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

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.

scholarly journals Sequential nutrient uptake as a potential mechanism for phytoplankton to maintain high primary productivity and balanced nutrient stoichiometry

2017 ◽  
Vol 14 (9) ◽  
pp. 2469-2480 ◽  
Author(s):  
Kedong Yin ◽  
Hao Liu ◽  
Paul J. Harrison
Keyword(s):  
Nutrient Uptake ◽  
Water Column ◽  
Primary Productivity ◽  
Nutrient Ratios ◽  
Vertical Profiles ◽  
Nutrient Stoichiometry ◽  
High Productivity ◽  
Limiting Nutrients ◽  
Limiting Nutrient

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.

scholarly journals ESTIMACIÓN DE LA PRODUCTIVIDAD PRIMARIA EN DOS BAJOS DE LA PARTE SUR DEL GOLFO DE CALIFORNIA, MÉXICO

2008 ◽  
Vol 23 (1-2) ◽  
pp. 39
Author(s):  
G. Verdugo-Díaz ◽  
R. Cervantes Duarte ◽  
M. O. Albáñez-Lucero
Keyword(s):  
Surface Temperature ◽  
Water Column ◽  
Primary Productivity ◽  
Gulf Of California ◽  
Inorganic Nutrients ◽  
Water Transparency ◽  
Vertical Profiles ◽  
Subsurface Maximum ◽  
Natural Fluorescence ◽  
Productivity Estimation

Primary productivity estimation in two seamounts in the southern Gulf of California, México Vertical profiles of temperature and natural fluorescence from 100 m deep were made during February 2005. Water transparency was measured using Secchi’s disc, as well samples of superficial water and at maximum of fluorescence deep were collected to analyze inorganic nutrients. In “El Bajo Espiritu Santo” temperature (20 °C at surface) diminished gradually with depth, without significant stratification.Primary productivity shows superficial values close to 6 mg C m-3 h-1, recahing undetectable values at 20 m of depth. In “El Bajo Gorda” surface temperature reached 22 °C and the water column shows a thermocline between 35 m and 45 m of depth. The profiles of primary productivity presented a subsurface maximum (approximately 2 mg C m-3 h-1) associated with the thermocline.

Decoupling primary productivity from silicate weathering – how ecosystems regulate nutrient uptake along a climate and vegetation gradient

2020 ◽  
Author(s):  
Ralf Oeser ◽  
Friedhelm von Blanckenburg
Keyword(s):  
Growth Rate ◽  
Nutrient Uptake ◽  
Primary Productivity ◽  
Hydrological Cycle ◽  
Nutrient Recycling ◽  
Biomass Growth ◽  
Weathering Rate ◽  
High Productivity ◽  
Weathering Processes ◽  
Vegetation Gradient

<p>Water flow as well as the presence and growth rate of land plants are commonly thought to present drivers of rock weathering. While plants are indeed key players in weathering, the quantitative evaluation of biota on total abiotic and biotic weathering processes remains vague.</p><p>Here, we report on weathering rates and nutrient uptake along the “EarthShape” climate and vegetation gradient in the Chilean Coastal Cordillera. The hypothesis we evaluated is whether weathering rate and degree does increase from north to south along the EarthShape climate gradient and whether the increase in biomass growth rate along this gradient is accommodated by additional nutrient-supply induced through weathering. We quantified the bio-available fraction of nutritive elements in regolith and we measured <sup>87</sup>Sr/<sup>86</sup>Sr isotope ratios in the different compartments of the Earth’s Critical Zone (bedrock, regolith, bio-available fraction in saprolite and soil, and vegetation) to identify the sources of mineral nutrients to plants. We were thus quantified gains and losses of nutritive elements in and out of these ecosystems and to quantify nutrient recycling.</p><p>We find that despite the increase in biomass growth the weathering rate is relatively uniform along the gradient. Instead of accelerating biogenic weathering ecosystems with high productivity rely on efficient recycling between plants and soil to sustain their nutrition. Thus, the organic nutrient pathway (between plants and litter on the foerst floor) intensifies, whereas the geogenic nutrient pathway (from minerals to plant) remains steady despite increasing precipitation and primary productivity. We further speculate that the presence of plants might compensate weathering downward by regulating the hydrological cycle, fostering secondary-mineral formation, and a microbial community specializing on nutrient-recycling rather than nutrient-acquisition through weathering.</p>

Production of Rhamnolipid Biosurfactant from Fed Batch Culture by Pseudomonas aeruginosa using Multiple Substrates

2020 ◽  
Vol 16 (6) ◽  
pp. 928-933
Author(s):  
Jujjavarapu S. Eswari
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Batch Process ◽  
Time Interval ◽  
Fed Batch ◽  
Multiple Substrates ◽  
Surface Active Agents ◽  
Limiting Nutrients ◽  
Limiting Nutrient ◽  
Surface Active ◽  
Rhamnolipid Biosurfactant

