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Ce numéro est constitué d’articles issus du colloque « Biodiversité et durabilité des agricultures » qui s’est tenu à Paris le 11 avril 2019.; The current economic, environmental and social context encourages a transition to agroecologicalpractices that limit the use of synthetic inputs and enhance planned biodiversity in agroecosystems.Such practices mobilize a number of ecosystem services provided by soil organisms. Thiscommunication presents the principal components of the soil biota and associated ecosystem services.The impacts of the main soil management practices (tillage, fertilization) and of alternative systems arethen described. In conclusion we stress the importance of soil biodiversity conservation foragroecosystem fertility and functioning, and suggest a few key improvements such as increasing plantdiversity in agricultural systems.; Notre contexte économique, environnemental et sociétal actuel nous incite à considérer, dans le cadrede la transition agroécologique, des pratiques agricoles limitant l’usage d’intrants de synthèse etfavorisant la biodiversité planifiée dans les agroécosystèmes. Ces pratiques mobilisent certains servicesécosystémiques réalisés par la biocénose du sol. Dans cette communication, nous présentons lesprincipales composantes de la biocénose du sol et certains services écosystémiques associés. Nousabordons ensuite les impacts des principales pratiques culturales (labour, fertilisation) et des modes degestion des terres alternatifs. Nous concluons sur l’importance de la préservation de la biodiversité dessols sur la fertilité des agroécosystèmes, et suggérons des pratiques clés d’amélioration telles quel’augmentation de la diversité végétale dans les systèmes de culture.

Notre contexte économique, environnemental et sociétal actuel nous incite à considérer, dans le cadre de la transition agroécologique, des pratiques agricoles limitant l’usage d’intrants de synthèse et favorisant la biodiversité planifiée dans les agroécosystèmes. Ces pratiques mobilisent certains services écosystémiques réalisés par la biocénose du sol. Dans cette communication, nous présentons les principales composantes de la biocénose du sol et certains services écosystémiques associés. Nous abordons ensuite les impacts des principales pratiques culturales (labour, fertilisation) et des modes de gestion des terres alternatifs. Nous concluons sur l’importance de la préservation de la biodiversité des sols sur la fertilité des agroécosystèmes, et suggérons des pratiques clés d’amélioration telles que l’augmentation de la diversité végétale dans les systèmes de culture., The current economic, environmental and social context encourages a transition to agroecological practices that limit the use of synthetic inputs and enhance planned biodiversity in agroecosystems. Such practices mobilize a number of ecosystem services provided by soil organisms. This communication presents the principal components of the soil biota and associated ecosystem services. The impacts of the main soil management practices (tillage, fertilization) and of alternative systems are then described. In conclusion we stress the importance of soil biodiversity conservation for agroecosystem fertility and functioning, and suggest a few key improvements such as increasing plant diversity in agricultural systems.

Estimates of photosynthetic and respiratory fluxes at large scales are needed to improve our predictions of the current and future global CO2 cycle. Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere and has been proposed as a new tracer of photosynthetic gross primary productivity (GPP), as the uptake of OCS from the atmosphere is dominated by the activity of carbonic anhydrase (CA), an enzyme abundant in leaves that also catalyses CO2 hydration during photosynthesis. However soils also exchange OCS with the atmosphere, which complicates the retrieval of GPP from atmospheric budgets. Indeed soils can take up large amounts of OCS from the atmosphere as soil microorganisms also contain CA, and OCS emissions from soils have been reported in agricultural fields or anoxic soils. To date no mechanistic framework exists to describe this exchange of OCS between soils and the atmosphere, but empirical results, once upscaled to the global scale, indicate that OCS consumption by soils dominates OCS emission and its contribution to the atmospheric budget is large, at about one third of the OCS uptake by vegetation, also with a large uncertainty. Here, we propose a new mechanistic model of the exchange of OCS between soils and the atmosphere that builds on our knowledge of soil CA activity from CO2 oxygen isotopes. In this model the OCS soil budget is described by a first-order reaction–diffusion–production equation, assuming that the hydrolysis of OCS by CA is total and irreversible. Using this model we are able to explain the observed presence of an optimum temperature for soil OCS uptake and show how this optimum can shift to cooler temperatures in the presence of soil OCS emission. Our model can also explain the observed optimum with soil moisture content previously described in the literature as a result of diffusional constraints on OCS hydrolysis. These diffusional constraints are also responsible for the response of OCS uptake to soil weight and depth observed previously. In order to simulate the exact OCS uptake rates and patterns observed on several soils collected from a range of biomes, different CA activities had to be invoked in each soil type, coherent with expected physiological levels of CA in soil microbes and with CA activities derived from CO2 isotope exchange measurements, given the differences in affinity of CA for both trace gases. Our model can be used to help upscale laboratory measurements to the plot or the region. Several suggestions are given for future experiments in order to test the model further and allow a better constraint on the large-scale OCS fluxes from both oxic and anoxic soils.

Research over the last few decades has shown that the characterization of microaggregates at the micrometer scale using Transmission Electron Microscopy (TEM) provides useful information on the influence of microorganisms on soil functioning. By taking soil heterogeneity into account, TEM provides qualitative information about the state of bacteria and fungi (e.g., intact state of living organisms, spores, residues) at the sampling date within organo-mineral associations, from the soil-root interface to the bulk soil, and in biogenic structures such as casts. The degree of degradation of organic matter can be related to the visualized enzymatic potential of microorganisms that degrade them, thus indicating organic matter dynamics within soil aggregates. In addition, analytical TEM characterization of microaggregates by EELS (Electron Energy Loss Spectroscopy) or EDX (Energy Dispersive X-rays spectroscopy) provides in situ identification of microbial involvement in the biogeochemical cycles of elements. Furthermore, micrometer characterization associated with other methodologies such as Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS) or soil fractionation, enables monitoring both incorporation of biodegraded litter within soil aggregates and impacts of microbial dynamics on soil aggregation, particularly due to production of extracellular polymeric substances. The present focused review suggests that such an approach using micrometer characterization of soil microhabitats provides relevant qualitative and quantitative information when monitoring and modelling microbial processes in dynamics of organo-mineral associations.

