scholarly journals Partitioning of Environmental and Taxonomic Controls on Brazilian Foliar Content of Carbon and Nitrogen and Stable Isotopes

2021 ◽  
Vol 4 ◽  
Author(s):  
Luiz A. Martinelli ◽  
Adibe L. Abdalla-Filho ◽  
Taciana F. Gomes ◽  
Silvia R. M. Lins ◽  
Eduardo Mariano ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Wood Density ◽  
C:N Ratio ◽  
High Density ◽  
N Fixation ◽  
Low Density ◽  
Data Set ◽  
Large Variability ◽  
Foliar N

The Neotropics harbor some of the most diversified woody species in the world, and to understand the nutrient dynamics in these ecosystems, it is crucial to understand the role of plant taxonomy. In addition, biological nitrogen (N) fixation (BNF) in the tropics is one of the key processes affecting the global N cycle. Our objective was to (i) investigate the role of taxonomy and sampling site as predictors of foliar carbon (C) and N concentration and its stable isotopes (i.e., δ13C and δ15N); (ii) assess differences in foliar N, C:N ratio, and δ15N among three functional groups: species of N2-fixers and non-fixers of the Fabaceae family, as well as non-Fabaceae species; and (iii) examine the effect of wood density on tree foliar properties. We hypothesized that Fabaceae specimens in symbiosis with N2-fixers would possess a higher foliar N than non-fixing plants, including those of the Fabaceae family, as well as high-density trees would have higher foliar C and C:N ratio relative to low-density trees, where the latter invest in nutrients instead of structural C. We used a data set composed of 3,668 specimens sampled in three main biomes of Brazil: Amazon, Atlantic Forest, and Cerrado. The partitioning of variance had a higher influence of taxonomy on leaf C, N, and C:N ratio. Conversely, foliar δ13C and δ15N were environmentally constrained. While family was the most important taxonomy level for C, N, and C:N ratio, species played a major role for δ13C and δ15N. Foliar N followed the pattern fixers > non-fixers > non-Fabaceae, while C:N ratio had an opposite trend. In addition, foliar C was correlated with wood density, where high-density > medium-density and low-density woods. The large variability of δ15N was observed among Fabaceae species, demonstrates the complexity of using δ15N as an indicator of BNF. The higher foliar N of Fabaceae non-fixers than non-Fabaceae specimens support the hypothesis that an N-demanding lifestyle is an inherent pattern in this family. Lastly, although observed in some studies, the prediction of foliar properties using wood density is challenging, and future research on this topic is needed.

scholarly journals Population Density or Populations Size. Which Factor Determines Urban Traffic Congestion?

2021 ◽  
Vol 13 (8) ◽  
pp. 4280
Author(s):  
Yu Sang Chang ◽  
Sung Jun Jo ◽  
Yoo-Taek Lee ◽  
Yoonji Lee
Keyword(s):  
Population Density ◽  
Population Size ◽  
Traffic Congestion ◽  
Critical Role ◽  
Small Population ◽  
High Density ◽  
Urban Traffic ◽  
Contradictory Result ◽  
Low Density

A large number of articles have documented that as population density of cities increases, car use declines and public transit use rises. These articles had a significant impact of promoting high-density compact urban development to mitigate traffic congestion. Another approach followed by other researchers used the urban scaling model to indicate that traffic congestion increases as population size of cities increases, thus generating a possible contradictory result. Therefore, this study examines the role of both density and population size on traffic congestion in 164 global cities by the use of Stochastic Impacts by Regression on Population, Affluence and Technology model. We divide 164 cities into the two subgroups of 66 low density cities and 98 high density cities for analysis. The findings from the subgroups analysis indicated a clear-cut difference on the critical role of density in low-density cities and the exclusive role of population size in high-density cities. Furthermore, using threshold regression model, 164 cities are divided into the two regions of large and small population cities to determine population scale advantage of traffic congestion. Our findings highlight the importance of including analysis of subgroups based on density and/or population size in future studies of traffic congestion.

