The Experts below are selected from a list of 99 Experts worldwide ranked by ideXlab platform

Laurent Philippot - One of the best experts on this subject based on the ideXlab platform.

  • Plant traits related to nitrogen uptake influence plant-microbe competition
    Ecology, 2015
    Co-Authors: Delphine Moreau, Laurent Philippot, David Bru, Barbara Pivato, Hugues Busset, Florence Deau, Céline Faivre, Annick Matejicek, Florence Strbik, Christophe Mougel
    Abstract:

    Plant species are important drivers of soil microbial communities. However, how plant functional traits are shaping these communities has received less attention though linking plant and microbial traits is crucial for better understanding plant-microbe interactions. Our objective was to determine how plant-microbe interactions were affected by plant traits. Specifically we analyzed how interactions between plant species and microbes involved in nitrogen cycling were affected by plant traits related to nitrogen nutrition in interaction with soil nitrogen availability. Eleven plant species, selected along an oligotrophic-nitrophilic gradient, were grown individually in a nitrogen-poor soil with two levels of Nitrate availability. Plant traits for both carbon and nitrogen nutrition were measured and the genetic structure and abundance of rhizosphere microbial communities, in particular the ammonia oxidizer and Nitrate Reducer guilds, were analyzed. The structure of the bacterial community in the rhizosphere differed significantly between plant species and these differences depended on nitrogen availability. The results suggest that the rate of nitrogen uptake per unit of root biomass and per day is a key plant trait, explaining why the effect of nitrogen availability on the structure of the bacterial community depends on the plant species. We also showed that the abundance of Nitrate reducing bacteria always decreased with increasing nitrogen uptake per unit of root biomass per day, indicating that there was competition for Nitrate between plants and Nitrate reducing bacteria. This study demonstrates that Nitrate-reducing microorganisms may be adversely affected by plants with a high nitrogen uptake rate. Our work puts forward the role of traits related to nitrogen in plant-microbe interactions, whereas carbon is commonly considered as the main driver. It also suggests that plant traits related to ecophysiological processes, such as nitrogen uptake rates, are more relevant for understanding plant-microbe interactions than composite traits, such as nitrophily, which are related to a number of ecophysiological processes.

  • Role of plant residues in determining temporal patterns of the activity, size, and structure of Nitrate Reducer communities in soil.
    Applied and environmental microbiology, 2010
    Co-Authors: D. Chèneby, Lionel Ranjard, David Bru, Noémie Pascault, Pierre-alain Maron, Laurent Philippot
    Abstract:

    The incorporation of plant residues into soil not only represents an opportunity to limit soil organic matter depletion resulting from cultivation but also provides a valuable source of nutrients such as nitrogen. However, the consequences of plant residue addition on soil microbial communities involved in biochemical cycles other than the carbon cycle are poorly understood. In this study, we investigated the responses of one N-cycling microbial community, the Nitrate Reducers, to wheat, rape, and alfalfa residues for 11 months after incorporation into soil in a field experiment. A 20- to 27-fold increase in potential Nitrate reduction activity was observed for residue-amended plots compared to the nonamended plots during the first week. This stimulating effect of residues on the activity of the Nitrate-reducing community rapidly decreased but remained significant over 11 months. During this period, our results suggest that the potential Nitrate reduction activity was regulated by both carbon availability and temperature. The presence of residues also had a significant effect on the abundance of Nitrate Reducers estimated by quantitative PCR of the narG and napA genes, encoding the membrane-bound and periplasmic Nitrate reductases, respectively. In contrast, the incorporation of the plant residues into soil had little impact on the structure of the narG and napA Nitrate-reducing community determined by PCR-restriction fragment length polymorphism (RFLP) fingerprinting. Overall, our results revealed that the addition of plant residues can lead to important long-term changes in the activity and size of a microbial community involved in N cycling but with limited effects of the type of plant residue itself.

