scholarly journals Exploring the distance between nitrogen and phosphorus limitation in mesotrophic surface waters using a sensitive bioassay

2017 ◽  
Vol 14 (2) ◽  
pp. 379-387 ◽  
Author(s):  
Enis Hrustić ◽  
Risto Lignell ◽  
Ulf Riebesell ◽  
Tron Frede Thingstad
Keyword(s):  
Baltic Sea ◽  
Incubation Time ◽  
Phosphorus Limitation ◽  
Early Summer ◽  
Parameter Estimates ◽  
Nitrogen And Phosphorus ◽  
Field Station ◽  
N Limitation ◽  
P Limitation ◽  
Two Samples

Abstract. The balance in microbial net consumption of nitrogen and phosphorus was investigated in samples collected in two mesotrophic coastal environments: the Baltic Sea (Tvärminne field station) and the North Sea (Espegrend field station). For this, we have refined a bioassay based on the response in alkaline phosphatase activity (APA) over a matrix of combinations in nitrogen and phosphorus additions. This assay not only provides information on which element (N or P) is the primary limiting nutrient, but also gives a quantitative estimate for the excess of the secondary limiting element (P+ or N+, respectively), as well as the ratio of balanced net consumption of added N and P over short timescales (days). As expected for a Baltic Sea late spring–early summer situation, the Tvärminne assays (n =  5) indicated N limitation with an average P+ =  0.30 ± 0.10 µM-P, when incubated for 4 days. For short incubations (1–2 days), the Espegrend assays indicated P limitation, but the shape of the response surface changed with incubation time, resulting in a drift in parameter estimates toward N limitation. Extrapolating back to zero incubation time gave P limitation with N+ ≈  0.9 µM-N. The N : P ratio (molar) of nutrient net consumption varied considerably between investigated locations: from 2.3 ± 0.4 in the Tvärminne samples to 13 ± 5 and 32 ± 3 in two samples from Espegrend. Our assays included samples from mesocosm acidification experiments, but statistically significant effects of ocean acidification were not found by this method.

scholarly journals Exploring the distance between nitrogen and phosphorus limitation in mesotrophic surface waters using a sensitive bioassay

2016 ◽  
Author(s):  
Enis Hrustic ◽  
Risto Lignell ◽  
Ulf Riebesell ◽  
Tron Frede Thingstad
Keyword(s):  
Baltic Sea ◽  
Incubation Time ◽  
N:P Ratio ◽  
Early Summer ◽  
Parameter Estimates ◽  
Nitrogen And Phosphorus ◽  
Field Station ◽  
N Limitation ◽  
P Limitation ◽  
Two Samples

Abstract. The balance in microbial consumption of nitrogen and phosphorus was investigated in samples collected in two mesotrophic coastal environments: the Baltic Sea (Tvärminne field station) and the North Sea (Espegrend field station). For this, we have refined a bioassay based on the response in alkaline phosphatase activity (APA) over a matrix of combinations in nitrogen and phosphorus additions. This assay not only provides information on which element (N or P) is the primary limiting, but also gives a quantitative estimate for the excess of the secondary limiting element (P* or N*, respectively), as well as the ratio between N and P consumption over short time scales (days). As expected for a Baltic Sea late spring-early summer situation, the Tvärminne assays (n=5) indicated N-limitation with an average P*=0.30 ± 0.10 µM-P, when incubated for 4 days. For short incubations (1–2 days), the Espegrend assays indicated P-limitation, but the shape of the response surface changed with incubation time, resulting in a drift in parameter estimates toward N-limitation. Extrapolating back to zero incubation time gave P-limitation with N* ≈ 0.9 µM-N. The N:P ratio (molar) of nutrient consumption varied considerably between investigated locations; from 2.3 ± 0.4 in the Tvärminne samples to 13 ± 5 and 32 ± 3 in two samples from Espegrend. Our assays included samples from mesocosm acidification experiments, but statistically significant effects of ocean acidification were not found by this method.

scholarly journals Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes

2012 ◽  
Vol 9 (11) ◽  
pp. 4707-4723 ◽  
Author(s):  
A. Laurent ◽  
K. Fennel ◽  
J. Hu ◽  
R. Hetland
Keyword(s):  
Gulf Of Mexico ◽  
Primary Production ◽  
Inorganic Nitrogen ◽  
Circulation Model ◽  
Phosphorus Limitation ◽  
Early Summer ◽  
Nitrogen And Phosphorus ◽  
River Plumes ◽  
Northern Gulf Of Mexico ◽  
Plume Region

