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The plant-available pools of calcium, magnesium and potassium are assumed to be stored in the soil as exchangeable cations adsorbed on the cation exchange complex. In numerous forest ecosystems, despite very low plant-available pools, elevated forest productivities are sustained. We hypothesize that trees access nutrient sources in the soil that are currently unaccounted by conventional soil analysis methods. We carried out an isotopic dilution assay to quantify the plant-available pools of calcium, magnesium and potassium and trace the soil phases that support these pools in 143 individual soil samples covering 3 climatic zones and 5 different soil types. For 81%, 87% and 90% of the soil samples (respectively for Ca, Mg and K), the plant-available pools measured by isotopic dilution were greater than the conventional exchangeable pool. This additional pool is most likely supported by secondary non-crystalline mineral phases in interaction with soil organic matter and represents in many cases (respectively 43%, 27% and 47% of the soil samples) a substantial amount of plant-available nutrient cations (50% greater than the conventional exchangeable pools) that is likely to play an essential role in the biogeochemical functioning of forest ecosystems, in particular when the resources of Ca, Mg and K are low.

Made available in DSpace on 2021-06-25T10:27:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 While a recent study showed that significant amounts of the nitrogen (N) requirements of young Eucalyptus trees can be provided by nitrogen-fixing trees (NFTs) in mixed-species plantations through short-term belowground N transfer, the consequences of soil fertility on this facilitation process remain unknown. We assessed the effect of fertilization on the percentage of N derived from transfer (%NDFT) from Acacia mangium trees to Eucalyptus trees in mixed-species plantations. A complete randomized block design with two treatments (fertilized vs unfertilized) and three blocks was set up in mixed-species plantations of A. mangium and Eucalyptus in Brazil, with 50% of each species at 2.5 m × 2.5 m spacing. Collection of litterfall and forest floor made it possible to estimate the annual N release from forest floor decomposition between 46 and 58 months after planting, close to harvest age. 15N-NO3- was injected into the stem of one dominant Acacia tree in each plot, 58 months after planting. The x(15N) values of Acacia and Eucalyptus fine roots sampled within 1.8 m of the labelled A. mangium tree were determined at 7, 14, 30 and 60 days after labelling. The x(15N) values in wood, bark, branch and leaf samples were also determined for the 6 labelled Acacia trees and their two closest Eucalyptus neighbours, just before and 60 days after labelling. The amount of N released from forest floor decomposition was 31% higher in fertilized (F+) than in unfertilized (F-) plots. Sixty days after labelling, the aboveground compartments of Eucalyptus trees were significantly 15N enriched in both treatments. The x(15N) values of Acacia fine roots were higher than background values from 7 days after labelling onwards in F+ and 30 days after labelling in F-. The x(15N) values of Eucalyptus fine roots were higher than background values in both treatments, from 30 days after labelling onwards. Mean %NDFT values were 18.0% in F+ and 33.9% in F- over the first 60 days after labelling, and 22.8% in F+ and 67.7% in F- from 30 to 60 days after labelling. Fertilization decreased short-term transfer belowground of N from Acacia trees to Eucalyptus trees. Our study suggests that belowground facilitation processes providing N from NFTs to Eucalyptus trees in mixed-species plantations are more pronounced in low-fertility soils than in nutrient-supplied stands. USP ESALQ Forest Science Department Eco&Sols INRA CIRAD IRD Montpellier SupAgro University of Montpellier CIRAD UMR Eco&Sols UNESP School of Agriculture São Paulo State University ‘Julio de Mesquita Filho,’ Department of Forest Science and Wood UFES IPEF Instituto de Pesquisas e Estudos Florestais UNESP School of Agriculture São Paulo State University ‘Julio de Mesquita Filho,’

Made available in DSpace on 2021-06-25T10:21:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-03-01 Aims: Belowground interactions are still poorly understood in mixed-species forests. We investigated the effects of soil fertility on belowground processes in mixed planted forests. Methods: The dynamics and traits of Eucalyptus and Acacia mangium fine roots (diameter < 2 mm) in plantations with 50% of each species were studied in a randomized block design established in a nutrient depleted soil. Stands with NPK fertilization applied at planting (F+) were compared to unfertilized stands (F-). Results: In the 0–15 cm soil layer, Eucalyptus root mass density (RMD) was higher than Acacia RMD by 50% in F+ and 10% in F-, considering both ages. At 34 months of age, Eucalyptus RMD was 94% higher near Acacia trees than near Eucalyptus trees in F-. In this layer, Eucalyptus specific root length (SRL) was 21% higher than Acacia SRL at 16 months of age and was 10% higher in F- than in F+ at 34 months of age. The cumulative Eucalyptus fine root length production between 16 and 34 months was 66% higher in F- than in F+ in the 0–1 m soil layer. Conclusions: Fertilization increased the competition between species and led to a partial exclusion of Acacia fine roots from the nutrient-rich topsoil. Soil exploration by Eucalyptus roots in the vicinity of Acacia trees was higher in F- than in F+, which suggests that unfertilized trees benefited from facilitation through higher soil N availability and direct N transfer from Acacia trees. ESALQ Forest Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo Université de Lorraine AgroParisTech INRAE UMR Silva School of Agriculture São Paulo State University (UNESP) Eco&Sols CIRAD INRA IRD Montpellier SupAgro Univ Montpellier CIRAD UMR Eco&Sols ESALQ Soil Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo UFES Centro de Ciências Agrárias e Engenharias Alto Universitário, S/N Guararema School of Agriculture São Paulo State University (UNESP)

International audience; Nutrient cycling in cocoa agroforestry systems (cAFS) is complex and poorly understood. To better understand the mass flow of carbon and nutrients into the soil sub-system under various contexts we quantified the mass flow of litterfall, its composition and seasonal variations in different agroforestry systems in Bokito (Central Cameroon). We studied litterfall dynamics and in situ leaf-litter cycling of cAFS established on past forest lands (F-cAFS) and savannah (S-cAFS). We also studied the decomposition of cocoa and associated tree leaf-litter in litterbags. Local secondary semi-deciduous forests were included as control. Annual litterfall in full-grown cAFS (> 15 years old) was high (9.4 Mg ha−1 y−1) and represented ca. 67% of litterfall in control forests. In full-grown cAFS, associated tree leaf-litter contributed to litterfall the most and ranged between 60 and 70% of the total amount recorded (6.3 Mg ha−1 y−1). The quantities and dynamics of the litter components monitored were similar in full-grown S- and F-cAFS. The microclimate was best buffered in forests and least buffered in young S-cAFS but could not be linked to leaf-litter decomposition. Forest leaf litterfall was higher and tended to cycle faster than total leaf-litter of cAFS, whose decomposition appeared limited by cocoa leaf-litter quality. Our study underlines (i) the critical contribution of associated trees to the nutrient cycle of agroecosystems established on poor soils and, (ii) the ability of farmers to channel associated tree communities towards similar functioning despite different past land-uses.

