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See detailMetal binding to the N-terminal cytoplasmic domain of the PIB ATPase HMA4 is required for metal transport in Arabidopsis.
Laurent, Clémentine ULg; Lekeux, Gilles ULg; Ukuwela, Ashwinie A et al

in Plant Molecular Biology (in press)

PIB ATPases are metal cation pumps that transport metals across membranes. These proteins possess N- and C-terminal cytoplasmic extensions that contain Cys- and His-rich high affinity metal binding ... [more ▼]

PIB ATPases are metal cation pumps that transport metals across membranes. These proteins possess N- and C-terminal cytoplasmic extensions that contain Cys- and His-rich high affinity metal binding domains, which may be involved in metal sensing, metal ion selectivity and/or in regulation of the pump activity. The PIB ATPase HMA4 (Heavy Metal ATPase 4) plays a central role in metal homeostasis in Arabidopsis thaliana and has a key function in zinc and cadmium hypertolerance and hyperaccumulation in the extremophile plant species Arabidopsis halleri. Here, we examined the function and structure of the N-terminal cytoplasmic metal-binding domain of HMA4. We mutagenized a conserved CCTSE metal-binding motif in the domain and assessed the impact of the mutations on protein function and localization in planta, on metal-binding properties in vitro and on protein structure by Nuclear Magnetic Resonance spectroscopy. The two Cys residues of the motif are essential for the function, but not for localization, of HMA4 in planta, whereas the Glu residue is important but not essential. These residues also determine zinc coordination and affinity. Zinc binding to the N-terminal domain is thus crucial for HMA4 protein function, whereas it is not required to maintain the protein structure. Altogether, combining in vivo and in vitro approaches in our study provides insights towards the molecular understanding of metal transport and specificity of metal P-type ATPases. [less ▲]

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See detailMetal binding to the N-terminal cytoplasmic domain of the PIB ATPase HMA4 is required for metal transport in Arabidopsis.
Laurent, Clémentine ULg; Lekeux, Gilles ULg; Ukuwela, Ashwinie A et al

in Plant Molecular Biology (in press)

PIB ATPases are metal cation pumps that transport metals across membranes. These proteins possess N- and C-terminal cytoplasmic extensions that contain Cys- and His-rich high affinity metal binding ... [more ▼]

PIB ATPases are metal cation pumps that transport metals across membranes. These proteins possess N- and C-terminal cytoplasmic extensions that contain Cys- and His-rich high affinity metal binding domains, which may be involved in metal sensing, metal ion selectivity and/or in regulation of the pump activity. The PIB ATPase HMA4 (Heavy Metal ATPase 4) plays a central role in metal homeostasis in Arabidopsis thaliana and has a key function in zinc and cadmium hypertolerance and hyperaccumulation in the extremophile plant species Arabidopsis halleri. Here, we examined the function and structure of the N-terminal cytoplasmic metal-binding domain of HMA4. We mutagenized a conserved CCTSE metal-binding motif in the domain and assessed the impact of the mutations on protein function and localization in planta, on metal-binding properties in vitro and on protein structure by Nuclear Magnetic Resonance spectroscopy. The two Cys residues of the motif are essential for the function, but not for localization, of HMA4 in planta, whereas the Glu residue is important but not essential. These residues also determine zinc coordination and affinity. Zinc binding to the N-terminal domain is thus crucial for HMA4 protein function, whereas it is not required to maintain the protein structure. Altogether, combining in vivo and in vitro approaches in our study provides insights towards the molecular understanding of metal transport and specificity of metal P-type ATPases. [less ▲]

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See detailCarbon substrate utilization and microbial biomass in European forest soils are related to tree species diversity
Carnol, Monique ULg; Baeten, Lander; Bosman, Bernard ULg et al

Poster (2015, December)

Tree species influence biogeochemical cycling through element deposition (throughfall, litterfall), root decomposition and exudates, and through their influence on the microbial activities in the soil ... [more ▼]