The Role of Low Density, High Density, and Very Low Density Lipoproteins in Steroidogenesis by the Human Fetal Adrenal Gland*

Endocrinology ◽  
1980 ◽  
Vol 106 (6) ◽  
pp. 1854-1860 ◽  
Author(s):  
BRUCE R. CARR ◽  
C. RICHARD PARKER ◽  
LEON MILEWICH ◽  
JOHN C. PORTER ◽  
PAUL C. MACDONALD ◽  
...  
Keyword(s):  
Adrenal Gland ◽  
Low Density Lipoproteins ◽  
High Density ◽  
Low Density ◽  
Very Low Density Lipoproteins

scholarly journals Global Adaptations Resulting from High Population Densities in Escherichia coli Cultures

2000 ◽  
Vol 182 (15) ◽  
pp. 4158-4164 ◽  
Author(s):  
XueQiao Liu ◽  
Christina Ng ◽  
Thomas Ferenci
Keyword(s):  
Escherichia Coli ◽  
Population Density ◽  
Outer Membrane ◽  
High Density ◽  
Low Density ◽  
Membrane Composition ◽  
High Culture ◽  
General Stress Response ◽  
Trehalose Synthesis

ABSTRACT The scope of population density effects was investigated in steady-state continuous cultures of Escherichia coli in the absence of complications caused by transient environmental conditions and growth rates. Four distinct bacterial properties reflecting major regulatory and physiological circuits were analyzed. The metabolome profile of bacteria growing at high density contained major differences from low-density cultures. The 10-fold-elevated level of trehalose at higher densities pointed to the increased role of the RpoS sigma factor, which controls trehalose synthesis genes as well as the general stress response. There was an eightfold difference in RpoS levels between bacteria grown at 108 and at 109cells/ml. In contrast, the cellular content of the DNA binding protein H-NS, controlling many genes in concert with RpoS, was decreased by high density. Since H-NS and RpoS also influence porin gene expression, the influence of population density on the intricate regulation of outer membrane composition was also investigated. High culture densities were found to strongly repress ompF porin transcription, with a sharp threshold at a density of 4.4 × 108 cells/ml, while increasing the proportion of OmpC in the outer membrane. The density-dependent regulation ofompF was maintained in rpoS or hnsmutants and so was independent of these regulators. The consistently dramatic changes indicate that actively growing, high-density cultures are at least as differentiated from low-density cultures as are exponential- from stationary-phase bacteria.

scholarly journals Exploring the Role of Breast Density on Cancer Prognosis among Women Attending Population-Based Screening Programmes

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Laia Domingo ◽  
Maria Sala ◽  
Javier Louro ◽  
Marisa Baré ◽  
Teresa Barata ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Breast Density ◽  
Proportional Hazards ◽  
Population Based ◽  
Cox Proportional Hazards ◽  
High Density ◽  
Cancer Prognosis ◽  
Low Density ◽  
Risk Of Death

Background. Our aim was to assess the role of breast density on breast cancer mortality and recurrences, considering patient and tumour characteristics and the treatments received among women attending population-based screening programmes. Methods. We conducted a retrospective cohort study among women aged 50–69 years attending population-based screening programmes, diagnosed with invasive breast cancer between 2000 and 2009, and followed up to 2014. Breast density was categorised as low density (≤25% dense tissue), intermediate density (25–50%), and high density (≥50%). Cox proportional hazards regression models were fitted to estimate the adjusted hazard ratios (aHR) and 95% confidence intervals (95% CI) for death and recurrences, adjusting by patient characteristics, mode of detection (screen-detected vs. interval cancer), and tumour features. Results. The percentage of deaths and recurrences was higher among women with intermediate- and high-density breasts than among women with low-density breasts (p=0.011 for death; p=0.037 for recurrences). Adjusted Cox proportional hazards regression models revealed that women with intermediate- and high-density breasts had a higher risk of death than women with low-density breasts, being statistically significant for intermediate densities (aHR = 2.19 [95% CI: 1.16–4.13], aHR = 1.44 [95% CI: 0.67–3.1], respectively). No association was found between breast density and recurrences. Conclusions. Breast density was associated with a higher risk of death, but not of recurrences, among women participating in breast cancer screening. These findings reinforce the need to improve screening sensitivity among women with dense breasts and to routinely assess breast density, not only for its role as a risk factor for breast cancer but also for its potential influence on cancer prognosis.

