A Statistical Comparison of the Two-Source δ15N and 15N Isotope Dilution Methods for Estimating Plant N2-Fixation using Trifolium pratense and Lolium perenne

1997 ◽  
Vol 24 (5) ◽  
pp. 631 ◽  
Author(s):  
O. Brendel ◽  
C. Wheeler ◽  
L. Handley
Keyword(s):  
N2 Fixation ◽  
Trifolium Pratense ◽  
Field Studies ◽  
Organic N ◽  
Isotopic Enrichment ◽  
Weather Variables ◽  
Signal Ratio ◽  
15N Enrichment ◽  
Uniform Background ◽  
The Individual

In field studies, 15N-enriched and 15N-natural abundance methods may yield similar mean estimates for N2-fixation, but with no correlation of the individual estimates. This study was designed as a glasshouse-based microcosm and aimed to remove the landform and weather variables found in previous field studies, while retaining other sources of variability such as mineralisation of organic N and whatever slight variations of environment may exist in the glasshouse. The results showed little or no correspondence among the estimates of N2-fixation at the three 15N-enrichment levels; however, estimates were consistent within each 15N-enrichment level. There was also no correlation between the results of acetylene reduction and those of any of the isotopic enrichment treatments. If the isotopic 15N-enrichment levels measured the same processes with varying accuracies, then the general patterns of the replicated results from each enrichment level should resemble each other against a generally uniform background. They did not. Hence, we conclude that the observed differences are due to unknown factors in addition to the varying noise-to-signal ratio at different enrichment levels.

scholarly journals The significance of nitrogen fixation to new production during early summer in the Baltic Sea

2006 ◽  
Vol 3 (4) ◽  
pp. 1279-1311 ◽  
Author(s):  
U. Ohlendieck ◽  
K. Gundersen ◽  
M. Meyerhöfer ◽  
P. Fritsche ◽  
K. Nachtigall ◽  
...  
Keyword(s):  
Primary Production ◽  
Baltic Sea ◽  
N2 Fixation ◽  
Organic N ◽  
Filamentous Cyanobacteria ◽  
The Baltic Sea ◽  
New Production ◽  
15N Enrichment ◽  
The Baltic ◽  
In Cells

Abstract. Rates of dinitrogen (N2) fixation and primary production were measured during two 9 day transect cruises in the Baltic proper in June–July of 1998 and 1999. Assuming that the early phase of the bloom of cyanobacteria lasted a month, total rates of N2 fixation contributed 15 mmol N m-2 (1998) and 33 mmol N m-2 (1999) to new production (sensu Dugdale and Goering, 1967). This constitutes 12–26% more new N than other annual estimates (mid July–mid October) from the same region. The between-station variability observed in both total N2 fixation and primary productivity greatly emphasize the need for multiple stations and seasonal sampling strategies in biochemical studies of the Baltic Sea. The majority of new N from N2 fixation was contributed by filamentous cyanobacteria. On average, cyanobacterial cells >20 µm were able to supply a major part of their N requirements for growth by N2 fixation in both 1998 (73%) and 1999 (81%). The between-station variability was high however, and ranged from 28–150% of N needed to meet the rate of C incorporation by primary production. Since the molar C:N rate incorporation ratio (C:NRATE) in filamentous cyanobacterial cells was almost twice as high as the molar C:N mass ratio (C:NMASS) in both years, we suggest that the diazotrophs incorporated excess C on a short term basis (for carbohydrate ballasting and buoyancy regulation), released nitrogen or utilized other regenerated sources of N nutrients. Measured rates of total N2 fixation contributed only a minor fraction of 13% (range 4–24) in 1998 and 18% (range 2–45) in 1999 to the amount of N needed for the community primary production. An average of 9 and 15% of total N2 fixation was found in cells <5 µm. Since cells <5 µm did not show any detectable rates of N2 fixation, the 15N-enrichment could be attributed to regenerated incorporation of dissolved organic N (DON) and ammonium generated from larger diazotroph cyanobacteria. Therefore, N excretion from filamentous cyanobacteria may significantly contribute to the pool of regenerated nutrients used by the non-diazotroph community in summer. Higher average concentrations of regenerated N (ammonium) coincided with higher rates of N2 fixation found during the 1999 transect and a higher level of 15N-enrichment in cells <5 µm. A variable but significant fraction of total N2 fixation (1–10%) could be attributed to diazotrophy in cells between 5–20 µm.