Microsporidia are obligate parasites that are closely related to Fungi. While the widely known “long-branch” Microsporidia infect mostly metazoans, the hosts of “short-branch” Microsporidia are only partially characterized or not known at all. Here, we used network analyses from Neotropical rainforest soil metabarcoding data, to infer co-occurrences between environmental lineages of short-branch microsporidians and their potential hosts. We found significant co-occurrences with several taxa, especially with Apicomplexa, Cercozoa, and Fungi, as well as some Metazoa. Our results are the first step to identify potential hosts of the environmental lineages of short-branch microsporidians, which can be targeted in future molecular and microscopic studies. Supplementary Information The online version contains supplementary material available at 10.1007/s00248-020-01657-9.

International audience; Tropical forests are generally considered to stand upon nutrient-poor soils, but soil nutrient concentrations and availabilities can vary greatly at local scale due to topographic effects on erosion and water drainage. In this study we physically and chemically characterised the soils of 12 study plots situated along a catena with a shallow slope in a tropical rainforest in French Guiana both during the wet and the dry season to evaluate seasonal differences. Soils along the catena were all Acrisols, but differed strongly in their water drainage flux. Over time, this differential drainage has led to differences in soil texture and mineral composition, affecting the adsorption of various nutrients, most importantly phosphorus. The more clayey soils situated on the slope of the catena had higher total concentrations of carbon, nitrogen, phosphorus and several micronutrients, while extractable nutrient concentrations were highest in the sandiest soils situated at the bottom of the catena. We found that carbon, nitrogen and extractable nutrients all varied seasonally, especially in the surface soil layer. These results are interesting because they show that, even at the local scale, small differences in topography can lead to large heterogeneity in nutrient concentrations, which can have large impacts on plant and microbial community organisation at the landscape level.

Resorption is the active withdrawal of nutrients before leaf abscission. This mechanism represents an important strategy to maintain efficient nutrient cycling; however, resorption is poorly characterized in old‐growth tropical forests growing in nutrient‐poor soils. We investigated nutrient resorption from leaves in 39 tree species in two tropical forests on the Guiana Shield, French Guiana, to investigate whether resorption efficiencies varied with soil nutrient, seasonality, and species traits. The stocks of P in leaves, litter, and soil were low at both sites, indicating potential P limitation of the forests. Accordingly, mean resorption efficiencies were higher for P (35.9%) and potassium (K; 44.6%) than for nitrogen (N; 10.3%). K resorption was higher in the wet (70.2%) than in the dry (41.7%) season. P resorption increased slightly with decreasing total soil P; and N and P resorptions were positively related to their foliar concentrations. We conclude that nutrient resorption is a key plant nutrition strategy in these old‐growth tropical forests, that trees with high foliar nutrient concentration reabsorb more nutrient, and that nutrients resorption in leaves, except P, are quite decoupled from nutrients in the soil. Seasonality and biochemical limitation played a role in the resorption of nutrients in leaves, but species‐specific requirements obscured general tendencies at stand and ecosystem level., Resorption is a key plant nutrition strategy in old‐growth tropical forests. Trees with high foliar nutrient concentration reabsorb more nutrients. Nutrients resorption in leaves, except P, are quite decoupled from nutrients in the soil. Seasonality and biochemical limitation played a role in the resorption of nutrients in leaves, but species‐specific requirements obscured general tendencies at stand and ecosystem level.

International audience; Mediterranean forests own distinct characteristics resulting from climate, soil, and vegetation that affect soil microbial communities’ assembly and their associated functions. We initiated a multi-scalar analysis of environmental drivers of soil functioning to (1) identify pertinent factorial scales and (2) determine the relative importance of soil, vegetation, and geoclimate influences in shaping soil microbial functions across the French Mediterranean forests. Soil samples (0–15 cm) were collected from 60 forest sites and soil physicochemical and microbiological properties were assessed across different factorial scales i.e., bioclimates, slope exposures, and forest stands. Patterns in microbial catabolic potential (i.e., extracellular enzymes and microbial respiration) and carbon (C) source utilization (i.e., catabolic-level physiological profiling) were partitioned between vegetation cover, soil characteristics, and geoclimate components. Our results reveal that the catabolic potential of soil microbes was strongly influenced by the forest stands and mainly relied on ammonium and nitrate contents. In contrast, variation in C source utilization was mainly explained by vegetation cover. Soil metabolic capacities of microorganisms and resulting C dynamics were largely constrained by climate parameters, which suggests potentially important consequences for soil C storage. Our study revealed diverse structuration patterns between the catabolic potential and the carbon source utilization of soil microbial communities, and gives insights into the underlying mechanisms of soil microbial functioning in Mediterranean forests.

International audience; Trees residues decomposition is a key step in forested ecosystems. In the context of sclerophyllous Mediterranean forests, the effects of residue quality on soil organic matter and microbial communities is still poorly documented. Using a mesocosm experiment, we explored microbial responses (enzyme activities, basal respiration, molecular fingerprints and catabolic profiles) and variations in soil chemical properties (pH, CaCO3, organic C and N contents, quality of soil organic matter via 13C CP/MAS NMR) induced by coarse woody debris (W) or fine residues (i.e. twigs -leaves/needles, hereafter TL) from mono-specific or mixed stands of Pinus halepensis and Quercus ilex, P. sylvestris and Q. pubescens. After a nineteen-month incubation period, we found that the origin of residues (Pinus spp. stand, Quercus spp. stand or mixed stand) shaped the genetic structure of both fungal and bacterial communities. TL inputs led to higher soil N content and increased enzyme activities and bacterial biomass. Aromatic compounds and C to N ratio increased with W inputs, strongly shaped fungal communities and increased tyrosinase activity. Thus, the type of residue and the tree species identity (Quercus spp. vs Pinus spp.) appeared to modulate the balance between fungal and bacterial biomass and soil microbial diversity. Our results revealed that logging residues management, by modulating the type of residues remaining on forest floor, could have significant impacts on soil functioning by modifying both chemical properties (e.g. soil C/N ratio) and microbial structure and functions. These findings need to be supported by in natura studies since deciphering such mechanisms controlling C fluxes in forest soils has important consequences under the context of climate change.

