146 research outputs found
A fat-enriched, glucose-enriched diet markedly attenuates adiponectin mRNA levels in rat epididymal adipose tissue
Adiponectin levels are decreased in subjects with obesity, diabetes and coronary artery disease. in the present study, we have investigated whether the decrease in the levels and mRNA expression of adiponectin is due to obesity or to the diet itself. Wistar rats were either fed standard laboratory chow throughout (controls) or given a fat-enriched, glucose-enriched diet (diet-fed) for 2 days or 16 weeks. After 2 days of diet feeding, total body weight, fat pad masses and the plasma levels of glucose, insulin and leptin were all comparable between the two groups, while plasma NEFA (non-esterified fatty acid) and triacylglycerol levels were increased in the diet-fed animals (P < 0.01 for both). There was a marked (P < 0.01) decrease in plasma adiponectin levels. After 16 weeks of diet feeding, diet-fed rats had significantly higher body weight, fat pad mass and plasma levels of leptin, adiponectin, NEFA and triacylglycerol (P < 0.001 for all) compared with chow-fed controls, whereas plasma levels of glucose and insulin were similar in the two groups. After 2 days of diet feeding, there were no significant changes in Ob mRNA levels in epididymal fat, whereas there was a marked decrease in adiponectin mRNA levels. After 16 weeks of diet feeding, rats had significantly increased levels of Ob mRNA, but decreased adiponectin mRNA levels, in epididymal fat compared with the chow-fed group (P < 0.001 for both). These findings suggest that obesity per se is not a factor in the decreased adiponectin levels observed in obese subjects. We propose that the lipid profile of the plasma and/or the constituents of the diet consumed by rats may contribute to adiponectin levels more than obesity per se.Univ Liverpool, Dept Med, Neuroendocrine & Obes Biol Unit, Liverpool L69 6GA, Merseyside, EnglandUniversidade Federal de São Paulo, Dept Physiol, São Paulo, BrazilUniv Complutense, Fac Biol Sci, Dept Anim Biol 2, E-28040 Madrid, SpainUniversidade Federal de São Paulo, Dept Physiol, São Paulo, BrazilWeb of Scienc
Above-ground biomass and structure of 260 African tropical forests.
We report above-ground biomass (AGB), basal area, stem density and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy tropical forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha⁻¹ (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha⁻¹) similar to those of Bornean forests, and significantly greater than East or West African forests. AGB therefore appears generally higher in palaeo- compared with neotropical forests. However, mean stem density is low (426 ± 11 stems ha⁻¹ greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean forests (cf. approx. 600) and is the signature structural feature of African tropical forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationships with C : N ratio (suggesting a positive soil phosphorus-AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy tropical forests may be particularly sensitive to future precipitation and temperature changes
Molecular, Cellular and Physiological Evidences for the Anorexigenic Actions of Nesfatin-1 in Goldfish
Nesfatin-1 is a recently discovered anorexigen encoded in the precursor peptide, nucleobindin-2 (NUCB2) in mammals. To date, nesfatin-1 has not been described in any non-mammalian species, although some information is available in the sequenced genomes of several species. Our objective was to characterize nesfatin-1 in fish.In the present study, we employed molecular, immunohistochemical, and physiological studies to characterize the structure, distribution, and appetite regulatory effects of nesfatin-1 in a non-mammalian vertebrate. A very high conservation in NUCB2 sequences, especially in the nesfatin-1 region was found in lower vertebrates. Abundant expression of NUCB2 mRNA was detected in several tissues including the brain and liver of goldfish. Nesfatin-1-like immunoreactive cells are present in the feeding regulatory nucleus of the hypothalamus and in the gastrointestinal tract of goldfish. Approximately 6-fold increase in NUCB2 mRNA levels was found in the liver after 7-day food-deprivation, and a similar increase was also found after short-term fasting. This points toward a possible liver specific role for NUCB2 in the control of metabolism during food-deprivation. Meanwhile, ∼2-fold increase at 1 and 3 h post-feeding and an ∼3-fold reduction after a 7-day food-deprivation was observed in NUCB2 mRNA in the goldfish hypothalamus. In vivo, a single intraperitoneal injection of the full-length native (goldfish; gf) nesfatin-1 at a dose of 50 ng/g body weight induced a 23% reduction of food intake one hour post-injection in goldfish. Furthermore, intracerebroventricular injection of gfnesfatin-1 at a dose of 5 ng/g body weight resulted in ∼50% reduction in food intake.Our results provide molecular, anatomical and functional evidences to support potential anorectic and metabolic roles for endogenous nesfatin-1 in goldfish. Collectively, we provide novel information on NUCB2 in non-mammals and an anorexigenic role for nesfatin-1 in goldfish
Long-term decline of the Amazon carbon sink