scholarly journals The significance of nitrogen fixation to new production during early summer in the Baltic Sea

2007 ◽  
Vol 4 (1) ◽  
pp. 63-73 ◽  
Author(s):  
U. Ohlendieck ◽  
K. Gundersen ◽  
M. Meyerhöfer ◽  
P. Fritsche ◽  
K. Nachtigall ◽  
...  
Keyword(s):  
Primary Production ◽  
Baltic Sea ◽  
N2 Fixation ◽  
Organic N ◽  
Filamentous Cyanobacteria ◽  
The Baltic Sea ◽  
New Production ◽  
15N Enrichment ◽  
The Baltic ◽  
In Cells

Abstract. Rates of dinitrogen (N2) fixation and primary production were measured during two 9 day transect cruises in the Baltic proper in June–July of 1998 and 1999. Assuming that the early phase of the bloom of cyanobacteria lasted a month, total rates of N2 fixation contributed 15 mmol N m−2 (1998) and 33 mmol N m−2 (1999) to new production (sensu Dugdale and Goering, 1967). This constitutes 12–26% more new N than other annual estimates (mid July–mid October) from the same region. The between-station variability observed in both total N2 fixation and primary productivity greatly emphasizes the need for multiple stations and seasonal sampling strategies in biogeochemical studies of the Baltic Sea. The majority of new N from N2 fixation was contributed by filamentous cyanobacteria. On average, cyanobacterial cells >20 µm were able to supply a major part of their N requirements for growth by N2 fixation in both 1998 (73%) and 1999 (81%). The between-station variability was high however, and ranged from 28–150% of N needed to meet the rate of C incorporation by primary production. The molar C:N rate incorporation ratio (C:NRATE) in filamentous cyanobacterial cells was variable (range 7–28) and the average almost twice as high as the Redfield ratio (6.6) in both years. Since the molar C:N mass ratio (C:NMASS) in filamentous cyanobacterial cells was generally lower than C:NRATE at a number of stations, we suggest that the diazotrophs incorporated excess C on a short term basis (carbohydrate ballasting and buoyancy regulation), released nitrogen or utilized other regenerated sources of N nutrients. Measured rates of total N2 fixation contributed only a minor fraction of 13% (range 4–24) in 1998 and 18% (range 2–45) in 1999 to the amount of N needed for the community primary production. An average of 9 and 15% of total N2 fixation was found in cells <5 µm. Since cells <5 µm did not show any detectable rates of N2 fixation, the 15N-enrichment could be attributed to regenerated incorporation of dissolved organic N (DON) and ammonium generated from larger diazotroph cyanobacteria. Therefore, N excretion from filamentous cyanobacteria may significantly contribute to the pool of regenerated nutrients used by the non-diazotroph community in summer. Higher average concentrations of regenerated N (ammonium) coincided with higher rates of N2 fixation found during the 1999 transect and a higher level of 15N-enrichment in cells <5 µm. A variable but significant fraction of total N2 fixation (1–10%) could be attributed to diazotrophy in cells between 5–20 µm.

Het belang van de context voor onderzoek binnen de organisatiepsychologie

2012 ◽  
Vol 25 (3) ◽  
Author(s):  
Wim van Breukelen
Keyword(s):  
Organizational Behavior ◽  
Contextual Factors ◽  
Field Studies ◽  
Cultural Factors ◽  
Organizational Characteristics ◽  
Research And Practice ◽  
Research Findings ◽  
The Individual ◽  
Underlying Processes ◽  
Voor Onderzoek