Made available in DSpace on 2020-12-12T02:29:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Colorado State University North Carolina State University Universidade Federal de Lavras Universidade Federal do Rio Grande do Norte Università degli Studi di Sassari U.S. Forest Service Universidade de São Paulo ArcelorMittal International Paper Brazilian roundwood industry is one of the most important and productive in the world, with Eucalyptus plantations alone representing 73% of the total planted forests. Deep rooting in these plantations represents a more common phenomena than generally expected. However, there is still a lack of information on environmental factors that drive root growth in deep soil layers, with particular emphasis on edaphoclimatic conditions, and related consequence in terms of soil water behavior. As a part of a larger project, this research aimed to investigate soil water and fine root system distribution in deep tropical soils under a commercial Eucalyptus plantation chronosequence. Along a 2800-km gradient (from south- to north-east Brazil), 14 experimental areas were planted with a “plastic” clone (E. urophylla) and investigated in terms of climatic conditions, soil and water features, and plant/stand development for an entire 6-years rotation period. Fine roots distribution were investigated in one site (in Brazil) till to 20 m deep at 3, 9, 24, 48, and 65 months after planting. Results showed a fast displacement of the root front down to 75, 325, 825, 1250, and 1575 cm at month 3, 9, 24, 48, and 65 after planting, respectively. Fine root densities (g cm−3) and proportional water capture exponentially decreased with soil depth. Deep fine roots showed a relativelly higher efficiency in acquiring water than the shallower, denser roots. The relationship between stand height vs root front depth followed an exponential trend, suggesting that these stands developed relatively faster in height rather than in depth during the first 48 months, with the opposite characterizing plantation afterwards. Regardless of stand age, E. urophylla trees rapidly explored a considerable volume of soil at a relatively limited carbon cost. Multivariate statistics showed that edaphoclimatic conditions play a major role in Eucalyptus plant/stand development. This study outlined the major role played by soil development. From poorly developed sandy Entisols, to medium developed Inceptisols, and to most developed fine textured Oxisols, both plant growth and stand productivity greatly improved accordingly. This study suggests that soil type, together with other environmental factors, are likely to influence both the development and behavior of Eucalyptus plantations for an extent greater than commonly anticipated. Vimef-Soluções Florestais Ltda, Rua Juca Prates, 1014 UNESP São Paulo State University School of Agricultural Sciences Department of Plant Protection Rural Engineering and Soils School of Engineering São Paulo State University Universidade de São Paulo Center of Nuclear Energy in Agriculture, Av. Centenário, 303 Institute of Food and Agricultural Sciences Indian River Research and Education Center University of Florida Eco&Sols Univ Montpellier CIRAD INRA IRD Montpellier SupAgro CIRAD UMR Eco&Sols Dipartimento di Scienze e Tecnologie Ambientali Biologiche e Farmaceutiche Università della Campania “Luigi Vanvitelli”, Via Vivaldi n◦ 43 Dipartimento di Architettura Design e Urbanistica Università degli Studi di Sassari Polo Bionaturalistico, Via Piandanna n° 4 School of Agricultural Forest and Food Sciences Bern University of Applied Science, Laenggasse 85 Desertification Research Centre Università degli Studi di Sassari, Viale Italia n◦ 39 UNESP São Paulo State University School of Agricultural Sciences Department of Plant Protection Rural Engineering and Soils School of Engineering São Paulo State University

The objective of our work was to evaluate soil quality in different cacao agroforestry systems (AFS) in the Colombian Amazon. We compared soil quality of AFS at the study site with soil quality of two control systems: a pasture and a secondary forest. The study was conducted at the Macagual Amazon Research Center in western Colombian Amazon. We set up eight 600 m² plots in each study system. We collected soil samples in each plot, and assessed macrofauna diversity, aggregate morphology, and physical and chemical soil properties. We integrated these variables in a General Indicator of Soil Quality (GISQ). We found GISQ values of 0.85 for forest, 0.5, 0.65 and 0.59 for AFS and 0.21 for pasture, and the values differed significantly between land uses. The establishment of cacao AFS on degraded pasture was found to significantly improve soil fertility, i.e., by 42%. The intensification level between land uses (Pasture > AFS > Forest) negatively affected macrofauna populations due to soil compaction (physical properties). Forest had the highest physical and biological quality. Our results show that AFS not only have the capacity to maintain key soil ecological functions, but also to restore soil quality of degraded pastureland. Cacao-based AFS could therefore be a key restoration strategy for degraded pastureland. These results are very important in the context of the Colombian Amazon, where cacao is currently known as the “crop of peace”.

International audience; Heterotrophic soil respiration (SRH) alone can contribute up to 50% of total ecosystem respiration in tropical forests. Whereas the abiotic controls of SRH have been extensively studied, the influence of plant traits is less well characterised. We used field experiments and a modelling approach to test the relative influence of plant traits on SRH in lowland tropical forest in French Guiana. We measured leaf- and root litter traits for five common tree species and conducted a root decomposition experiment to evaluate the influence of root chemistry on decay rates. We measured SRH in trenched plots and used our field measurements to parameterize and test the Century model of soil C dynamics. Overall, the Century model performed well in simulating SRH, and species-specific root decomposition in Century corresponded well to decomposition rates measured in situ. Root litter characterized by low lignin-to-nitrogen ratios decomposed more rapidly than low-quality root litter during the first 6 months. Model runs over different time scales revealed that litter quality substantially influenced SRH on an annual time-scale by determining the rates of root- and leaf litter decomposition. However, litter mass had an overriding influence on SRH over the longer term in 20-year model runs. Synthesis Using simple plant trait data to parameterise the Century model, we were able to accurately simulate changes in SRH in a lowland tropical forest. Our results suggest that this approach could be used to predict changes in tropical soil C dynamics under global change scenarios by including data on changes in plant productivity and C inputs to the soil (for example litterfall and root turnover).