Tree species influence biogeochemical cycling through element deposition (throughfall, litterfall), root decomposition and exudates, and through their influence on the microbial activities in the soil. Yet, the effect of mixing tree species on soil functioning is unclear, in particular concerning the microbial diversity and activity in soils. Here we synthesize results from the Exploratory Platform of the FunDivEUROPE project (http://www.fundiveurope.eu/). This network of 209 comparative plots covering tree diversity levels of 1 to 5 species was established in existing mature forests in 6 European regions. These six focal regions represent a gradient of major European forest types from boreal to Mediterranean forests. The aims of this study were to determine the soil microbial biomass and metabolic diversity of soil bacteria for these 6 European forest regions, presenting each a tree species richness gradient and to analyse the impact of tree species richness and the role of other controlling factors. We analysed the relation between tree species diversity, the proportion of coniferous tree species and soil factors (pH, soil organic carbon, water soluble carbon and nitrogen) and the carbon substrate utilisation pattern of soil bacteria (BIOLOG Ecoplate), soil microbial biomass (fumigation-extraction), hot water carbon and nitrogen in the forest floor and the upper mineral soil horizon (linear mixed models, GLM for multivariate abundance data, discriminant correspondence analysis). Mean values of microbial biomass carbon ranged from 3264 (Italy) to 8717 (Finland) mg kg-1 in the forest floor and from 465 (Italy) to 3748 (Finland) mg kg-1 in the mineral soil. Statistical models predicted microbial biomass to increase in both soil layers by 7-8% with each step increase in tree diversity. Increased proportion of conifers was linked to a decrease in the number of carbon substrates used by soil bacteria. The types of carbon sources used were dependent on region, proportion of conifers, soil pH and water-soluble carbon and nitrogen. [less ▲]

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See detailLes sols, richesses cachées de la planète
Garré, Sarah ULg; Carnol, Monique ULg; Cornelis, Jean-Thomas ULg

Speech/Talk (2015)

Toute forme de vie sur terre doit beaucoup aux sols. Aussi discrets que dynamiques, vitaux que complexes, les sols sont des réacteurs bio-physico-chimiques, situés à l’interface entre les roches, la ... [more ▼]

Toute forme de vie sur terre doit beaucoup aux sols. Aussi discrets que dynamiques, vitaux que complexes, les sols sont des réacteurs bio-physico-chimiques, situés à l’interface entre les roches, la végétation, l’air et l’eau. L’étude de cette ressource non renouvelable, soumise à des pressions croissantes, requiert une approche interdisciplinaire, indispensable pour une gestion raisonnée et durable des écosystèmes. Comment sont définis les sols, comment les étudions-nous, comment aborder leur diversité et leurs fonctionnalités ? Quels secrets ont-ils à nous livrer ? La leçon inaugurale abordera la formation des sols, leur diversité ainsi que leurs fonctions écologiques. La variété des organismes au sein des sols et la notion de qualité des sols seront évoquées à travers la triangulation biodiversité – fonctions – services écosystémiques. Des techniques innovantes, permettant d’étudier cette interface extrêmement complexe et diversifiée, seront présentées et le fonctionnement ainsi que l’intérêt des sols seront illustrés par des exemples concrets issus de recherches récentes. [less ▲]

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See detailZinc triggers a complex transcriptional and post-transcriptional regulation of the metal homeostasis gene FRD3 in Arabidopsis relatives
Charlier, Jean_Benoit; Polese, Catherine; Nouet, Cécile ULg et al

in Journal of Experimental Botany (2015), 66

In Arabidopsis thaliana, FRD3 (Ferric Chelate Reductase Defective 3) plays a central role in metal homeostasis. FRD3 is among a set of metal homeostasis genes that are constitutively highly expressed in ... [more ▼]