The importance of context in research on organizational behavior The importance of context in research on organizational behavior This article emphasizes the need to pay more attention to the context in field studies of organizational behavior. The context refers to factors external to the individual, which include organizational characteristics and societal and cultural factors. The context may offer additional explanations for research findings and may improve insights in underlying processes. In addition, a focus on contextual factors in a study may increase the fit between research and practice. This article describes the potential effects of contextual factors and offers possible reasons for the lack of attention to context in many studies. Finally, several recommendations are presented in order to bring contextual factors back into the study of behavior in organizations.

scholarly journals Nitrogen isotopic evidence for a shift from nitrate- to diazotroph-fueled export production in the VAHINE mesocosm experiments

2016 ◽  
Vol 13 (16) ◽  
pp. 4645-4657 ◽  
Author(s):  
Angela N. Knapp ◽  
Sarah E. Fawcett ◽  
Alfredo Martínez-Garcia ◽  
Nathalie Leblond ◽  
Thierry Moutin ◽  
...  
Keyword(s):  
N2 Fixation ◽  
Significant Fraction ◽  
Organic N ◽  
Total Biomass ◽  
Export Production ◽  
Dominant Source ◽  
Isotopic Evidence ◽  
Surface Ocean ◽  
Eukaryotic Phytoplankton ◽  
Mesocosm Experiments

Abstract. In a coastal lagoon with a shallow, 25 m water column off the southwest coast of New Caledonia, large-volume ( ∼  50 m3) mesocosm experiments were undertaken to track the fate of newly fixed nitrogen (N). The mesocosms were intentionally fertilized with 0.8 µM dissolved inorganic phosphorus to stimulate diazotrophy. N isotopic evidence indicates that the dominant source of N fueling export production shifted from subsurface nitrate (NO3−) assimilated prior to the start of the 23-day experiments to N2 fixation by the end of the experiments. While the δ15N of the sinking particulate N (PNsink) flux changed during the experiments, the δ15N of the suspended PN (PNsusp) and dissolved organic N (DON) pools did not. This is consistent with previous observations that the δ15N of surface ocean N pools is less responsive than that of PNsink to changes in the dominant source of new N to surface waters. In spite of the absence of detectable NO3− in the mesocosms, the δ15N of PNsink indicated that NO3− continued to fuel a significant fraction of export production (20 to 60 %) throughout the 23-day experiments, with N2 fixation dominating export after about 2 weeks. The low rates of organic N export during the first 14 days were largely supported by NO3−, and phytoplankton abundance data suggest that sinking material primarily comprised large diatoms. Concurrent molecular and taxonomic studies indicate that the diazotroph community was dominated by diatom–diazotroph assemblages (DDAs) at this time. However, these DDAs represented a minor fraction (< 5 %) of the total diatom community and contributed very little new N via N2 fixation; they were thus not important for driving export production, either directly or indirectly. The unicellular cyanobacterial diazotroph, a Cyanothece-like UCYN-C, proliferated during the last phase of the experiments when N2 fixation, primary production, and the flux of PNsink increased significantly, and δ15N budgets reflected a predominantly diazotrophic source of N fueling export. At this time, the export flux itself was likely dominated by the non-diazotrophic diatom, Cylindrotheca closterium, along with lesser contributions from other eukaryotic phytoplankton and aggregated UCYN-C cells, as well as fecal pellets from zooplankton. Despite comprising a small fraction of the total biomass, UCYN-C was largely responsible for driving export production during the last  ∼  10 days of the experiments both directly ( ∼  5 to 22 % of PNsink) and through the rapid transfer of its newly fixed N to other phytoplankton; we infer that this newly fixed N was transferred rapidly through the dissolved N (including DON) and PNsusp pools. This inference reconciles previous observations of invariant oligotrophic surface ocean DON concentrations and δ15N with incubation studies showing that diazotrophs can release a significant fraction of their newly fixed N as some form of DON.

scholarly journals THE EPIDEMIOLOGY OF FOWL CHOLERA

1930 ◽  
Vol 51 (2) ◽  
pp. 249-258 ◽  
Author(s):  
Ida W. Pritchett ◽  
F. R. Beaudette ◽  
T. P. Hughes
Keyword(s):  
Field Studies ◽  
Colony Type ◽  
Fowl Cholera ◽  
Poultry Farms ◽  
High Virulence ◽  
Commercial Poultry ◽  
The Individual ◽  
High Level ◽  
Serum Agglutination ◽  
Healthy Carriers

