Catabolic Diversity Research Articles

Soil Microbial Functions After Forest Fires Affected by the Compost Quality

AbstractComposts are frequently used to restore various degraded lands especially after fire. We investigated how different organic amendments after frequent wildfires can affect soil microbial functions. We crossed three times since fire (1, 5 and 18 years) with three different compost qualities (i.e. young, intermediate and old). After 5 months, alkaline phosphatase increased by the intermediate compost in early post‐fire chronosequence (1 and 5 year after fires). This increase was confirmed 10 months after amendment with the three composts but only for the most recent fire. The net nitrification increased 5 months after amendment under both the young and intermediate composts in the 5 and 18 years of time since fire plots. This increase was confirmed 10 months after amendment with the intermediate and old compost treatments for the 1 and 5 years of time since fire plots. In this case, compost amendment even induced positive nitrification rates for the 5 years of time since fire plots. Moreover, older composts affected catabolic diversity after 5 months, whereas at the same time, we detected an increase in biomass of cultivable bacteria. Urease activity gradually increased with the age of composts after 10 months. β‐glucosidase activity increased under the young and intermediate composts and did not change with the older. This study suggests compost addition can result in an artificial acceleration of the nutrient cycles. Thus organic amendments in burned ecosystems should be reasoned according to both the step of the Mediterranean post‐fire recovery and the quality of organic amendments. Copyright © 2015 John Wiley & Sons, Ltd.

Carbohydrate catabolic diversity of bifidobacteria and lactobacilli of human origin

Because increased proportions of particular commensal bacteria such as bifidobacteria and lactobacilli have been linked to human health through a variety of mechanisms, there is corresponding interest in identifying carbohydrates that promote growth and metabolic activity of these bacteria. We evaluated the ability of 20 carbohydrates, including several commercially available carbohydrates that are sold as prebiotic ingredients, to support growth of 32 human-derived isolates belonging to the genera Bifidobacterium and Lactobacillus, including those isolated from healthy elderly subjects. In general, bifidobacterial strains were shown to display more diverse carbohydrate utilization profiles compared to the tested Lactobacillus species, with several bifidobacterial strains capable of metabolizing xylo-oligosaccharide (XOS), arabinoxylan, maltodextrin, galactan and carbohydrates containing fructo-oligosaccharide (FOS) components. In contrast, maltodextrin, galactan, arabinogalactan and galactomannan did not support robust growth (≥0.8 OD600nm) of any of the Lactobacillus strains assessed. Carbohydrate fermentation was variable among strains tested of the same species for both genera. This study advances our knowledge of polysaccharide utilization by human gut commensals, and provides information for the rational design of selective prebiotic food ingredients.

Secondary successional trajectories of structural and catabolic bacterial communities in oil-polluted soil planted with hybrid poplar.

Poplars have widely been used for rhizoremediation of a broad range of organic contaminants for the past two decades. Still, there is a knowledge gap regarding the rhizosphere-associated bacterial communities of poplars and their dynamics during the remediation process. It is envisaged that a detailed understanding of rhizosphere-associated microbial populations will greatly contribute to a better design and implementation of rhizoremediation. To investigate the long-term succession of structural and catabolic bacterial communities in oil-polluted soil planted with hybrid poplar, we carried out a 2-year field study. Hybrid aspen (Populus tremula × Populus tremuloides) seedlings were planted in polluted soil excavated from an accidental oil-spill site. Vegetated and un-vegetated soil samples were collected for microbial community analyses at seven different time points during the course of 2 years and sampling time points were chosen to cover the seasonal variation in the boreal climate zone. Bacterial community structure was accessed by means of 16S rRNA gene amplicon pyrosequencing, whereas catabolic diversity was monitored by pyrosequencing of alkane hydroxylase and extradiol dioxygenase genes. We observed a clear succession of bacterial communities on both structural and functional levels from early to late-phase communities. Sphingomonas type extradiol dioxygenases and alkane hydroxylase homologs of Rhodococcus clearly dominated the early-phase communities. The high-dominance/low-diversity functional gene communities underwent a transition to low-dominance/high-diversity communities in the late phase. These results pointed towards increased catabolic capacities and a change from specialist to generalist strategy of bacterial communities during the course of secondary succession.