In Arabidopsis thaliana, FRD3 (Ferric Chelate Reductase Defective 3) plays a central role in metal homeostasis. FRD3 is among a set of metal homeostasis genes that are constitutively highly expressed in roots and shoots of Arabidopsis halleri, a zinc hyperaccumulating and hypertolerant species. Here, we examined the regulation of FRD3 by zinc in both species to shed light on the evolutionary processes underlying the evolution of hyperaccumulation in A. halleri. We combined gene expression studies with the use of GUS and GFP reporter constructs to compare the expression profile, transcriptional and post-transcriptional regulation of FRD3 in both species. The AtFRD3 and AhFRD3 genes display a conserved expression profile. In A. thaliana, alternative transcription initiation sites from two promoters determine transcript variants which are differentially regulated by zinc supply in roots and shoots to favour the most highly translated variant under zinc excess conditions. In A. halleri, a single transcript variant with higher transcript stability and enhanced translation has been maintained. The FRD3 gene thus undergoes complex transcriptional and post-transcriptional regulation in Arabidopsis relatives. Our study reveals that a diverse set of mechanisms underlie increased gene dosage in the A. halleri lineage and illustrates how an environmental challenge can alter gene regulation. [less ▲]

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See detailThe role of tree species diversity in drought resistance of oak and beech sapling
Rahman, Md Masudur ULg; Carnol, Monique ULg

Scientific conference (2015, March 21)

Drier condition during the growing season have been predicted in the future. It has been suggested that diverse forest could maintain productivity and provide better ecosystem services under stress ... [more ▼]

Drier condition during the growing season have been predicted in the future. It has been suggested that diverse forest could maintain productivity and provide better ecosystem services under stress condition such as drought. However, those studies focused mainly on mature forest and little known about young forest. Oak and beech are the important species in European forestry, and may face a strong challenge in the future. Drought effects on young ( ̴5yr) oak and beech saplings in monoculture and mixed with other species are not known. Moreover, single studies evaluating both above- and below-ground ecosystem response to drought are scarce. A two-year manipulative field experiment has been planned to answer the following questions. (i) Can species mixtures improve oak and beech sapling performances under drought conditions? (ii) What are the mechanisms underlying ecosystem functioning and sapling performance in mixed species stands subjected to drought? A 3m × 3m rainout shelter will be placed only in growing season in Zedelgem sites of FORBIO experimental platform (http://www.treedivbelgium.ugent.be/pl_forbio.html). Tree diversity vary from 1 to 4 species and about 50% of precipitation will be taken off. Both aboveground sapling performance and belowground microbial properties and biogeochemical processes will be investigated. We will present the design of the experimental tree species diversity plantation of Zedelgem site, the setting of the drought experiment and planned analysis [less ▲]

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See detailFunctional analysis of the three HMA4 copies of the metal hyperaccumulator Arabidopsis halleri
Nouet, Cécile ULg; Charlier, Jean-Benoit; Carnol, Monique ULg et al

in Journal of Experimental Botany (2015), 66

In Arabidopsis halleri, the AhHMA4 gene has an essential function in Zn/Cd hypertolerance and hyperaccumulation by mediating root to shoot translocation of metals. Constitutive high expression of AhHMA4 ... [more ▼]

In Arabidopsis halleri, the AhHMA4 gene has an essential function in Zn/Cd hypertolerance and hyperaccumulation by mediating root to shoot translocation of metals. Constitutive high expression of AhHMA4 results from a tandem triplication and cis-activation of the promoter of all three copies. The three AhHMA4 copies possess divergent promoter sequences, but highly conserved coding sequences, and display identical expression profiles in the root and shoot vascular system. Here, we expressed an AhHMA4::GFP fusion under the control of each three A. halleri HMA4 promoters in a hma2hma4 double mutant of Arabidopsis thaliana to individually examine the function of each A. halleri AhHMA4 copy. The protein localized non-polarly at the plasma membrane of the root pericycle cells of both A. thaliana and A. halleri. The expression of each AhHMA4::GFP copy complemented the severe Zn deficiency phenotype of the hma2hma4 mutant by restoring root-to-shoot translocation of zinc. However, each copy had different impact on metal homeostasis in the A. thaliana genetic background: AhHMA4 copies 2 and 3 were more highly expressed and provided higher Zn tolerance in roots and accumulation in shoots than copy 1, whereas AhHMA4 copy 3 also increased Cd tolerance in roots. Our data suggest a certain extent of functional differentiation among the three A. halleri HMA4 copies, stemming from differences in expression levels rather than in expression profile. HMA4 is a key node of the Zn homeostasis network and small changes in expression level can have major impact on Zn allocation to root or shoot tissues. [less ▲]

