Laetitia Bernard

Laetitia Bernard
Institute of Research for Development | IRD · 210 - Functional Ecology and Biochemistry of Soils and Agroecosystems (Eco&Sols)

PhD

About

68
Publications
25,601
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
3,103
Citations
Introduction
My works are focused on microbial mechanisms generating priming effect in Phosphorus-depleted tropical soils. I am trying to identify the main actors implied and their drivers. I would like to understand how to control the priming effect in tropical agricultural soils in order to liberate nutrients in function of crops demand and restore the stocks. This could lead to propose some innovative agricultural practices based on organic matter and macrofaunal populations management.
Additional affiliations
October 2007 - present
Institute of Research for Development
Position
  • Researcher
Description
  • I am working on microbial diversity and organisms interactions implied in organic matter decomposition and mineralization processes.
October 2004 - July 2006
French National Institute for Agriculture, Food, and Environment (INRAE)
Position
  • PostDoc Position
Description
  • Dynamique et caractérisation des populations microbiennes du sol, impliquées dans le cycle du carbone : approche par DNA et RNA-SIP.
November 2001 - October 2003
Commissariat à l'Energie atomique
Position
  • PostDoc Position
Description
  • Optimisation par génie génétique de la photobioproduction d’hydrogène chez l'algue verte unicellulaire Chlamydomonas reinhardtii.

Publications

Publications (68)
Article
Full-text available
Priming effect (PE) is defined as a stimulation of the mineralization of soil organic matter (SOM) following a supply of fresh organic matter. This process can have important consequences on the fate of SOM and on the management of residues in agricultural soils, especially in tropical regions where soil fertility is essentially based on the manage...
Article
Full-text available
Phosphorus (P) scarcity and the need for ecologically sound intensification of agroecosystems are major challenges we face. To improve nutrient efficiency in agriculture, especially for P, multispecies crop stands may outperform their monospecific counterparts, especially under low input conditions. There is increasing evidence that biomass, grain...
Article
Full-text available
This work is the first report on the use of DNA-, RNA-SIP approaches to elucidate the dynamics and the diversity of bacterial populations actively assimilating C derived from plant residues labelled at more than 90% (13)C. Wheat-residues, were incorporated and incubated into soil microcosms for 28 days. At the end of the incubation time, no more th...
Article
Full-text available
Les sols hébergent une importante biodiversité. Ils sont essentiels pour nourrir l'humanité et jouent un rôle fondamental dans les cycles biogéochimiques de la planète. Alors qu'à l'échelle du globe, un tiers des sols sont dégradés, comprendre les processus écologiques qui s'y déroulent pour mieux les préserver et les restaurer est un enjeu majeur....
Article
Full-text available
Bacterial-feeding nematodes are abundant soil animals regulating microbial communities and enhancing plant nutrition and growth. However, the biological metrics driving the variable within-trophic group effects of these organisms on soil and plant functions are not yet identified. In this study, we determined the effects of eight bacterial-feeding...
Article
Full-text available
Le « priming effect » (PE) est un mécanisme clé contribuant au bilan de carbone de l'écosystème sol. Depuis sa découverte en 1926, près de 100 ans de recherche ont conduit à un riche corpus de publications scientifiques pour identifier les déterminants et les mécanismes impliqués. Quelques articles de synthèse ont résumé les connaissances acquises,...
Article
The priming effect (PE) is a key mechanism contributing to the carbon balance of the soil ecosystem. Almost 100 years of research since its discovery in 1926 have led to a rich body of scientific publications to identify the drivers and mechanisms involved. A few review articles have summarised the acquired knowledge; the last major one was publish...
Article
A positive Priming Effect (PE) is defined as an acceleration of the decomposition of soil organic matter (SOM) by a fresh organic matter (FOM) input. But in the literature many studies present this phenomenon as an extra loss of carbon from SOM to the atmosphere. SOM is actually a mixture of pools with different turnover rates, and microorganisms g...
Article
Full-text available
Free-living nematodes have beneficial effects on plant growth and nutrition. Exploring how agricultural practices modulate these beneficial effects is still challenging. A study was conducted in Ferralsols from Madagascar from one unmanaged grassland and 16 upland rainfed rice fields, representative of different agricultural practices: rotation, ag...
Chapter
Full-text available
With the development of agroecology, soil plays a particularly important role in the design of sustainable agricultural practices. The soils are the place of many processes operated by living organisms interacting with one another. Soil biodiversity performs various processes which determine the main aggregated functions and finally agrosystem serv...