Phylogenetic and Functional Diversity Within Toluene-Degrading, Sulphate-Reducing Consortia Enriched from a Contaminated Aquifer

Three toluene-degrading microbial consortia were enriched under sulphate-reducing conditions from different zones of a benzene, toluene, ethylbenzene and xylenes (BTEX) plume of two connected contaminated aquifers. Two cultures were obtained from a weakly contaminated zone of the lower aquifer, while one culture originated from the highly contaminated upper aquifer. We hypothesised that the different habitat characteristics are reflected by distinct degrader populations. Degradation of toluene with concomitant production of sulphide was demonstrated in laboratory microcosms and the enrichment cultures were phylogenetically characterised. The benzylsuccinate synthase alpha-subunit (bssA) marker gene, encoding the enzyme initiating anaerobic toluene degradation, was targeted to characterise the catabolic diversity within the enrichment cultures. It was shown that the hydrogeochemical parameters in the different zones of the plume determined the microbial composition of the enrichment cultures. Both enrichment cultures from the weakly contaminated zone were of a very similar composition, dominated by Deltaproteobacteria with the Desulfobulbaceae (a Desulfopila-related phylotype) as key players. Two different bssA sequence types were found, which were both affiliated to genes from sulphate-reducing Deltaproteobacteria. In contrast, the enrichment culture from the highly contaminated zone was dominated by Clostridia with a Desulfosporosinus-related phylotype as presumed key player. A distinct bssA sequence type with high similarity to other recently detected sequences from clostridial toluene degraders was dominant in this culture. This work contributes to our understanding of the niche partitioning between degrader populations in distinct compartments of BTEX-contaminated aquifers.

A Pseudomonas syringae Diversity Survey Reveals a Differentiated Phylotype of the Pathovar syringae Associated with the Mango Host and Mangotoxin Production

Pseudomonas syringae pv. syringae, the causal agent of bacterial apical necrosis (BAN) in mango crops, has been isolated in different mango-producing areas worldwide. An extensive collection of 87 P. syringae pv. syringae strains isolated from mango trees affected by BAN from different countries, but mainly from Southern Spain, were initially examined by repetitive sequence-based polymerase chain reaction (rep-PCR) to analyze the genetic diversity with an epidemiological aim. rep-PCR was powerful in assessing intrapathovar distribution and also allowing clustering of the P. syringae pv. syringae strains isolated from mango, depending on the isolation area. A clear pattern of clustering was observed for all the P. syringae pv. syringae strains isolated from mango distinct from strains from other hosts, including strains for the same geographical regions as the mango isolates. For this reason, a representative group of 51 P. syringae pv. syringae strains isolated from mango and other hosts, as well as some P. syringae strains from other pathovars, were further characterized to determine their possible genetic, phenotypic, and phylogenetic relationships. Similar to the rep-PCR results, the randomly amplified polymorphic DNA PCR (RAPD-PCR) and catabolic diversity analysis using the Biolog GN2 profile grouped 90% of the mango isolates together in a unique cluster. Interestingly, the majority of P. syringae pv. syringae strains isolated from mango produced mangotoxin. The analysis of the phylogenetic distribution using the multilocus sequence typing analysis strongly supports the existence of a differentiated phylotype of the pathovar syringae mainly associated with the mango host and characterized by the mangotoxin production.

Influence of ciprofloxacin on the microbial catabolic diversity in soil

In this study, the effect of ciprofloxacin (CIP) on the catabolic diversity of soil microbial communities was evaluated. Soil samples were spiked with ciprofloxacin (0, 1, 5 and 50 mgċkg−1) and were incubated for 1, 3, 9, 22 and 40 days. Untreated controls received only water. The functional diversity of the microbial community studied was characterized using a catabolic response profile (CRP). Six substrate groups were tested: carbohydrates, amino acids, carboxylic acids, aromatic chemicals, alcohols and polymers. After 40 days, the CIP concentrations in the soil samples ranged from 25% to 58% of the initial concentrations. Soil respiratory responses to the individual substrates D-glucose, lactose, D-mannose, L-glutamic, Na-citrate, malic acid and inosine were inhibited at the high CIP concentrations (5 and 50 mg·kg−1) in the soils and were increased at the lowest CIP concentration (1 mg·kg−1). Soil respiration was inhibited at all of the CIP concentrations after the addition of D-galactose and glycerol. The CIP concentration and incubation time explained 45.3% of the variance of the catabolic responses. The CRP analysis clearly discriminated among the different CIP concentrations. The results suggest that CIP strongly affects the catabolic diversities of soil microbial communities and that its effect is more significant than that of incubation time.