  • Response of total and Nitrate-dissimilating bacteria to reduced N deposition in a spruce forest soil profile
    FEMS Microbiology Ecology, 2009
    Co-Authors: Ellen Kandeler, Thomas Brune, Esther Enowashu, Nicole Dörr, Georg Guggenberger, Norbert Lamersdorf, Laurent Philippot
    Abstract:

    A field-scale manipulation experiment conducted for 16 years in a Norway spruce forest at Solling, Central Germany, was used to follow the long-term response of total soil bacteria, Nitrate Reducers and denitrifiers under conditions of reduced N deposition. N was experimentally removed from throughfall by a roof construction ('clean rain plot'). We used substrate-induced respiration (SIR) to characterize the active fraction of soil microbial biomass and potential Nitrate reduction to quantify the activity of Nitrate Reducers. The abundance of total bacteria, Nitrate Reducers and denitrifiers in different soil layers was analysed by quantitative PCR of 16S rRNA gene, Nitrate reduction and denitrification genes. Reduced N deposition temporarily affected the active fraction of the total microbial community (SIR) as well as Nitrate reductase activity. However, the size of the total, Nitrate Reducer and denitrifier communities did not respond to reduced N deposition. Soil depth and sampling date had a greater influence on the density and activity of soil microorganisms than reduced deposition. An increase in the nosZ/16S rRNA gene and nosZ/nirK ratios with soil depth suggests that the proportion of denitrifiers capable of reducing N2O into N2 is larger in the mineral soil layer than in the organic layer.

  • Effect of primary mild stresses on resilience and resistance of the Nitrate Reducer community to a subsequent severe stress
    FEMS microbiology letters, 2008
    Co-Authors: Laurent Philippot, D. Chèneby, Mickael Cregut, Fabrice Martin-laurent, Lionel Ranjard, Mélanie Bressan, Stéphane Dequiet, Philippe Lemanceau
    Abstract:

    The factors regulating soil microbial stability (e.g. resistance and resilience) are poorly understood, even though microorganisms are essential for ecosystem functioning. In this study, we tested whether a functional microbial community subjected to different primary mild stresses was equally resistant or resilient to a subsequent severe stress. The Nitrate Reducers were selected as model community and analysed in terms of Nitrate reduction rates and genetic structure by narG PCR-restriction fragment length polymorphism fingerprinting. Heat, copper and atrazine were used as primary stresses and mercury at a high concentration as a severe stress. None of the primary stresses had any significant impact on the Nitrate Reducer community. Although primary stress with heat, copper or atrazine had no effect on the resilience of the Nitrate Reducer activity to mercury stress, pre-exposure to copper, another heavy metal, resulted in increased resilience. In contrast, the resistance of both structure and activity of the Nitrate Reducer community to severe mercury stress was not affected by any of the primary stresses tested. Our experiment suggests that the hypothetical effect of an initial stress on the response of a microbial community to an additional stress is complex and may depend on the relatedness of the two consecutive stresses and the development of positive cotolerance.

  • Disentangling the rhizosphere effect on Nitrate Reducers and denitrifiers: insight into the role of root exudates
    Environmental microbiology, 2008
    Co-Authors: Sonia Henry, D. Chèneby, S. Texier, S. Hallet, David Bru, Christophe Dambreville, F. Bizouard, J. C. Germon, Laurent Philippot
    Abstract:

    To determine to which extent root-derived carbon contributes to the effects of plants on Nitrate Reducers and denitrifiers, four solutions containing different proportions of sugar, organic acids and amino acids mimicking maize root exudates were added daily to soil microcosms at a concentration of 150 microg C g(-1) of soil. Water-amended soils were used as controls. After 1 month, the size and structure of the Nitrate Reducer and denitrifier communities were analysed using the narG and napA, and the nirK, nirS and nosZ genes as molecular markers respectively. Addition of artificial root exudates (ARE) did not strongly affect the structure or the density of Nitrate Reducer and denitrifier communities whereas potential Nitrate reductase and denitrification activities were stimulated by the addition of root exudates. An effect of ARE composition was also observed on N(2)O production with an N(2)O:(N(2)O + N(2)) ratio of 0.3 in microcosms amended with ARE containing 80% of sugar and of 1 in microcosms amended with ARE containing 40% of sugar. Our study indicated that ARE stimulated Nitrate reduction or denitrification activity with increases in the range of those observed with the whole plant. Furthermore, we demonstrated that the composition of the ARE affected the nature of the end-product of denitrification and could thus have a putative impact on greenhouse gas emissions.