Field studies of fowl cholera on two commercial poultry farms are described. One farm, previously free of cholera, was studied during an active epidemic, which occurred during the winter months. The strains of P. avicida recovered, both from "autopsy" and from "healthy carriers" proved generally similar, and to be of the "fluorescent" or "intermediate" colony type, which is of relatively high virulence. After the subsidence of the epidemic, these strains tended to disappear. The second flock consisted of a small group of birds which had survived an epidemic of cholera the previous year, and in which the infection was prevailing in endemic form. No deaths occurred during the period of observation, but the number of birds with localized lesions and the number of carriers increased to a high level during the winter months. The strains of P. avicida were apparently of the "blue" colony form, although some, as shown by their acid and serum agglutination reactions, resembled the "intermediates." These strains appeared to be spreading rather than dying out. The individual fowls differed in their response to the presence of infection; some showed localized lesions, others were carriers, while still others seemed entirely refractory.

Heroic leadership illusions in football teams: Rationality, decision making and noise-signal ratio in the firing of football managers

Leadership ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 169-185 ◽  
Author(s):  
Jan Ketil Arnulf ◽  
John Erik Mathisen ◽  
Thorvald Hærem
Keyword(s):  
Decision Making ◽  
Team Leadership ◽  
Noise Signal ◽  
Decision Makers ◽  
Signal Ratio ◽  
Management Positions ◽  
The Individual ◽  
Long Term Performance ◽  
Term Performance

Similar to practices in top management positions worldwide, there has been an increasing tendency in recent decades to fire football managers when the team does not perform to the stakeholders' expectations. Previous research has suggested that improvements after change of manager are a statistical artefact. Based on 12 years of data from the Norwegian Premier League, we conduct a natural experiment showing what would have taken place if the manager had not been fired. In this case, the performance might have improved just as well and even quicker. Building on theories in expertise and decision making, we explore the data and argue that decision makers may be fooled by randomness and learn wrong lessons about team leadership. Our analyses support a post-heroic view of team leadership as an emergent, output variable. Exaggerated focus on the individual manager may ruin long-term performance. Practical implications are discussed.

scholarly journals The effects of hybrid pay incentives on work-team performance: A longitudinal study

2015 ◽  
Vol 18 (4) ◽  
pp. 463-474
Author(s):  
Mbusi Dlamini ◽  
Margie Sutherland ◽  
Merle Werbeloff
Keyword(s):  
Work Performance ◽  
Field Studies ◽  
Individual Performance ◽  
Work Team ◽  
Team Members ◽  
Incentive Structures ◽  
Improved Performance ◽  
The Individual ◽  
Pay Incentives

Despite the widespread use of pay incentives to drive performance, few studies empirically demonstrate their long-term benefits within work-team settings in field studies; even fewer studies incorporate hybrid pay incentives in their design. This longitudinal field study explored the effects on individual work performance of allocating tellers to teams with supervisors who received hybrid pay incentives, where 60 per cent of their incentive was based on the individual performance of each of their team members and 40 per cent on their own performance. It was conducted on bulk-cash tellers working in 19 centres, using a time-series design. The results, derived from quantitative data collected from 82 individual tellers over 24 months, showed that hybrid pay incentives for supervisors of teams of tellers, some of whom were individually incentivised, were associated with significant increases in the volume, speed and accuracy of deposit processing by all the tellers. The findings empirically demonstrate the long term sustainability of improved performance associated with the introduction of hybrid pay incentive structures within work teams.