Atmospheric carbon dioxide records indicate that the land surface has acted as a strong global carbon sink over recent decades1, 2, with a substantial fraction of this sink probably located in the tropics3, particularly in the Amazon4. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historical evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above-ground biomass declined by one-third during the past decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while biomass mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity5. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale1, 2, and is contrary to expectations based on models6
Tree mode of death and mortality risk factors across Amazon forests
The carbon sink capacity of tropical forests is substantially affected by tree mortality. However, the main drivers of tropical tree death remain largely unknown. Here we present a pan-Amazonian assessment of how and why trees die, analysing over 120,000 trees representing > 3800 species from 189 long-term RAINFOR forest plots. While tree mortality rates vary greatly Amazon-wide, on average trees are as likely to die standing as they are broken or uprooted—modes of death with different ecological consequences. Species-level growth rate is the single most important predictor of tree death in Amazonia, with faster-growing species being at higher risk. Within species, however, the slowest-growing trees are at greatest risk while the effect of tree size varies across the basin. In the driest Amazonian region species-level bioclimatic distributional patterns also predict the risk of death, suggesting that these forests are experiencing climatic conditions beyond their adaptative limits. These results provide not only a holistic pan-Amazonian picture of tree death but large-scale evidence for the overarching importance of the growth–survival trade-off in driving tropical tree mortality
Carbon uptake by mature Amazon forests has mitigated Amazon nations' carbon emissions
Background: Several independent lines of evidence suggest that Amazon forests have provided a significant carbon
sink service, and also that the Amazon carbon sink in intact, mature forests may now be threatened as a result of
different processes. There has however been no work done to quantify non-land-use-change forest carbon fluxes on
a national basis within Amazonia, or to place these national fluxes and their possible changes in the context of the
major anthropogenic carbon fluxes in the region. Here we present a first attempt to interpret results from groundbased
monitoring of mature forest carbon fluxes in a biogeographically, politically, and temporally differentiated way.
Specifically, using results from a large long-term network of forest plots, we estimate the Amazon biomass carbon balance
over the last three decades for the different regions and nine nations of Amazonia, and evaluate the magnitude
and trajectory of these differentiated balances in relation to major national anthropogenic carbon emissions.
Results: The sink of carbon into mature forests has been remarkably geographically ubiquitous across Amazonia,
being substantial and persistent in each of the five biogeographic regions within Amazonia. Between 1980 and 2010,
it has more than mitigated the fossil fuel emissions of every single national economy, except that of Venezuela. For
most nations (Bolivia, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname) the sink has probably additionally
mitigated all anthropogenic carbon emissions due to Amazon deforestation and other land use change. While the
sink has weakened in some regions since 2000, our analysis suggests that Amazon nations which are able to conserve
large areas of natural and semi-natural landscape still contribute globally-significant carbon sequestration.
Conclusions: Mature forests across all of Amazonia have contributed significantly to mitigating climate change for
decades. Yet Amazon nations have not directly benefited from providing this global scale ecosystem service. We suggest
that better monitoring and reporting of the carbon fluxes within mature forests, and understanding the drivers
of changes in their balance, must become national, as well as international, priorities
Seasonal drought limits tree species across the Neotropics
AcceptedArticle in Press© 2016 Nordic Society Oikos.Within the tropics, the species richness of tree communities is strongly and positively associated with precipitation. Previous research has suggested that this macroecological pattern is driven by the negative effect of water-stress on the physiological processes of most tree species. This implies that the range limits of taxa are defined by their ability to occur under dry conditions, and thus in terms of species distributions predicts a nested pattern of taxa distribution from wet to dry areas. However, this 'dry-tolerance' hypothesis has yet to be adequately tested at large spatial and taxonomic scales. Here, using a dataset of 531 inventory plots of closed canopy forest distributed across the western Neotropics we investigated how precipitation, evaluated both as mean annual precipitation and as the maximum climatological water deficit, influences the distribution of tropical tree species, genera and families. We find that the distributions of tree taxa are indeed nested along precipitation gradients in the western Neotropics. Taxa tolerant to seasonal drought are disproportionally widespread across the precipitation gradient, with most reaching even the wettest climates sampled; however, most taxa analysed are restricted to wet areas. Our results suggest that the 'dry tolerance' hypothesis has broad applicability in the world's most species-rich forests. In addition, the large number of species restricted to wetter conditions strongly indicates that an increased frequency of drought could severely threaten biodiversity in this region. Overall, this study establishes a baseline for exploring how tropical forest tree composition may change in response to current and future environmental changes in this region.This paper is a product of the RAINFOR and ATDN networks and of ForestPlots.net
