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The recovery of soil conditions is crucial for successful ecosystem restoration and, hence, for achieving the goals of the UN Decade on Ecosystem Restoration. Here, we assess how soils resist forest conversion and agricultural land use, and how soils recover during subsequent tropical forest succession on abandoned agricultural fields. Our overarching question is how soil resistance and recovery depend on local conditions such as climate, soil type and land-use history. For 300 plots in 21 sites across the Neotropics, we used a chronosequence approach in which we sampled soils from two depths in old-growth forests, agricultural fields (i.e. crop fields and pastures), and secondary forests that differ in age (1-95 years) since abandonment. We measured six soil properties using a standardized sampling design and laboratory analyses. Soil resistance strongly depended on local conditions. Croplands and sites on high-activity clay (i.e. high fertility) show strong increases in bulk density and decreases in pH, carbon (C) and nitrogen (N) during deforestation and subsequent agricultural use. Resistance is lower in such sites probably because of a sharp decline in fine root biomass in croplands in the upper soil layers, and a decline in litter input from formerly productive old-growth forest (on high-activity clays). Soil recovery also strongly depended on local conditions. During forest succession, high-activity clays and croplands decreased most strongly in bulk density and increased in C and N, possibly because of strongly compacted soils with low C and N after cropland abandonment, and because of rapid vegetation recovery in high-activity clays leading to greater fine root growth and litter input. Furthermore, sites at low precipitation decreased in pH, whereas sites at high precipitation increased in N and decreased in C : N ratio. Extractable phosphorus (P) did not recover during succession, suggesting increased P limitation as forests age. These results indicate that no single solution exists for effective soil restoration and that local site conditions should determine the restoration strategies. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'., Philosophical Transactions of the Royal Society B: Biological Sciences, 378 (1867), ISSN:0962-8436, ISSN:1471-2970, ISSN:0080-4622

International audience

Soil health is defined as the soil's capacity to deliver ecosystem functions within environmental constraints. On tree plantations, clear-cutting and land preparation between two crop cycles cause severe physical disturbances to the soil and seriously deplete soil organic carbon and biodiversity. Rubber, one of the main tropical perennial crops worldwide, has a plantation life cycle of 25 to 40 years, with successive replanting cycles on the same plot. The aim of this study was to assess the effects of clear-cutting disturbance on three soil functions (carbon transformation, nutrient cycling and structure maintenance) and their restoration after the planting of the new rubber crop, in two contrasting soil situations (Arenosol and Ferralsol) in Côte d'Ivoire. In this 18-month diachronic study, we intensively measured soil functions under different scenarios as regards the management of logging residues and the use or not of a legume cover crop. We investigated the relationship between soil macrofauna diversity and soil heath. At both sites, clear-cutting and land preparation disturbed carbon transformation and nutrient cycling significantly and, to a lesser extent, structure maintenance function. When logging residues were applied, carbon transformation and structure maintenance functions were fully restored within 12 to 18 months after disturbance. By contrast, no restoration of nutrient cycling was observed over the study period. A legume cover crop mainly improved the restoration of carbon transformation. We found a strong relationship (P ≤ 0.001; R2 = 0.62–0.66) between soil macrofauna diversity and soil health. Our overall results were very similar at the two sites, despite their contrasting soil conditions. Keeping logging residues in the plots and sowing a legume in the inter-row at replanting accelerated the restoration of soil functions after major disturbance caused by clear-cutting and land preparation. Our results confirm the necessity of taking soil macrofauna diversity into account in the management of tropical perennial crops.

