alkaline phosphatase (AP) after nutrient termination stimulated bacterial phosphorus acquisition, which caused the decrease in algal phosphorus levels, in terms of the increase of bacterial abundance and bacterial production, as well as the decrease in chlorophyll a and particulate organic carbon. The algal collapse resulted in dissolved organic carbon secretion, further fuelling bacterial growth. In Group B, excess phosphorus input urged algae to store phosphorus as poly-phosphate. When phosphorus input ceased, in order to maintain their used high phosphorus demand, algae strengthened to gain phosphorus through the hydrolysis of dissolved organic phosphorus in water column and ploy-phosphate inside the cells by AP, evidenced by high algal alkaline phosphatase activity, algal growth continuation, and bacterial growth decline. These facts indicated that phosphorus content should reduce to a lower level than expected, so that algal bloom can be effectively controlled in eutrophic water bodies.

KEYWORDS:

• Algae
• alkaline phosphatase
• bacteria
• mesocosm
• nutrient utilization strategies

Additional information

Funding

This work was supported by the Sino-Danish scientific and technological cooperation grant “Metabolic coupling between phytoplankton and bacterioplankton in nutrient cycling mediated by extracellular enzyme during algae bloom' (AM 14:06), the grants from the National Natural Science Foundation of China (41230748; 41273089; 41573110), and the State Key Laboratory of Freshwater Ecology and Biotechnology (2016FBZ07). The authors also gratefully acknowledged the support of Theis Kragh, Anne Jensinius Jacobsen and Nils Willumsen for the help in experimental operation.