La problèmatique de l'érosion en forêt. Journées scientifique Zone atelier bassin de la Moselle

International audience; Meta-data analyses and the model based hypotheses state that global soil C storage is controlled by microbial scale processes of fungal competition for available nitrogen (N). The details of these microbe-dependent feedback mechanisms on N and C dynamics in European soils are largely unknown and contentious. Global trends of increasing atmospheric N deposition and the continuing use of inorganic N fertilizer in both agriculture and forestry mean that the soils vital function as a carbon sink is potentially under threat. We set out to experimentally investigate these hypotheses across a Trans-European gradient of forest soils and provide reliable information on soil microbial responses to nitrogen inputs for predictive climate change models. Changes in nutrient status could result in a chain reaction of interacting microbial mechanisms which in turn could lead to the shifts in underlying ecosystem biogeochemical process rates. Recent meta-analysis has shown that plant fungal symbiont community structure, exerts a greater fundamental control over soil C storage than temperature, precipitation or net primary production. Based on the hypothesis that plant associated fungi effectively scavenge all available organic and inorganic N leaving little N for the growth of the free-living decomposer microbial community and preventing further breakdown of SOM. To investigate these possible effects we have sampled forest soils across a trans European gradient (ALTER-net-MSII network) which have received additional inputs of inorganic nitrogen fertilizer or carbon in the form of sugar, over a three year period. We have studied both nitrogen and carbon dynamics in these systems using a tool box of stable isotopes, high through-put sequencing for microbial community analysis and be-spoke litter bags to tease out the dominant drivers of decomposition. The results and conclusions from these analyses will be presented.

The patterns of the distribution of fungal species and their potential interactions with trees remain understudied in Neotropical rainforests, which harbor more than 16,000 tree species, mostly dominated by endomycorrhizal trees. Our hypothesis was that tree species shape the non-mycorrhizal fungal assemblages in soil and litter and that the diversity of fungal communities in these two compartments is partly dependent on the coverage of trees in the Neotropical rainforest. In French Guiana, a long-term plantation and a natural forest were selected to test this hypothesis. Fungal ITS1 regions were sequenced from soil and litter samples from within the vicinity of tree species. A broad range of fungal taxa was found, with 42 orders and 14 classes.Significant spatial heterogeneity in the fungal communities was found without strong variation in the species richness and evenness among the tree plots. However, tree species shaped the fungal assemblages in the soil and litter, explaining up to 18 % of the variation among the communities in the natural forest.These results demonstrate that vegetation cover has an important effect on the structure of fungal assemblages inhabiting the soil and litter in Amazonian forests, illustrating the relative impact of deterministic processes on fungal community structures in these highly diverse ecosystems.

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.

Forest soil fertility is generally estimated by studying the water and nutrient cycles essential to living organisms (i.e. biogeochemical cycles). Use of geochemical and/or isotopic tracers is an innovative, complementary approach to more traditional studies. Experimental procedures and results of some recent studies in forest ecosystems using natural tracers (e.g. 18O, 13C, 26Mg) or artificially supplied tracers (e.g. enrichment in Sr, Rb, 15N, 44Ca, 26Mg, 32P) are presented. Results are discussed in terms of relevance for using these tools to identify sources, to estimate residence times of water and elements, and to trace nutrient fluxes, of both organic and mineral origins, that are internal or external to the ecosystem.; La fertilité des sols forestiers est généralement estimée par l'étude des cycles de l'eau et des éléments nutritifs essentiels aux êtres vivants (cycles biogéochimiques). Parmi l'ensemble des méthodes d'étude de ces cycles, une approche innovante, complémentaire des études plus classiques, consiste à utiliser des traceurs géochimiques ou isotopiques. Les démarches expérimentales et résultats de quelques études récentes dans le domaine, utilisant des traceurs naturellement présents dans les écosystèmes (ex. 18O, 13C, 26Mg) ou artificiellement apportés (ex. enrichissements en Sr, Rb, 15N, 44Ca, 26Mg, 32P) seront présentés. Ces résultats seront discutés pour faire un point sur la pertinence d'utilisation de ces outils pour définir les sources, avoir accès au temps de résidence de l'eau et des éléments, et tracer les flux de nutriments qu'ils soient d'origine organique ou minérale, internes ou externes à l'écosystème.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; Forest soil fertility is generally estimated by studying the water and nutrient cycles essential to living organisms (i.e. biogeochemical cycles). Use of geochemical and/or isotopic tracers is an innovative, complementary approach to more traditional studies. Experimental procedures and results of some recent studies in forest ecosystems using natural tracers (e.g. 18O, 13C, 26Mg) or artificially supplied tracers (e.g. enrichment in Sr, Rb, 15N, 44Ca, 26Mg, 32P) are presented. Results are discussed in terms of relevance for using these tools to identify sources, to estimate residence times of water and elements, and to trace nutrient fluxes, of both organic and mineral origins, that are internal or external to the ecosystem.; La fertilité des sols forestiers est généralement estimée par l'étude des cycles de l'eau et des éléments nutritifs essentiels aux êtres vivants (cycles biogéochimiques). Parmi l'ensemble des méthodes d'étude de ces cycles, une approche innovante, complémentaire des études plus classiques, consiste à utiliser des traceurs géochimiques ou isotopiques. Les démarches expérimentales et résultats de quelques études récentes dans le domaine, utilisant des traceurs naturellement présents dans les écosystèmes (ex. 18O, 13C, 26Mg) ou artificiellement apportés (ex. enrichissements en Sr, Rb, 15N, 44Ca, 26Mg, 32P) seront présentés. Ces résultats seront discutés pour faire un point sur la pertinence d'utilisation de ces outils pour définir les sources, avoir accès au temps de résidence de l'eau et des éléments, et tracer les flux de nutriments qu'ils soient d'origine organique ou minérale, internes ou externes à l'écosystème.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; National audience; Determining the identity and function of forest soil organisms is essential to understand their relative roles, but also to determine their resilience after environmental perturbations. These characteristics are scientific challenges because of the high biological diversity of forest soil organisms, but also because many of them currently remain unknown. In this context, this review presents a snapshot of the difficulty associated with soil organism characterization, the uniqueness of forest soils and methodological and conceptual developments of the last decade. This review also presents the progress in political consideration of soil biology and highlights recent projects related to soil biology and ecosystem services.; Appréhender le cortège d'organismes des sols forestiers est essentiel, que ce soit pour recenser ces communautés, comprendre leur rôle, ou déterminer leur comportement face à des perturbations. Cette caractérisation se révèle être un réel défi scientifique du fait de la diversité de ces organismes et du nombre important d'espèces encore inconnues. Dans ce contexte, cet article présente un aperçu des contraintes liées à leur étude, les singularités des sols forestiers et les développements méthodologiques et conceptuels ayant eu lieu ces dix dernières années. Il aborde les avancées dans la prise en considération de la biologie au niveau politique qui s'est traduite par une augmentation des appels d'offres dans le domaine des sols, de leur biologie et des services écosystémiques rendus