Meloidogyne spp. and Hirschmanniella spp. are among the most damaging plant-parasitic nematodes (PPNs). They threaten rice production, the main staple food in Asia. Cropping systems that promote natural biocontrol and plant tolerance to diseases are put forward as sustainable solutions to protect rice from these pests. In particular, cropping systems managed under conservation agriculture (CA) are promising because they improve soil health and functioning. We investigated the effects of two cropping system components in a Cambodian field, (i) CA practices, i.e., no-tillage with a cover crop Stylosanthes guianensis (cv. Nina), versus conventional plow-based tillage with no cover crop, and (ii) using IR504, IR64, Azucena and Zhonghua 11 rice varieties, on PPNs in roots and on communities (bacteria, fungi and nematodes) in the rhizosphere. We used a sequencing approach via amplicon barcoding to target microbial marker genes (16 S and ITS rRNA gene) and a microscopic approach to identify and quantify nematodes in the rhizosphere compartment. The variety had less effect than agricultural practices on the infection by PPNs and on the assembly of the three rhizosphere communities. Under CA, the abundance of PPNs extracted from the roots was reduced by 88%. Soil quality was substantially improved (+83% of total Kjeldahl nitrogen, +34% of available phosphorus, +10% of exchangeable potassium, +110% of soil organic carbon, +30% for the cation exchange capacity), thus providing more basal resources for microbial decomposers, especially fungi (+164% putative saprotrophs). Characterization of the three rhizosphere communities revealed a shift in the structure associated with soil enrichment. Both microbial richness (+3% for bacteria and +38% for fungi) and diversity (Shannon index, +11% for fungi and +5% for nematodes) increased. The relative abundance of taxa was modified by CA with notably more mycorrhizal fungi (+329% Glomeromycota spp.) and fewer Pratylenchidae nematodes (−92% Hirschmanniella spp.) in the rhizosphere. The reassembly of the communities using CA was associated with regulation of PPN populations. The reduction in Meloidogyne spp. abundance in roots (−64%) was correlated with the maturity of the food web (maturity index, +10% under CA) and with the increase in the relative abundance of omnivorous nematodes in the rhizosphere (+68% under CA). Seven years of CA in this field enabled the whole soil food web to mature thus creating a favorable niche for potentially predatory nematodes and microbes antagonistic against PPNs. This study confirms that CA is an alternative to nematicides to limit infection by PPNs in rice cropping systems.

Em zonas de colonização antiga da Amazônia, como o Nordeste do Pará, os sistemas de produção agrícola, baseados principalmente em cultivos anuais em sistemas de corte e queima, enfrentam desafios para se manter. Nesse contexto, atores estão promovendo Sistemas Agroflorestais (SAF) para viabilizar a restauração das áreas degradadas, geração de renda e soberania alimentar das famílias agrícolas. Essa transição requer a transformação de todo o sistema agrário. Neste artigo objetiva-se identificar os eventos históricos e as mudanças nos fatores externos ao sistema de produção que condicionaram as transformações para a introdução/modificação dos SAF em Irituia –PA. Utilizou-se a abordagem sistêmica, entrevistas históricas, questionários, análise documental e análise de paisagem. Os incentivos públicos locais foram os principais precursores da consolidação dos SAFs dentro dos sistemas de produção familiares. Com essas iniciativas, que proporcionaram mudanças estruturais multiescalares, a trajetória dos sistemas de produção indica uma perspectiva diferenciada, com incremento de sustentabilidade.

International audience; The In Situ Chemical Reduction (ISCR) process was tested in a nitisol in a French Caribbean banana plantation using five different soil amendments. The addition of 2.8% or 4.0% of Zero Valent Iron (ZVI; dw/dw, 2 different trial plots) in the 0–40-cm soil layer lowered the initial chlordecone (CLD) concentration by up to 74% or 69% in 37 days or 94 days, with 75% of the decrease achieved after only 21 or 24 days of treatment depending on the trial plot. The addition of commercially available Daramend® was also tested by applying the 6% dose (dw/dw) recommended by the manufacturer and using either the regular alfalfa-based product or a bagasse-based product specifically formulated for the study. Both significantly lowered CLD concentrations, but to a lesser extent than with the ZVI-only amendment. A bagasse-ZVI mixture prepared on site produced results slightly better than the two Daramend®. The percentage decreases in CLD concentrations were correlated with the negative redox potentials achieved. In all the trial plots, dechlorinated transformation products appeared in the soil and soil water as the CLD concentrations decreased, with H atoms replacing up to 4 and 7 of the 10 Cl atoms, respectively. None of these degradation products appeared to accumulate in the soil or soil water during the treatment. Instead, the reverse occurred, with an overall downward trend in their concentrations over time. The effects of ISCR treatment on agronomic and human health–related parameters were measured in three different crops. The radishes produced with some treatments were visually of lower quality or smaller in size than those grown in the control plots. Lower yields were observed for the cucumbers and sweet potatoes grown after applying the bagasse-based amendments. Mortality among cucumber seedlings was observed after treatment with ZVI only. Simple operational solutions should suffice to remedy these negative agronomic effects. As regards human health–related effects, the CLD concentrations in radishes grown with three of the amendments were significantly lower than in the two control plots and well below the maximum residue level (MRL), which was substantially exceeded in the radishes grown on untreated soil. For cucumbers, the treatments with regular Daramend® and with a local bagasse-ZVI mixture produced fruits with CLD below the MRL and also below the concentrations in one of the two control plots. As for the sweet potatoes, adding a bagasse-ZVI mixture had a significant positive effect by decreasing contamination below the levels in the two control plots and below the MRL.