Halogenated volatile organic compounds (VOCs) emitted by terrestrial ecosystems, such as chloromethane (CH3Cl), have pronounced effects on troposphere and stratosphere chemistry and climate. The magnitude of the global CH3Cl sink is uncertain since it involves a largely uncharacterized microbial sink. CH3Cl represents a growth substrate for some specialized methylotrophs, while methanol (CH3OH), formed in much larger amounts in terrestrial environments, may be more widely used by such microorganisms. Direct measurements of CH3Cl degradation rates in two field campaigns and in microcosms allowed the identification of top soil horizons (i.e., organic plus mineral A horizon) as the major biotic sink in a deciduous forest. Metabolically active members of Alphaproteobacteria and Actinobacteria were identified by taxonomic and functional gene biomarkers following stable isotope labeling (SIP) of microcosms with CH3Cl and CH3OH, added alone or together as the [C-13]-isotopologue. Well-studied reference CH3Cl degraders, such as Methylobacterium extorquens CM4, were not involved in the sink activity of the studied soil. Nonetheless, only sequences of the cmuA chloromethane dehalogenase gene highly similar to those of known strains were detected, suggesting the relevance of horizontal gene transfer for CH3Cl degradation in forest soil. Further, CH3Cl consumption rate increased in the presence of CH3OH. Members of Alphaproteobacteria and Actinobacteria were also C-13-labeled upon [C-13]-CH3OH amendment. These findings suggest that key bacterial CH3Cl degraders in forest soil benefit from CH3OH as an alternative substrate. For soil CH3Cl-utilizing methylotrophs, utilization of several one-carbon compounds may represent a competitive advantage over heterotrophs that cannot utilize one-carbon compounds.

EABIOmE INRA; Pourquoi faut-il se préoccuper de la toxicité des pesticides pour les microorganismes du sol ?

Plant-microbes interactions in the rhizosphere of maize inoculated with Azospirillum lipoferum CRT1: implications for soil N-cycling microorganisms. Sfécologie-2016, International Conference of Ecological Sciences

Soils are exposed to nanoparticles (NPs) as a result of their increasing use in many commercial products. Adverse effects of NPs on soil microorganisms have, been reported in several ecotoxicological studies using microcosms. Although repeated exposures are more likely to occur in soils, most of these previous studies were performed as a single exposure to NPs. Contrary to single, contamination, the study of multiple NP contaminations in soils requires the use of specialized setups. Using a soil column experiment, we compared the influence of single and repeated exposures (one, two, or three exposures that resulted in the same final concentration applied) on the transport of titanium dioxide (TiO2) NPs through soil and the effect of these different exposure scenarios on the abundance and activity of soil nitrifying microbial communities after a 2 month incubation. The transport of TiO2 NPs was very limited under both single and repeated exposures and was highest for the lowest concentration injected during the first application. Significant decreases in nitrification-activity and ammonia-oxidizing archaea and bacteria populations were observed only for the repeated exposure scenario (three TiO2 NP contaminations). These results suggest that, under repeated exposures, the transport of TiO2 NPs to deep soil layers and groundwater is limited and that a chronic contamination is more harmful for the soil microbiological functioning than a single exposure.

L’Observatoire pérenne de l’environnement (OPE) de l’ANDRA a mis en œuvre depuis 2007 un réseau d’inventaires et d’observations à long terme des différents milieux de l’environnement sur un territoire de 240 km2 dans les départements de la Meuse et de la Haute-Marne. Un réseau de suivi et d’observation de la qualité des sols a ainsi été mis en place selon un maillage systématique en suivant un protocole d’échantillonnage et d’analyse de type « RMQS » conduit à l’échelle du paysage sur une grille de 1,5 km x 1,5 km. Des prélèvements d’échantillons composites ont été effectués lors de 4 campagnes successives entre 2009 et 2012 sur un total de 127 sites, dont 57 disposaient en plus d’une fosse pédologique. Les propriétés physico-chimiques (texture, carbone, pH, calcaire, azote, CEC, phosphore assimilable, cations échangeables et éléments majeurs totaux) et microbiologiques (structure des communautés microbiennes) ont été analysées dans le but d’établir un état de référence des sols de la zone d’observation. Ces observations ont servi de base à une analyse statistique afin de comprendre la distribution spatiale de la diversité pédologique et des micro-organismes telluriques à l’échelle d’un paysage, et les facteurs qui la pilotent. Pour cela, nous avons eu recours aux techniques de cartographie numérique. Nous avons ainsi couplé des analyses en composantes principales (ACP) sous contraintes spatiales avec des outils de régression et de géostatistique (krigeage universel). Les ACP ont été réalisées sur trois matrices différentes regroupant respectivement les données des principales propriétés pédologiques, les communautés bactériennes et les communautés de champignons toutes deux caractérisées par les empreintes moléculaires issues des analyses de type ARISA. Nous avons ensuite tenté d’expliquer les trois premiers axes de chacune des ACP en les mettant en relation avec des covariables environnementales dont la couverture spatiale est exhaustive sur la zone d’étude. Deux algorithmes ont été testés : les arbres de régressions boostés implémentés dans la librairie « gbm » et dans la librairie Cubist du logiciel de statistique R. Les covariables environnementales retenues sont : (1) les dérivées morphométriques issues du MNA à la résolution de 25 mètres (15 variables), (2) l’occupation du sol, (3) le fond géologique (carte géologique à 1/50 000) et (4) les unités cartographiques du sol issues de la carte pédologique à 1/50 000. Enfin, les résidus des modèles de régression ont été interpolés par des techniques géostatiques. L’ensemble de la procédure a été validée par validation croisée. Malgré une relative homogénéité, les propriétés physico-chimiques des sols se distribuent selon la nature géologique et pédologique de la zone ainsi que selon la géomorphologie du paysage (MNA et ses dérivées) et l’occupation du sol. La structure génétique des communautés bactériennes et fongiques présente des structures spatiales moyennement marquées à l’échelle du paysage. Les communautés bactériennes s’organisent selon la morphologie du relief (rugosité, orientation des pentes), les unités cartographiques des sols et les structures hydrologiques (distance au plus proche court d’eau). La distribution des communautés fongiques est impactée par la topographie, et les structures hydrographiques. La performance des 6 modèles construits mesurée par le R² varie de 0,13 à 0,94. Nos résultats confirment qu’il est possible d’identifier et de hiérarchiser les filtres environnementaux qui pilotent les diversités physico-chimiques et biologiques du sol à l’échelle d’un paysage.