Performance of Genetically Modified Soybean Expressing the Cry1A.105, Cry2Ab2, and Cry1Ac Proteins Against Key Lepidopteran Pests in Brazil

2020 ◽  
Vol 113 (6) ◽  
pp. 2883-2889
Author(s):  
Fabiana B Bacalhau ◽  
Patrick M Dourado ◽  
Renato J Horikoshi ◽  
Renato A Carvalho ◽  
Altair Semeão ◽  
...  
Keyword(s):  
Genetically Modified ◽  
Leaf Disc ◽  
Field Studies ◽  
Field Conditions ◽  
Anticarsia Gemmatalis ◽  
Genetically Modified Soybean ◽  
Lepidopteran Pests ◽  
Highly Effective ◽  
The Individual ◽  
Gm Soybean

Abstract The pyramided genetically modified (GM) soybean [Glycine max L. (Merr.)] MON87751 × MON87708 × MON87701 × MON89788, expressing Cry1A.105, Cry2Ab2, and Cry1Ac from Bacillus thuringiensis Berliner, was approved for commercial use in Brazil. We conducted laboratory, greenhouse, and field studies to assess the efficacy of this Bt soybean against key soybean lepidopteran pests. Neonates of Anticarsia gemmatalis (Hübner) (Lepidoptera: Erebidae), Chrysodeixis includens (Walker), and Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were exposed to Bt proteins in diet-overlay bioassays. MON87751 × MON87708 × MON87701 × MON89788 soybean and individual components were evaluated in laboratory (leaf disc), greenhouse (high artificial infestations), and in field conditions (natural infestations). Neonates of A. gemmatalis, C. includens, and H. armigera were highly susceptible to Cry1A.105 (LC50 from 0.79 to 48.22 ng/cm2), Cry2Ab2 (LC50 from 1.24 to 8.36 ng/cm2), and Cry1Ac (LC50 from 0.15 to 5.07 ng/cm2) in diet-overlay bioassays. In laboratory leaf disc bioassays and greenhouse trials, MON87751 × MON87708 × MON87701 × MON89788 soybean as well as the individual components were highly effective in controlling A. gemmatalis, C. includens, and H. armigera. Similarly, under field conditions, the pyramided genotypes expressing Cry1A.105, Cry2Ab2, and Cry1Ac were highly effective at protecting soybean against C. includens. We concluded that the individual Bt proteins expressed by GM soybean MON87751 × MON87708 × MON87701 × MON89788 killed all or nearly all the susceptible A. gemmatalis, C. includens, and H. armigera, fulfilling one important criterion for successfully delaying resistance to pyramided Bt crops.

Nitrogen fixation in chickpea. II. Comparison of 15N enrichment and 15N natural abundance methods for estimating nitrogen fixation

1995 ◽  
Vol 46 (1) ◽  
pp. 225 ◽  
Author(s):  
JA Doughton ◽  
PG Saffigna ◽  
I Vallis ◽  
RJ Mayer
Keyword(s):  
Nitrogen Fixation ◽  
N2 Fixation ◽  
Full Range ◽  
15N Natural Abundance ◽  
Natural Abundance ◽  
Enrichment Method ◽  
Mineral N ◽  
Crop Establishment ◽  
15N Enrichment ◽  
15N Natural Abundance Method

The 15N enrichment and 15N natural abundance methods for estimating N2 fixation in chickpea were compared over a range of soil NO3-N levels at crop establishment varying from 10 to 326 kg N/ha (0-120 cm depth). Barley was used as a non-N2 fixing control crop. Both methods estimated reduced N2 fixation as soil NO3-N levels at crop establishment increased. Similar estimates of % N2 fixation were obtained at high values, but at low values the enrichment method gave lower estimates, some of which were negative. The 15N natural abundance method provided realistic estimates of % N2 fixation across all soil N03-N levels at crop establishment. An asymptotic curve described a close ( R2 = 0.95) relationship between these factors. Standard errors of estimates of means for the 15N natural abundance method remained acceptable and relatively stable over the full range of measurements; however, with the 15N enrichment method they became unacceptably large at low values of % N2 fixation. These large errors may have been partly due to legume and control plants assimilating mineral N of differing 15N enrichment. High mineral N levels associated with low values of % N2 fixation were also shown to reduce reliability of N2 fixation values estimated by the 15N enrichment method. These errors caused potentially greater inaccuracy at low values of % N2 fixation than at high values. To compare N2 fixation means statistically, transformations were necessary to stabilize variance and to impart lower weightings to plots with low values of % N2 fixation.

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