International audience; Due to their central role in ecosystems functioning and their ability to rapidly respond to environmental changes, soil microorganisms could potentially be used for monitoring ecosystems recovery in the context of degraded land restoration. However, these belowground organisms have been, to date, largely neglected. Here, we investigated fungal and bacterial community diversity, composition, and structure from ultramafic soils in New Caledonia, an archipelago in the southwest Pacific recognized as a priority for conservation and restoration. The emerging approach of high-throughput amplicon sequencing of environmental DNA (eDNA)-metabarcoding of eDNAwas used to compare soil microbial communities from four different native vegetation types, representing different stages of a chronosequence and defined as reference ecosystems, to five distinct post-mining sites revegetated several years ago. Our results clearly revealed changes in soil microbial phyla and functional groups along the reference chronosequence and variable responses at the different revegetated sites, with two of the five sites showing a good trajectory of recovery. We thus propose three ratios as metrics for monitoring the restoration trajectory of soil microorganisms: the Ascomycota:Basidiomycota and Saprotrophic:Ectomycorrhizal ratios for fungi, and the Cyanobacteria:Chloroflexi ratios for bacteria. Our study, combined with recent works undertaken in other geographical areas, underpins the great promise that could represent soil microbial eDNA metabarcoding for monitoring restoration progress and success. With the emergence of these new cost-effective and scalable sequencing technologies, soil microbes could, in the near future, be included in guidelines for restoration operations in complement to more conventional approaches.

Rapport pour le Projet « Réhabilitation et protection des sols dégradés et renforcement des instances foncières locales dans les zone rurales du Burkina Faso » de l’Initiative « Un seul Monde sans Faim“ (SEWoH), mis en oeuvre par la Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH »; International audience; Cette étude porte sur l’économie de la dégradation des terres au Burkina Faso : elle vise à quantifier les bénéfices économiques et financiers liés aux aménagements des terres qui ont été réalisés pour prévenir la dégradation des terres, entretenir la qualité des sols et restaurer leur fertilité affectée par les processus de dégradation et de désertification.

International audience; The rapidly growing human population in West Africa has generated increasing demand for agricultural land and forest products. Consequently 90% of the original rainforest cover has now disappeared and the remainder is heavily fragmented and highly degraded. Although many studies have focused on carbon stocks and fluxes in intact African forests, little information exists on biomass recovery rates in secondary forests. We studied a chronosequence of 96 secondary and old-growth forest fragments (0.2 ha each) where 32.103 trees with Diameter at Breast Height > 2.5 cm have been censused. We modelled the biomass recovery trajectories in a time explicit Bayesian framework and tested the effect on recovery rates of a large set of covariates related to the physical environment, plot history, and forest connectivity. Recovery rate trajectory is highly non-linear: recovery rates accelerated from 1 to 37 years, when biomass recovery reached 4.23 Mg.ha(-1).yr(-1), and decelerated afterwards. We predict that, on average, 10%, 25% and 50% of the old-growth forest biomass is respectively recovered 17, 30, and 51 years after abandonment. Recovery rates are strongly shaped by both the number of remnant trees (residuals of the former old-growth forest) and the previous crop cultivated before abandonment. The latter induced large differences in the time needed to recover 50% of an old-growth forest biomass: from 38 years for former Yam fields up to 86 years for former rice fields. Our results emphasize (i) the very slow recovery rates of West African forests, as compared to Neotropical forests (ii) the long-lasting impacts of past human activities and management choices on ecosystem biomass recovery in West African degraded forests.