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See detailTree species diversity effects on soil microbial biomass, diversity and activity across European forest types
Carnol, Monique ULg; Baeten, Lander; Bosman, Bernard ULg et al

Conference (2014, December)

Increasing tree species diversity in forests might contribute to ecosystem-service maintenance, as well as to the reconciliation of regulating, provisioning and supporting services within the frame of ... [more ▼]

Increasing tree species diversity in forests might contribute to ecosystem-service maintenance, as well as to the reconciliation of regulating, provisioning and supporting services within the frame of multifunctional and sustainable forestry. Individual tree species influence biogeochemical cycling through element deposition (throughfall, litterfall), and through microbial activities in the soil. Yet, the influence of mixing tree species on these ecosystem processes is unclear, in particular concerning the microbial diversity and activity in soils. Here we synthesize results from the Exploratory Platform of the FunDivEUROPE project (http://www.fundiveurope.eu/). This network of 209 comparative plots covering a tree diversity gradient of 1 to 5 tree species was established in existing mature forests in 6 European regions. These six focal regions represent a gradient of major European forest types from boreal to Mediterranean forests. We analysed the impact of tree species diversity and the role of other controlling factors on the metabolic diversity of soil bacteria (BIOLOG Ecoplate), soil microbial biomass (fumigation-extraction) and potential nitrification (shaken soil slurry) in the forest floor and the upper organo-mineral soil horizon. Mean values of microbial biomass carbon ranged from 240 (Poland) to 1762 (Germany) mg kg-1 in the forest floor and from 4197 (Italy) to 11207 (Finland) mg kg-1 in the upper organo-mineral horizon. Tree diversity and soil water content were important controlling factors. Statistical models predict microbial biomass to increase in both horizons by 7-8% with each step increase in tree diversity. Metabolic diversity of soil bacteria (% of substrates used) showed high variability both within and between sites. Further results analysed with mixed linear models will be presented and discussed. [less ▲]

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See detailEffect of tree species mixture on earthworm communities on a continental scale
De Wandeler, Hans; Baeten, Lander; Carnol, Monique ULg et al

Poster (2014, December)

The belowground food web represents a major part of associated biodiversity in forest ecosystems, and plays a significant role in the ecosystem processes of litter decomposition and nutrient turnover ... [more ▼]

The belowground food web represents a major part of associated biodiversity in forest ecosystems, and plays a significant role in the ecosystem processes of litter decomposition and nutrient turnover. Past research has demonstrated overwhelming evidence of strong tree species identity effects on earthworm communities. It has been proposed that increased plant community diversity would be beneficial to the abundance and diversity of the belowground food web, but effects of tree species diversity on earthworm communities have seldom been reported, and are inconclusive. In this study at continental scale we evaluated whether tree species diversity positively affects earthworm biomass and diversity. For this purpose the FunDivEUROPE Exploratory Platform was used with 209 plots in 6 regions well spread over Europe with a low within-region site variability, but a within-region tree species diversity gradient from monocultures to 3 or 4 species plots. In every plot earthworms were sampled using a combined method of mustard extraction and hand sorting of litter and a soil monolith. Data are being analysed with multivariate tools and mixed effects models. First results suggest only limited influence of tree diversity on the biomass of earthworm communities at continental scale. Tree diversity effects are weak, context specific and interacting with tree identity. In nutrient poor soils we found a negative tree diversity effect on earthworm biomass when deciduous monocultures are enriched with coniferous species, while in rich soils we found a positive tree diversity effect which could be related with the food security this provides to the earthworm community. [less ▲]