Carbon utilization, microbial biomass, and respiration in biological soil crusts in the Negev Desert

Biological soil crusts (BSCs) and the soils directly below crusts (SDBCs) (0-5 mm) were collected in the Negev Desert (Israel) during the wet and dry seasons of 2007 and 2008, gently separated, and microbial basal respiration, mi- crobial biomass carbon (Cmic), carbon (C) source utilization rates, and catabolic diversity were analyzed using MicroResp TM plates. The seasonal-change patterns of these parameters were similar to those of soil organic C (Corg )i n the BSCs, i.e., increases were observed during the dry seasons relative to the wet seasons. Few seasonal variations in qCO2 and Cmic/Corg in the BSCs indicated that the increases in crustal organism basal respiration and C source utilization rates can be attributed to microbial propagation as a result of the increases in available C during the dry seasons. High frequency of rain events, with precipitation higher than 0.1 mm during spring, can enable crustal organisms to maintain photosynthetic activity and can facilitate microbial propagation and Corg accumulation in the BSCs. The sea- sonal dynamics of the four biotic parameters in the SDBCs were the opposite of those of the BSCs, and C source utilization rates and catabolic diversity were higher than in the BSCs during the wet seasons. Downward migration of exopolysaccharides, crustal organism cell contents, and in- tracellular solutes with water infiltration can increase C and nutrient availability and enhance microbial catabolic activi- ties and propagation in the SDBCs.

The earthworm species Metaphire posthuma modulates the effect of organic amendments (compost vs. vermicompost from buffalo manure) on soil microbial properties. A laboratory experiment

The aim of this study was to determine the influence of compost and vermicompost produced from buffalo manure on soil bacterial diversity and activity in the presence and absence of the endogeic earthworm Metaphire posthuma. This experiment was carried out for 15 months with a maize–tomato–maize cycle under greenhouse conditions in Northern Vietnam. It showed a positive influence of compost and vermicompost on soil microbial properties, with higher cultivable bacteria, higher bacterial and catabolic diversity (Shannon diversity ‘H’ and Richness ‘S’) indices and higher enzymatic activities than control soils which only received mineral fertilizers. Differences also occurred between compost and vermicompost with lower activity and diversity in the soil amended with vermicompost, probably because of its higher molecular stability. The presence of M. posthuma led to divergent dynamics of bacterial community in soils amended with compost and vermicompost. Earthworms negatively influenced soil microbial properties in composted soil (lower Average Well Color Development ‘AWCD’), probably because of competition between bacteria and earthworms for organic resources and/or because of the consumption of microbes by earthworms. Conversely, the presence of earthworms increased bacterial diversity and activity with higher AWCD, and H and S indices for the vermicompost treatment, probably as a result of a stimulation of microorganisms that allow the degradation of stable organic matter and its further consumption by earthworms. In conclusion, this study clearly confirmed the different impacts of compost and vermicompost on bacterial activity and diversity and highlighted the importance considering the interaction of these organic substrates with local endogeic earthworms.

Effect of Disposal of Effluent and Paunch from a Meat Processing Factory on Soil Chemical and Microbial Properties

The effects of irrigation with meat processing factory effluent (MPE) in combination with additions of paunch to three arable sites and one pasture site on soil chemical and microbial properties were investigated in fields surrounding a beef meat processing factory. A pasture site that had only received MPE was also sampled along with adjoining arable and pasture control fields that had never received MPE or paunch. Additions of MPE/paunch caused increases in electrical conductivity, exchangeable Na and K, exchangeable sodium percentage (ESP), extractable P, organic C, total N, microbial biomass C, and metabolic quotient and decreases in exchangeable Ca and Mg, pH, and the proportion of organic C present as microbial biomass. The structure and diversity of bacterial and fungal communities was measured by polymerase chain reaction-denaturing gradient gel electrophoresis of 16S rDNA and internal transcribed spacer-RNA amplicons respectively and catabolic diversity by analysis of catabolic response profiles to 25 substrates. Principal component analysis of catabolic response profiles clearly separated control from MPE/paunch-treated sites, and this was associated with greater catabolic responses to the carboxylic acids α-ketoglutaric, α-ketobutyric, l-ascorbic, and citric acid in the control. At the arable sites, application of MPE and paunch caused increases in bacterial, fungal, and catabolic diversity. Canonical correspondence analysis of the relationship between catabolic, bacterial, and fungal fingerprints and soil properties indicated that the main soil variables separating MPE/paunch treatments from controls were the higher organic C, ESP, and extractable P and a lower pH, exchangeable Ca, and Mg. It was concluded that, although long-term MPE/paunch additions induce soil salinity, sodicity, and acidity, in general, they cause an increase in the size, activity, and structural and functional diversity of in the soil microbial community.