Report for the project « Rehabilitation and protection of degraded land and the reinforcement of the local institutions in land issues in the rural areas of Burkina Faso » of the initiative “An only world without hunger” (SEWoH), implemented by Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH; International audience; This ELD study relates to the economics of land degradation in Burkina Faso: it aims to quantify the economic and financial benefits linked to land developments implemented to prevent land degradation, maintain the quality of the soil and restore its fertility affected by the processes of degradation and desertification.

Made available in DSpace on 2020-12-12T01:29:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-11-10 Silpakorn University Ministry of Science and Technology of Thailand Agence Nationale de la Recherche Many studies have shown that introducing N2-fixing trees (e.g. Acacia mangium) in eucalypt plantations can increase soil N availability as a result of biological N2 fixation and faster N cycling. Some studies have also shown improved eucalypt P nutrition. However, the effects of N2-fixing trees on P cycling in tropical soils remain poorly understood and site-dependent. Our study aimed to assess the effects of planting A. mangium trees in areas managed over several decades with eucalypt plantations on soil organic P (Po) forms and low molecular weight organic acids (LMWOAs). Soil samples were collected from two tropical sites, one in Brazil and one in the Congo. Five different treatments were sampled at each site: monospecific acacia, monospecific eucalypt, below acacias in mixed-species, below eucalypts in mixed-species as well as native vegetation. Po forms and LMWOAs were identified in sodium hydroxide soil extracts using ion chromatography and relationships between these data and available P were determined. At both sites, the concentrations of most Po forms and LMWOAs were different between native ecosystems and monospecific eucalypt and acacia plots. Also, patterns of Po and LMWOAs were clearly separated, with glucose-6-P found mainly under acacia and phytate and oxalate mainly under eucalypt. Despite the strongest changes occurred at site with a higher N2 fixation and root development, acacia introduction was able to change the profile of organic P and LMWOAs in

International audience; The agricultural development on newly reclaimed lands has led to many national debates about food security and budget deficits, and the living conditions of the new settlers at the local level. This debate is still crucial for present day Egypt, a country facing major challenges, including food security, agriculture modernization, employment generation, and land fragmentation due to dramatic population growth. In this context, policy makers are always seeking the best land allocation system for these new lands. This paper analyzes the land tenure and land use dynamics of farmers' settlements during a program of land reclamation (from 1960 to 2010) in the Western Desert of the Nile Delta. The objective is to describe the land development paths of farm settlement and to identify promising dynamics by cross-referencing the farmers' stories and their livelihood achievements. To accomplish that, we conducted household surveys and interviews to learn the life stories' of 175 family farms. Our study finds that, beyond the rules and institutions that fixed the land tenure regimes and its distribution in these new lands, settlers have found different ways to hold on and secure their land farm, even if the unequal land distribution still structure the population. The results highlight also the dynamism of small-scale settlers, regarding livelihood diversification, to face the challenges of these desert environments. In addition, the dual-purpose system embedded in mixed crop-livestock systems can contribute to settlers' livelihood security. These realities confound the unchanged rhetoric of government and this calls for more social consideration of these new rural spaces based on a combination of heterogeneous networks off relationships and knowledge. The apparent gap between the macro- and micro-perspectives analyses also requires multi-scale assessments. Finally, the life-story method proves to be a complementary and useful approach to integrate the livelihood representation and dynamic.

