Mineral types and tree species determine the functional and taxonomic structures of forest soil bacterial communities

Although minerals represent important soil constituents, their impact on the diversity and structure of soil microbial communities remains poorly documented. In this study, pure mineral particles with various chemistries (i.e., obsidian, apatite, and calcite) were considered. Each mineral type was conditioned in mesh bags and incubated in soil below different tree stands ( beech, coppice with standards, and Corsican pine) for 2.5 years to determine the relative impacts of mineralogy and mineral weatherability on the taxonomic and functional diversities of mineral-associated bacterial communities. After this incubation period, the minerals and the surrounding bulk soil were collected to determine mass loss and to perform soil analyses, enzymatic assays, and cultivation-dependent and -independent analyses. Notably, our 16S rRNA gene pyrosequencing analyses revealed that after the 2.5-year incubation period, the mineral-associated bacterial communities strongly differed from those of the surrounding bulk soil for all tree stands considered. When focusing only on minerals, our analyses showed that the bacterial communities associated with calcite, the less recalcitrant mineral type, significantly differed from those that colonized obsidian and apatite minerals. The cultivation-dependent analysis revealed significantly higher abundances of effective mineral-weathering bacteria on the most recalcitrant minerals (i.e., apatite and obsidian). Together, our data showed an enrichment of Betaproteobacteria and effective mineral-weathering bacteria related to the Burkholderia and Collimonas genera on the minerals, suggesting a key role for these taxa in mineral weathering and nutrient cycling in nutrient-poor forest ecosystems.IMPORTANCE Forests are usually developed on nutrient-poor and rocky soils, while nutrient-rich soils have been dedicated to agriculture. In this context, nutrient recycling and nutrient access are key processes in such environments. Deciphering how soil mineralogy influences the diversity, structure, and function of soil bacterial communities in relation to the soil conditions is crucial to better understanding the relative role of the soil bacterial communities in nutrient cycling and plant nutrition in nutrient-poor environments. The present study determined in detail the diversity and structure of bacterial communities associated with different mineral types incubated for 2.5 years in the soil under different tree species using cultivation-dependent and - independent analyses. Our data showed an enrichment of specific bacterial taxa on the minerals, specifically on the most weathered minerals, suggesting that they play key roles in mineral weathering and nutrient cycling in nutrient-poor forest ecosystems

Les mecanismes des alterations hydrothermales dans les granites fractures

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Dépôts atmosphériques particulaires sur les écosystèmes forestiers de la moitié Nord de la France (influence sur les cycles biogéochimiques)

Quantifier la totalité des apports atmosphériques, notamment particulaires, est nécessaire pour mieux comprendre les cycles biogéochimiques en vue d'une gestion durable des écosystèmes forestiers. En effet, l'intensification des récoltes de bois-énergie induit une pression nutritive supplémentaire sur les forêts. Le but de ce travail est de combler les lacunes concernant le dépôt atmosphérique particulaire (taux de dépôt, composition minéralogique et chimique), ainsi que d'étudier son influence sur les cycles biogéochimiques forestiers. Pour ce faire, un échantillonnage de 2 ans a été mis en place dans 4 hêtraies de la moitié Nord de la France. Un développement métrologique a été nécessaire pour concevoir les capteurs hors et sous canopée et pour séparer les particules de la phase dissoute puis compartimenter le dépôt particulaire en fonction du modèle conceptuel organo-minéral établi dans cette étude. Les résultats obtenus valident ce modèle et montrent (i) un taux de dépôt annuel de 19+-3 kg.ha-1.an-1 de minéraux peu solubles témoignant d'origines diverses, (ii) des flux de nutriments inférieurs à ceux des dépôts dissous et de l'altération des minéraux du sol mais qui contribuent à améliorer la fertilité des forêts, (iii) un captage supplémentaire induit par la canopée et (iv) une dissolution des particules minérales lors de leur transport atmosphérique qui enrichit les précipitations en nutriments. Un échantillonnage optimisé sur le long terme est indispensable pour confirmer et préciser les tendances observées, en particulier concernant les épisodes de très fort dépôt particulaire et le dépôt sous la canopéeQuantifying the little-known inputs of atmospheric particulate deposition (APD) is critically important for a sustainable management of forest ecosystems. Indeed, harvesting and subsequent nutrient losses are going to increase so as to meet the demand in renewable energy, including fuel-wood. This work aims at filling this gap by (i) describing the deposition rate, mineralogical and chemical compositions of APD and (ii) evaluating the influence of APD nutrient inputs on forest biogeochemical cycles. To do so, 4 beech stands in North French forests were equipped for a 4-week sampling. After a metrological development, samplers out of and below canopy were used for a 2-year sampling, as well as methods to separate APD from atmospheric dissolved deposition. These methods were conceived to separate the organic and mineral fractions of APD according to the conceptual model designed in this work. My results validated this model and indicated (i) a quite constant deposition rate of 19+-3 kg.ha-1.year-1 of hardly soluble minerals over the North of France, made of various minerals suggesting heterogeneous sources of particles, (ii) nutrient inputs inferior to those of atmospheric dissolved deposition and soil weathering, but improving ecosystem fertility, (iii) an interception effect of the canopy, and (iv) the dissolution of mineral particles in the atmosphere which enriched atmospheric dissolved deposition in nutrients. Extending and optimizing the sampling would allow confirming and clarifying these results, especially concerning high atmospheric load periods and APD below canopyMETZ-SCD (574632105) / SudocNANCY1-Bib. numérique (543959902) / SudocNANCY2-Bibliotheque electronique (543959901) / SudocNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Input-output nutrient budgets as a diagnostic tool for sustainable forest management