National audience

Avec les remerciements pour Jodie Thénard; Conventional agriculture strongly alters soil quality due to industrial practices that often have negative effects on soil life. Alternative systems such as conservation agriculture and organic farming could restore better conditions for soil organisms. Improving soil life should in turn improve soil quality and farming sustainability. Here, we have compared for the first time the long-term effects of conservation agriculture, organic farming, and conventional agriculture on major soil organisms such as microbes, nematofauna, and macrofauna. We have also analyzed functional groups. Soils were sampled at the 14-year-old experimental site of La Cage, near Versailles, France. The microbial community was analyzed using molecular biology techniques. Nematofauna and macrofauna were analyzed and classified into functional groups. Our results show that both conservation and organic systems increased the abundance and biomass of all soil organisms, except predaceous nematodes. For example, macrofauna increased from 100 to 2,500 %, nematodes from 100 to 700 %, and microorganisms from 30 to 70 %. Conservation agriculture showed a higher overall improvement than organic farming. Conservation agriculture increased the number of many organisms such as bacteria, fungi, anecic earthworms, and phytophagous and rhizophagous arthropods. Organic farming improved mainly the bacterial pathway of the soil food web and endogeic and anecic earthworms. Overall, our study shows that long-term, no-tillage, and cover crops are better for soil biota than periodic legume green manures, pesticides, and mineral fertilizers.

International audience; The distribution of rhcRST genes encoding the type III secretion system (T3SS) in a collection of Bradyrhizobium strains was characterized by PCR and Southern blot hybridization. The polymorphism of the corresponding sequences amplified by PCR was characterized by RFLP and sequencing together with those available in the databank. Genomic group I is characterized by the presence of Bradyrhizobium elkanii strains and group II by the presence of B. japonicum and B. liaoningense strains. Highly conserved T3SS-like genes were detected by PCR in all Bradyrhizobium strains isolated from soybean belonging to genomic group II, and in none of the strains belonging to genomic group I. These data were confirmed by Southern blot hybridization that further indicated the presence of sequences showing similarity to the rhcRST sequence in B. elkanii strains. The high level of conservation of rhcRST among Bradyrhizobia of genomic group II and sharing the same host-plant suggests that T3SS-like genes might have undergone horizontal genetic transfer within this genomic group. When considering the three Rhizobiaceae genera, a clear congruence was recorded between the rhcRST, rRNA gene and ITS sequences in bacteria harbouring sequences encoding T3SS, suggesting a relatively ancient emergence of the T3SS in these genera.

Soil organic mater decompositon – the roles of microbial habitats and of microbial communites. International symposium on biogeochemical interfaces in soil – toward a comprehensive and mechanistic understanding of soil functions

Hierarchy of two drivers of soil organic matter biodegradation. Habitat properties versus habitat community structure. 20. World Congress of Soil Science

Predicting the response of soil organic matter microbial decomposition to moisture. EGU General Assembly 2014

International audience; Photosynthesis (GPP), the largest CO2 flux from the land surface, is currently estimated with considerable uncertainty between 100-175 Pg C yr-1. More robust estimates of global GPP could be obtained from the atmospheric budgets of other tracers such as, the oxygen isotopic composition (δ18O) of atmospheric CO2 or carbonyl sulfide (COS). However, the partitioning of GPP and soil respiration using these tracers hinges on a better understanding of how soil micro-organisms modify the atmospheric concentrations of CO18O and COS at large scales. In particular, understanding better the role and activity of the enzyme Carbonic Anhydrase (CA) in soil micro-organisms is a critical factor underpinning the successful partitioning of gross fluxes at the global scale. Within this presentation I will review our understanding of the function of CA in soil micro-organisms and how its activity is likely to be influenced by environmental drivers that give rise to variations in soil CA activity observed in the field.

A loamy clay soil containing unextractable 14C-ring labeled atrazine residues was incubated in microcosms under abiotic and biotic conditions. The mineralization activity of the soil microflora was evaluated by the release of total CO2 and 14C02. After 63 days of sample incubation the total organic carbon mineralization was of 1.71%, that of 14C-residues was of 0.72% of the initial radioactivity. No direct relationship was established between the mineralization of atrazine residues and the global mineralization. The contribution of soil microorganisms in the release of 14C-residues was weak. The availability of non-extractable residues was mainly controlled by physico-chemical factors. The low value of the reextractability rate and the distribution of bound residues during the soil sample incubation shown the active role of organic matter in detoxification procedure. Ninety percent of the residues remained bound after 63 days of incubation and were thus, potentially available without biocide activity. The fractionation of soil organic matter allowed to specify the distribution of bound residues within the organic compartments. After a long-stay of pesticides in soils, approximately 65% of bound residues were associated with humin.

International audience; Technosols (USS Working Group WRB 2006) are soils, whose properties and pedogenesis are dominated by artificial or transported materials. In the case of industrial brownfield management, constructed Technosols can be used intentionally to reclaim ecosystem. These Technosols are made of anthropogenic materials that are legally considered as wastes or by-products. Sponsored by the French National Soil Programme GESSOL, and within the GISFI (Groupement d’Intérêt Scientifique sur les Friches Industrielles, www.gisfi.fr), a consortium of soil biologists has been constituted to study a model constructed Technosol ecosystem at the field scale on a derelict brownfield in the Lorraine Region (France). The studied Technosol, implemented in 2007, is made of a layer of green-waste compost at the surface, a layer of a mixture of treated industrial soil and paper-mill sludge, and a bottom layer of pure paper-mill sludge. The pedogenesis of this Technosol has been studied for several years demonstrating its capacity to perform basic soil functions (Séré, Schwartz et al. 2008). The working group comprised soil ecologist specialists of various biota (bacteria and mycorhiza, nematodes, microarthropods, macroarthropods and earthworms), agronomists, and soil bio-physicians. Sampling has occurred each year at spring time since 2008. The main question of the project focuses on the capacity of the Technosols to fulfill essential functions of a natural soil, particularly vegetation development, which means restoration of physical and chemical fertility. Our hypothesis is that soil organisms, by their diversity and functional complementarities, are essential actors in the system for the main physical (aggregation, bioturbation) and chemical (carbon and nitrogen cycles) processes. In this context, our objective is to assess the colonisation dynamic of the Technosol by soil biota and their impact on several soil functions. The results obtained within the 4 first years (2008 to 2011) of the project indicate that the initial system is typical of pioneer ecosystems, with the presence of bacterivorous nematodes and the absence of macrofauna. Initial Collembola communities are mainly influenced by the initial materials (origins of the composts) and the borders of the field, showing a centripetal colonisation during the first 2 years. However, an increase of species richness, particularly concerning nematodes, is observed between 2008 and 2009. Furthermore, in 2011, an explosion of earthworm densities is observed, showing a fast colonisation of soil engineers. Finally this soil biota development can be strongly linked with the evolution of the soil structure and leads to a biomass production similar to a “natural” pasture, which conducts to the occurrence of a brumifer horizon.