Abstract. The continental shelf of the northern Gulf of Mexico receives high dissolved inorganic nitrogen and phosphorus loads from the Mississippi and Atchafalaya rivers. The nutrient load results in high primary production in the river plumes and contributes to the development of hypoxia on the Louisiana shelf in summer. While phytoplankton growth is considered to be typically nitrogen-limited in marine waters, phosphorus limitation has been observed in this region during periods of peak river discharge in spring and early summer. Here we investigate the presence, spatio-temporal distribution and implications of phosphorus limitation in the plume region using a circulation model of the northern Gulf of Mexico coupled to a multi-nutrient ecosystem model. Results from a 7-yr simulation (2001–2007) compare well with several sources of observations and suggest that phosphorus limitation develops every year between the Mississippi and Atchafalaya deltas. Model simulations show that phosphorus limitation results in a delay and westward shift of a fraction of river-stimulated primary production. The consequence is a reduced flux of particulate organic matter to the sediment near the Mississippi delta, but slightly enhanced fluxes west of Atchafalaya Bay. Simulations with altered river phosphate concentrations (±50%) show that significant variation in the spatial extent of phosphorus limitation (±40% in July) results from changes in phosphate load.

Carbon flux response and recovery to drought years in a hemi-boreal peat bog between different vegetation types

2020 ◽  
Author(s):  
Chris R Taylor ◽  
Ben Keane ◽  
Iain Hartley ◽  
Gareth Phoenix
Keyword(s):  
Carbon Dioxide ◽  
Nutrient Availability ◽  
Anthropogenic Activities ◽  
Terrestrial Ecosystems ◽  
Phosphorus Limitation ◽  
Atmospheric Concentration ◽  
Ecosystem Responses ◽  
N Limitation ◽  
Plant Soil ◽  
P Limitation

<p>Terrestrial ecosystems absorb 30% of anthropogenic carbon dioxide (CO<sub>2</sub>) emissions, slowing its rising atmospheric concentration and substantially inhibiting climate change. This uptake is believed to be due to elevated CO<sub>2</sub> (eCO<sub>2</sub>) stimulating plant photosynthesis and growth, thus increasing carbon (C) storage in plants and soil organic matter. However, nitrogen (N) limitation can reduce ecosystem C uptake capacity under eCO<sub>2</sub> by as much as 50%. Phosphorus (P) limitation in ecosystems is almost as common as N-limitation and is increasing due to ongoing deposition of N from anthropogenic activities. Despite this, we do not know how P-limited ecosystems will respond to eCO<sub>2</sub>, constituting a major gap in our understanding of how large areas of the biosphere will impact atmospheric CO<sub>2</sub> over the coming decades.</p><p>In the first study conducted into the effect of eCO<sub>2</sub> on P-limited ecosystems with manipulated nutrient availability, the Phosphorus Limitation And ecosystem responses to Carbon dioxide Enrichment project (PLACE), investigates the effects of eCO<sub>2</sub> on C cycling in grasslands, which are a critical global C store. Turf mesocosms from P-limited acidic and limestone grasslands, where N and P inputs have been manipulated for 20 years (control, low N (3.5 g m<sup>-2</sup> y<sup>-1</sup>), high N (14 g m<sup>-2</sup> y<sup>-1</sup>), and P (3.5 g m<sup>-2</sup> y<sup>-1</sup>)), have been exposed to either ambient or eCO<sub>2</sub> (600 ppm) in a miniFACE (mini Free Air Carbon Enrichment) system. Long-term P addition has alleviated P limitation while N additions have exacerbated it. The two contrasting grasslands contain different amounts of organic versus mineral P in their soils and, thus, plants may have to use contrasting strategies to acquire the additional P they need to increase growth rates under elevated CO<sub>2</sub>.</p><p>We present data from the first two growing seasons, including above and below ground productivity, and C, N and P cycling through plant, soil and microbial pools. Aboveground harvest data from the second year have shown eCO<sub>2</sub> has only increased biomass production in the limestone grassland (by 17%; p< 0.0001), and not in the acid grassland. There was also a significant effect of nutrient treatment (p< 0.001) with biomass increasing under P and HN, indicating some co-NP limitation. Stable isotope tracing, using the fumigation CO<sub>2</sub> signal has shown the fate of newly assimilated C and its contribution to gaseous C flux to the atmosphere in the form of methane (CH<sub>4</sub>) and respired CO<sub>2</sub>.  In summary, our first two years of eCO<sub>2</sub> treatment suggests that productivity of limestone and acidic grassland respond differently and that these responses depend on nutrient availability, indicating the complexity of predicting P-limited ecosystem responses as atmospheric CO<sub>2 </sub>continues to rise.</p>

scholarly journals Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes

2012 ◽  
Vol 9 (5) ◽  
pp. 5625-5657 ◽  
Author(s):  
A. Laurent ◽  
K. Fennel ◽  
J. Hu ◽  
R. Hetland
Keyword(s):  
Gulf Of Mexico ◽  
Primary Production ◽  
Inorganic Nitrogen ◽  
Circulation Model ◽  
Phosphorus Limitation ◽  
Early Summer ◽  
Nitrogen And Phosphorus ◽  
River Plumes ◽  
Northern Gulf Of Mexico ◽  
Plume Region