Objective: Biosurfactants are the surface active agents which are used for the reduction of surface and interfacial tensions of liquids. Rhamnolipids are the surfactants produced by Pseudomonas aeruginosa. It requires minimum nutrition for its growth as it can also grow in distilled water. The rhamnolipids produced by Pseudomonas aeruginosa are extra-cellular glycolipids consisting of L-rhamnose and 3-hydroxyalkanoic acid. Methods: The fed-batch method for the rhamnolipid production is considered in this study to know the influence of the carbon, nitrogen, phosphorous substrates as growth-limiting nutrients. Pulse feeding is employed for limiting nutrient addition at particular time interval to obtain maximum rhamnolipid formation from Pseudomonas aeruginosa compared with the batch process. Results: Out of 3 fed batch strategies constant glucose fed batch strategy shows best and gave maximum rhamnolipid concentration of 0.134 g/l.

scholarly journals Modelling the biogeochemical effects of heterotrophic and autotrophic N<sub>2</sub> fixation in the Gulf of Aqaba (Israel), Red Sea

2018 ◽  
Vol 15 (24) ◽  
pp. 7379-7401 ◽  
Author(s):  
Angela M. Kuhn ◽  
Katja Fennel ◽  
Ilana Berman-Frank
Keyword(s):  
Water Column ◽  
Red Sea ◽  
N2 Fixation ◽  
Large Scale ◽  
Gulf Of Aqaba ◽  
Nutrient Concentrations ◽  
Nutrient Ratios ◽  
Biogeochemical Models ◽  
Deep Waters ◽  
Direct Measurements

Abstract. Recent studies demonstrate that marine N2 fixation can be carried out without light by heterotrophic N2 fixers (diazotrophs). However, direct measurements of N2 fixation in aphotic environments are relatively scarce. Heterotrophic as well as unicellular and colonial photoautotrophic diazotrophs are present in the oligotrophic Gulf of Aqaba (northern Red Sea). This study evaluates the relative importance of these different diazotrophs by combining biogeochemical models with time series measurements at a 700 m deep monitoring station in the Gulf of Aqaba. At this location, an excess of nitrate, relative to phosphate, is present throughout most of the water column and especially in deep waters during stratified conditions. A relative excess of phosphate occurs only at the water surface during nutrient-starved conditions in summer. We show that a model without N2 fixation can replicate the observed surface chlorophyll but fails to accurately simulate inorganic nutrient concentrations throughout the water column. Models with N2 fixation improve simulated deep nitrate by enriching sinking organic matter in nitrogen, suggesting that N2 fixation is necessary to explain the observations. The observed vertical structure of nutrient ratios and oxygen is reproduced best with a model that includes heterotrophic as well as colonial and unicellular autotrophic diazotrophs. These results suggest that heterotrophic N2 fixation contributes to the observed excess nitrogen in deep water at this location. If heterotrophic diazotrophs are generally present in oligotrophic ocean regions, their consideration would increase current estimates of global N2 fixation and may require explicit representation in large-scale models.

scholarly journals Seabed Resuspension in the Chesapeake Bay: Implications for Biogeochemical Cycling and Hypoxia

2020 ◽  
Vol 44 (1) ◽  
pp. 103-122
Author(s):  
Julia M. Moriarty ◽  
Marjorie A. M. Friedrichs ◽  
Courtney K. Harris
Keyword(s):  
Organic Matter ◽  
Chesapeake Bay ◽  
Water Column ◽  
Primary Productivity ◽  
Environmental Changes ◽  
Light Attenuation ◽  
Sediment Resuspension ◽  
Nitrogen Dynamics ◽  
Biogeochemical Model ◽  
Order Of Magnitude

AbstractSediment processes, including resuspension and transport, affect water quality in estuaries by altering light attenuation, primary productivity, and organic matter remineralization, which then influence oxygen and nitrogen dynamics. The relative importance of these processes on oxygen and nitrogen dynamics varies in space and time due to multiple factors and is difficult to measure, however, motivating a modeling approach to quantify how sediment resuspension and transport affect estuarine biogeochemistry. Results from a coupled hydrodynamic–sediment transport–biogeochemical model of the Chesapeake Bay for the summers of 2002 and 2003 showed that resuspension increased light attenuation, especially in the northernmost portion of the Bay, shifting primary production downstream. Resuspension also increased remineralization in the central Bay, which experienced larger organic matter concentrations due to the downstream shift in primary productivity and estuarine circulation. As a result, oxygen decreased and ammonium increased throughout the Bay in the bottom portion of the water column, due to reduced photosynthesis in the northernmost portion of the Bay and increased remineralization in the central Bay. Averaged over the channel, resuspension decreased oxygen by ~ 25% and increased ammonium by ~ 50% for the bottom water column. Changes due to resuspension were of the same order of magnitude as, and generally exceeded, short-term variations within individual summers, as well as interannual variability between 2002 and 2003, which were wet and dry years, respectively. Our results quantify the degree to which sediment resuspension and transport affect biogeochemistry, and provide insight into how coastal systems may respond to management efforts and environmental changes.

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