Impact of distribution heterogeneity of microorganisms and 2,4-D on biodegradation processes in soil : experiment and modelling. Conference on Pesticide Behaviour in Soils, Water and Air (York 2013)

Living in soil pores: physical and nutritional constraints for microbial decomposers of soil organic matter. Goldschmidt 2013

The experiment was conducted in the long term P fertilizer trial of INRA research centre at Auzeville(43.5oN, 1.43oE) in south western France. The three P regimes corresponded to fertilizer levels applied since1968: P0 (no fertilization), P1 (fertilization rate to balance the mean annual P removal by crops) and P4(fertilization rate representing three-­‐ to four-­‐fold that of P1). Durum wheat and faba bean were grown aloneor as durum wheat/faba bean intercrops in this field trial. Their rhizospheres were collected at the faba beanflowering stage, as well as the corresponding bulk soils. Soil DNA and RNA were extracted in these varioussamples and qPCR was used to assess the number of gene copies of fungi, bacteria, as well as several bacterialphyla (Actinobacteria, α-­‐Proteobacteria and Firmicutes (strongly dominated with P-­‐cycling taxa)) and betapropeller phytase (BPP).

IV Sessione – Gestione del suolo nelle politiche agro-alimentari; Conservazione delle risorse genetiche microbiche associate a produzioni agricole tipiche. La centralità del suolo nel sistema agrario e forestale

Prise en compte de l’hétérogénéité des sols à l’échelle des habitats microbiens pour modéliser la biodégradation des substrats carbonés dans les sols. 11. Journées d'Etude des Sols

I microrganismi di interesse agrario svolgono un ruolo chiave sia nella produzione di cibo (fertilità del suolo, nutrizione delle colture, biocontrollo, biofertilizzazione) sia nei riguardi della conservazione delle derrate alimentari (tossine e patogeni), sia nella produzione di alimenti trasformati (latte e formaggi, vino, olio, ecc.), pertanto la loro biodiversità è funzionale al sostentamento degli organismi viventi sulla terra. Le comunità microbiche delle filiere agro-alimentari in realtà sono strettamente correlate e il loro comportamento è il risultato di continue interazioni geniche e di competizioni nutrizionali, che si instaurano dalla messa a dimora della coltura alla trasformazione e conservazione del prodotto. Questi rapporti sono alla base di tutti i processi microbici che caratterizzano le filiere produttive, dalle produzioni vegetali al prodotto trasformato finito. Per tutte queste ragioni è necessario, da un lato, garantire la conservazione delle risorse genetiche disponibili valorizzandone le potenzialità applicative mediante screening del germoplasma disponibile e, dall’altro, rivolgersi all’ampia frazione di biodiversità non ancora accessibile, migliorando la capacità di recupero dei microrganismi e regolandone gli aspetti normativi (proprietà, conservazione in situ, scambio con Paesi terzi) in funzione dei possibili benefici nei settori interessati a una loro applicazione. In questo quadro emerge l’importanza delle risorse genetiche microbiche nell’ambito del miglioramento genetico dei microrganismi e della loro valorizzazione biotecnologica, con particolare riguardo alle principali tecnologie agroalimentari, alle interazioni con i vegetali (simbiosi, micorrize, ecc.), alla fertilità dell’ecosistema suolo, nonché alle nuove applicazioni quali ad esempio la produzione di energia, di biocombustibili, ed il biorisanamento dell’acqua e dei suoli. Mantenere in collezione i microrganismi del suolo rappresenta dunque una necessità irrinunciabile soprattutto nel caso di studi a livello ambientale per comprendere quali pressioni realmente possano intervenire da parte dell’uomo o di eventi ambientali sul suolo, quali i cambiamenti climatici. Nel presente lavoro verranno forniti alcuni esempi di conservazione delle risorse genetiche microbiche ex situ ed in situ/on farm., Microorganisms of Agricultural and Agroindustrial concern are key players in food production (soil biological fertility, crop nutrition, biocontrol, biofertilization), in foodstuffs conservation (toxins and pathogens), in food production (milk and cheeses, wine, olive oil, etc.), and in the biogeochemical cycles of nutrients for ecosystem productivity, therefore they are a crucial factor for providing life on Earth. This relatively thin layer on earth is essentially non-renewable that plays a vital resource in maintaining a functional biosphere. Microbial communities involved in food farming are strictly related and are influenced by many genomic interactions and food competitions throughout the entire farm and food supply chain. For all of these reasons it is necessary, on the one hand, collecting the available microbial genetic resources (MGR) and on the other hand assessing microbial biodiversity not yet available, improving the ability of isolating new strains, as well as managing legislation aspects (property rights, in situ conservation, exchanges of microbial genetic resources). While the most visible role of agricultural uses of microorganisms is probably that of producing and delivering food, microbiology is critical to other agricultural sectors as well, for example for production of energy based on plant or other organic materials and for bioremediation of agricultural wastes. Some examples about ex situ and in situ/on farm conservation of microbial genetic resources will be given in the present work.