D. Chèneby - One of the best experts on this subject based on the ideXlab platform.

  • Role of plant residues in determining temporal patterns of the activity, size, and structure of Nitrate Reducer communities in soil.
    Applied and environmental microbiology, 2010
    Co-Authors: D. Chèneby, Lionel Ranjard, David Bru, Noémie Pascault, Pierre-alain Maron, Laurent Philippot
    Abstract:

    The incorporation of plant residues into soil not only represents an opportunity to limit soil organic matter depletion resulting from cultivation but also provides a valuable source of nutrients such as nitrogen. However, the consequences of plant residue addition on soil microbial communities involved in biochemical cycles other than the carbon cycle are poorly understood. In this study, we investigated the responses of one N-cycling microbial community, the Nitrate Reducers, to wheat, rape, and alfalfa residues for 11 months after incorporation into soil in a field experiment. A 20- to 27-fold increase in potential Nitrate reduction activity was observed for residue-amended plots compared to the nonamended plots during the first week. This stimulating effect of residues on the activity of the Nitrate-reducing community rapidly decreased but remained significant over 11 months. During this period, our results suggest that the potential Nitrate reduction activity was regulated by both carbon availability and temperature. The presence of residues also had a significant effect on the abundance of Nitrate Reducers estimated by quantitative PCR of the narG and napA genes, encoding the membrane-bound and periplasmic Nitrate reductases, respectively. In contrast, the incorporation of the plant residues into soil had little impact on the structure of the narG and napA Nitrate-reducing community determined by PCR-restriction fragment length polymorphism (RFLP) fingerprinting. Overall, our results revealed that the addition of plant residues can lead to important long-term changes in the activity and size of a microbial community involved in N cycling but with limited effects of the type of plant residue itself.

  • Differential Responses of Nitrate Reducer Community Size, Structure, and Activity to Tillage Systems
    Applied and Environmental Microbiology, 2009
    Co-Authors: D. Chèneby, A. Brauman, B. Rabary, L. Philippot
    Abstract:

    The main objective of this study was to determine how the size, structure, and activity of the Nitrate Reducer community were affected by adoption of a conservative tillage system as an alternative to conventional tillage. The experimental field, established in Madagascar in 1991, consists of plots subjected to conventional tillage or direct-seeding mulch-based cropping systems (DM), both amended with three different fertilization regimes. Comparisons of size, structure, and activity of the Nitrate Reducer community in samples collected from the top layer in 2005 and 2006 revealed that all characteristics of this functional community were affected by the tillage system, with increased Nitrate reduction activity and numbers of Nitrate Reducers under DM. Nitrate reduction activity was also stimulated by combined organic and mineral fertilization but not by organic fertilization alone. In contrast, both negative and positive effects of combined organic and mineral fertilization on the size of the Nitrate Reducer community were observed. The size of the Nitrate Reducer community was a significant predictor of the Nitrate reduction rates except in one treatment, which highlighted the inherent complexities in understanding the relationships the between size, diversity, and structure of functional microbial communities along environmental gradients.

  • Effect of primary mild stresses on resilience and resistance of the Nitrate Reducer community to a subsequent severe stress
    FEMS microbiology letters, 2008
    Co-Authors: Laurent Philippot, D. Chèneby, Mickael Cregut, Fabrice Martin-laurent, Lionel Ranjard, Mélanie Bressan, Stéphane Dequiet, Philippe Lemanceau
    Abstract:

    The factors regulating soil microbial stability (e.g. resistance and resilience) are poorly understood, even though microorganisms are essential for ecosystem functioning. In this study, we tested whether a functional microbial community subjected to different primary mild stresses was equally resistant or resilient to a subsequent severe stress. The Nitrate Reducers were selected as model community and analysed in terms of Nitrate reduction rates and genetic structure by narG PCR-restriction fragment length polymorphism fingerprinting. Heat, copper and atrazine were used as primary stresses and mercury at a high concentration as a severe stress. None of the primary stresses had any significant impact on the Nitrate Reducer community. Although primary stress with heat, copper or atrazine had no effect on the resilience of the Nitrate Reducer activity to mercury stress, pre-exposure to copper, another heavy metal, resulted in increased resilience. In contrast, the resistance of both structure and activity of the Nitrate Reducer community to severe mercury stress was not affected by any of the primary stresses tested. Our experiment suggests that the hypothetical effect of an initial stress on the response of a microbial community to an additional stress is complex and may depend on the relatedness of the two consecutive stresses and the development of positive cotolerance.