Conclusions based on studies of the impacts of soil organic carbon (SOC) fractions and soil texture on macroaggregation and SOC stabilization in long-term (> 20 years) no-till (NT) fields remain debatable. This study was based on the hypothesis that the amount and frequency of biomass-C input associated with NT can be a pathway to formation of macroaggregates and to SOC buildup. The objectives were to: 1) assess the macroaggregate distribution (proportional mass, class mass) and the SOC and particulate organic carbon (POC) stocks of extra-large (8–19 mm), large (2–8 mm) and small (0.25–2 mm) macroaggregate size classes managed for two decades by NT, and 2) assess the recovery of SOC stocks in extra-large macroaggregates compared to adjacent native vegetation (Andropogon sp., Aristida sp., Paspalum sp., and Panicum sp.). The crop rotation systems were: soybean (Glycine max L.), maize (Zea mays L.) and beans (Phaseolus vulgaris L.) in summer; and black oat (Avena strigosa Schreb), white oat (Avena sativa), vetch (Vicia sativa L.), black oat. + vetch (Avena strigosa Schreb + vetch) and wheat (Triticum aestivum L.) in winter. The experimental was laid out as 2 × 2 randomized block factorial with 12 replicates of a NT experiment established in 1997 on two highly weathered Oxisols. The factors comprised of: (a) two soil textural types: clay loam and sandy clay, and (b) two sampling depths: 0–5 and 5–20 cm. The three classes of macroaggregates were obtained by wet sieving, and the SOC content was determined by the dry combustion method. The extra-large macroaggregate classes in 0–20 cm depth for sandy clay (SdC) and clay loam (CL) Oxisol represented 75.2 and 72.4% of proportional mass, respectively. The SOC and POC stocks among macroaggregate classes in 0–5 and 5–20 cm depths decreased in the order: 8–19 mm > 2–8 mm ≈ 0.25–2 mm. The SdC plots under soybean/maize at 3:1 ratio recovered 58.3%, while those at 1:1 ratio (high maize frequency) in CL recovered 73.1% of SOC stock in the extra-large macroaggregates compared with the same under native vegetation for 0–20 cm depth. Thus, partial restoration of the SOC stock in original extra-large macroaggregate confirms the hypothesis that NT through higher maize cultivation frequency can be a pathway to fomation of macroaggregates and SOC buildup.

Différentes jachères arborées plantées d'Acacia polyacantha, de Senna siamea ou d'Eucalyptus camaldulensis et une jachère naturelle herbacée, ont été installées en comparaison, sur un sol appauvri en matière organique et en nutriments, dans la région de Garoua au Cameroun (1050 mm de pluviosité). L'objectif était d'évaluer leurs effets sur la dynamique du carbone, les cycles des nutriments, les propriétés du sol et le rendement des cultures annuelles après jachère. Par rapport à la jachère herbacée, les jachères arborées de 7 ans ont augmenté considérablement l'accumulation de matière organique et de nutriments dans la biomasse aérienne et souterraine et aussi le prélèvement des nutriments de la profondeur du sol. Ces processus ont permis, lors de l'exploitation des jachères arborées et du brûlis des résidus, d'améliorer les caractéristiques du complexe absorbant (somme des cations échangeables, en particulier Ca) dans l'horizon de surface (0-10 cm) des jachères ligneuses par rapport à la jachère herbacée. Par la fixation de l'azote et son recyclage, l'espèce fixatrice d'azote, A. polyacantha, a augmenté considérablement le bilan d'azote du système. L'espèce a accumulé dans son système racinaire autant d'azote qu 'E. camaldulensis et S. siamea dans leur biomasse totale et leur litière. En outre, seul A. polyacantha a montré une augmentation significative des stocks de carbone et d'azote du sol (couche 0-20 cm) après 6 ans d'âge. Le stock d'azote plus élevé et facilement minéralisable et l'accumulation de matière organique du sol dans la jachère à A. polyacantha, ont été associés à un triplement du rendement du maïs en première année de remise en culture par rapport aux précédents, et un doublement en deuxième année. Cette augmentation très importante des rendements des cultures après jachère n'a pas été observée après les autres précédents arborés. Ces résultats soulignent l'importance des compartiments organiques et le potentiel des arbres fixateurs d'azote dans la restauration de la fertilité des sols dégradés.

International audience; As part of the « post-accidental » management, the DEMETERRES project (RSNR PIA) proposes to develop innovative and environmentally friendly methods for removal of cesium and strontium from soils and liquid matrices in order to rehabilitate them for an agricultural use while minimizing the volume of generated wastes in accordance with the nuclear waste existing processes. Complementary approaches are used: they are based on physico-chemical technologies (such as foams flotation, supercritical CO2 extraction, extractants in fluidized bed reactor …) and biological ones (bioextractants, phytoextraction) which concepts are described. These researches aim to design innovative and performing extractants in term of selectivity and to achieve the pilot reactor phase for each of them. These pilots will group in a network to provide a technological platform lasting the project, to which will be attached an available network of experts. The respective advances of these researches are presented, completed of tests initiated in Japan on contaminated soils through partnerships.