International audience; Nutrient fluxes were determined in a chronosequence of Douglas-fir stands in the Beaujolais Mounts (France). Annual and seasonal variations occurred during the 3 years of investigation; fluxes were generally highest in autumn-winter. Atmospheric inputs were among the mean values from a monitoring network of forest ecosystems in France. Nutrient outputs from the soil profile were higher than average and occurred mainly during vegetation dormancy. Mean input-output budgets were negative for N, S, K, Ca and Mg, characterising an imbalance of the site chemistry dynamics. The P budget was positive. Most of the nutrient output from the ecosystem occurred as losses in the drainage water. These losses were related to excess nitrification and consecutive cation mobilisation throughout the soil profile. Surface water, however, had a neutral pH and very low nitrate and aluminium contents, which may have been buffered by the subsoil. Budgets differed between stands and tended to be more negative in the youngest stand. Part of this behaviour was related to stand age and part to the former land use of plots. Theoretical budgets were calculated for forest rotation lengths of 20, 40 and 60 years; it was concluded that shorter rotations would increase nutrient losses. The trend of a decrease in budget deficits with stand age suggests that the effect of vegetation change will be reduced at the next rotation but the impact of stand development may remain. Predicted nutrient budgets for a second 60 year Douglas-fir rotation suggested that available Ca in the soil would be depleted and that this depletion would be even more drastic if whole tree harvesting were adopted. In conclusion, Douglas-fir stands introduced changes in soil function that may impoverish the soil if present trends remain the same over the next forest rotations. The maintenance of sustainability will require nutrient input by fertilisation.

Document Type : Proceedings Paper Conference Date : SEP 19-23, 2010 Conference Location : FRANCE Conference Sponsor : Bioemco Lab (Biogeochemistry and Ecol Continental Ecosystems), Soil Organ Matter Grp; International audience; We compared the properties of the clay mineral fraction and the composition of soil solutions in a Fagus sylvatica coppice (native forest) and four adjacent plantations of Pseudotsuga menziesii, Pinus nigra, Picea abies and Quercus sessiliflora planted in 1976. The results revealed changes of clay fraction properties due to tree species effect. Clay samples from Douglas fir and pine stands differ when compared to other species. Twenty-eight years after planting, we observed the following changes: a more pronounced swelling after citrate extraction and ethylene glycol solvation, a higher CEC and a smaller poorly crystallised aluminium content. All these changes affecting the clay fraction agreed well with soil solution analyses which revealed high NO3 (-), H+ and Al concentrations under Douglas fir and pine. These changes were explained by a strong net nitrification under Douglas fir and pine stands when compared with other tree species. The higher NO3 (-) concentrations in soil solutions should be linked to the presence, type and activity of ammonia-oxiding bacteria which are likely influenced by tree species. The production of NO3 (-) in excess of biological demand leads to a net production of hydrogen ion and enhances the dissolution of poorly crystallised Al-minerals. Secondary Al-bearing minerals constituted the principal acid-consuming system in these soils. As a consequence, the depletion of interlayer spaces of hydroxyinterlayered minerals increases the number of sites for exchangeable cation fixation and increases CEC of the clay fraction. The dissolution of Al oxy-hydroxides explain the increase in Al concentrations of soil solutions under Douglas fir and pine stands when compared to other species. Nitrate and dissolved aluminium were conjointly leached in the soil solutions. A change in environmental conditions, like an introduction of tree species, enough modifies soil processes to induce significant changes in the soil mineralogical composition even over a period of time as short as some tens of years. Generally, mineral weathering has been considered to be very slow and unlikely to change over tens of years, resulting in few studies capable of detecting changes in mineralogy. This study appears to have detected changes in clay mineralogy during a period of 28 years after the planting of forest species. Our study represents a single location with a limited block design, but causes us to conclude that the observed changes could be widely representative. Where available, archived samples should be utilized and long-term experiments set up so that similar changes can be tested for and detected using more robust designs. The plausible hypothesis we present to explain apparent changes in clay mineralogy has strong relevance to the sustainable management of land.

[b][u]Background and Aims[/u][/b][br/] [br/] Forest trees directly contribute to carbon cycling in forest soils through the turnover of their fine roots. In this study we aimed to calculate root turnover rates of common European forest tree species and to compare them with most frequently published values.[br/] [br/] [b][u]Methods[/u][/b][br/] [br/] We compiled available European data and applied various turnover rate calculation methods to the resulting database. We used Decision Matrix and Maximum-Minimum formula as suggested in the literature.[br/] [br/] [b][u]Results[/u][/b][br/] [br/] Mean turnover rates obtained by the combination of sequential coring and Decision Matrix were 0.86 yr−1 for Fagus sylvatica and 0.88 yr−1 for Picea abies when maximum biomass data were used for the calculation, and 1.11 yr−1 for both species when mean biomass data were used. Using mean biomass rather than maximum resulted in about 30 % higher values of root turnover. Using the Decision Matrix to calculate turnover rate doubled the rates when compared to the Maximum-Minimum formula. The Decision Matrix, however, makes use of more input information than the Maximum-Minimum formula.[br/] [br/] [b][u]Conclusions[/u][/b][br/] [br/] We propose that calculations using the Decision Matrix with mean biomass give the most reliable estimates of root turnover rates in European forests and should preferentially be used in models and C reporting.

International audience; Soil quality or health is a fuzzy concept that has been vigorously criticized due to the extreme variability of soil and the difficulty of linking soil indicators to soil functions and sustainability. In most soil quality studies some obvious factors or typologies are used as a basis to select the “best indicators” of soil quality, i.e. those that best explain the differences among the plots under study. This is not the case for a variety of natural or agroecosystems including the Talamanca cacaobased agroforestry systems (AFS), which present neither a preestablished typology nor a clear framework to evaluate their soil quality. This situation required a selection of indicators based on the literature that was oriented by the nonequilibrium thermodynamic theory. A framework was elaborated through full and minimum indicator sets of baseline soil physical and chemical indicators, along with macrofauna groups. A minimum set of four wellaccepted abiotic soil quality indicators (bulk density, sum of bases, pH and carbon) was able to separate cacao AFS plots and forests into five distinct clusters along a lowtohigh “soil quality” gradient. The AFS rated as “good” soil quality did not differ from the forest. Abundances of selected macrofauna groups were well correlated with these indicators and helped elucidate the soil quality clusters identified. In particular, high predator abundance indicated proper energy flow and confirmed the high abiotic soil quality, thus confirming the potential of macrofauna groups as apt soil quality indicators. However, these indicators need to be tailored to local conditions. Consequentially, cacaobased AFS in Talamanca are able to conserve soil and provide a high level of soilrelated ecological services. Considering the soil an open system where the nonequilibrium thermodynamic theory applies successfully guided indicator selection and could help to reformulate the soil quality definition.

