Project

fungi; calcium; bacteria; soil; carbonate; oxalate

Lead
La formation de carbonate de calcium (calcaire) dans des sols acides grâce à la dégradation d’origine biologique de l’oxalate repose directement à l’interface entre biologie et géologie. La voie oxalate-carbonate (OCP), mécanisme responsable de cette transformation, se fonde sur l’action conjointe de plantes, champignons et bactéries dans le sol, conduisant au stockage de carbone. Ce puits de carbone revêt un grand intérêt dans le contexte des changements climatiques.
Lay summary
L’objectif poursuivi par cette continuation de projet s’articule autour de la caractérisation des binômes naturels champignons-bactéries isolés de sols sous l’influence de l’OCP. Il vise aussi à établir le lien fonctionnel entre facteurs environnementaux variables au cours du temps lors de l’établissement de l’OCP (tels le pH, la biodisponibilité du Ca2+, la matière organique, les caractéristiques géochimiques du sol, sa texture, sa rétention en eau) et la prévalence des interactions bactéries-champignons. L’interaction bactéries-champignons est mise en avant car il s’agit véritablement d’un élément crucial des services écosystémiques fournis par les sols. En outre, rares sont les études expérimentales mettant en évidence cette interaction. Dans ce contexte, l’OCP reste un modèle naturel idéal permettant à la fois d’étudier le rôle fonctionnel de cette interaction (i.e. la dégradation de l’oxalate de calcium et la production de calcite) et les effets des paramètres environnementaux (i.e. changement de pH, nutriments, formation du sol). Ce projet contribuera significativement à notre compréhension des interactions biologiques dans les écosystèmes associant les sols.

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Last update: 05.10.2013

Lead
The formation of calcium carbonate (limestone) in acidic soils through the biological degradation of oxalate is at the interface between geology and biology. The oxalate-carbonate pathway (OCP) is the mechanism responsible, linking plants, fungi, and bacteria with soil and its capability to store carbon. By its geographical distribution and the long-term stability of these mineral carbon deposits, this carbon sink is of a crucial interest in the context of climate change.
Lay summary
The aim of this continuation project is to advance on the characterization of the native couples of fungi and bacteria isolated from soils under the OCP influence, and to establish the link between environmental factors that change temporarily on an active OCP (pH, Ca2+ bioavailability, OM, soil geochemistry, soil texture, and humidity) and the prevalence of fungi-bacteria interactions and their activity in the context of the OCP.  The interaction of fungi and bacteria has been put to the fore as one crucial element for ecosystem services provided by soils, however to date only a few experimental evidence of this has been obtained.  In this context, the OCP is an ideal natural model that allows simultaneously the investigation of the functional role of the interaction (i.e. the degradation of CaOx and the production of calcite) as well as the effect of environmental factors on it (i.e. changing pH, nutrients, soil genesis).  This project can have great impact on the understanding of the importance of biological interactions in the ecosystem functioning of soils.

Direct link to Lay Summary

Last update: 05.10.2013

Active participation

Number	Title	Start	Funding scheme

The formation of calcium carbonate in acidic soils through the biological degradation of oxalate is a process dubbed the oxalate-carbonate pathway (OCP), which occurs at the interface between geological and biological systems. This pathway starts with the fixation of atmospheric CO2 by the photosynthetic activity of oxalogenic plants that will use part of the C for the production of oxalate. Intracellular oxalate helps regulating Ca2+ concentrations by forming calcium oxalate (CaOx). The decay of plant material by saprophytic fungi or other organic matter (OM) degraders (e.g. termites) results in a source of CaOx for other trophic levels. Additional CaOx can be provided by fungi, which are able to produce this organic acid to cope with elevated metal concentrations. In spite of its abundance as a substrate, CaOx is very stable and can only be metabolized by oxalotrophic bacteria that use it as a carbon and energy source. The catabolism of CaOx changes the local soil pH and releases Ca2+ and HCO3- and, if the conditions are adequate, will indirectly lead to the precipitation of secondary calcium carbonate (calcite) under unexpected geological settings. If Ca2+ originates from a non-carbonate source, this pathway constitutes a soil mineral carbon sink. By its geographical distribution and the long-term stability of these mineral C deposits, this terrestrial C sink is of a crucial interest in the context of climate change and global C budget.Our knowledge of the OCP has been the result of a multidisciplinary approach that combines expertise in geology and microbiology, as well as field expeditions and laboratory work. In the SNF interdisciplinary project CR22I2-137994, our team has developed an experimental approach for the evaluation of the prevalence of biological interactions between bacteria and fungi in the OCP. In addition, we have assessed the importance of the Ca2+ source for pedogenic carbonate accumulations. In the first case, we have shown that fungi-bacteria interactions occur in soils under the OCP influence. In the second case, we have evidence for the conversion of a Ca-poor into a Ca-rich system due to the positive feedback affecting soil and the OCP overtime. The aim of this continuation project is to advance on the characterization of the native couples of fungi and bacteria isolated from soils under the OCP influence, and to establish the link between the environmental factors that change temporarily on an active OCP (pH, Ca2+ bioavailability, OM, soil geochemistry, soil texture, and humidity) and the prevalence of fungi-bacteria interactions and their activity in the context of the OCP. The interaction of fungi and bacteria has been put to the fore as one crucial element for the ecosystem services provided by soils, however to date really few experimental evidence of this has been obtained. In this context, the OCP is an ideal natural model that allows simultaneously the functional role of the interaction (i.e. the degradation of CaOx and the production of calcite) as well as the effect of environmental factors on it (i.e. changing pH, nutrients, soil genesis) to be evaluated. This project can have great impact on the understanding of the importance of biological interactions in the ecosystem functioning of soils.