Past applications of chlordecone, a persistent organochlorine pesticide, have resulted in diffuse pollution of agricultural soils, and these have become sources of contamination of cultivated crops as well as terrestrial and marine ecosystems. Chlordecone is a very stable and recalcitrant molecule, mainly present in the solid phase, and has a strong affinity for organic matter. To prevent consumer and ecosystem exposure, factors that influence chlordecone migration in the environment need to be evaluated. In this study, we measured the impact of incorporating compost on chlordecone sequestration in andosols as a possible way to reduce plant contamination. We first characterized the transfer of chlordecone from soil to plants (radish, cucumber, and lettuce). Two months after incorporation of the compost, soil-plant transfers were reduced by a factor of 1.9-15 depending on the crop. Our results showed that adding compost modified the fractal microstructure of allophane clays thus favoring chlordecone retention in andosols. The complex structure of allophane and the associated low accessibility are important characteristics governing the fate of chlordecone. These results support our proposal for an alternative strategy that is quite the opposite of total soil decontamination: chlordecone sequestration.

Pour les chercheurs en biologie, les légumineuses arborées présentent de nombreuses qualités pour l'agronomie, en particulier la capacité à fixer l'azote atmosphérique. Celle-ci permet la production de parties végétales riches en matière azotée qui, lorsqu'elles se décomposent dans le sol, sont supposées en améliorer la " fertilité ". D'autre part, on met souvent en avant leur " richesse " pour la nutrition des hommes et des animaux et la qualité de leur bois. Les spécialistes du reboisement soulignent leur capacité de multiplication sexuée et végétative ainsi que leur aptitude à se développer en milieu peu fertile et ouvert. Les agro-sylvo-pastoralistes travaillant en terrains tropicaux constatent bien ces vérités scientifiques, parfois devenues de véritables paradigmes, mais en éprouvent au quotidien les limites. Il est bien connu que toutes les légumineuses ne fixent pas l'azote et aussi que cette fixation dépend des espèces, de leur association rhizobienne et des conditions environnementales, mais ceci n'est pas toujours dit dans les messages destinés à la " vulgarisation ". Si des transferts " directs " d'azote entre plantes ont été mis en évidence, l'importance du transfert d'azote et d'autres nutriments au bénéfice de plantes associées ou en rotation dépend du recyclage des organes des plantes fixatrices. A l'inverse, la récolte de leurs bois, fruits ou feuilles, peut aboutir à un appauvrissement de la fertilité du sol qui les porte. Leur formidable capacité à se multiplier et à s'ancrer durablement dans un milieu, en particulier lorsqu'il est dégradé, a aussi son " revers de médaille ", à savoir qu'elles peuvent souvent devenir envahissantes. Par ailleurs, les écologistes dogmatiques regretteront que des légumineuses provenant d'autres continents soient maintenant présentes dans la plupart des forêts. D'autres, plus pragmatiques, y verront l'émergence de " forêts nouvelles " dont il faut étudier l'écosystème mais aussi valoriser les biens et services, comme le font souvent les paysans. Il reste cependant que ces légumineuses arborées occupent une place de choix dans la palette des possibilités disponibles pour le praticien en charge de la restauration de milieux dégradés ou de la création de systèmes agro-sylvo-pastoraux productifs et résilients face aux changements globaux, à condition de manier avec prudence la lancinante tentation de l'introduction de la " plante miracle " qui peut parfois, si on n'y prend pas garde, devenir une " plante cauchemar ".