Phylogenetic and functional changes in the microbial community of long-term restored soils under semiarid climate

In semiarid climates, soils are often found in pre-desertic states with constrained vegetation, organic matter and ecosystem functionality. These limitations negatively impact soil microbial communities which are important drivers of biogeochemical processes and strongly influence soil quality. The long-term impacts of restoration on the phylogenetic structure and metabolic functionality of soil microbial communities were studied in a representative degraded field area located in southeast-Spain. Restoration was undertaken 25 years ago by the singly application of two doses of organic domestic waste at 65 Mg ha−1 (LD plots) and 195 Mg ha−1 (HD plots). Control soils without amendment were also evaluated. Pyrosequencing of 16S- and 18S-rRNA genes did not reveal significant differences in phylogenetic diversity between restored and control soils. However, principal coordinates analysis of unweighted Unifrac distances showed variation in the structure of bacterial and fungal communities of HD plots. The number of Alpha-proteobacteria sequences was higher in HD plots than in LD and control plots, while Actinobacteria abundance diminished in HD plots. In contrast to Basidiomycota, the number of Ascomycota sequences responded positively to restoration. Changes in microbial phylogenetic structure were related to changes in functional structure established by multivariate analysis of community-level-physiological profiles. Interestingly, despite the absence of phylogenetic diversity, restoration decreased the catabolic diversity in HD plots. This effect is likely due to the aboveground plant influences in restored plots. Overall, in the long-term, soil restoration under semiarid conditions did not increase microbial diversity but influenced microbial community structure and functionality.

Rhizosphere bacterial communities associated with healthy and Heterodera glycines-infected soybean roots

Bacterial communities in rhizosphere soil of soybean plants that were healthy, infected with soybean cyst nematode (SCN, Heterodera glycines), and infected with SCN but treated with Purpureocillium lilacinus YES-2 were investigated with community-level physiological profile (Biolog) and 16S rDNA clone library analyses. Biolog data indicated significant differences in substrate utilization patterns of the rhizosphere bacterial communities associated with healthy, SCN-infected, and SCN-infected plus P. lilacinus-treated plants; among the three treatments, substrate richness and catabolic diversity were lowest in the rhizosphere of healthy soybeans. Analysis of 16S rDNA profiles placed the soybean rhizosphere bacteria into seven groups: Proteobacteria, Actinobacteria, Acidobacteria, Firmicutes, Bacteroidetes, Chloroflexi, and an unclassified bacterial clade. The percentages of Rhizobiales and Actinobacteria clones were greater in the rhizosphere of healthy plants than SCN-infected plants, while the opposite was true for the proportions of Bacteroidetes and Firmicutes clones. Addition of P. lilacinus did significantly affect the rhizosphere bacterial community of SCN-infected plants. These results suggest that rhizosphere bacterial community may play an important role in the changes of soybean rhizosphere biological conditions during the infection process. Further studies will identify more specific changes in the rhizosphere bacterial community during the establishment and progression of SCN disease, and relate these changes to potential effects on disease management, soybean health, and soybean productivity.