Article
Full-text available
The effects of earthworm inoculation and cropping systems on upland rice systems were examined over a four-year period in the Highlands of Madagascar. Each year, endogeic earthworms Pontoscolex corethrurus (Rhinodrilidae) were inoculated (EW+) at a density of 75 ind m−2 or were not inoculated (EW0). Inoculation was tested in three cropping systems:...
Article
Revealing belowground-aboveground relationships (BAR) is essential to drive ecological processes to address agriculture dysfunctions, especially in the management of aboveground plant diseases. Earthworms are one of the most important soil organisms involved in BAR, and silicon (Si) has been identified as a crucial element regulating aboveground pl...
Article
Full-text available
Aims: In Madagascar, agroecological practices to increase and sustain upland rice productivity are based on an intensification of soil ecological processes. Study Design: The effects of earthworm presence and identity (Pontoscolex corethrurus, Dichogaster saliens, or no earthworms), residue presence and identity [Crotalaria grahamiana (Fabaceae), D...
Article
En 2017-2018, en Guyane française, la réserve naturelle des Nouragues a collaboré avec l'équipe du projet LongTIme (Labex CEBA) pour favoriser le partage des recherches en cours auprès des habitants du territoire. Suivi de missions, échanges avec les chercheurs, organisation de rencontres, création d'outils pédagogiques et réalisation d'un document...
Article
L'année 2015 a été déclarée Année Internationale des Sols par les Nations Unies. A cette occasion, un événement de sensibilisation du grand public et du jeune public, à la connaissance des sols, a eu lieu à Madagascar du 8 au 19 décembre 2015. Cette opération a été co-organisée par l'IRD (UMR Eco&Sols) et le LRI (laboratoire des RadioIsotopes de l'...
Article
Soil bacterivorous nematodes are key plant mutualists that increase nutrient availability for plants either by enhancing the mineralization of organic compounds (the “mineralization pathway”) or by increasing plant lateral root branching following shifts in internal plant metabolism, and subsequently leading to a higher volume of soil prospected by...
Article
L’agriculture climato-intelligente (Climate Smart Agriculture) vise à lutter contre le changement climatique et à s’y adapter tout en combattant l’insécurité alimentaire. À Madagascar, différentes pratiques agricoles ont été testées depuis une vingtaine d’années par des organisations non gouvernementales et des institutions de recherche afin d’accr...
Article
Full-text available
Soil bacterivorous nematodes are key plant mutualists that increase nutrient availability for plants either by enhancing the mineralization of organic compounds (the "mineralization pathway") or by increasing plant lateral root branching following shifts in internal plant metabolism, and subsequently leading to a higher volume of soil prospected by...
Article
Full-text available
In soil, the link between microbial diversity and carbon transformations is challenged by the concept of functional redundancy. Here, we hypothesized that functional redundancy may decrease with increasing carbon source recalcitrance, and that coupling of diversity with C-cycling may change accordingly. We manipulated microbial diversity to examine...
Article
Full-text available
The priming effect (PE) in soil, when induced by a fresh carbon supply, is believed to result from two different mechanisms, "stoichiometric decomposition" and "nutrient mining", and contributes to either long-term SOM stabilization or depletion. Understanding how to affect the balance between both mechanisms can provide valuable insight into agroe...
Article
Climate smart agriculture is presented as a solution to alleviate food insecurity, mitigate climate change and contribute to climate change adaptation. In Madagascar, different sustainable agricultural practices were implemented in the last 20 years by many non-governmental organizations in order to increase crop yields, maintain soil fertility and...
Article
Full-text available
The priming effect in soil is proposed to be generated by two distinct mechanisms: ‘stoichiometric decomposition’ and/or ‘nutrient mining’ theories. Each mechanism has its own dynamics, involves its own microbial actors, and targets different soil organic matter (SOM) pools. The present study aims to evaluate how climatic parameters drive the inten...
Article
We assessed the impact of intercropping on the microbial communities in the rhizosphere of wheat (Triticum turgidum L. ssp durum) and pea (Pisum sativum L.). Using a RNA based approach coupled with bacterial phylum specific real time PCR, we found that the active bacterial communities in the wheat-pea association were distinct from those in the rhi...
Article
Full-text available
Background and aims Positive below-ground interactions (facilitation) should be more pronounced when resources limit crop growth, according to the stress-gradient hypothesis. Our aim was to test this hypothesis for intercropped durum wheat and faba bean along a P-fertilizer gradient. Methods A field experiment was conducted in a long-term P-fertili...
Poster
Full-text available
This poster relate how microbial (bacterial an fungal) diversity is implicated in priming effect mechanisms along two different climate gradients, allowing to discriminate annual temperature from rainfall effect, in Malagasy Highlands.