scholarly journals Invasive acacias experience higher ant seed removal rates at the invasion edges

Web Ecology ◽  
2012 ◽  
Vol 12 (1) ◽  
pp. 33-37 ◽  
Author(s):  
D. Montesinos ◽  
S. Castro ◽  
S. Rodríguez-Echeverría
Keyword(s):  
Removal Rate ◽  
European Population ◽  
High Density ◽  
Low Density ◽  
Seed Removal ◽  
Native Range ◽  
Ant Communities ◽  
Acacia Dealbata ◽  
Introduced Plants

Abstract. Seed dispersal is a key process for the invasion of new areas by exotic species. Introduced plants often take advantage of native generalist dispersers. Australian acacias are primarily dispersed by ants in their native range and produce seeds bearing a protein and lipid rich reward for ant mutualists (elaiosome). Nevertheless, the role of myrmecochory in the expansion of Australian acacias in European invaded areas is still not clear. We selected one European population of Acacia dealbata and another of A. longifolia and offered elaiosome-bearing and elaiosome-removed seeds to local ant communities. For each species, seeds were offered both in high-density acacia stands and in low-density invasion edges. For both acacia species, seed removal was significantly higher at the low-density edges. For A. longifolia, manual elimination of elaiosomes reduced the chance of seed removal by 80% in the low-density edges, whereas it made no difference on the high-density stands. For A. dealbata, the absence of elaiosome reduced seed removal rate by 52%, independently of the acacia density. Our data suggests that invasive acacias have found effective ant seed dispersers in Europe and that the importance of such dispersers is higher at the invasion edges.

scholarly journals Cell density modulates the decrease of cytosolic free Ca2+ induced by atrial natriuretic hormone, S-nitroso-N-acetylpenicillamine and 8-bromo cyclic GMP in cultured rat mesangial cells

1991 ◽  
Vol 274 (2) ◽  
pp. 323-328 ◽  
Author(s):  
F Lermioglu ◽  
J Goyal ◽  
A Hassid
Keyword(s):  
Cell Density ◽  
Cyclic Gmp ◽  
Mesangial Cells ◽  
High Density ◽  
Low Density ◽  
Natriuretic Hormone ◽  
Atrial Natriuretic Hormone ◽  
High Concentrations ◽  
Atrial Natriuretic

Cyclic GMP-elevating agents, including atrial natriuretic hormone and NO-generating vasodilators, decrease cytosolic free Ca2+ levels in mesangial cells. We have investigated the role of cell density as a modulator of the decrease in cytosolic free Ca2+ induced by the cyclic GMP (cGMP)-elevating vasodilators atrial natriuretic peptide (99-126) [ANP (99-126); ‘atriopeptin 28′] and the NO-generating vasodilator S-nitroso-N-acetylpenicillamine (SNAP), in cultured rat mesangial cells. Increasing cell density was significantly correlated with the decrease in cytosolic free Ca2+ induced by ANP (99-126) or SNAP. Moreover, this effect was independent of the cells' proliferative status. ANP (99-126) and SNAP induced greater fold stimulation of cGMP accumulation in high-density cells, but the levels of cGMP elicited by high concentrations of ANP (99-126) or SNAP were similar in high- and low-density cells. 8-Bromo cGMP was more effective in decreasing cytosolic free Ca2+ in high- than in low-density cells, suggesting that the greater effectiveness of ANP (99-126) and SNAP was, in part, due to greater effectiveness of endogenous cGMP in high-density cells. The results document that cell density, but not proliferative status, plays an important role in the modulation of intracellular Ca2+ dynamics in rat mesangial cells by atriopeptins, NO-generating vasodilators and cGMP.

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