Effet de la connection et déconnection spatiale des microorganismes et du 2,4-D sur la biodégradation du 2,4-D. 11. Journées d'Etude des Sols

International audience; Although the impact of bioremediation of PCB-contaminated sites on the indigenous microbial community is a key question for soil restoration, it remains poorly understood. Therefore, a small-scale bioremediation assay made of (a) a biostimulation treatment with carvone, soya lecithin and xylose and (b) two bioaugmentation treatments, one with a TSZ7 mixed culture and another with a Rhodococcus sp. Z6 pure strain was set up. Changes in the structure of the global soil microbial community and in the abundances of different taxonomic phyla were monitored using ribosomal intergenic spacer analysis (RISA) and real-time PCR. After an 18-month treatment, the structure of the bacterial community in the bioremediated soils was significantly different from that of the native soil. The shift observed in the bacterial community structure using RISA analysis was in accordance with the monitored changes in the abundances of 11 targeted phyla and classes. Actinobacteria, Bacteriodetes and α- and γ-Proteobacteria were more abundant under all three bioremediation treatments, with Actinobacteria representing the dominant phylum. Altogether, our results indicate that bioremediation of PCB-contaminated soil induces significant changes in the structure and abundance of the total microbial community, which must be addressed to implement bioremediation practices in order to restore soil functions.

project SEST 009; International audience; Listeria monocytogenes is a ubiquitous opportunistic pathogen responsible for listeriosis. In order to study the processes underlying its ability to adapt to the soil environment, whole-genome arrays were used to analyse transcriptome modifications 15 minutes, 30 minutes and 18 h after inoculation of L. monocytogenes EGD-e in soil extracts. Growth was observed within the first day of incubation and large numbers were still detected in soil extract and soil microcosms one year after the start of the experiment. Major transcriptional reprofiling was observed. Nutrient acquisition mechanisms (phosphoenolpyruvate-dependent phosphotransferase systems and ABC transporters) and enzymes involved in catabolism of specific carbohydrates (b-glucosidases; chitinases) were prevalent. This is consistent with the overrepresentation of the CodY regulon that suggests that in a nutrient depleted environment, L. monocytogenes recruits its extensive repertoire of transporters to acquire a range of substrates for energy production.

National audience

Proteins are important compounds in soils, made up of monomeric amino acids joined by peptide bonds, and there are several reasons for studying their fate in soil: (i) their amino acids are an important source of soil nitrogen, (ii) enzymes secreted by soil microorganisms, plant roots and soil invertebrate guts can be involved in the biogeochemical cycles of soil organic matter (Quiquampoix, 2000; Quiquampoix and Mousain, 2005), (iii) pathogenic proteins such as prions involved in transmissible spongiform encephalopathies (Brown and Gajdusek, 1991; Revault et al., 2005) or insecticidal toxins expressed in transgenic plants (Tapp and Stotzky, 1998; Pagel-Wieder et al;, 2004) represent a growing environmental concern. Proteins generally have a strong affinity for all types of interfaces found in soil, both the solid–liquid interfaces of soil minerals and organic colloids and the liquid–gas interfaces developed in a microporous system and dependent on the soil pore-water content. The affinity for various types of interfaces originates in the flexibility of the polypeptide chain and in the diversity of the 20 amino acids that can be classified on an electrical scale as positively, neutrally or negatively charged and on a hydrophobic scale from polar to non-polar. These properties give rise to a large variety of interactions with soil surfaces, relationships that may be dominated by enthalpic or entropic contributions to the free energy. The strong and often largely irreversible adsorption of proteins on the mineral phase of the soil has important consequences not only on their mobility, but also on their resistance to breakdown (proteins as N source in soil) and functional activity (catalylic for enzymes, infectious for prions, toxic for Bt proteins). Extracellular enzymes can be secreted into soil solution by microorganisms. This process makes possible the degradation of the soil organic matter since polymers cannot usually pass through the membranes of the microorganisms and need to be hydrolysed into soluble low molecular weight compounds which can reach membrane permeases specific for monomers (sugars, amino acids) or occasionally oligomers. For this reason, they will play an important role in the biogeochemical cycles of C, N, P and S in soil. A consequence of the adsorption of these extracellular enzymes on mineral surfaces is a shift of the optimal pH of the catalytic activity toward more alkaline values and a general decrease of their activity. All proteins can make an important contribution as biochemical substrates in proteolysis reactions in the N cycle when released in soil after death of biota and lysis of the membranes since they have an average N content of 16%. Prion proteins are an infective agent of several transmissible spongiform encephalopathies (TSE). Epidemiological studies of ovine scrapie in Europe and, more recently, the chronic wasting disease of wild cervids (deer, elk and moose) in North America, suggest the possible horizontal transmission from a soil reservoir.

Communication orale, résumé; Among the microbial functions involved in biogeochemical cycles, those related to carbon cycle play a central role in the biological functioning of agro-ecosystems, in particular because of their involvement in soil fertility, environment quality and global changes. In spite of its major role in organic matter degradation processes, the microbial component involved is poorly documented, particularly in terms of populations and functions, and then considered as a "functional black box". In this context, our objective was to progress in our knowledge of the microbial populations responsible for organic matter degradation in soil. Crop residues represent one of the most important hot spots (zones of increased biological activity) and ecological niches to study microbes involved in organic matter degradation. Our objective was to characterize, in a field experiment, the dynamics of the microbial communities in the detritusphere (zone of the soil under the influence of crop residues) in relation to the biochemical quality of the residue and the evolution of the soil organic matter. For this, residues from different plant types: wheat, colza, and alfalfa were incorporated separately in different plots. From the incorporation date, soils were sample each 1 month for 1 year. The responses of microbial communities to residue supply have been assessed by using molecular methods allowing the characterization of the diversity of microorganisms (DNA fingerprinting, clone libraries). In parallel, the dynamics of the biochemical quality of the residues have been monitored (Near Infra Red Spectrometry).Results showed a strong influence of residue biochemical quality on the dynamics of microbial communities. Furthermore, most of the microbial modifications occurred in the close neighbourhood of the residue, highlighting the particular ecological significance of the detritusphere. Coupling of microbial data and organic mater biochemical data allowed linking the dynamics of microbial communities with the fate of organic matter in soil.

National audience

It is hypothesized that metal hyperaccumulator plants have specific rhizosphere conditions, potentially modifying the bioavailability of soil metals. This article aims to further the knowledge about the rhizosphere of the hyperaccumulator Thlaspi caerulescens, focusing on its microflora isolated from metalliferous soils collected in situ where the plants grow naturally. We characterized the cultivable microbial communities isolated from the rhizosphere of one population of this Ni hyperaccumulator species grown on a serpentine soil. The rhizosphere soil harbored a wide variety of microorganisms, predominantly bacteria, confirming the stimulatory effect of the T. caerulescens rhizosphere on microbial growth and proliferation. We tested the hypothesis that the rhizosphere of T. caerulescens influences (1) the metabolic diversity of the bacterial community and (2) the bacterial resistance to metals. The principal component analysis of the Biolog plate's data confirmed a structural effect of the rhizosphere of T. caerulescens on bacterial communities. The percentage of Ni-resistant bacteria was higher in the rhizosphere than in the bulk soil, suggesting a direct effect of the rhizosphere on Ni tolerance, reflecting a greater bacterial tolerance to Ni in the rhizosphere.