Assessment of shifts in microbial community structure and catabolic diversity in response to Rehmannia glutinosa monoculture

Rehmannia glutinosa, a widely used Chinese medicinal herb, has been shown to suffer from serious consecutive monoculture problems that cause significant decline in both yield and quality. The objective of this study was to evaluate the response of the soil microbial community and the effect on catabolic diversity to consecutive monoculture regime using three different techniques: substrate-induced respiration (SIR), phospholipid fatty acid (PLFA) and community-level physiological profiles (CLPP) analyses. We found that basal soil respiration (BSR) was significantly higher in the control and newly planted soils than in the second and third year consecutive monoculture soils. However, no significant difference was observed in SIR among the newly planted, second and third year consecutive monoculture soils. The PLFA signatures indicated that the bacterial biomass was larger than the fungal biomass in all four treatments and both enhanced with the increasing years of monoculture and attained the peak in SM. The ratio of cyclopropyl PLFAs to their metabolic precursors (cy/pre), a measure of physiological stress in microbial communities, in the second and third year consecutive monoculture soils was significantly greater than that in the control and newly planted soils. Biolog analysis results revealed that the consumption of carboxylic acids, phenolic acids and amines, especially acid carbon substrates, in the consecutively monocultured soil was significantly greater than that in the newly planted soil. Both PLFA- and CLPP-based principal component analysis (PCA) and cluster analysis revealed the distinct separation between the control, newly planted plots and the second, third year consecutive monoculture plots. Through our PLFA-based and Biolog analysis, together with microbial respiration determination, we were able to reveal characteristic differences in the microbial community composition and activities in the rhizosphere following R. glutinosa monoculture.

CO2 and O2 respiration kinetics in hydrocarbon contaminated soils amended with organic carbon sources used to determine catabolic diversity

Multiple substrate induced respiration (MSIR) assays which assess the response of soils to carbon source amendment are effective approaches to determine catabolic diversity of soils. Many assays are based on a single short term (<6 h) time point measurement and usually limited to CO2 production only. However, repeated measurements of both CO2 and O2 simultaneously can provide additional valuable information. In this study, a MSIR assay involving eight carbon sources was applied to three hydrocarbon contaminated soils using continuous CO2 and O2 respiration measurements. Based on cumulative CO2 and O2 measurements at 4, 24 and 120 h, the soils were found to be distinct in terms of their catabolic diversity. Most noteworthy, however, was the response to the addition of maleic acid which provided strong evidence of abiotic CO2 efflux to be the overriding process, raising questions about the interpretation of CO2 only responses from organic acid addition in MSIR assays.

Comparison of soil microbial community catabolic diversity between rhizosphere and bulk soil induced by tillage or residue retention

The effects of long term no-till and crop residue on soil microbial community catabolic function and relevant carbon cycle in the rhizosphere and bulk soils were assessed in the 10th year of a maize-winter wheat-soybean crop rotation. Conventional and zero tillage were coupled with residue removal and residue retention in a factorial design. Soil microbial community catabolic diversity was determined using Biolog-Eco plate. Average well colour development value (AWCD) of the microbial community in the rhizosphere soil was significantly higher than that in the bulk soil. Soil organic carbon (SOC) and microbial biomass carbon (MB-C) content of rhizosphere soil under both zero tillage and residue removal treatments were significantly higher than those in the bulk soil. Microbes in bulk soil presented a preferential utilization of diverse carbon sources when crop residue was retained. Zero tillage significantly increased the utilization of most carbon sources of microbial in the rhizosphere compared to conventional tillage. Principal component analysis (PCA) of the distribution of carbon substrate utilization for all treatments suggests that the microbial community catabolic diversity is different between the tillage management treatments and between soil sampling positions. Effects of zero tillage and crop residue retention were different with respect to the microbial catabolic diversity in the rhizosphere and the bulk soil.

In silico modeling and evaluation of Gordonia alkanivorans for biodesulfurization

The genus Gordonia is well known for its catabolic diversity and ability to transform several compounds including the various recalcitrant polyaromatic sulfur heterocycles (PASHs) found in the fossil fuels. In fact, some strains offer the unique ability to desulfurize even benzothiophene (BT) and other thiophenic compounds, which most of the commonly studied rhodococci strains cannot. In this work, we present the first genome scale metabolic model for G. alkanivorans, a desulfurizing strain, to enable a holistic study of its metabolism and comparison with R. erythropolis. Our model consists of 881 unique metabolites and 922 reactions associated with 568 ORFs/genes and 544 unique enzymes. It successfully predicts the growth rates from experimental studies and quantitatively elucidates the pathways for the desulfurization of the commonly studied sulfur compounds, namely dibenzothiophene (DBT) and benzothiophene (BT). Using our model, we identify the minimal media for G. alkanivorans, and show the significant effect of carbon sources on desulfurization with ethanol as the best source. Our model shows that the sulfur-containing amino acids such as cysteine and methionine decrease desulfurization activity, and G. alkanivorans prefers BT over DBT as a sulfur source. It also suggests that this preference may be driven by the lower NADH requirements for BT metabolism rather than the higher affinity of the transport system for BT. Our in silico comparison of R. erythropolis and G. alkanivorans suggests the latter to be a better desulfurizing strain due to its versatility for both BT and DBT, higher desulfurization activity, and higher growth rate.