The taxonomic status of eleven rhizospheric bacterial strains belonging to the genus Burkholderia and isolated from roots of Costularia (Cyperaceae), tropical herbaceous pioneer plants growing on ultramafic soils in New Caledonia, was investigated using a polyphasic taxonomic approach. The genetic analyses (16S rRNA genes, gyrB, recA, nreB and cnr) confirmed that all strains are Burkholderia and cluster into two separated groups. The DNA hybridization results showed low relatedness values to the closest relatives Burkholderia species. The phenotypic analyses confirmed that the two groups of strains could be differentiated from each other and from other known Burkholderia species. This polyphasic study revealed that these two groups of strains represent each a novel species of Burkholderia, for which the names Burkholderia novacaledonica sp. nov. (type strain STM10272(T)=LMG28615(T)=CIP110887(T)) and B. ultramafica sp. nov. (type strain STM10279(T)=LMG28614(T)=CIP110886(T)) are proposed, respectively. These strains of Burkholderia presented specific ecological traits such as the tolerance to the extreme edaphic constraints of ultramafic soils: they grew at pH between 4 and 8 and tolerate the strong unbalanced Ca/Mg ratio (1/19) and the high concentrations of heavy metals i.e. Co, Cr, Mn and Ni. Noteworthy B. ultramafica tolerated nickel until 10mM and B. novacaledonica up to 5mM. The presence of the nickel (nreB) and cobalt/nickel (cnr) resistance determinants encoding for protein involved in metal tolerance was found in all strains of both groups. Moreover, most of the strains were able to produce plant growth promoting molecules (ACC, IAA, NH3 and siderophores). Such ecological traits suggest that these new species of Burkholderia might be environmentally adaptable plant-associated bacteria and beneficial to plants.

National audience

International audience; Land use governance in the Brazilian Amazon has undergone significant changes in the last decade. At the national level, law enforcement capacity has increased and downstream industries linked to commodity chains responsible for deforestation have begun to monitor some of their suppliers’ impacts on forests. At the municipal level, local actors have launched a Green Municipality initiative, aimed at eliminating deforestation and supporting green supply chains at the territorial level. In this paper, we analyze the land use transition since 2001 in Paragominas—the first Green Municipality—and discuss the limits of the governance arrangements underpinning these changes. Our work draws on a spatially explicit analysis of biophysical variables and qualitative information collected in interviews with key private and public stakeholders of the main commodity chains operating in the region. We argue that, up to now, the emerging multi-level scheme of land governance has not succeeded in promoting large-scale land use intensification, reforestation and rehabilitation of degraded lands. Moreover, private governance mechanisms based on improved product standards, fail to benefit from potential successful partnerships between the public and private sector at the territorial level. We propose a governance approach that adopts a broader territorial focus as a way forward.

L’érosion par décapage ou par ravinement reste insignifiante sous la forêt dense tro- picale. Une érosion sérieuse peut certes se manifester localement sous couvert forestier, sous la forme de glissement de terrains saturés d’eau. De tels cas peuvent être observés à Madagascar, dans la forêt d’Anamalazoatra ou dans celle de Marojejy. Un cas connu d’érosion généralisée sous forêt dense se situe en Amazonie péruvienne, près de la petite localité de la Merced, sur des pentes très abruptes. Mais ce sont là des exceptions. Dans les temps géologiques, durant les périodes de transformations tectoniques, l’érosion peut aussi avoir été intense sous forêt dense, générant des reliefs tourmentés, parfois des « badlands ». Mais dans tous ces cas, l’érosion ne se produit sous forêt que lorsqu’il y a élé- vation du niveau de base des fleuves par rapport au niveau des océans, comme cela s’est manifesté durant les glacia- tions quaternaires. Là où la forêt manque aujourd’hui, se manifestent en revanche des phénomènes d’érosion parfois spec- taculaires. Ceux-ci peuvent prendre des proportions spectaculaires dans des régions autrefois forestières, récemment et sévèrement éclaircies. Les situations les plus extrêmes sont observées à Ma- dagascar, au Congo, au Gabon, au Brésil et dans la partie tempérée des USA, tout particulièrement dans le bassin cupri- fère du Tennessee. Ces exemples confir- ment pleinement la vertu antiérosive des forêts. Lorsque l’érosion est déclenchée, celle-ci ne peut être arrêtée qu’à grands frais, et dans des zones restreintes. La fo- rêt joue donc un rôle anti-érosif préventif à la fois naturel, peu coûteux, et opérant sur de larges étendues.Résumé adapté par la rédaction de la revue.