Article
Full-text available
Dispersion of bacterivorous nematodes in soil is a crucial ecological process that permits settlement and exploitation of new bacterial-rich patches. Although plant roots, by modifying soil structure, are likely to influence this process, they have so far been neglected. In this study, using an original three-compartment microcosm experimental desi...
Article
Full-text available
Microbes are phylogenetically (Archaea, Bacteria, Eukarya, and viruses) and functionally diverse. They colonize highly varied environments and rapidly respond to and evolve as a response to local and global environmental changes, including those induced by pollutants resulting from human activities. This review exemplifies the Microbial Ecology EC2...
Article
Full-text available
An optimized method, based on the coupling of two commercial kits, is described for the extraction of soil nucleic acids, with simultaneous extraction and purification of DNA and RNA following a cascade scheme and avoiding the use of harmful solvents. The protocol canmonitor the variations in the recovery yield of DNA and RNA from soils of various...
Conference Paper
Climate smart agriculture is presented recently as a solution for food security and climate change impacts. In Madagascar, different sustainable agricultural practices were implemented in the next 20 years by many NGOs in order to increase crop yield, to maintain soil fertility and to increase household income. These practices are conservation agri...
Article
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 hav...
Article
Full-text available
Background and aims Intercropping of legumes and cereals appears as an alternative agricultural practice to decrease the use of chemical fertilizers while maintaining high yields. A better understanding of the biotic and abiotic factors determining interactions between plants in such associations is required. Our study aimed to analyse the effect o...
Technical Report
Full-text available
Au cours des dernières décennies, l’utilisation d’intrants a permis d’augmenter significativement la productivité des agro-écosystèmes, mais dans le cas de l’azote (N) et du phosphore (P), cette augmentation s’est accompagnée d’une diminution significative de l’efficience de N et P. Cela est en partie lié à des pertes de N et P conduisant à des imp...
Article
Full-text available
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 hav...
Conference Paper
Background and aims: In legume- based intercrops, nitrogen is supposed to be transferred from the legume to the companion crop. However, nitrogen transfer in annual intercrops remains difficult to assess and poorly documented. We aimed to quantify bi-directional transfer between durum wheat and field pea using 15N labeling methods. Method: In a fir...
Poster
Full-text available
In Conservation Agriculture (CA) (FAO, http://www.fao.org/ag/ca/fr/), reduction or cessation of mechanical disturbance of soil and the presence of mulches of plants living or dead (plant residues) at its surface leads to profound changes in the functioning of the agro-ecosystem. These farming systems are potentially very interesting to increase soi...
Article
The objective of this laboratory study was to determine the influence of a tropical endogeic earthworm, Pontoscolex corethrurus, on CO2 and N2O fluxes from a tropical Ferralsol and microorganisms potentially involved in these gases emissions. CO2 and N2O fluxes were measured during 35 days from soil mesocosms with and without earthworms. At the end...
Article
Full-text available
A soil microcosm experiment was conducted to evaluate the influence of copper contamination on the dynamics and diversity of bacterial communities actively involved in wheat residue decomposition. In the presence of copper, a higher level of CO2 release was observed, which did not arise from greater wheat decomposition but from a higher level of st...
Article
Type II NADH dehydrogenases (NDH-2) are monomeric flavoenzymes catalyzing electron transfer from NADH to quinones. While most NDH-2 preferentially oxidize NADH, some of these enzymes have been reported to efficiently oxidize NADPH. With the aim to modify the NADPH vs NADH specificity of the relatively NADH specific Agrobacterium tumefaciens NDH-2,...
Article
Full-text available
his work is the first report on the use of DNA-, RNA- SIP approaches to elucidate the dynamics and the diversity of bacterial populations actively assimilating C derived from plant residues labelled at more than 90% 13C. Wheat-residues, were incorporated and incu- bated into soil microcosms for 28 days. At the end of the incubation time, no more th...
Article
Type II NADH dehydrogenases (NDH-2) are monomeric enzymes that catalyse quinone reduction and allow electrons to enter the respiratory chain in different organisms including higher plant mitochondria, bacteria and yeasts. In this study, an Agrobacterium tumefaciens gene encoding a putative alternative NADH dehydrogenase (AtuNDH-2) was isolated and...
Article
We have now determined the complete gene sequence of the cyclohexanol (chn) degradation pathway in Acinetobacter sp. NCIMb 9871 as well as the putative genes for the beta-oxidation of adipic acid to acetyl-CoA and succinyl-CoA. In addition, a new insertion sequence, potentially useful in strain characterization, was identified. Knowledge of the nuc...