Abstract. The continental shelf of the northern Gulf of Mexico receives high dissolved inorganic nitrogen and phosphorus loads from the Mississippi and Atchafalaya rivers. The nutrient load results in high primary production in the river plumes and contributes to the development of hypoxia on the Texas-Louisiana shelf in summer. While phytoplankton growth is considered to be typically nitrogen-limited, phosphorus limitation has been observed in this region during periods of peak river discharge in spring and early summer. Here we investigate the presence, spatio-temporal distribution and implications of phosphorus limitation in the plume region using a circulation model of the northern Gulf of Mexico coupled to a multi-nutrient ecosystem model. Results from a 7 yr simulation (2001–2007) compare well with available observations and suggest that phosphorus limitation develops every year between the Mississippi and Atchafalaya deltas. Model simulations show that phosphorus limitation results in a delay and westward shift of a fraction of river-stimulated primary production. The consequence is a reduced flux of particulate organic matter to the sediment near the Mississippi delta, but enhanced fluxes westward in the Atchafalaya and far-field regions. Two discharge scenarios with altered river phosphate concentrations (±50 %) reveal a significant variation (±40 % in July) in the spatial extent of phosphorus limitation with changes in phosphate load.

scholarly journals Assessment of Nutrient Limitation in Floodplain Forests with Two Different Techniques

2008 ◽  
Vol 2008 ◽  
pp. 1-4 ◽  
Author(s):  
Matthew A. Neatrour ◽  
Robert H. Jones ◽  
Stephen W. Golladay
Keyword(s):  
Nutrient Limitation ◽  
Root Length Density ◽  
Phosphorus Limitation ◽  
Nitrogen And Phosphorus ◽  
Ingrowth Cores ◽  
P Limitation ◽  
N:P Ratios ◽  
Native Soil ◽  
Fine Root Length ◽  
Southern Georgia

We assessed nitrogen and phosphorus limitation in a floodplain forest in southern Georgia in USA using two commonly used methods: nitrogen to phosphorus (N:P) ratios in litterfall and fertilized ingrowth cores. We measured nitrogen (N) and phosphorus (P) concentrations in litterfall to determine N:P mass ratios. We also installed ingrowth cores within each site containing native soil amended with nitrogen (N), phosphorus (P), or nitrogen and phosphorus (N + P) fertilizers or without added fertilizer (C). Litter N:P ratios ranged from 16 to 22, suggesting P limitation. However, fertilized ingrowth cores indicated N limitation because fine-root length density was greater in cores fertilized with N or N + P than in those fertilized with P or without added fertilizer. We feel that these two methods of assessing nutrient limitation should be corroborated with fertilization trials prior to use on a wider basis.

scholarly journals Initial Validation of the Teacher-Created Empowering and Disempowering Motivational Climate Questionnaire in Physical Education

2018 ◽  
Vol 37 (4) ◽  
pp. 340-351 ◽  
Author(s):  
Daniel Milton ◽  
Paul R. Appleton ◽  
Anna Bryant ◽  
Joan L. Duda
Keyword(s):  
Physical Education ◽  
Secondary School ◽  
Structural Equation ◽  
Factor Model ◽  
Motivational Climate ◽  
Equation Modeling ◽  
Physical Education Teachers ◽  
Parameter Estimates ◽  
Two Samples ◽  
Secondary School Pupils

Purpose: Guided by Duda’s hierarchical conceptualization of the motivational climate that draws from self-determination and achievement goal theories, this study provides initial evidence of the psychometric properties of the Empowering and Disempowering Motivational Climate Questionnaire in physical education (EDMCQ-PE). Method: Questionnaire based with two samples of Welsh secondary school pupils. Results: Exploratory structural equation modeling provided a better fit of the data to the hypothesized model than confirmatory factor analysis. Moreover, a two-factor composite (i.e., empowering and disempowering) lower-order model provided an acceptable fit and clear parameter estimates. This two-factor model also demonstrated scalar gender measurement invariance. Discussion: The evidence from this study suggests the EDMCQ-PE is a promising scale for the assessment of secondary school pupils’ perceptions of the empowering and disempowering features of the motivational climate created by their physical education teachers. Conclusion: Moving forward, the statistical approach employed in this paper can inform future studies that develop questionnaire methodology in physical education and from an applied perspective; the EDMCQ-PE can be used by researchers and teachers to assess the motivational climate in PE and help inform the pedagogy underpinning teachers’ classes.

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