Les travaux présentés dans cet article résultent d’une thèse qui s’inscrit dans la convention de recherche Cemagref-ONF et s’intéresse au renouvellement des peuplements mélangés chêne – pin en forêt d’Orléans. Vu la différence d’exploitabilité des deux essences cela suppose de doser le couvert arboré pour permettre l’installation de semis sans les exposer à une trop forte concurrence de la végétation. Il s’agit donc de préciser les besoins en lumière des semis de pin sylvestre et d’étudier les mécanismes de compétition entre semis et végétation interférente.

International audience; Les communautés de montagne ont, depuis un passé très lointain, établi des relations de cause à effet entre certaines pratiques culturales et forestières d'une part, et des phénomènes d’érosion d’autre part. Cela les a conduites à mettre en oeuvre des actions préventives, consistant surtout en des restrictions d’exploitation de la forêt pouvant aller jusqu’à des interdictions totales. Ce n’est qu’au XXe siècle que cette préoccupation est devenue nationale. Cette évolution peut être directement imputée à des incendies catastrophiques et des surpâturages excessifs, mais cette dégradation des ressources naturelles n’aurait pas eu un tel impact si un mouvement de l’opinion "éclairée" n’avait pas, dés le début du siècle, conduit à la formation d’un véritable "parti du reboisement" capable de l’emporter sur le "parti des propriétaires". A travers cette étude, il est visé d’analyser la mise en place des différentes phases de la construction d'une véritable gestion et préservation des terrains de montagne, en distinguant trois phases essentielles : l’évolution des idées conduisant à l’élaboration d'une véritable doctrine de la restauration et du reboisement, la définition de la politique forestière au moyen d’une succession de lois et la mise en oeuvre de cette politique à travers les différents programmes de développement, depuis la guerre de libération nationale jusqu'à nos jours. Nous traiterons enfin un exemple, les monts de Béni Chougrane situés dans la région ouest algérienne (Mascara), où nous dresserons un bilan des actions réalisées et de leur impact sur l'environnement et la population.

Maintenance and monitoring of soil fertility is a key issue for sustainable forest management. Vital ecosystem processes may be affected by management practices which change the physical, chemical and biological properties of the soil. This study is the first in Europe to use electrical resistivity as a non-invasive method to determine forest soil properties rapidly in the field in a monitoring purpose. We explored the correlations between electrical resistivity and forest soil properties on two permanent plots of the French long-term forest ecosystem monitoring network (International Cooperative Program Forests, Level II). We used electrical resistivity measurements to determine soil sampling locations and define sampling design. Soil cores were taken in the A horizon and analyzed for pH, bulk density, residual humidity, texture, organic matter content and nutrients. Our results showed high variability within the studied plots, both in electrical resistivity and analyzed soil properties. We found significant correlations between electrical resistivity and soil properties, notably cation exchange capacity, soil humidity and texture, even though the magnitude of the correlations was modest. Despite these levels of correlations, we were able to assess variations in soil properties without having to chemically analyze numerous samples. The sampling design based on an electrical resistivity survey allowed us to map basic soil properties with a small number of samples.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; Forest management can seriously modify the biodiversity of forest dwelling species, but the consequences are poorly known for certain taxa, particularly soil fauna, for which few studies have been published. We compared the biodiversity of dictyostelids cellular slime moulds in a managed and an unmanaged forest in the French Alps and analysed the influence of environmental factors on species richness and abundance of dictyostelids. To our knowledge, this study is the first one undertaken in the European Alps. We must better understand the influence of various environmental factors on the biodiversity of these organisms if we want to accurately define their functional role in the soil. In our study, dictyostelids showed lower levels of diversity compared to previously published results. The mean species richness of dictyostelids was marginally higher in unmanaged than in managed forests and biodiversity indices were significantly correlated with elevation and pH. This suggests that environmental factors have a predominant effect on the biodiversity of dictyostelids and that the effect of forest management is secondary.

L'intensification de la récolte de biomasse forestière a des impacts sur la biodiversité des écosystèmes forestiers, sur la physico-chimie des sols et des ressources en eau. Ce chapitre présente les préconisations en l'état des connaissances actuelles pour limiter ces impacts, lors des opérations de récolte du bois, pour la conduite des peuplements (régénération, choix des essences, âges d'exploitabilité) et dans le cas particulier des cultures dédiées (TTCR). / The increase in forest biomass harvesting has an impact on forest biodiversity and natural resources (soils, water). In ordre to limit these impacts, this chapter gives guidelines concerning biomass harvesting, forest stand management (regeneration, objective species, rotation age) as also the particular case of short rotation coppices.

Ce chapitre conclusif se veut une synthèse de l'étude Bio2 en même temps qu'un lien avec de nouveaux approfondissements souhaitables. / This last chapter of the Bio2 study synthesizes the work and makes some recommandations, with a particular stress on what is needed to fill knowledge gaps. Bio2 is a collective report financed by the Ministry of Ecology on the interactions between the potential increase in forest biomass harvesting and biodiversity and natural resources (soils, water...).

