The C : N : P stoichiometry of autotrophs – theory and observations

Evolution has set biochemical constraints on the chemical composition of living organisms. These constraints seem to lead to increases in N : C and P : C ratios with increasing relative growth rate for all types of organisms. The N : P ratio also seems to decrease with relative growth rate for heterotrophs whereas autotrophs may show a more complex behaviour. Here I will show that, from biochemical considerations, N : C should increase linearly and P : C quadratically with relative growth rate in autotrophs with the consequence that N : P increases at low relative growth rates, passes a maximum and then decreases at high relative growth rates. These predictions are verified against observations for a freshwater alga (Selenastrum minutum) and a tree seedling (Betula pendula). Changes in temperature, light or other factors that affect the growth rate of autotrophs interact with nutrient supply in such a way that there are no simple rules for as to how N : P will change.     

High‐frequency fire alters C : N : P stoichiometry in forest litter

Fire is a major driver of ecosystem change and can disproportionately affect the cycling of different nutrients. Thus, a stoichiometric approach to investigate the relationships between nutrient availability and microbial resource use during decomposition is likely to provide insight into the effects of fire on ecosystem functioning. We conducted a field litter bag experiment to investigate the long‐term impact of repeated fire on the stoichiometry of leaf litter C, N and P pools, and nutrient‐acquiring enzyme activities during decomposition in a wet sclerophyll eucalypt forest in Queensland, Australia. Fire frequency treatments have been maintained since 1972, including burning every 2 years (2yrB), burning every 4 years (4yrB) and no burning (NB). C : N ratios in freshly fallen litter were 29–42% higher and C : P ratios were 6–25% lower for 2yrB than NB during decomposition, with correspondingly lower 2yrB N : P ratios (27–32) than for NB (34–49). Trends in litter soluble and microbial N : P ratios were similar to the overall litter N : P ratios across fire treatments. Consistent with these, the ratio of activities for N‐acquiring to P‐acquiring enzymes in litter was higher for 2yrB than NB, whereas 4yrB was generally intermediate between 2yrB and NB. Decomposition rates of freshly fallen litter were significantly lower for 2yrB (72 ± 2% mass remaining at the end of experiment) than for 4yrB (59 ± 3%) and NB (62 ± 3%), a difference that may be related to effects of N limitation, lower moisture content, and/or litter C quality. Results for older mixed‐age litter were similar to those for freshly fallen litter although treatment differences were less pronounced. Overall, these findings show that frequent fire (2yrB) decoupled N and P cycling, as manifested in litter C : N : P stoichiometry and in microbial biomass N : P ratio and enzymatic activities. Furthermore, these data indicate that fire induced a transient shift to N‐limited ecosystem conditions during the postfire recovery phase.     

Radiothérapie vectorisée : les nouvelles molécules

Although the efficacy of radionuclide therapy has been demonstrated in several indications, the development of this new therapeutic modality is limited. However, promising results have been obtained, especially using different radiolabeled somatotatin analogs for neuroendocrine tumors or radioimmunotherapy for lymphoma. Toxicity is limited, particularly if patients are selected based on their background. The use of new vectors (bombesin, anti-PMSA monoclonal antibody), pretargeting system and innovative radionuclides (Copper-67, Astatine-211) suggests interesting perspectives, particularly to target small tumor masses or residual disease.     

Aux origines de la Spiritualité : la notion de transcendance au Paléolithique

In a previous note we presented the expression of the late paleolithic spirituality (Welté and Lambert, 2004). A special analytic grid was used as a possible tool for a demonstration. We separeted rationality from metaphysic; notions which are linked with dialectic relations between necessity (daily constraints), thought, action and evolution in the paleolithic period. Starting from the no direct material activities like burials, funeral materials and art, we purpose now that such notions existed before the upper Paleolithic. We infer that a privilegious set of interactions between the animal and the human appeared early in the thought of the people, before the upper Paleolithic. A metaphysic univers forced itself upon them as an evident “anti-world” which is the symmetric shape of the real and tangible world. In such a context, the social system(s) could not discard these duality.     

Tumeurs brunes disséminées : à propos d’un cas

We report a case of multiple brown tumours concerning a 46-year-old, operated for a parathyroid adenoma, who is presenting clinical and biological signs of hyperparathyroidism recurrence. Unusual features in this case were the disseminated distribution of brown tumour and the bone scan pseudo-metastatic aspect.     