The effects of maize expressing the Bacillus thuringiensis Cry1Ab protein (Bt maize) on soil microarthropods were assessed in the field at four European locations (two in Denmark and two in France) that differ in their climatic conditions or soil properties. Each site was considered as a separate experiment, with separate statistical comparison. Effects of farming practices using Bt maize were compared with conventional farming practices using near-isogenic non-Bt maize and also (at some of the sites) other conventional varieties. Furthermore, at one field site (Foulum, Denmark), the effects of Bt crops were studied in both conventional tillage and reduced tillage contexts. At another field site (Askov, Denmark), Bt maize effects were also compared to the effects of the chemical insecticide dimethoate. Moreover, at three of the field sites (all except Narbons, France), the possibility of a localised Bt effect around the rhizosphere compared to the bulk soil was assessed by sampling within and between maize rows. There were some significant negative effects of Bt maize on microarthropods in soils with a high clay content. Significant differences of the same magnitude also occurred between different conventional varieties of maize, but the effect of dimethoate appeared clearly greater than Bt effects. It is thus debatable if the Bt maize effect is an effect of the Bt toxin or just an effect of the maize variety. Based on the results, it can be concluded that the effect of Bt maize on soil microarthropods was small and within the normal variation expected in conventional agricultural systems. (C) 2007 Elsevier GmbH. All rights reserved.

International audience; The effects of Cu amendment on indigenous soil microorganisms were investigated in two soils, a calcareous silty clay (Ep) and a sandy soil (Au), by means of a 1-year field experiment and a two-month microcosm incubation. Cu was added as 'Bordeaux mixture' [CuSO4, Ca(OH)2] at the standard rate used in viticulture (B1=16 kg Cu kg−1 soil) and at a higher level of contamination (B3=48 kg Cu ha−1 soil). More extractable Cu was observed in sandy soil (Au) than in silty soil (Ep). Furthermore, total Cu and Cu-EDTA declined with time in Au soil, whereas they remained stable in Ep soil. Quantitative modifications of the microflora were assessed by C-biomass measurements and qualitative modifications were assessed by the characterization of the genetic structure of bacterial and fungal communities from DNA directly extracted from the soil, using B- and F-ARISA (bacterial and fungal automated ribosomal intergenic spacer analysis). In the field study, no significant modifications were observed in C-biomass whereas microcosm incubation showed a decrease in B3 contamination only. ARISA fingerprinting showed slight but significant modifications of bacterial and fungal communities in field and microcosm incubation. These modifications were transient in all cases, suggesting a short-term effect of Cu stress. Microcosm experiments detected the microbial community modifications with greater precision in the short-term, while field experiments showed that the biological effects of Cu contamination may be overcome or hidden by pedo-climatic variations.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; The aim of this study was to evaluate the ability of nonpathogenic F. oxysporum and Trichoderma isolates from suppressive soils in South Africa to suppress fusarium wilt of banana in the glasshouse. Several biological control agents and commercial biological control products were included in the study. The isolates were first screened in vitro on potato dextrose agar. In glasshouse evaluations, the fungal and bacterial isolates were established on banana roots before they were replanted in pathogen-infested soil, while the commercial biocontrol agents were applied as directed by the supplier. Banana plantlets were evaluated for disease development after 7 weeks. In vitro tests showed none of the nonpathogenic isolates suppressed Fusarium oxysporum f.sp. cubense (Foc), while slight suppression was observed with the two Trichoderma isolates. Results of the glasshouse evaluations revealed that two of the nonpathogenic F. oxysporum isolates, CAV 255 and CAV 241, reduced fusarium wilt incidence by 87·4 and 75·0%, respectively. The known biological control agent Fo47 did not suppress Foc significantly. Pseudomonas fluorescens strain WCS 417, known for its ability to suppress other fusarium wilt diseases (WCS 417), reduced disease incidence by 87·4%. These isolates should be further evaluated for potential application in the field, independently and in combination.

The aim of this study is to establish correlations between different descriptors and pathological potential of soils towards plants, in order to identify indicators of soil biological quality. Three cultural practices were applied in an experimental field before carrot culture (conventional, organic amendment with cattle manure and biofumigation with fodder radish). Twenty-one soil samples were collected in each plot at 3 key points during the cropping sequence (before treatment, before and after carrot culture). Physicochemical (carbon, nitrogen and organic matter contents, C/N ratio, pH, EC, ions and trace elements), biological (densities of cultivable bacteria and fungi, microbial biomass and basal respiration, densities of plant-parasitic nematode populations), microbial diversity (bacterial and fungal community structure by T-RFLP) and plant-pathological (receptivity to Rhizoctonia solani damping-off) properties were measured and correspondences were analysed by Principal Component Analysis. Before application of the cultural practices, soil characteristics were very similar in the 3 plots. Biofumigation resulted in a significant increase of the microbial densities, biomass and basal respiration. Both organic amendment and biofumigation modified the microbial community structures. Intra and inter-class PCA enabled to distinguish any effect between treatments and dates. The soil biological characteristics showed resilience to the situation that occurred before cultural practices. Relations between physicochemical, biological and molecular data sets, provided by co-inertia analysis, will be discussed and dealt with the receptivity of the soil samples to R. solani damping-off. This strategy will enable us to propose a bunch of soil biological quality indicators.

The objective of this study was to explore the long-term effects of different organic and inorganic fertilizers on activity and composition of the denitrifying and total bacterial communities in arable soil. Soil from the following six treatments was analyzed in an experimental field site established in 1956: cattle manure, sewage sludge, Ca(NO 3 ) 2 , (NH 4 ) 2 SO 4 , and unfertilized and unfertilized bare fallow. All plots but the fallow were planted with corn. The activity was measured in terms of potential denitrification rate and basal soil respiration. The nosZ and narG genes were used as functional markers of the denitrifying community, and the composition was analyzed using denaturing gradient gel electrophoresis of nosZ and restriction fragment length polymorphism of narG , together with cloning and sequencing. A fingerprint of the total bacterial community was assessed by ribosomal intergenic spacer region analysis (RISA). The potential denitrification rates were higher in plots treated with organic fertilizer than in those with only mineral fertilizer. The basal soil respiration rates were positively correlated to soil carbon content, and the highest rates were found in the plots with the addition of sewage sludge. Fingerprints of the nosZ and narG genes, as well as the RISA, showed significant differences in the corresponding communities in the plots treated with (NH 4 ) 2 SO 4 and sewage sludge, which exhibited the lowest pH. In contrast, similar patterns were observed among the other four treatments, unfertilized plots with and without crops and the plots treated with Ca(NO 3 ) 2 or with manure. This study shows that the addition of different fertilizers affects both the activity and the composition of the denitrifying communities in arable soil on a long-term basis. However, the treatments in which the denitrifying and bacterial community composition differed the most did not correspond to treatments with the most different activities, showing that potential activity was uncoupled to community composition.