Article
Full-text available
In the cyanobacterium Synechocystis PCC 6803 and in the microalga Chlamydomonas reinhardtii, transient hydrogen photo-production is observed when cells are exposed to light in anoxia. We measured changes in H2, O2, and CO2 concentrations using time-resolved mass spectrometry in wild-type and mutant strains of Chlamydomonas and Synechocystis. In bot...
Article
Full-text available
Bacterial diversity and activity were simultaneously investigated by microbial ecological and molecular biological methods along an estuarine gradient from the Rhone River to the Mediterranean Sea. Following a Lagrangian strategy, we sampled plume, frontal and marine layers. The sampled estuarine gradient exhibited large changes both in physico-che...
Article
Discrimination among viable, active, and inactive cells in aquatic ecosystems is of great importance to understand which species participate in microbial processes. In this study, a new approach combining flow cytometry (FCM), cell sorting, and molecular analyses was developed to compare the diversity of viable cells determined by different methods...
Article
Background Discrimination among viable, active, and inactive cells in aquatic ecosystems is of great importance to understand which species participate in microbial processes. In this study, a new approach combining flow cytometry (FCM), cell sorting, and molecular analyses was developed to compare the diversity of viable cells determined by differ...
Article
A mesocosm experiment was performed to study the influence of nutrients on activity and diversity of bacterial assemblages from the Mediterranean Sea. Changes in the diversity of the predominant bacterial populations were monitored by DGGE fingerprinting of PCR products derived from 16S rRNA encoding genes. Fluctuations in the diversity of the most...
Article
Quantitative and qualitative changes in bacterial communities from the Mediterranean Sea were compared in duplicate batch mesocosms with or without addition of inorganic nutrients. Methods including traditional microbial ecology techniques, molecular biology and flow cytometry were combined to determine abundances, production, cell size, activity,...
Article
Full-text available
The genetic diversity of marine bacteria from coastal Mediterranean water was analyzed using denaturing gradient gel electrophoresis (DGGE) and comparative sequence analysis of PCR-amplified 16S rRNA genes. The diversity of the whole bacterial assemblage was compared to the diversity of the fraction of actively respiring bacterial cells and of cult...
Article
Full-text available
The study of relationships between cell size and productivity is of key importance in microbial ecology to understand which members of natural aquatic communities are responsible for the overall activity and/or productivity. Flow sorting of microorganisms from different environmental samples was used to analyze the activity of bacterial cells depen...
Article
Quantitative and qualitative changes in bacterial communities from the Mediterranean Sea were analysed under eutrophication conditions simulated in batch mesocosms (addition of inorganic nutrients or phytoplanktonic lysate). A wide variety of methods including traditional microbial ecology techniques, molecular biology and flow cytometry were combi...
Article
The CSE dye (Chemunex, Maisons-Alfort, France) was combined with an activity marker to improve bacterial activity assessment in natural waters. Its effectiveness to counterstain dead cells with permeabilised membranes was investigated on live and dead cells of a variety of strains from collections or isolated from the natural environment. Cells wer...
Article
The CSE dye (Chemunex, Maisons-Alfort, France) was combined with an activity marker to improve bacterial activity assessment in natural waters. Its effectiveness to counterstain dead cells with permeabilised membranes was investigated on live and dead cells of a variety of strains from collections or isolated from the natural environment. Cells wer...
Article
Full-text available
Analysis of PCR products of 16S rDNA of 680 isolates from Mediterranean Sea mesocosm experiments with taxon-specific 16S rDNA oligonucleotides revealed that 262 isolates belonged to the alpha subclass of the class Proteobacteria. Partial 16S rDNA sequence analysis of selected isolates and oligonucleotide probing with a Sulfitobacter-specific 16S rD...
Article
Small subunit rDNA clone libraries were generated from amplified DNA of bacterioplankton taken at different time points from a mesocosm containing eutrophied Mediterranean seawater and made eutrophic by the addition of N and P. Analysis of 96 partial sequences indicated that 22% of the clones formed four clusters which showed the highest sequence s...
Article
For the practical training on the concepts and methods of studying marine biodiversity, going from the gene to the ecosystem level, held in the Observatoire océanologique of Banyuls-sur-Mer (1998), participants were invited to compare three different methods that are commonly used to assess the genetic and physiological diversity of bacterial popul...
Article
Flow cytometry is more used in microbial ecology to provide accurate counts of bacteria and phytoplankton, for biomass assessment, to investigate the heterogeneity of natural communities and for diversity assessment. Non-pigmented organisms can be detected after staining with fluorescent probes. Physiological and taxonomic probes can be used to det...