International audienc

The dissolution of biotite single crystals in dilute HNO3 at 24ø C : evidence of an anisotropic corrosion process of micas in acidic solutions

International audienc

Input-output nutrient budgets as a diagnostic tool for sustainable forest management

International audienc

Rhizosphere in the forest ecosystems: A favorable interface for tree nutrition

International audienc

Complementary methods to distinguish organic and mineral matter in atmospheric particulate deposition and their respective nutrient inputs to temperate forest ecosystems

International audienceSampling atmospheric particulate deposition (APD) in forest ecosystems highlights the need for methods to measure and analyze its organic and mineral repartition. We validated an organo-mineral repartition model of APD composition in open fields and below canopy with a mineral fraction, named mineral dust deposition (MOD), and particulate organic matter (POM). MDD is subdivided into soluble (S-MDD) and hardly soluble (H-MDD) fractions. To (i) monitor APD and its nutrient fluxes in forest ecosystems in the north of France and (ii) quantify the relative contribution of POM and MDD to APD, we adapted sampling materials and preparation methods that were developed for regions close to mineral dust sources. We have also compared two protocols. The "APD" protocol led to quick results for APD rates and POM contents. The "H-MDD" protocol is a treatment for soil samples that uses hydrogen peroxide, which solubilized both POM and S-MDD, and allowed detailed analyses of H-MDD. Both protocols induced a mass loss that was a maximum for the "H-MDD" protocol (31 +/- 3%). The contribution of POM in APD in open fields (49 +/- 10%) was lower than below the canopy (at least 66 +/- 6%). H-MDD accounted for approximately 80% of the MDD mass and contained the largest portion of low-solubility elements (Si, Al and Fe). The fractions S-MDD and POM contained the largest portion of Ca and P (more than 70%). The two protocols were complementary and may be used successively to accurately describe APD

Clay minerals: Precise markers of the spatial and temporal variability of the biogeochemical soil environment

International audienceAs clay minerals develop a large surface area, they have a considerable capacity to react with the other soil phases and eventually record the subtle chemical changes (in space and time) occurring during these interactions. To test this hypothesis, we characterized the spatial variability of forest soil properties (at the infra-millimetre scale) around the roots. Temporal variations of these properties were followed over a period of 3 months. Chemical extractions and mineralogical studies indicated that the bulk soil and the rhizospheric soil fraction presented different characteristics which changed with the seasons. In agreement with Si and Al extracted by the citrate treatment (Sic, Alc), XRD behaviour of the 2:1 phyllosilicates reflected temporal and spatial variations of the interlayer occupation. In addition, both the dissolution and precipitation of minerals were observed. In the bulk soil, weathering was more pronounced in June and resulted in an increase in the amount of Sic in the surface layer and Alc amounts in layers 2 and 3. The increase in the amount of Alc was attributed to aluminium compounds precipitated between March and June, mainly located outside the clay interlayers and only slightly polymerised. The high weathering rate in June was attributed to microbiological activity, and especially to organic matter mineralisation associated with nitrification and proton production. In the rhizosphere, uptake of nitrates in June resulted in the excretion of large quantities of OH− around the roots. Higher hydroxylation of the aluminium compounds in these sites was shown by a reduction in the aluminiumhydroxide charge,weaker collapse of the clay interlayers and a decrease in the CEC. Also, the excess of K input by mass flow and mineral weathering relative to root uptake led to an increase in K in the rhizosphere solution, fixation ofKin the interlayers and irreversible collapse of part of the expanding minerals. This process should have a decelerating effect on weathering and aluminisation of the vermiculites. The unleached part of K remains available for plant nutrition when the environmental conditions change

Rhizosphere impact on the dissolution of test minerals in a forest ecosystem

International audienceAs soil minerals are the principal input of nutrients in non-fertilized forests, the parameters which influence their dissolution must be determined to predict ecosystem sustainability. Notably, biological activities within the rhizosphere, such as root and micro-organism exudation and respiration, considerably affect mineral dissolution rate. Numerous laboratory studies have even demonstrated that certain biological processes involved in mineral weathering can be stimulated in low-nutrient availability conditions, resulting in an improvement of plant nutrition. The objective of this work was to determine in the field if the mineral dissolution rate linked to root and root-associated micro-organism activity is increased in low-nutrient availability conditions. Here, the impact of the rhizosphere on the dissolution of test minerals containing Ca (fluorapatite and labradorite plagioclase) was assessed in an acid forest soil in two stands of mature beeches (Fagus sylvatica) presenting two levels of Ca availability: a control plot as well as a plot fertilized with Ca. Mineral-test bags were inserted at three different depths (−2.5, −10 and −20 cm) in the control and the Ca-fertilized plots into both a zone with roots as well as a zone where roots had been excluded, thus permitting to assess the effect of the rhizosphere on the mineral dissolution. After four years of incubation in the soil, the minerals were weighed and observed by scanning electron microscope. In the control stand, linear dissolution voids were only observed on the mineral surfaces incubated in the zone with roots, suggesting that local biological activities occurring in the rhizosphere affect mineral weathering. This positive effect of the rhizosphere in the control stand was confirmed by quantification of the mineral dissolution, which revealed an increase of fluorapatite and labradorite weathering, reaching factors 3 to 4 at 20-cm depth. In contrast, the beech rhizosphere did not increase mineral dissolution, hyphae colonisation or linear dissolution marks in the Ca-fertilized stand. These results suggest that the rhizospheric biological activities acting on mineral weathering could be regulated by the nutrient availability in the ecosystem. This plasticity of the rhizospheric biological activities may thus contribute to the maintenance of ecosystem sustainability