Little research has been done on pesticide dissipation in cold climates and there is a need to focus on the influence of climate on pesticide degradation in soil. Glyphosate, N-(phosphonomethyl)glycine, is a herbicide frequently used for controlling perennial weeds through application after harvest and was used as a model compound for this study. The effect of freeze-thaw activity on the availability of glyphosate in soil, and consequently its mineralization by soil microorganisms, was studied through laboratory incubations of repacked soil cores treated with 14C-labelled glyphosate and subjected to different freeze-thaw treatments. Winter simulation regimes applied were constant thaw (+5 degrees C), constant freezing (-5 degrees C), unstable conditions with short fluctuations (24 h of -5 degrees C followed by 24 h of +5 degrees C), and long duration fluctuations (3 weeks of -5 degrees C followed by 3 weeks of +5 degrees C). Distribution of 14C-glyphosate was followed during the incubation through measurements of the mineralized fraction (14CO2), soil water fraction, KOH extractable fraction, and non-extractable fraction. Microbial parameters used to characterize the soils were estimates of size of microbial biomass, overall microbial activity and microbial diversity. The constant freezing treatment exhibited the lowest amount of glyphosate mineralization. The constant thawed treatment and the treatments with fluctuating temperature exhibited significantly increased mineralization. These results were in accordance with the observed concentration of glyphosate in soil water; the higher the activity, the lower the concentration. The amount of glyphosate extractable with KOH and the resulting non-extractable fraction, however, were not significantly affected by soil type or temperature regime. The glyphosate mineralization pattern was comparable with the overall microbial activity in the soils. Observed different levels of diversity might explain some of the difference in total glyphosate mineralization between soils.

International audience; Soil algae are photosynthetically active microorganisms showing changeable community structure, depending on the soil type, the agricultural practices and the application of pesticides. To characterise algal community structure, molecular approaches complementary to classical microbiological approaches based on the isolation and the culture of soil algae are required. Our study describes a polymerase chain reaction (PCR) approach targeting algal 18S rDNA sequences of desoxyribonucleic acid (DNA) samples extracted either from unialgal eukaryotic microalgae culture, complex assemblages of microalgae populations or natural soil communities. Our first results showed that microalgae rDNA can be amplified by PCR from soil DNA samples. They also indicated difficulties extracting DNA from diatoms directly from soils, probably because of the presence of robust silicate valves. An 18S rDNA library has been established and preliminary phylogenetic analysis showed the feasibility of applying molecular methods to studying edaphic algae community structure. This is promising for soil algae ecology and for developing soil biological indicators.

We studied the 14C-tagged biochemical compartments such as proteins, lipids and polysaccharides from bacterial and fungal cultures supplied with 14C-pesticides and 14C-glucose. We showed that 14C incorporation depends both on the substrate structure and on the nature of the micro-organism. Both bacterial and fungal cells incorporated glucose 14C mainly into cell wall proteins. By contrast, glyphosate 14C was mainly incorporated into cytoplasm carbohydrates by fungi. On the other hand, 2,4-dichlorophenoxyacetic acid 14C was mainly found in the carbohydrate fractions of the bacteria walls.

*INRA, Laboratoire de science du sol Diffusion du document : INRA, Laboratoire de science du sol Diplôme : Dr. Ing.

The biodegradation of the fuel oil hydrocarbons contained in drilling cuttings was studied in soil microcosms during a 270-day experiment. Concentration and chemical composition of residual hydrocarbons were periodically monitored by quantitative capillary gas chromatography. The decrease in hydrocarbon concentration was logarithmic with time. At the end of the experiment, the fuel oil was 75% degraded. In the saturated fraction, normal and branched alkanes were almost totally eliminated in 16 days ; 22% of the cycloalkanes were not assimilated. The aromatic fraction was 71% degraded ; some polycyclic aromatics were persistent. The resin fraction (10% of the initial weight) was completely refractory to biodegradation. The inorganic part of drilling cuttings had no influence on the biodegradation rates of hydrocarbons. Biogenic hydrocarbons and traces of degradable fuel oil hydrocarbons were protected from microbial activity by the soil and cuttings matrix. Enumerations of total heterotrophic bacteria and hydrocarbon-utilizing bacteria showed a strong stimulation in both populations. Hydrocarbon-degrading strains of bacteria and fungi were isolated and identified at the generic or specific level.

* INRA Centre de Recherche d'Avignon, Unite Regionale de Documentation, Domaine St Paul, BP 91, 84143 Montfavet cedex Diffusion du document : INRA Centre de Recherche d'Avignon, Unite Regionale de Documentation, Domaine St Paul, BP 91, 84143 Montfavet cedex Diplôme : DEA

L’effet de paillages plastiques continus avec trois types de films (polyéthylène simple, éthylvinylacétate, polyéthylène alvéolé « Bulle ») sur l’échauffement du sol a été mesuré en serres et en plein air dans le Sud-Est de la France. Dans les meilleurs cas, on atteint en été des températures comparables à celles réalisées dans des pays subtropicaux où l’effet de ces techniques sur quelques agents pathogènes a été démontré. L’action sur la microflore et la nématofaune globales du paillage le plus performant a été analysée. Des modifications sensibles et durables des effectifs et une diminution de la diversité des genres et des espèces, variable selon les organismes considérés, ont été obtenues. Elles paraissent plus nettes dans les sols non soumis aux désinfections artificielles et peuvent représenter une forme de désinfection sélective des milieux de culture., The effect of three types of plastic - film mulching (plain polythene, ethylvinylacetate, polythene with air bubbles) on soil heating was measured in summer, outdoors and in glasshouses. The best mulching resulted in temperatures like those obtained in subtropical countries where the control of soil - borne pathogens has been demonstrated. The effect of the best mulching treatment on the soil microflora and nematofauna showed marked and lasting changes in the number and the diversity of genera and species, which appeared more clearly in soils previously not artificially disinfested. A selective type of soil disinfestation can be achieved.