researchers (http://www.forestplots.net). RAINFOR and ForestPlots have been
supported by a Gordon and Betty Moore Foundation grant, the European Union’s
Seventh Framework Programme (283080, ‘GEOCARBON’; 282664,
‘AMAZALERT’); European Research Council (ERC) grant ‘Tropical Forests in the
Changing Earth System’ (T-FORCES), and Natural Environment Research Council
(NERC) Urgency Grant and NERC Consortium Grants ‘AMAZONICA’
(NE/F005806/1) and ‘TROBIT’ (NE/D005590/1). Additional funding for fieldwork was
provided by Tropical Ecology Assessment and Monitoring (TEAM) Network, a
collaboration among Conservation International, the Missouri Botanical Garden, the
Smithsonian Institution, and the Wildlife Conservation Society. A.E.M. receives a PhD
scholarship from the T-FORCES ERC grant. O.L.P. is supported by an ERC Advanced
Grant and a Royal Society Wolfson Research Merit Award. We thank Jon J. Lloyd,
Chronis Tzedakis, David Galbraith, and two anonymous reviewers for helpful
comments and Dylan Young for helping with the analyses. This study would not be
possible without the extensive contributions of numerous field assistants and rural
communities in the Neotropical forests. Alfredo Alarcón, Patricia Alvarez Loayza,
Plínio Barbosa Camargo, Juan Carlos Licona, Alvaro Cogollo, Massiel Corrales
Medina, Jose Daniel Soto, Gloria Gutierrez, Nestor Jaramillo Jarama, Laura Jessica
Viscarra, Irina Mendoza Polo, Alexander Parada Gutierrez, Guido Pardo, Lourens
Poorter, Adriana Prieto, Freddy Ramirez Arevalo, Agustín Rudas, Rebeca Sibler and
Javier Silva Espejo additionally contributed data to this study though their RAINFOR
participations. We further thank those colleagues no longer with us, Jean Pierre Veillon,
Samuel Almeida, Sandra Patiño and Raimundo Saraiva. Many data come from Alwyn
Gentry, whose example has inspired new generations to investigate the diversity of the
Neotropics
Seasonal drought limits tree species across the Neotropics
Within the tropics, the species richness of tree communities is strongly and positively associated with precipitation. Previous research has suggested that this macroecological pattern is driven by the negative effect of water-stress on the physiological processes of most tree species. This process implies that the range limits of taxa are defined by their ability to occur under dry conditions, and thus in terms of species distributions it predicts a nested pattern of taxa distribution from wet to dry areas. However, this ‘dry-tolerance’ hypothesis has yet to be adequately tested at large spatial and taxonomic scales. Here, using a dataset of 531 inventory plots of closed canopy forest distributed across the Western Neotropics we investigated how precipitation, evaluated both as mean annual precipitation and as the maximum climatological water deficit, influences the distribution of tropical tree species, genera and families. We find that the distributions of tree taxa are indeed nested along precipitation gradients in the western Neotropics. Taxa tolerant to seasonal drought are disproportionally widespread across the precipitation gradient, with most reaching even the wettest climates sampled; however, most taxa analysed are restricted to wet areas. Our results suggest that the ‘dry tolerance’ hypothesis has broad applicability in the world's most species-rich forests. In addition, the large number of species restricted to wetter conditions strongly indicates that an increased frequency of drought could severely threaten biodiversity in this region. Overall, this study establishes a baseline for exploring how tropical forest tree composition may change in response to current and future environmental changes in this region
Tree mode of death and mortality risk factors across Amazon forests
The carbon sink capacity of tropical forests is substantially affected by tree mortality. However, the main drivers of tropical tree death remain largely unknown. Here we present a pan-Amazonian assessment of how and why trees die, analysing over 120,000 trees representing > 3800 species from 189 long-term RAINFOR forest plots. While tree mortality rates vary greatly Amazon-wide, on average trees are as likely to die standing as they are broken or uprooted—modes of death with different ecological consequences. Species-level growth rate is the single most important predictor of tree death in Amazonia, with faster-growing species being at higher risk. Within species, however, the slowest-growing trees are at greatest risk while the effect of tree size varies across the basin. In the driest Amazonian region species-level bioclimatic distributional patterns also predict the risk of death, suggesting that these forests are experiencing climatic conditions beyond their adaptative limits. These results provide not only a holistic pan-Amazonian picture of tree death but large-scale evidence for the overarching importance of the growth–survival trade-off in driving tropical tree mortality
Hyperdominance in Amazonian Forest Carbon Cycling
While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few ‘hyperdominant’ species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ≈1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region
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