Simulating microbial degradation of organic matter in a simple porous system using the 3-D diffusion-based model MOSAIC

This paper deals with the simulation of microbial degradation of organic matter in soil within the pore space at a microscopic scale. Pore space was analysed with micro-computed tomography and described using a sphere network coming from a geometrical modelling algorithm. The biological model was improved regarding previous work in order to include the transformation of dissolved organic compounds and diffusion processes. We tested our model using experimental results of a simple substrate decomposition experiment (fructose) within a simple medium (sand) in the presence of different bacterial strains. Separate incubations were carried out in microcosms using five different bacterial communities at two different water potentials of −10 and −100 cm of water. We calibrated the biological parameters by means of experimental data obtained at high water content, and we tested the model without changing any parameters at low water content. Same as for the experimental data, our simulation results showed that the decrease in water content caused a decrease of mineralization rate. The model was able to simulate the decrease of connectivity between substrate and microorganism due the decrease of water content

Understanding logical connectives: a comparative study of language influence.

Operators called 'logical connectives' convey in a\ud precise way the logical relationships between truth\ud functional propositions and hence determine what can be\ud inferred from them. Mathematical reasoning therefore\ud relies heavily on their use. Whilst the operators are\ud free of ambiguity, this is not so for the linguistic\ud items (called 'linguistic connectives') by which they\ud are codified. In English, at least, there is a widely\ud reported mismatch between the logical concepts and the\ud 'meanings' of the linguistic connectives with which\ud they are frequently identified.\ud This study compares the provision for expressing\ud logical concepts in Japanese, Arabic and English and\ud seeks to ascertain to what extent the problems reported\ud for English are generalisable to the other two\ud languages. It also aims to establish whether the\ud concepts underlying certain logical connectives are\ud 'more readily available' or 'better established' in the\ud speakers of one or other of these languages and, if so,\ud whether this can be attributed to differing provision\ud in the lexicon.\ud Two experiments were carried out using as subjects\ud adults who were native speakers of either English,\ud Japanese or Arabic. One was designed to determine to\ud what extent the appropriate linguistic connectives in\ud each of the three languages convey the associated\ud logical concepts. The second compared performance on\ud five concept identification tasks where the concepts\ud tested were conjunction, inclusive and exclusive\ud disjunction, the conditional and biconditional.\ud The results indicated no significant differences\ud between language groups in the understanding of the\ud linguistic expressions of logical connectives.\ud However, the Japanese language group consistently\ud outperformed the other two groups in all five concept\ud identification tasks and also offered descriptions of\ud these concepts which were more succinct and less\ud variable. Possible explanations for the superior\ud performance of the Japanese group are suggested and\ud some implications for the teaching and learning of\ud mathematics proposed

Modeling the effect of soil meso- and macropores topology on the biodegradation of a soluble carbon substrate

Soil structure and interactions between biotic and abiotic processes are increasingly recognized as important for explaining the large uncertainties in the outputs of macroscopic SOM decomposition models. We present a numerical analysis to assess the role of meso- and macropore topology on the biodegradation of a soluble carbon substrate in variably water saturated and pure diffusion conditions . Our analysis was built as a complete factorial design and used a new 3D pore-scale model, LBioS, that couples a diffusion Lattice-Boltzmann model and a compartmental biodegradation model. The scenarios combined contrasted modalities of four factors: meso- and macropore space geometry, water saturation, bacterial distribution and physiology. A global sensitivity analysis of these factors highlighted the role of physical factors in the biodegradation kinetics of our scenarios. Bacteria location explained 28% of the total variance in substrate concentration in all scenarios, while the interactions among location, saturation and geometry explained up to 51% of it

Microscale heterogeneity of the spatial distribution of organic matter can promote bacterial biodiversity in soils: Insights from computer simulations