  • Disentangling the rhizosphere effect on Nitrate Reducers and denitrifiers: insight into the role of root exudates
    Environmental microbiology, 2008
    Co-Authors: Sonia Henry, D. Chèneby, S. Texier, S. Hallet, David Bru, Christophe Dambreville, F. Bizouard, J. C. Germon, Laurent Philippot
    Abstract:

    To determine to which extent root-derived carbon contributes to the effects of plants on Nitrate Reducers and denitrifiers, four solutions containing different proportions of sugar, organic acids and amino acids mimicking maize root exudates were added daily to soil microcosms at a concentration of 150 microg C g(-1) of soil. Water-amended soils were used as controls. After 1 month, the size and structure of the Nitrate Reducer and denitrifier communities were analysed using the narG and napA, and the nirK, nirS and nosZ genes as molecular markers respectively. Addition of artificial root exudates (ARE) did not strongly affect the structure or the density of Nitrate Reducer and denitrifier communities whereas potential Nitrate reductase and denitrification activities were stimulated by the addition of root exudates. An effect of ARE composition was also observed on N(2)O production with an N(2)O:(N(2)O + N(2)) ratio of 0.3 in microcosms amended with ARE containing 80% of sugar and of 1 in microcosms amended with ARE containing 40% of sugar. Our study indicated that ARE stimulated Nitrate reduction or denitrification activity with increases in the range of those observed with the whole plant. Furthermore, we demonstrated that the composition of the ARE affected the nature of the end-product of denitrification and could thus have a putative impact on greenhouse gas emissions.

L. Philippot - One of the best experts on this subject based on the ideXlab platform.

  • Differential Responses of Nitrate Reducer Community Size, Structure, and Activity to Tillage Systems
    Applied and Environmental Microbiology, 2009
    Co-Authors: D. Chèneby, A. Brauman, B. Rabary, L. Philippot
    Abstract:

    The main objective of this study was to determine how the size, structure, and activity of the Nitrate Reducer community were affected by adoption of a conservative tillage system as an alternative to conventional tillage. The experimental field, established in Madagascar in 1991, consists of plots subjected to conventional tillage or direct-seeding mulch-based cropping systems (DM), both amended with three different fertilization regimes. Comparisons of size, structure, and activity of the Nitrate Reducer community in samples collected from the top layer in 2005 and 2006 revealed that all characteristics of this functional community were affected by the tillage system, with increased Nitrate reduction activity and numbers of Nitrate Reducers under DM. Nitrate reduction activity was also stimulated by combined organic and mineral fertilization but not by organic fertilization alone. In contrast, both negative and positive effects of combined organic and mineral fertilization on the size of the Nitrate Reducer community were observed. The size of the Nitrate Reducer community was a significant predictor of the Nitrate reduction rates except in one treatment, which highlighted the inherent complexities in understanding the relationships the between size, diversity, and structure of functional microbial communities along environmental gradients.

David Bru - One of the best experts on this subject based on the ideXlab platform.

  • Plant traits related to nitrogen uptake influence plant-microbe competition
    Ecology, 2015
    Co-Authors: Delphine Moreau, Laurent Philippot, David Bru, Barbara Pivato, Hugues Busset, Florence Deau, Céline Faivre, Annick Matejicek, Florence Strbik, Christophe Mougel
    Abstract:

    Plant species are important drivers of soil microbial communities. However, how plant functional traits are shaping these communities has received less attention though linking plant and microbial traits is crucial for better understanding plant-microbe interactions. Our objective was to determine how plant-microbe interactions were affected by plant traits. Specifically we analyzed how interactions between plant species and microbes involved in nitrogen cycling were affected by plant traits related to nitrogen nutrition in interaction with soil nitrogen availability. Eleven plant species, selected along an oligotrophic-nitrophilic gradient, were grown individually in a nitrogen-poor soil with two levels of Nitrate availability. Plant traits for both carbon and nitrogen nutrition were measured and the genetic structure and abundance of rhizosphere microbial communities, in particular the ammonia oxidizer and Nitrate Reducer guilds, were analyzed. The structure of the bacterial community in the rhizosphere differed significantly between plant species and these differences depended on nitrogen availability. The results suggest that the rate of nitrogen uptake per unit of root biomass and per day is a key plant trait, explaining why the effect of nitrogen availability on the structure of the bacterial community depends on the plant species. We also showed that the abundance of Nitrate reducing bacteria always decreased with increasing nitrogen uptake per unit of root biomass per day, indicating that there was competition for Nitrate between plants and Nitrate reducing bacteria. This study demonstrates that Nitrate-reducing microorganisms may be adversely affected by plants with a high nitrogen uptake rate. Our work puts forward the role of traits related to nitrogen in plant-microbe interactions, whereas carbon is commonly considered as the main driver. It also suggests that plant traits related to ecophysiological processes, such as nitrogen uptake rates, are more relevant for understanding plant-microbe interactions than composite traits, such as nitrophily, which are related to a number of ecophysiological processes.

  • Role of plant residues in determining temporal patterns of the activity, size, and structure of Nitrate Reducer communities in soil.
    Applied and environmental microbiology, 2010
    Co-Authors: D. Chèneby, Lionel Ranjard, David Bru, Noémie Pascault, Pierre-alain Maron, Laurent Philippot
    Abstract:

    The incorporation of plant residues into soil not only represents an opportunity to limit soil organic matter depletion resulting from cultivation but also provides a valuable source of nutrients such as nitrogen. However, the consequences of plant residue addition on soil microbial communities involved in biochemical cycles other than the carbon cycle are poorly understood. In this study, we investigated the responses of one N-cycling microbial community, the Nitrate Reducers, to wheat, rape, and alfalfa residues for 11 months after incorporation into soil in a field experiment. A 20- to 27-fold increase in potential Nitrate reduction activity was observed for residue-amended plots compared to the nonamended plots during the first week. This stimulating effect of residues on the activity of the Nitrate-reducing community rapidly decreased but remained significant over 11 months. During this period, our results suggest that the potential Nitrate reduction activity was regulated by both carbon availability and temperature. The presence of residues also had a significant effect on the abundance of Nitrate Reducers estimated by quantitative PCR of the narG and napA genes, encoding the membrane-bound and periplasmic Nitrate reductases, respectively. In contrast, the incorporation of the plant residues into soil had little impact on the structure of the narG and napA Nitrate-reducing community determined by PCR-restriction fragment length polymorphism (RFLP) fingerprinting. Overall, our results revealed that the addition of plant residues can lead to important long-term changes in the activity and size of a microbial community involved in N cycling but with limited effects of the type of plant residue itself.

  • Disentangling the rhizosphere effect on Nitrate Reducers and denitrifiers: insight into the role of root exudates
    Environmental microbiology, 2008
    Co-Authors: Sonia Henry, D. Chèneby, S. Texier, S. Hallet, David Bru, Christophe Dambreville, F. Bizouard, J. C. Germon, Laurent Philippot
    Abstract:

    To determine to which extent root-derived carbon contributes to the effects of plants on Nitrate Reducers and denitrifiers, four solutions containing different proportions of sugar, organic acids and amino acids mimicking maize root exudates were added daily to soil microcosms at a concentration of 150 microg C g(-1) of soil. Water-amended soils were used as controls. After 1 month, the size and structure of the Nitrate Reducer and denitrifier communities were analysed using the narG and napA, and the nirK, nirS and nosZ genes as molecular markers respectively. Addition of artificial root exudates (ARE) did not strongly affect the structure or the density of Nitrate Reducer and denitrifier communities whereas potential Nitrate reductase and denitrification activities were stimulated by the addition of root exudates. An effect of ARE composition was also observed on N(2)O production with an N(2)O:(N(2)O + N(2)) ratio of 0.3 in microcosms amended with ARE containing 80% of sugar and of 1 in microcosms amended with ARE containing 40% of sugar. Our study indicated that ARE stimulated Nitrate reduction or denitrification activity with increases in the range of those observed with the whole plant. Furthermore, we demonstrated that the composition of the ARE affected the nature of the end-product of denitrification and could thus have a putative impact on greenhouse gas emissions.

Lionel Ranjard - One of the best experts on this subject based on the ideXlab platform.