Metaproteomic analysis of ratoon sugarcane rhizospheric soil

BackgroundThe current study was undertaken to elucidate the mechanism of yield decline in ratoon sugarcane using soil metaproteomics combined with community level physiological profiles (CLPP) analysis.ResultsThe available stalk number, stalk diameter, single stalk weight and theoretical yield of ratoon cane (RS) were found to be significantly lower than those of plant cane (NS). The activities of several carbon, nitrogen and phosphorus processing enzymes, including invertase, peroxidase, urease and phosphomonoesterase were found to be significantly lower in RS soil than in NS soil. BIOLOG analysis indicated a significant decline in average well-color development (AWCD), Shannon’s diversity and evenness indices in RS soil as compared to NS soil. To profile the rhizospheric metaproteome, 109 soil protein spots with high resolution and repeatability were successfully identified. These proteins were found to be involved in carbohydrate/energy, amino acid, protein, nucleotide, auxin and secondary metabolisms, membrane transport, signal transduction and resistance, etc. Comparative metaproteomics analysis revealed that 38 proteins were differentially expressed in the RS soil as compared to the control soil or NS soil. Among these, most of the plant proteins related to carbohydrate and amino acid metabolism and stress response were up-regulated in RS soil. Furthermore, several microbial proteins related to membrane transport and signal transduction were up-regulated in RS soil. These proteins were speculated to function in root colonization by microbes.ConclusionsOur experiments revealed that sugarcane ratooning practice induced significant changes in the soil enzyme activities, the catabolic diversity of microbial community, and the expression level of soil proteins. They influenced the biochemical processes in the rhizosphere ecosystem and mediated the interactions between plants and soil microbes.

Effects of anthracene on microbial activities and organic matter decomposition in a Pinus halepensis litter from a Mediterranean coastal area

Due to increasing atmospheric pollution, it has become highly important to investigate how anthropic chronic contaminations may affect ecosystem functioning. To explore the effect of polycyclic aromatic hydrocarbons (PAHs) on indigenous microbial activities, anthracene was used as a model PAH in a mesocosm experiment with Pinus halepensis litter from the Massif of Marseilleveyre (Marseille, France). The effects of anthracene on microbial activities were followed after 1- and 3- month incubations by: Catabolic Level Physiological Profile (CLPP) using ECO and FF plates and four enzyme activities (cellulase, β-glucosidase, acid phosphatase and lipase). Moreover the chemical variations in organic matter were evaluated by solid-state 13C NMR and C/N ratio. These experiments revealed an increase in cellulase, β-glucosidase and phosphatase activities and a decrease in lipase activities after a 3-month incubation in the presence of anthracene. Principal Component Analysis (PCA) from CLPP showed that bacterial catabolic diversity is more influenced than that of fungal communities by anthracene. Correlation between both chemical and biological indicators revealed that the increase in lignocellulolytic enzymes (cellulase, laccase and β-glucosidase) was significantly correlated to the decrease in phenolic compounds. In addition, aromaticity ratio also decreased in the presence of anthracene suggesting that transformation of the recalcitrant part of organic matter was enhanced. Our results highlight the difference in sensitivity of bacterial and fungal communities to PAHs, the later especially active while exposed to high concentrations of pollutant. This suggests that microbial communities inhabiting P. halepensis litters in Mediterranean coastal areas may resist to chronic pollution involving PAH.