Territoires et mobilité des groupes moustériens en Vercors : analyse et discussion

This article focus with recent studies realized on the Vercors Mountain about middle paleolithic site in altitude context. It proposes to make the synthesis of the data concerning the exploitation and especially circulation of the various types of flint inside and near this geographic area. This level of analysis makes it possible to discuss on the mobility degree of the mousterians groups in Vercors and to advance hypotheses on the settlement system within this territory.     

N : P stoichiometry and protein : RNA ratios in vascular plants: an evaluation of the growth-rate hypothesis

The growth-rate hypothesis states that fast-growing organisms need relatively more phosphorus-rich RNA to support rapid rates of protein synthesis, and therefore predicts, within and among taxa, increases in RNA and phosphorus content (relative to protein and nitrogen content) with increased growth rate. Here, we present a test of this hypothesis in vascular plants. We determined nitrogen : phosphorus ratios and protein : RNA ratios in pines growing at different rates due to nutrient conditions. In general, when comparing leaves of the same species at low and high growth rates, the faster-growing plants had higher RNA content, higher %N and %P, and lower protein : RNA ratios, but not consistently lower N : P ratios. We found no link between growth rate and foliar N : P or protein : RNA when comparing multiple species of different inherent growth rates. We conclude that plants adjust the balance of protein and RNA to favour either speed or efficiency of protein synthesis, but this balance does not alone dictate leaf stoichiometry.     

Mégalithes et sociétés préhistoriques : concepts et terminologie

The restitution of the megalith’s technical manufacture, whith their assemblies lines and their sequences, enlarges the coast of the sens incluse in each Corsican monoliths. From the megalithics sites of Poghjaredda of Monte Rotondu (Sotta), Ciutulaghja (Appietu), and Presa (Altaghjè), some specifics activities area (pastoralism for example) or activities structured in the space (villages and tombs of middle Neolithic) interest this study. The contributions of many sciences permit to give an economic and social dimension to the choice of megalithics sites. Then, those choices are an aspect of the Neolithic process in Corsica, making part of sculpture and architecture. This study is conclued by a consideration on the actual worked stones’ terminology.     

Lactobacilli-Host mutualism: "learning on the fly"

Metazoans establish with microorganisms complex interactions for their mutual benefits. Drosophila, which has already proven useful host model to study several aspects of innate immunity and host-bacteria pathogenic associations has become a powerful model to dissect the mechanisms behind mutualistic host-microbe interactions. Drosophila microbiota is composed of simple and aerotolerant bacterial communities mostly composed of Lactobacillaceae and Acetobactereaceae. Drosophila mono- or poly-associated with lactobacilli strains constitutes a powerful model to dissect the complex interplay between lactobacilli and host biologic traits. Thanks to the genetic tractability of both Drosophila and lactobacilli this association model offers a great opportunity to reveal the underlying molecular mechanisms. Here, we review our current knowledge about how the Drosophila model is helping our understanding of how lactobacilli shapes host biology.     

First records of <Emphasis Type="Italic">Trichodectes canis</Emphasis> (Insecta: Phthiraptera: Trichodectidae) from Darwin’s fox, <Emphasis Type="Italic">Pseudalopex fulvipes</Emphasis> (Mammalia: Carnivora: Canidae)

The presence of the dog biting louse, Trichodectes canis (De Geer, 1778; Ischnocera: Trichodectidae), is reported for the first time in the critically endangered Pseudalopex fulvipes (Martin, 1837) in Chiloé Island, south Chile.     

Perturbateurs endocriniens et contamination orale : l’intestin oublié

Endocrine disruptors are a diverse group of compounds of natural origin (phytoestrogens and mycotoxins) or chemicals (phthalates, bisphenols, parabens or pesticides) that could create an imbalance in the homeostasis of the hormonal system, primarily in the signaling pathways involving sex steroids and thyroid hormones. Animal studies have extensively documented deleterious effects on the body, on reproductive function, metabolic and cerebral functions, particularly when exposure begins during fetal and neonatal life. If the oral contamination is a major route of contamination by these agents, a hormonal imbalance in the digestive functions has rarely been taken into account. In particular, estrogen receptors are expressed abundantly in the intestine, from the fetal stage, where endocrine disruptors, mainly xenoestrogens, are likely to have an effect. This article presents a review of known effects of xenoestrogens on gut barrier function, from the perinatal period through adulthood. Although the aetiology of diseases of the digestive system is complex and still poorly understood, clinical data contribute to the present chronic use of steroids in women (oral contraception, hormone replacement therapy) as risk factors in the development or activity of Crohn's disease or ulcerative colitis, where xenoestrogens may act as cofactors.