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See detailDo tree species influence community structure and richness of Ammonia Oxidizing Bacteria at three temperate forest sites?
Malchair, Sandrine ULg; Carnol, Monique ULg

Poster (2014, July 15)

Introduction: The relationship between biodiversity and ecosystem function remains a controversial subject with numerous open questions. In Europe, the conversion of coniferous monocultures into ... [more ▼]

Introduction: The relationship between biodiversity and ecosystem function remains a controversial subject with numerous open questions. In Europe, the conversion of coniferous monocultures into broadleaved or mixed stand is considered to face ecological and economical risks posed by coniferous monocultures. Belowground effects of such a change in the dominant tree species is however largely unknown, although bacteria regulate many soil processes and some groups, like ammonia oxidizing bacteria (AOB) are highly sensitive to environmental stress. Objectives: The aims of this study were to investigate (i) AOB community structure and richness under several tree species, (ii) microbial/environmental factors related to AOB diversity, (iii) the relationship between AOB diversity and the nitrification process. Materials and methods: Forest floor (Of, Oh) was sampled under European beech, sessile oak, Norway spruce and Douglas fir at three sites. AOB community structure and richness was assessed by PCR-DGGE and sequencing. Samples were analysed for net N mineralization, potential nitrification, basal respiration, microbial biomass, microbial or metabolic quotient, pH, total nitrogen, extractable ammonium, organic matter content and exchangeable cations. Results: AOB community structure and tree species effects on AOB diversity were site-specific. Factors regulating ammonium availability, i.e. net N mineralization or microbial biomass, were related to AOB community structure. AOB richness was not related to nitrification. Conclusions: Our research revealed that, at larger spatial scales, site specific characteristics may be more important that tree species in determining AOB richness and community structure. Within sites, tree species influence AOB diversity. The absence of a relation between AOB richness and nitrification points to a possibly role of AOB abundance, phenotypic plasticity or the implication of ammonia oxidizing archaea in this process. [less ▲]

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See detailBiological indicators of soil quality over landscape spatial scales: a case study in Southern Belgium
Krüger, Inken ULg; Chartin, Caroline; Van Wesemael, Bas et al

Poster (2014, July)

Biological indicators are organisms or biological processes whose values give quantitative information on the capacity of a soil to function. Their fast dynamic allows to detect changes on short ... [more ▼]

Biological indicators are organisms or biological processes whose values give quantitative information on the capacity of a soil to function. Their fast dynamic allows to detect changes on short timescales. Five biological indicators (basal respiration, nitrogen mineralisation, microbial carbon and nitrogen, earthworm abundance and biomass, functional microbial diversity) as well as two ecophysiological indices (microbial quotient and metabolic quotient) were tested for their power to characterize the biological soil quality on a landscape level at 60 sites in two South-Belgian landscape units were investigated. All biological indicators differed significantly between the two landscape units showing the biological indicators to be discriminatory on a landscape level. Within each landscape unit, no relationships between biological indicators were found, underlining the need to measure multiple biological indicators. The results represent the first data for a South-Belgian monitoring network of biological soil quality. [less ▲]

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See detailEcosystem services of mixed species forest stands and monocultures: comparing practitioners' and scientists' perceptions with formal scientific knowledge
Carnol, Monique ULg; Baeten, Lander; Branquart, Etienne et al

in Forestry (2014), 87(5), 639-653

Mixed species stands might contribute to important goals of sustainable forest management, such as higher biological diversity, more resistance and resilience to disturbances and higher carbon storage ... [more ▼]