A partir d'un projet d'agro ecologie de restauration des sols dans l'Etat de Oaxaca (Mexique), cette etude decrit les formes concretes d'articulations entre savoirs scientifiques et savoirs paysans et leurs justifications par des agronomes. Il s'agit de questionner tant les modalites des traductions operees que les espaces d'incommensurabilite auxquelles elles sont confrontees. L'analyse de deux types de dispositifs pour la diffusion des savoirs agro ecologiques (ateliers de formation et feria de la milpa ) montre la mobilisation par les agronomes de valeurs, representations, pratiques, davantage que des savoirs per se propres aux agricul teurs. Un ensemble de redefinitions est realise au travers de l'articulation des savoirs. La categorie " savoirs paysans actuels " (qui regroupe selon les agronomes des savoirs nuisibles a l'environne ment) apparait comme une categorie cognitive " politisee " servant un objectif de transformation socio environnementale. Il semble que l'une des principales contraintes a la definition de savoirs agro ecologiques veritablement " pluri epistemologiques " reside dans une conception de la traduction entendue comme un moyen de valoriser, autant que de valider, les savoirs paysans. (Resume d'auteur)

Metal-rich soils, especially heavy metal-polluted soils and ultramafic soils, are generally toxic to non-adapted plants and microorganisms. The role of mycorrhizal fungi in the metal tolerance of adapted plant species has become clear in the last decade. This review aims to synthesize the findings of representative studies of the effects of mycorrhizas on the alleviation of heavy metal toxicity on plants and on the absorption/accumulation of heavy metals in their roots and shoots. The adaptation to heavy metals by mycorrhizal symbionts is associated with their efficiency in metal-rich soils. More than 80 % of the studies have indicated a positive role of mycorrhizal fungi in the adaptation of plants to heavy metals in these soils, but the relationships between plant tolerance to heavy metals and the absorption of metals are complex and depend on a range of biological, physical and chemical factors.

The association of the legume Anthyllis vulneraria and the grass Festuca arvernensis, was found to be very efficient for the phytostabilisation of highly multi-metal contaminated mine tailings. Our objective was to quantify the contribution of Anthyllis inoculated with its symbiotic bacteria Mesorhizobium metallidurans to the soil N pool and to test whether a starter nitrogen fertilization may improve symbiotic nitrogen fixation and the growth of Festuca. Methods Plants of Festuca and of Anthyllis inoculated with M. metallidurans were grown separately during eight months in pots filled with mine contaminated soil. Estimation of the N fluxes was realized using 15?N isotopic methods. Results Starter N fertilization (28 kg N ha?1) improved symbiotic N2 fixation and the growth of both species. Belowground N balance (N rhizodeposition - soil N uptake) of the non-fertilized Anthyllis at maturity was negative (?30.6 kg N ha?1). However, the amount of N derived from fixation, including above- and belowground parts, was 78.6 kg N ha?1, demonstrating the ability of this symbiotic association to improve soil N content after senescence. Conclusions i) soil N enrichment by the N2-fixing symbiotic association occurs after plant senescence, when decaying leaves and shoots are incorporated into the soil; ii) application of a starter fertilization is an efficient solution to improve phytostabilisation of highly contaminated sites.

Acacia mangium# is a leguminous tree used in industrial plantations for the production of pulp wood, and for the rehabilitation of degraded soils. Its ability to grow in very poor soils is due to its symbiotic association with nitrogen-fixing #Bradyrhizobium#. In this study, 33 isolates of #Bradyrhizobium# and #Rhizobium# obtained from #A. mangium# plantations in Sabah, Malaysia, were characterised by PCR amplification of ribosomal DNA and RFLP analysis, host spectrum and antibiotic resistance. The Sabah isolates were also compared with isolates collected from Singapore, Australia, and Africa. The results distinguished two main groups of #Bradyrhizobium#. Group I strains were prevalent, widely dispersed but genetically closely related. They were also closely related to the Singapore and Australian strains. Strains from Group II were less widely dispersed and more distantly related. Greenhouse and field inoculation trials with #A. mangium# seedlings showed that the Group I strains were more effective in enhancing plant growth than Group II strains. (Resume d'auteur)

The present invention relates to the reforestation of a soil area with co culture oftree species with nurse plants.