Métabolisme de base | EPFL Graph Search

vignette|Tableau du métabolisme de base (le même que celui plus bas) Le métabolisme de base (MB), ou métabolisme basal, correspond aux besoins énergétiques « incompressibles » de l'organisme, c’est-à-dire la dépense d'énergie minimum quotidienne permettant à l'organisme de survivre ; au repos, l’organisme consomme en effet de l’énergie pour maintenir en activité ses fonctions (cœur, cerveau, respiration, digestion, maintien de la température du corps), via des réactions biochimiques (qui utilisent l'ATP). Il est exprimé sur la base d'une journée, donc en joules ou en calories par jour, ou en watts. Il est différent des besoins énergétiques que l'alimentation ou les réserves (en cas de jeûne) doivent fournir, plus élevés lorsque les organismes sont actifs, ce qui est généralement le cas, et sous l'influence de la température extérieure et des conditions météorologique (vent, pluie etc.) ; ou plus rarement plus bas en cas d'hibernation. Le métabolisme de base des humains dépend de la ta

Scaling as a key conceptual tool for the interpretation of empirical and experimental patterns in ecology and biology

Silvia Zaoli

This thesis is concerned with regular patterns found in ecology and biology, their linkages and the statistical description of their fluctuations around average trends. Among such patterns, often conforming to power laws, well-known examples include the Species-Area relationship (SAR), quantifying the increase of the number of species S inhabiting an ecosystem with ecosystem area, and the scale-invariant body size spectrum, routinely observed, e.g., in aquatic ecosystems. In biology, Kleiber's law is an allometric relationship describing how metabolic rates scale with an organism's body size. While ecological laws have often been studied independently, simple heuristic reasonings show that they are linked. The need for a unifying effort in ecology, coherently synthesizing the vast and diverse set of empirical observations across scales, has been often voiced. However, a theoretical framework answering this need was still lacking. Furthermore, ecological variables are the result of the interplay between several stochastic ecological processes, and are therefore stochastic variables fluctuating around average values. Ecological and biological scaling laws typically make predictions for such averages, but the issue of fluctuations received scarce attention in the literature. Similarly, biological fluctuations have been typically neglected in the study of the size-scaling of metabolic rates, even though body sizes and metabolic rates may have a significant variability within a species. Fluctuations may be relevant to interpret empirical observations, judge the reliability of predictions and understand ecosystem dynamics. An hypothesis for the distribution of abundances and body sizes of species inhabiting an ecosystem of finite area is proposed here. The hypothesis is inspired by finite-size scaling and is used to derive macroecological patterns and their linkages within a coherent theoretical framework. Stochastic models of community dynamics are used to support the hypothesis, and the derived linkages are tested on empirical datasets. Several stochastic models of community dynamics are also used here to study the fluctuations of S and how they scale with the average S. The intra-specific variability of metabolic rates and body sizes is investigated experimentally using freshwater phytoplankton species by nanoscale secondary ion mass spectrometry (NanoSIMS). The linkages among ecological scaling laws predicted by the theoretical framework are verified in several empirical datasets. Theoretical generalizations including deviations from pure power-law behavior and heavy-tailed intra-specific size distributions are also addressed. The theoretical study of the relative scaling of the fluctuations of S with the mean

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in various community dynamics models shows that different ecological processes predict radically different fluctuations scalings, highlighting the need of empirical investigations to sort out which scenario applies to real ecosystems. Experiments on phytoplankton metabolic rate scaling with body size suggest that intra-specific metabolic rate distributions are described by a universal scaling form across different taxa and over three orders of magnitude in body size. This thesis, along with previous works, suggests that scaling concepts derived for inanimate systems can provide new insights into the dynamics of ecosystems and help unraveling regularities across scales of biological complexity.

EPFL2018

Primary and Net Ecosystem Production in a Large Lake Diagnosed From High-Resolution Oxygen Measurements

Hannah Elisa Chmiel, Bieito Fernandez Castro, Shubham Krishna, Camille Roland Marie Minaudo, Pascal Perolo, Alfred Johny Wüest

The rates of gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) provide quantitative information about the cycling of carbon and energy in aquatic ecosystems. In lakes, metabolic rates are often diagnosed from diel oxygen fluctuations recorded with high-resolution sondes. This requires that the imprint of ecosystem metabolism can be separated from that of physical processes. Here, we quantified the vertical and temporal variability of the metabolic rates of a deep, large, mesotrophic lake (Lake Geneva, Switzerland–France) by using a 6-month record (April–October 2019) of high-frequency, depth-resolved (0–30 m) dissolved oxygen measurements. Two new alternative methods (in the time and frequency domain) were used to filter low-frequency basinscale internal motions from the oxygen signal. Both methods proved successful and yielded consistent metabolic estimates showing net autotrophy (NEP = GPP − R = 55 mmol m−2 day−1) over the sampling period and depth interval, with GPP (235 mmol m−2 day−1) exceeding R (180 mmol m−2 day−1). They also revealed significant temporal variability, with at least two short-lived blooms occurring during calm periods, and a vertical partitioning of metabolism, with stronger diel cycles and positive NEP in the upper ∼10 m and negative NEP below, where the diel oxygen signal was dominated by internal motions. The proposed methods expand the range of applicability of the diel oxygen technique to large lakes hosting energetic, low-frequency internal motions, offering new possibilities for unveiling the rich spatiotemporal metabolism dynamics in these systems.

2021

Mitigating the variability of hydrogen production in mixed culture through bioaugmentation with exogenous pure strains

Nicolas Bernet, Simon Marius Jean Poirier

Process stability is a key operational issue when operating dark fermentation with mixed microbial cultures for hydrogen production. This study aimed at mitigating the instability of hydrogen production by separately adding exogenous pure strains suspected to have key roles in fermentative cultures. Among them, Clostridium acetobutylicum, Clostridium pasteurianum and Lactobacillus bulgaris which became predominant within the mixed culture strongly reduced the spectrum of produced metabolites and H-2 production variability. Interestingly, Escherichia coli and Cupriavidus necator, which remained in minor abundance, maintained a high and stable H-2 production while lowering the metabolic variability. 16S rRNA revealed that this could correlate to a simplification of the microbial diversity and the non-emergence of spore-forming competitors such as Sporolactobacillus sp. These results illustrate the potential beneficial role of minor OTUs as keystone species on H-2-producing complex ecosystem and support the possibility of using them to engineer the ecosystem and maintain high and stable performances. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

PERGAMON-ELSEVIER SCIENCE LTD2020

Scaling as a key conceptual tool for the interpretation of empirical and experimental patterns in ecology and biology

Silvia Zaoli

\langle S \rangle

EPFL2018