Mixed species stands might contribute to important goals of sustainable forest management, such as higher biological diversity, more resistance and resilience to disturbances and higher carbon storage. Knowledge of stakeholders' perceptions of such ecosystem services in mixed species stands is required for effective policy development. We showed that practitioners' and scientists' perceptions of ecosystem services in mixed species stands in Belgium differed from formal scientific knowledge derived from a synthesis of published studies. The positive perception of supporting, regulating and cultural services in mixed species stands contrasted with less conclusive results from the literature, where positive, negative and neutral effects were reported. Many respondents also signified a lack of information about regulating services. Furthermore, provisioning services were perceived as equal in mixed species stands and monocultures, in contrast to higher productivity demonstrated in mixed species stands in the literature. The regional (Flanders and Wallonia) ecological and socio-economic context influenced both the perception of ecosystem services and of the importance of management objectives. Our results highlighted the need to address the lack of scientific data, to adapt communication to the ecological and socio-economic context, as well as to improve information flow on regulating services and productivity. [less ▲]

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See detailFifty years of crop residue management have a limited impact on soil heterotrophic respiration.
Buysse, Pauline ULg; Schnepf-Kiss, Anne-Caroline; Carnol, Monique ULg et al

in Agricultural and Forest Meteorology (2013), 180

The impacts of crop residue management on soil microbial biomass, labile carbon and heterotrophic respiration (HR) were assessed at a long-term experimental site in the Hesbaye region in Belgium. Three ... [more ▼]

The impacts of crop residue management on soil microbial biomass, labile carbon and heterotrophic respiration (HR) were assessed at a long-term experimental site in the Hesbaye region in Belgium. Three treatments, residue export (RE), farmyard manure addition (FYM) and residue restitution after harvest (RR), have been applied continuously since 1959. The soil is a Eutric Cambisol with, in 2010, significantly different total soil organic carbon contents of 4.4, 5.1 and 5.9 kg C m-2 under the RE, RR and FYM treatments, respectively. Manual field HR measurements were carried out during the 2010 and 2012 crop seasons using a dynamic closed chamber system. Microbial biomass, labile C content and metabolic diversity of soil bacteria were assessed in spring 2012. Fifty-one years after the beginning of the treatments, residue management had a limited impact on HR. Based on daily averaged values, the treatment had a significant impact (α = 10%) in 2012 but not in 2010. Based on the individual measurement dates, the treatment impact was less obvious in 2012; with the observation of a significant impact (α = 10%) on HR in only 7% and 36.8% of the measurement dates in 2010 and 2012, respectively. Labile C and microbial biomass were significantly lower in the RE treatment than in FYM and RR. Residue management had no significant effect on cold-water extracted carbon and metabolic diversity of heterotrophic soil bacteria. The limited impact of residue management on HR could be explained by (i) the relatively low amounts of recent above-ground crop inputs, (ii) the large proportion of below-ground residues and other non-exportable above-ground residues reducing the potential differences between treatments and (iii) the relatively large spatial variability of HR. In conclusion, carbon losses due to heterotrophic respiration did not differ between RE, FYM and RR treatments in the studied soil. This contrasts with the different soil organic carbon contents observed in these three treatments after fifty years of experiment. Further investigations regarding the reduction of spatial variability and the potential roles played by organic matter protection within aggregates and biochemical composition of inputs are needed. [less ▲]

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See detailBiochar impact on CO2 and N2O emissions from cereal fields in Norway
Rasse, Daniel, P.; O'Toole, Adam; Carnol, Monique ULg et al

Conference (2013, September)

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See detailMetabolic diversity and microbial biomass in forest soils across climatic and tree species diversity gradients
Carnol, Monique ULg; Bosman, Bernard ULg; Vanoppen, Astrid et al

Poster (2013, August)

The biogeochemical cycling in forest ecosystems is highly dependent on the interactions between plants and soil. Tree species affect element cycling through deposition in throughfall, litterfall ... [more ▼]