National audience; Pourquoi mesurer la résistivité électrique des sols ? L'hétérogénéité spatiale des sols forestiers doit être prise en compte tant par le gestionnaire que par le scientifique, notamment lorsqu'il s'agit d'étudier d'éventuelles modifications sur le long terme. Actuellement, les méthodes qui permettent de rendre compte de cette hétérogénéité sont peu nombreuses et conduisent la plupart du temps à l'altération, voire la destruction, du milieu étudié. Au cours des dernières décennies, plusieurs études ont montré des relations entre les propriétés physiques et chimiques du sol et la résistivité électrique. La résistivité électrique (ρ) est définie comme suit : ρ = K.ΔV/I où K est un facteur géométrique qui dépend de la configuration utilisée lors de la mesure, ΔV la différence de potentiel et I l'intensité (donc ΔV/I la résistance). La majorité des études actuelles sont menées sur les sols agricoles alors que les études sur les sols forestiers sont très rares. Le but de notre étude est : (i) d'identifier dans quelle mesure les propriétés des sols forestiers influencent la résistivité électrique ; (ii) de préciser les éventuelles implications pour la prise en compte de l'hétérogénéité spatiale du sol lors de la mise en place de protocoles expérimentaux. Comment mesure-t'on la résistivité électrique des sols ? Les mesures de résistivité sur une maille de 5x10m sur l'ensemble de la placette nous a permis de tracer une carte de résistivité électrique du sol. Cette carte est ensuite utilisée pour définir un protocole d'échantillonnage du sol équilibré entre les différentes classes de résistivité et relier ainsi les propriétés mesurées du sol à une valeur de résistivité in situ. La campagne de mesure se déroule sur 2 jours : la mesure de résistivité le premier jour ; le prélèvement des 24 échantillons de sol le second jour, la localisation des points d'échantillonnage étant définie à partir de la carte de résistivité. Pour que ces mesures soient valables, il ne doit pas pleuvoir entre les 2 phases de travail. Les résultats présentés ont été obtenus sur la placette RENECOFOR EPC74, située dans la forêt domaniale des Voirons, en Haute-Savoie. Deux exemples de caractérisation des variations des propriétés du sol : la teneur en argile et la forme d'humus On observe des corrélations significatives entre certaines propriétés du sol et la résistivité mesurée sur la placette. Ainsi, la résistivité traduit 57% des variations de la teneur en argile du sol et 41% des variations des formes d'humus.La résistivité représente une mesure indirecte et non destructive des propriétés du sol qui permet d'établir une cartographie assez précise de ces propriétés. Sur la placette EPC74, les zones de forte résistivité (brun foncé) correspondent à des sols sableux drainants, pauvres en cations échangeables et à humus peu actifs (Dysmull), probablement issus de la désagrégation de moraines glaciaires. Les zones de faible résistivité (jaune) correspondent à des sols argileux riches en cations et à formes d'humus actives (Eumull). Nos résultats confirment ceux obtenus en terrains agricoles pour les propriétés intrinsèques du sol (texture, chimie). La corrélation avec la forme d'humus est plus originale et permet une cartographie ce compartiment clé du milieu forestier qui assure de nombreuses fonctions de l'écosystème. Cependant, la calibration des mesures de résistivité par au minimum 6 échantillons de sol doit être reproduite pour chaque site étudié car les variations spatiales et temporelles de propriétés telles que l'humidité influencent fortement les mesures et ne permettent pas de construire un modèle général de relation résistivité / propriétés du sol. Implications pour le réseau RENECOFOR: L'utilisation de la résistivité électrique a un triple intérêt car elle permet : (i) d'obtenir des informations spatialisées sur la placette étudiée ; (ii) de définir des protocoles expérimentaux qui prennent en compte la variabilité spatiale des propriétés du sol ; (iii) de réaliser des suivis dans le temps dans le but de détecter des modifications de fertilité.

International audience

Les champignons du sol dont les espèces mycorhiziennes sont pour la plupart indétectables par des méthodes autres que la biologie moléculaire au cours de la majeure partie de leur cycle reproductif Pour analyser leurs populations il apparaît nécessaire de pouvoir déterminer la répartition spatiale de leurs mycéliums ainsi que d'en estimer leurs biomasses et les variations temporelles de ces paramètres. D'un point de vue expérimental, ceci peut être réalisé par quantification d'une séquence d'ADN propre à l'espèce étudiée; séquence présente dans un pool d'ADN extrait directement d'une quantité connue de sol. Une méthode appropriée pour cette quantification spécifique d'une faible quantité d'ADN est la PCR compétitive. Cette méthode a été utilisée pour suivre au stade mycélien des populations naturelles du Basidiomycète ectomycorhizien Hebeloma cylindrosporum dans les sols de forêts de Pins maritimes le long de la côte Landaise. La séquence sélectionnée pour la quantification est un fragment de l'espaceur intergénique (IGS) des ADN ribosomiques nucléaires amplifié à l'aide d'un couple d'amorces spécifiques de l'espèce étudiée. Le seuil de détection de la méthode est de l'ordre de 3 pg d'ADN génomique introduit par gramme de sol. Sur le terrain, de l'ADN de l'espèce étudiée a été détecté dans des sols prélevés directement sous des groupes de fructifications. Cependant, les quantités d'ADN mesurées décroissent rapidement lorsque l'on s'éloigne des fructifications et l'ADN est indétectable à plus de 50 cm de celles-ci. De la même manière, aucune trace d'ADN de H. cylindrosporum n'a pu être mise en évidence un an ou plus après la disparition des fructifications. Ces résultats confirment que les mycéliums de H. cylindrosporum ne sont pas répartis de façon uniforme dans les sols forestiers et qu'ils disparaissent rapidement après la période de fructification. Ces résultats illustrent la grande flexibilité de la symbiose ectomycorhizienne en conditions naturelles qui est caractérisée par un renouvellement constant et rapide de certaines espèces et génotypes fongiques sur le système racinaire d'une même plante hôte pérenne.

Le materiau bois a depuis longtemps fait l'objet de traitements fongicides ou insecticides dont l'impact sur les sols apres lessivage constitue un reel probleme ecologique. A ce jour, l'essentiel des etudes sur la degradation de ces produits toxiques a ete mene a partir des micro-organismes isoles en laboratoire. La presente etude a cherche a affiner les connaissances concernant ces microorganismes, en particulier les champignons lignivores degradant les polluants in situ, pour lesquels peu de donnees sont en fait disponibles. En vue de depolluer des bois traites, la capacite des micro-organismes lignivores issus de sols forestiers tropicaux de la Guyane et de la Reunion pour degrader des biocides toxiques a ete evaluee. Il s'agit du pentachlorophenol (PCP) et des composes a base de cuivre chrome arsenic (CCA). Le suivi de la degradation d'eprouvettes de pin rouge, Pinus resinosa, montre que le sol de Guyane est plus performant que celui de la Reunion en termes d'activite microbienne vis-a-vis de ces deux biocides. Une difference significative de la perte de masse des eprouvettes de pin rouge traitees au CCA et au PCP peut aller du simple au double (respectivement 18 % et 30 %). Ces resultats confirment que le CCA est moins lessivable et moins degradable par les microorganismes de ces sols que le PCP. D'apres le bareme des pertes de masse en essais de laboratoire, ces bois ainsi traites seraient classes peu durables apres trois ans de mise en contact avec le sol, alors que le traitement est prevu comme tres durable. (Resume d'auteur)