  • Role of plant residues in determining temporal patterns of the activity, size, and structure of Nitrate Reducer communities in soil.
    Applied and environmental microbiology, 2010
    Co-Authors: D. Chèneby, Lionel Ranjard, David Bru, Noémie Pascault, Pierre-alain Maron, Laurent Philippot
    Abstract:

    The incorporation of plant residues into soil not only represents an opportunity to limit soil organic matter depletion resulting from cultivation but also provides a valuable source of nutrients such as nitrogen. However, the consequences of plant residue addition on soil microbial communities involved in biochemical cycles other than the carbon cycle are poorly understood. In this study, we investigated the responses of one N-cycling microbial community, the Nitrate Reducers, to wheat, rape, and alfalfa residues for 11 months after incorporation into soil in a field experiment. A 20- to 27-fold increase in potential Nitrate reduction activity was observed for residue-amended plots compared to the nonamended plots during the first week. This stimulating effect of residues on the activity of the Nitrate-reducing community rapidly decreased but remained significant over 11 months. During this period, our results suggest that the potential Nitrate reduction activity was regulated by both carbon availability and temperature. The presence of residues also had a significant effect on the abundance of Nitrate Reducers estimated by quantitative PCR of the narG and napA genes, encoding the membrane-bound and periplasmic Nitrate reductases, respectively. In contrast, the incorporation of the plant residues into soil had little impact on the structure of the narG and napA Nitrate-reducing community determined by PCR-restriction fragment length polymorphism (RFLP) fingerprinting. Overall, our results revealed that the addition of plant residues can lead to important long-term changes in the activity and size of a microbial community involved in N cycling but with limited effects of the type of plant residue itself.

  • Effect of primary mild stresses on resilience and resistance of the Nitrate Reducer community to a subsequent severe stress
    FEMS microbiology letters, 2008
    Co-Authors: Laurent Philippot, D. Chèneby, Mickael Cregut, Fabrice Martin-laurent, Lionel Ranjard, Mélanie Bressan, Stéphane Dequiet, Philippe Lemanceau
    Abstract:

    The factors regulating soil microbial stability (e.g. resistance and resilience) are poorly understood, even though microorganisms are essential for ecosystem functioning. In this study, we tested whether a functional microbial community subjected to different primary mild stresses was equally resistant or resilient to a subsequent severe stress. The Nitrate Reducers were selected as model community and analysed in terms of Nitrate reduction rates and genetic structure by narG PCR-restriction fragment length polymorphism fingerprinting. Heat, copper and atrazine were used as primary stresses and mercury at a high concentration as a severe stress. None of the primary stresses had any significant impact on the Nitrate Reducer community. Although primary stress with heat, copper or atrazine had no effect on the resilience of the Nitrate Reducer activity to mercury stress, pre-exposure to copper, another heavy metal, resulted in increased resilience. In contrast, the resistance of both structure and activity of the Nitrate Reducer community to severe mercury stress was not affected by any of the primary stresses tested. Our experiment suggests that the hypothetical effect of an initial stress on the response of a microbial community to an additional stress is complex and may depend on the relatedness of the two consecutive stresses and the development of positive cotolerance.

  • E¡ectof primarymild stresseson resilienceand resistanceofthe Nitrate Reducer community toa subsequent severe stress
    2007
    Co-Authors: Mickael Cregut, Fabrice Martin-laurent, Lionel Ranjard
    Abstract:

    Nitrate Reducers; stress; pesticide; heavy metal; functional stability; soil. The factors regulating soil microbial stability (e.g. resistance and resilience) are poorly understood, even though microorganisms are essential for ecosystem functioning. In this study, we tested whether a functional microbial community subjected to different primary mild stresses was equally resistant or resilient to a subsequent severe stress. The Nitrate Reducers were selected as model community and analysed in terms of Nitrate reduction rates and genetic structure by narG PCR-restriction fragment length polymorphism fingerprinting. Heat, copper and atrazine were used as primary stresses and mercury at a high concentration as a severe stress. None of the primary stresses had any significant impact on the Nitrate Reducer community. Although primary stress with heat, copper or atrazine had no effect on the resilience of the Nitrate Reducer activity to mercury stress, pre-exposure to copper, another heavy metal, resulted in increased resilience. I