The biogeochemical cycling in forest ecosystems is highly dependent on the interactions between plants and soil. Tree species affect element cycling through deposition in throughfall, litterfall, microbial activities in soil and rhizosphere processes. Tree species diversification has been suggested for maintaining forest ecosystem services and combining provisioning and supporting services within multifunctional and sustainable forestry. However, the understanding of the role of biodiversity in forests is unclear, in particular concerning the microbial diversity and activity in soils. Here we synthesize results from measurements of bacterial metabolic diversity and microbial biomass in soils sampled in the 209 plots of the Exploratory Platform of the FunDivEUROPE project (http://www.fundiveurope.eu/). This Exploratory Platform is a network of comparative plots of 1-5 tree species established in existing mature forest in 6 countries. These six focal regions represent important European forest types along the gradient from boreal forest to Mediterranean forest. We analysed the impact of tree species richness and the role of other controlling factors on the metabolic diversity of soil bacteria and on microbial biomass. [less ▲]

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See detailAOB community structure and richness under European beech, sessile oak, Norway spruce and Douglas-fir at three temperate forest sites
Malchair, Sandrine ULg; Carnol, Monique ULg

in Plant and Soil (2013), 366(1-2),

Abstract Background and aims The relations between tree species, microbial diversity and activity can alter ecosystem functioning. We investigated ammonia oxidizing bacteria (AOB) community structure and ... [more ▼]

Abstract Background and aims The relations between tree species, microbial diversity and activity can alter ecosystem functioning. We investigated ammonia oxidizing bacteria (AOB) community structure and richness, microbial/environmental factors related to AOB diversity and the relationship between AOB diversity and the nitrification process under several tree species. Methods Forest floor (Of, Oh) was sampled under European beech, sessile oak, Norway spruce and Douglas-fir at three sites. AOB community structure was assessed by PCR-DGGE and sequencing. Samples were analyzed for net N mineralization, potential nitrification, basal respiration, microbial biomass, microbial or metabolic quotient, pH, total nitrogen, extractable ammonium, organic matter content and exchangeable cations. Results AOB community structure and tree species effect on AOB diversity were site-specific. AOB richness was not related to nitrification. Factors regulating ammonium availability, i.e. net N mineralization or microbial biomass, were related to AOB community structure. Conclusion Our research shows that, at larger spatial scales, site specific characteristics may be more important than the nature of tree species in determining AOB diversity (richness and community structure). Within sites, tree species influence AOB diversity. The absence of a relation between AOB richness and nitrification points to a possibly role of AOB abundance, phenotypic plasticity or the implication of ammonia oxidizing archaea. [less ▲]

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See detailShort-term temperature impact on soil heterotrophic respiration in limed agricultural soil samples
Buysse, Pauline ULg; Goffin, Stéphanie ULg; Carnol, Monique ULg et al

in Biogeochemistry (2013), 112(1-3), 441-455

This study sought to investigate the hourly and daily timescale responses of soil CO2 fluxes to temperature in a limed agricultural soil. Observations from different incubation experiments were compared ... [more ▼]

This study sought to investigate the hourly and daily timescale responses of soil CO2 fluxes to temperature in a limed agricultural soil. Observations from different incubation experiments were compared with the results of a model combining biotic (heterotrophic respiration) and abiotic (carbonate weathering) components. Several samples were pre-incubated for 8-9 days at three temperatures (5, 15 and 25°C) and then submitted to short-term temperature cycles (where the temperature was increased from 5 to 35°C in 10°C stages, with each stage being 3 h long). During the temperature cycles (hourly timescale), the soil CO2 fluxes increased significantly with temperature under all pre-incubation temperature treatments. A hysteresis effect and negative fluxes during cooling phases were also systematically observed. At a given hourly timescale temperature, there was a negative relationship of the CO2 fluxes with the pre-incubation temperature. Using the combined model allowed the experimental results to be clearly described, including the negative fluxes and the hysteresis effect, showing the potentially large contribution of abiotic fluxes to total fluxes in limed soils, after short-term temperature changes. The fairly good agreement between the measured and simulated flux results also suggested that the biotic flux temperature sensitivity was probably unaffected by timescale (hourly or daily) or pre-incubation temperature. The negative relationship of the CO2 fluxes with the pre-incubation temperature probably derived from very labile soil carbon depletion, as shown in the simulations. This was not, however, confirmed by soil carbon measurements, which leaves open the possibility of adaptation within the microbial community. [less ▲]

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