Le diverse specie di microrganismi presenti nel suolo hanno ruoli prioritari nelle trasformazioni dell’energia e nei processi biogeochimici, intervenendo nella decomposizione del materiale organico attraverso processi biodegradativi e nel riciclo di elementi essenziali quali carbonio, fosforo, azoto ed altri; in tal modo portano a termine specifiche reazioni di ossido-riduzione che permettono agli elementi di rendersi così disponibili in forme utilizzabili soprattutto dalle piante (Alexander, 1977); ai microrganismi del suolo è deputata infatti la conservazione dei numerosi servizi ecosistemici che si svolgono nel suolo (Bunning e Jiménez, 2003). La Convenzione Internazionale sulla Biodiversità (CBD) descrive la biodiversità agricola come “le componenti della diversità biologica relative al cibo e all’agricoltura e tutte le componenti della diversità biologica che costituiscono gli ecosistemi agricoli, anche chiamati agroecosistemi. Le varietà e la variabilità degli animali, delle piante e dei microrganismi a livello genetico, di specie e di ecosistema, necessari a mantenere le funzioni chiave degli agroecosistemi, la loro struttura ed i loro processi”. La Strategia nazionale per la biodiversità (7 ottobre 2010, www.minambiente.it) pone tre obiettivi principali per la conservazione della biodiversità il primo dei quali è quello di massimizzare la salvaguardia e il recupero della biodiversità e dei servizi ecosistemici al fine di garantire il ruolo chiave per la vita sulla Terra e il benessere umano. Il secondo vuole favorire l'adattamento delle specie e degli ecosistemi naturali e semi-naturali ai cambiamenti climatici e adottare le opportune misure di mitigazione, mentre il terzo integrare la conservazione della biodiversità nelle politiche economiche e di settore. La conservazione dei microrganismi ex situ permette il mantenimento delle risorse genetiche microbiche del suolo sottoforma di ceppi distinti in coltura pura. Anche se la biodiversità dei microrganismi coltivabili rappresenta solo una piccolissima parte della realtà ambientale, essa risulta essere estremamente utile ed interessante per conservare e studiare ex situ organismi riconosciuti artefici di un determinato processo o azione. La conservazione in situ prevede lo studio e la conseguente valutazione della biodiversità microbica associata ad una determinata coltura o specie vegetale. È noto dalla letteratura che ogni specie vegetale rilascia nel suolo, in funzione anche delle caratteristiche pedoclimatiche ed ambientali, essudati radicali, che selezioneranno una determinata popolazione microbica (Pinton et al., 2001). Questo comporta che una conservazione del solo germoplasma vegetale ex situ, potrebbe non garantire il desiderato risultato di conservazione. Pertanto, nel caso della conservazione della biodiversità in funzione della fertilità del suolo e delle sue funzioni legate ai servizi ecosistemici da esso garantiti, questa va tutelata e garantita attraverso un approccio di ecosistemico pianta-suolomicrorganismo e l’attivazione di collezioni in situ. Sarà il monitoraggio in situ spazio temporale a garantire la salvaguardia della biodiversità microbica (Cardinali e Benedetti, in press)., Scientists now know that the complex processes carried out by the soil biota (including plant roots) have significant effects on the health of ecosystems, the quality of soils, the incidence of soilborne plant and animal pests and diseases and, consequently, on the quality and yields of crops. The ecosystem services provided by soil organisms that may influence agricultural productivity include the decomposition and cycling of organic matter, the regulation of nutrients availability and uptake, the suppression of pests and diseases, the maintenance of soil structure and the regulation of soil hydrological processes, gas exchanges and carbon sequestration, soil detoxification, plant growth control, and pollination of horticultural crops (Bunning and Jimenez, 2003). Biological diversity is defined by the Convention on International Biodiversity (CBD) as “the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems”. The national strategy for biodiversity (7th October 2010, www.minambiente.it) sets three main objectives for biodiversity conservation, the first one deals with protecting and recovering biodiversity and ecosystem services in order to provide life on Earth and human health. The second one aims to promote species and natural and semi-natural ecosystem adaptability to climate change, whereas the third one deals with including biodiversity conservation in current policies. Ex-situ conservation means the conservation of microbial genetic resources outside their natural habitats in pure cultures. Although culturable microbial diversity represents only a small fraction of total microbial diversity (Lynch et al., 2004), it’s extremely important for studying microrganisms responsible of certain processes and functions. In-situ conservation means the conservation of ecosystems and natural habitats and the maintenance and recovery of viable populations of microbial species in their natural surroundings associated with domesticated or cultivated species. Each specie releases in soil different plant root exudates depending on pedoclimatic and environmental conditions, resulting in the selection of certain microbial taxa (Pinton et al., 2001). This means that ex situ conservation alone could not always guarantee biodiversity conservation. Therefore, microbial biodiversity associated with soil biological fertility and ecosystem services provided by the soil biota should be preserved through an ecosystem plant-soil-microrganism-based approach.

International audience; Population dynamics and food preferences of the testate amoeba species complex Nebela tincta major-bohemica-collaris (“Nebela collaris sensu lato”) were described from a Sphagnum peatland over one growing season. The average abundance of Nebela collaris sensu lato was 29582 ind. l-1 active, and 2263 ind. l-1 encysted forms. On average, 17.4% of Nebela collaris sensu lato specimens were observed associated with prey, 71% of which could not be identified because of their poor preservation state. Among the identified prey, those most frequently ingested were micro-algae (45% of the total predator-prey associations, especially diatoms: 33%), and spores and mycelia of fungi (36%). Large ciliates, rotifers and small testate amoebae were also ingested, but mainly in summer. The seasonal variations in the proportions of prey categories in the ecosystem and the percentage of identifiable prey lead us to hypothesise that (1) Nebela collaris sensu lato ingest mainly immobile, senescent or dead organisms, and (2) that the more mobile micro-organisms such as ciliates and micro-Metazoa become more accessible, in relatively dry conditions, when the water film is thin

Les effets du travail du sol sur le transfert des pesticides sont complexes : de multiples processus sont impliqués, avec des effets contradictoires. Des travaux récents montrent que l’augmentation de l’activité microbienne à la surface d’un sol en non-labour ne réduit pas systématiquement les risques de transfert de pesticides