There is still no satisfactory understanding of the factors that enable soil microbial populations to be as highly biodiverse as they are. The present article explores in silico the hypothesis that the heterogeneous distribution of soil organic matter, in addition to the spatial connectivity of the soil moisture, might account for the observed microbial biodiversity in soils. A multi-species, individual-based, pore-scale model is developed and parameterized with data from 3 Arthrobacter sp. strains, known to be, respectively, competitive, versatile, and poorly competitive. In the simulations, bacteria of each strain are distributed in a 3D computed tomography (CT) image of a real soil and three water saturation levels (100, 50, and 25%) and spatial heterogeneity levels (high, intermediate, and low) in the distribution of the soil organic matter are considered. High and intermediate heterogeneity levels assume, respectively, an amount of particulate organic matter (POM) distributed in a single (high heterogeneity) or in four (intermediate heterogeneity) randomly placed fragments. POM is hydrolyzed at a constant rate following a first-order kinetic, and continuously delivers dissolved organic carbon (DOC) into the liquid phase, where it is then taken up by bacteria. The low heterogeneity level assumes that the food source is available from the start as DOC. Unlike the relative abundances of the 3 strains, the total bacterial biomass and respiration are similar under the high and intermediate resource heterogeneity schemes. The key result of the simulations is that spatial heterogeneity in the distribution of organic matter influences the maintenance of bacterial biodiversity. The least competing strain, which does not reach noticeable growth for the low and intermediate spatial heterogeneities of resource distribution, can grow appreciably and even become more abundant than the other strains in the absence of direct competition, if the placement of the resource is favorable. For geodesic distances exceeding 5 mm, microbial colonies cannot grow. These conclusions are conditioned by assumptions made in the model, yet they suggest that microscale factors need to be considered to better understand the root causes of the high biodiversity of soils

Determinación de vitamina a por cromatografía líquida de alta eficiencia (clae) en bienestarina cruda

En el presente trabajo se valida una técnica de Cromatografía Liquida de Alta Eficiencia (CLAE) para la determinación y cuantificación de la vitamina A en Bienestarina cruda (mezcla alimenticia infantil producida por el Instituto Colombiano de Bienestar Familiar ICBF)

In situ modeling of PAH dynamics in agricultural soils amended with composts using the “VSOIL” platform

In situ modeling of PAH dynamics in agricultural soils amended with composts using the “VSOIL” platform. EGU 2017, European Geophysical Union General Assembly 201

Pore-scale monitoring of the effect of microarchitecture on fungal growth in a two-dimensional soil-like micromodel

In spite of the very significant role that fungi are called to play in agricultural production and climate change over the next two decades, very little is known at this point about the parameters that control the spread of fungal hyphae in the pore space of soils. Monitoring of this process in 3 dimensions is not technically feasible at the moment. The use of transparent micromodels simulating the internal geometry of real soils affords an opportunity to approach the problem in 2 dimensions, provided it is confirmed that fungi would actually want to propagate in such artificial systems. In this context, the key objectives of the research described in this article are to ascertain, first, that the fungus Rhizoctonia solani can indeed grow in a micromodel of a sandy loam soil, and, second, to identify and analyze in detail the pattern by which it spreads in the tortuous pores of the micromodel. Experimental observations show that hyphae penetrate easily inside the micromodel, where they bend frequently to adapt to the confinement to which they are subjected, and branch at irregular intervals, unlike in current computer models of the growth of hyphae, which tend to describe them as series of straight tubular segments. A portion of the time, hyphae in the micromodels also exhibit thigmotropism, i.e., tend to follow solid surfaces closely. Sub-apical branching, which in unconfined situations seems to be controlled by the fungus, appears to be closely connected with the bending of the hyphae, resulting from their interactions with surfaces. These different observations not only indicate different directions to follow to modify current mesoscopic models of fungal growth, so they can apply to soils, but they also suggest a wealth of further experiments using the same set-up, involving for example competing fungal hyphae, or the coexistence of fungi and bacteria in the same pore space