Gastropod grazers affect periphyton nutrient stoichiometry by changing benthic algal taxonomy and through differential nutrient uptake

Abstract. We hypothesize that phytoplankton have the sequential nutrient uptake strategy to maintain nutrient stoichiometry and high primary productivity in the water column. According to this hypothesis, phytoplankton take up the most limiting nutrient first until depletion, continue to draw down non-limiting nutrients and then take up the most limiting nutrient rapidly when it is available. These processes would result in the variation of ambient nutrient ratios in the water column around the Redfield ratio. We used high-resolution continuous vertical profiles of nutrients, nutrient ratios and on-board ship incubation experiments to test this hypothesis in the Strait of Georgia. At the surface in summer, ambient NO3− was depleted with excess PO43− and SiO4− remaining, and as a result, both N : P and N : Si ratios were low. The two ratios increased to about 10 : 1 and 0. 45 : 1, respectively, at 20 m. Time series of vertical profiles showed that the leftover PO43− continued to be removed, resulting in additional phosphorus storage by phytoplankton. The N : P ratios at the nutricline in vertical profiles responded differently to mixing events. Field incubation of seawater samples also demonstrated the sequential uptake of NO3− (the most limiting nutrient) and then PO43− and SiO4− (the non-limiting nutrients). This sequential uptake strategy allows phytoplankton to acquire additional cellular phosphorus and silicon when they are available and wait for nitrogen to become available through frequent mixing of NO3− (or pulsed regenerated NH4). Thus, phytoplankton are able to maintain high productivity and balance nutrient stoichiometry by taking advantage of vigorous mixing regimes with the capacity of the stoichiometric plasticity. To our knowledge, this is the first study to show the in situ dynamics of continuous vertical profiles of N : P and N : Si ratios, which can provide insight into the in situ dynamics of nutrient stoichiometry in the water column and the inference of the transient status of phytoplankton nutrient stoichiometry in the coastal ocean.

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Sequential Nutrient Uptake by Phytoplankton Maintains High Primary Productivity and Balanced Nutrient Stoichiometry

10.5194/bg-2016-426 ◽

2016 ◽

Author(s):

Kedong Yin ◽

Paul J. Harrison

Keyword(s):

Nutrient Uptake ◽

Water Column ◽

Primary Productivity ◽

Nutrient Ratios ◽

Vertical Profiles ◽

Nutrient Stoichiometry ◽

High Productivity ◽

Limiting Nutrients ◽

Limiting Nutrient ◽

Nutrient Profiles

Abstract. We hypothesize that phytoplankton have the sequential nutrient uptake strategy in order to maintain nutrient stoichiometry and high primary productivity in the water column. Nutrient limited phytoplankton are capable of taking up the limiting nutrient first and they take up non-limiting nutrients when the limiting nutrient debt has been overcome. We used high resolution continuous vertical profiles of nutrients, nutrient ratios and on-board ship incubation experiments to test this hypothesis in the Strait of Georgia. At the surface in summer, ambient nitrate was depleted with excess phosphate and silicate remaining, and as a result, both N : P and N : Si ratios were low. The two ratios increased to about 10 : 1 and 0.45 : 1, respectively, at 20 m. Time series of vertical profiles showed that the leftover phosphate continued to be removed, resulting in additional phosphorus storage by phytoplankton. There were various shapes of vertical profiles of N : P and at the nutricline it changed quickly in response to mixing events. A field incubation of seawater also demonstrated the sequential uptake of nitrate (the most limiting nutrient) and then phosphate and silicate (the non-limiting nutrients). This sequential uptake strategy allows phytoplankton to acquire additional cellular phosphorus and silicon when they are available and wait for nitrogen to become available through frequent mixing of nitrate (or pulsed regenerated ammonium). Thus, phytoplankton show variability of nutrient stoichiometry and are capable of maintaining high productivity by taking advantage of vigorous mixing regimes. To our knowledge, this is the first study to show the dynamics of continuous vertical profiles of N : P and N : Si ratios and to examine the responses of phytoplankton to nutrients supplied naturally by mixing events. The continuous nutrient profiles provided insight into the in situ dynamics of nutrient stoichiometry in the water column and the transient status of nutrient stoichiometry of phytoplankton in the field.

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Effect of Some Natural Mineral Waters in Nutrient Uptake by Caco-2 Cells

International Journal for Vitamin and Nutrition Research ◽

10.1024/0300-9831/a000013 ◽

2010 ◽

Vol 80 (2) ◽

pp. 131-143 ◽

Cited By ~ 3

Author(s):

Pedro Gonçalves ◽

João R. Araújo ◽

Fátima Martel

Keyword(s):

Nutrient Uptake ◽

Mineral Waters ◽

Distilled Water ◽

Natural Mineral ◽

Minute Exposure

We studied the effect of some mineral waters and some of their constituents on the apical uptake of 14C-butyrate (14C-BT) and 3H-O-methyl-D-glucose (3H-OMG) by Caco-2 cells. Uptake of 14C-BT increased after a 20-minute exposure to 1 % (v/v) distilled water, and, compared to distilled water, it was decreased by Pedras Salgadas® 1 % (v/v) and Melgaço® 5 % (v/v), and increased by Vidago® 5 % (v/v). Moreover, it increased after a 48-hour exposure to Vidago® or Melgaço® waters (5 % (v/v)). Also, uptake of 14C-BT was reduced after a 20-minute exposure to MgCl2, MgSO4, or CaCl2. Uptake of 3H-OMG was reduced after a 20-minute exposure to Melgaço® water [1 % (v/v)], when compared to distilled water. Also, a 48-hour exposure to Pedras Salgadas® or Melgaço® water (5 % (v/v)) increased and decreased uptake, respectively. Finally, uptake of 3H-OMG decreased after a 20-minute exposure to MgSO4 or NaF. In conclusion, uptake of 14C-BT and 3H-OMG by Caco-2 cells is differently modulated by distinct mineral waters.

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