Non disponible / Not available, Le but de ce travail était de mesurer l'impact acidifiant de quelques essences épicéa (picea abies), sapin (abies alba), pin (pinus sylvestris), douglas (pseudotsuga menziesii), hêtre (fagus sylvatica) et chêne (quercus petraea et quercus robur) sur les sols. Chacun des 30 sites étudiés a entre 2 et 5 plusieurs peuplements d'essences différentes. Plusieurs approches ont été menées parallèlement : I) les sols ont été analysés. II) une masse fixe de plagioclase a été enfouie dans les sols et laissée en incubation pendant 9 ans. III) des vermiculites échangeuses de cations ont été enfouies dans les sols et laissés sur place pendant 3 ans. IV) les solutions capillaires ont été récoltées pendant 1 an. V) la composition de la végétation a été étudiée et mise en relation avec les exigences écologiques de chaque espèce. Les stocks de graines dans le sol ont été caractérisés. Les résultats sont : I) les litières sont les plus épaisses, acides et avec un c/n élevé sous l'épicéa et le pin. Ce sont ces essences qui acidifient le plus les sols. Le sapin et l'épicéa captent plus les dépôts atmosphériques que le hêtre et le chêne. II) les essences résineuses provoquent une plus forte dissolution des plagioclases-test que les essences feuillues. III) l'épicéa et le sapin sont les essences qui acidifient et altèrent le plus les vermiculites-test, alors que le chêne et le hêtre sont celles qui les modifient le moins. IV) l'acidité des solutions est supérieure sous l'épicéa par rapport au chêne. Le douglas et l'épicéa captent plus les dépôts atmosphériques que le chêne. V) la végétation sous l'épicéa et le sapin est plus caractéristique de conditions acides que celle sous le hêtre. La capacité des essences à acidifier le milieu, à altérer les minéraux du sol et à augmenter le rapport c/n suit globalement le gradient suivant : épicéa (pin, sapin) douglas (chêne, hêtre). L'impact des essences sur les sols dépend fortement du pouvoir tampon initial de ceux-ci.

National audience; De par la masse importante de carbone qu’elles contiennent (81% du carbone de la biomasse terrestre) et en raison de la lenteur des cycles forestiers, les forêts pourraient contribuer à limiter l’effet de serre, en immobilisant à moyen ou long terme une part du carbone émis lors de l’utilisation de sources d’énergies fossiles. Nous estimons, dans ce travail, la contribution actuelle de la forêt française au budget global du carbone. Nous calculons, dans un premier temps, le stock de carbone dans la biomasse des forêts françaises à partir des volumes de tiges mesurés par l’Inventaire forestier national, en appliquant des coefficients multiplicateurs afin de prendre en compte la proportion de branches et de racines, la densité du bois et le taux de carbone. La masse totale de carbone est de 860 Mt C pour 14,5 millions d’hectares de forêt. Ce stock est probablement encore sous-évalué en raison du manque de connaissances sur les masses de bois mort et d’arbustes non comptabilisés. Le stock de carbone des sols est calculé à partir du réseau systématique européen de suivi de l’état de santé des forêts. Il est de 1140 Mt C, soit 9 t C/ha de litière et 70 t C/ha entre 0 et 30cm de profondeur. Le stock total, sol et biomasse, des forêts françaises est donc de 2000Mt C. Dans un second temps, le flux global de carbone dû aux variations du stock dans la biomasse entre 1979 et 1991 est calculé de deux façons indépendantes (variation du stock total sur pied ou différence entre croissance et prélèvements annuels). On constate, dans les deux cas, un stockage net dans les forêts françaises de 10,5 Mt C/an entre ces deux dates, soit 10% de nos émissions annuelles de carbone fossile. Ce puits est lié à l’accroissement de la surface forestière, de la productivité des peuplements, au vieillissement de la forêt française alors que les niveaux de prélèvements de bois restent très modérés (61% de la croissance). Nous discutons enfin les options forestières permettant d’accroître cette fonction "puits" de la forêt : augmentation des surfaces forestières, utilisation d’essences à croissance rapide, vieillissement des peuplements, diminution du niveau des éclaircies et du travail du sol, mise en réserve intégrale... Lorsque l’on considère conjointement les pools de carbone de la forêt et des produits bois qui en sont issus, la durée de vie des produits bois devient un paramètre clef d’orientation des choix sylvicoles. Les écobilans qui permettraient d’asseoir ces choix sur des données fiables manquent encore. Les possibilités de stockage de bois dans la forêt ou les produits bois ne sont pas illimitées, et ne peuvent en aucun cas apporter une réponse définitive aux problèmes posés par les émissions de carbone fossile. Par contre, l’utilisation du bois en remplacement de matériaux à coût énergétique élevé, ou directement comme source d’énergie, amène à une baisse effective de la consommation d’énergies fossiles, et représente donc une solution plus efficace à long terme, qui, si elle était mise en oeuvre, réclamerait de la forêt une productivité accrue

Ce cédérom contient les actes du 16ème congrès mondial de science du sol, soit 2129 communications avec leur résumé, et 1551 communications avec le texte complet, ainsi que les 15 communications de la journée introductive. La consultation est possible selon deux modes : à partir de la liste des premiers auteurs de chaque symposium, ou en interrogeant la base de données des communications. Le congrès était organisé en 45 symposia et 6 ateliers. Les deux thèmes généraux étaient : la science du sol sous tous ses aspects ; le sol dans ses relations avec les activités humaines actuelles et passées

Cet article présente une synthèse des recherches effectuées depuis une dizaines d'années sur l'acidification des sols et des eaux dans le massif vosgien et ses conséquences biologiques. L'acidité des sols et des eaux est définie et sa distribution géographique présentée. L'acidification récente des sols et des eaux est démontrée et les facteurs responsables de cette tendance sont discutés à l'aide de bilans d'éléments minéraux. Puis, les conséquences biologiques sur la faune aquatique, le dépérissement forestier et la santé humaine sont analysés.

La mission avait pour but de participer au congrès d'une part et de rencontrer l'équipe du laboratoire de culture in vitro dans le cadre de projet sur la culture de tissus des Acacias et Casuarinas