The effects of land use on biomass and catabolic diversity of soil microbial communities

An understanding of the factors influencing microbial diversity in soils is essential to predict the effects of current land use trends on diversity. In this study, the effects of soil management (high and low input systems and pasture) on microbial biomass and diversity was investigated. Respiration responses to specific substrate were used to measure soil microbial diversity. Catabolic evenness and richness of microorganisms as a measure of soil microbial diversity was measured. In comparison with agricultural systems, pasture resulted in an increase in organic matter and microbial biomass. However, in the soil managements, in high input systems, basal respiration was higher than other soil managements, suggesting the presence of a small but highly metabolically active micro floral community. Analysis of catabolic response profiles demonstrated that there were large differences in the catabolic capability of the soil microbial communities under different soil management type. Values for Shannon’s and Simpson’s diversity indices indicated that greatest catabolic existed under native grassland and least diversity under high input systems. This was attributed to broad range of organic pool in pasture. It was concluded that soil management has a substantial effects on the size, activity and diversity of the soil microbial community and that these changes could be broadly related to changes in soil organic matter content. Although the implications of losses of microbial diversity are unknown, but diversity may results more resilient to stresses or disturbances. Key words: Microbial diversity, land use, microbial biomass, catabolic response profiles methodology.

Response of native soil microbial functions to the controlled mycorrhization of an exotic tree legume, Acacia holosericea in a Sahelian ecosystem

Fifty years of overexploitation have disturbed most forests within Sahelian areas. Exotic fast growing trees (i.e., Australian Acacia species) have subsequently been introduced for soil improvement and fuelwood production purposes. Additionally, rhizobial or mycorrhizal symbioses have sometimes been favored by means of controlled inoculations to increase the performance of these exotic trees in such arid and semiarid zones. Large-scale anthropogenic introduction of exotic plants could also threaten the native biodiversity and ecosystem resilience. We carried out an experimental reforestation in Burkina Faso in order to study the effects of Acacia holosericea mycorrhizal inoculation on the soil nutrient content, microbial soil functionalities and mycorrhizal soil potential. Treatments consisted of uninoculated A. holosericea, preplanting fertilizer application and arbuscular mycorrhizal inoculation with Glomus intraradices. Our results showed that (i) arbuscular mycorrhizal (AM) inoculation and prefertilizer application significantly improved A. holosericea growth after 4 years of plantation and (ii) the introduction of A. holosericea trees significantly modified soil microbial functions. The results clearly showed that the use of exotic tree legume species should be directly responsible for important changes in soil microbiota with great disturbances in essential functions driven by microbial communities (e.g., catabolic diversity and C cycling, phosphatase activity and P availability). They also highlighted the importance of AM symbiosis in the functioning of soils and forest plantation performances. The AM effect on soil functions was significantly correlated with the enhanced mycorrhizal soil potential recorded in the AM inoculation treatment.

Soil organic matter quality and microbial catabolic functions along a gradient of wildfire history in a Mediterranean ecosystem

The principal aim of this research was to determine the influence of an increasing wildfire history on the recovery at short and long term of soil organic matter (SOM) composition and microbial properties. The contemporary wildfire events (since 1950) were recorded for 27 plots located on the siliceous part of the French Mediterranean region (Maures mountain ranges). A wildfire history index was built, tested and calculated in order to display numerical values representative of the different wildfire history parameters (i.e. number of fires, time since fire and mean fire interval). Microbial basal respiration and biomass were analysed as well as intensity of the use of 31 C-substrates, catabolic diversity and C-substrates utilisation profiles. Furthermore, a qualitative characterisation of the SOM was carried out by solid state 13C NMR. Potential drivers of the microbial recovery were identified by studying the relationships between microbial activities and chemical functions of SOM. Our results showed that fire histories resulting in considerable losses or alterations of SOM, such as recent or close fires, decreased the microbial catabolic evenness. This could be attributed to a preferential utilisation of N-containing compounds and complex substrates such as aromatic and polymers reflecting a greater N microbial demand and a selection of specific catabolic functions. Moreover, a large number of fires (4 fires in 57 years compared to 1–2) resulted in lasting degradation of the relative intensity of methyl C function in polymethylene, O-Alkyl C, aromatic C and phenolic C functions inducing a slow-down in recovery of microbial properties. These results also confirm our hypothesis that some chemical functions of SOM can be in equilibrium with wildfire history. Finally, this research demonstrates that FT-NIR analysis can be used as a valuable tool to assess both the wildfire history and the vulnerability of soil quality to shifts in historical fire regimes.