Soils Of Natural Ecosystems Research Articles

Phylogenetic relationship between Australian Fusarium oxysporum isolates and resolving the species complex using the multispecies coalescent model

BackgroundThe Fusarium oxysporum species complex (FOSC) is a ubiquitous group of fungal species readily isolated from agroecosystem and natural ecosystem soils which includes important plant and human pathogens. Genetic relatedness within the complex has been studied by sequencing either the genes or the barcoding gene regions within those genes. Phylogenetic analyses have demonstrated a great deal of diversity which is reflected in the differing number of clades identified: three, five and eight. Genetic limitation within the species in the complex has been studied through Genealogical Concordance Phylogenetic Species Recognition (GCPSR) analyses with varying number of phylogenetic ‘species’ identified ranging from two to 21. Such differing views have continued to confuse users of these taxonomies.ResultsThe phylogenetic relationships between Australian F. oxysporum isolates from both natural and agricultural ecosystems were determined using three datasets: whole genome, nuclear genes, and mitochondrial genome sequences. The phylogenies were concordant except for three isolates. There were three concordant clades from all the phylogenies suggesting similar evolutionary history for mitochondrial genome and nuclear genes for the isolates in these three clades. Applying a multispecies coalescent (MSC) model on the eight single copy nuclear protein coding genes from the nuclear gene dataset concluded that the three concordant clades correspond to three phylogenetic species within the FOSC. There was 100% posterior probability support for the formation of three species within the FOSC. This is the first report of using the MSC model to estimate species within the F. oxysporum species complex. The findings from this study were compared with previously published phylogenetics and species delimitation studies.ConclusionPhylogenetic analyses using three different gene datasets from Australian F. oxysporum isolates have all supported the formation of three major clades which delineated into three species. Species 2 (Clade 3) may be called F. oxysporum as it contains the neotype for F. oxysporum.

Quantifying global N<sub>2</sub>O emissions from natural ecosystem soils using trait-based biogeochemistry models

Abstract. A group of soil microbes plays an important role in nitrogen cycling and N2O emissions from natural ecosystem soils. We developed a trait-based biogeochemical model based on an extant process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), by incorporating the detailed microbial physiological processes of nitrification. The effect of ammonia-oxidizing Archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) was considered in modeling nitrification. Microbial traits, including microbial biomass and density, were explicitly considered. In addition, nitrogen cycling was coupled with carbon dynamics based on stoichiometry theory between carbon and nitrogen. The model was parameterized using observational data and then applied to quantifying global N2O emissions from global terrestrial ecosystem soils from 1990 to 2000. Our estimates of 8.7±1.6 Tg N yr−1 generally agreed with previous estimates during the study period. Tropical forests are a major emitter, accounting for 42 % of the global emissions. The model was more sensitive to temperature and precipitation and less sensitive to soil organic carbon and nitrogen contents. Compared to the model without considering the detailed microbial activities, the new model shows more variations in response to seasonal changes in climate. Our study suggests that further information on microbial diversity and ecophysiology features is needed. The more specific guilds and their traits shall be considered in future soil N2O emission quantifications.

Soil as a Biological System and Its New Category—Health

It is proposed that soil should be considered a biological system with the following notions: “soil ecosystem” or “ecosystem of soil.” A new, integral characteristic of the soil ecosystem—soil health—is addressed. Parameters and methods essential to define soil health and characterize this new category are provided. Natural soil ecosystems and agroecosystems are discussed and compared. Conventional and organic land use systems are addressed in relation to agroecosystems. The need to determine and assess the health of soil ecosystems with respect to the land-use type is highlighted. Activities and methods required to preserve and protect the health of soil ecosystems, the significance of “activity suppression” in soil ecosystems, and means to diagnose soil health and to use therapy in modern agroecosystems are discussed.

Use of magnetic susceptibility to assess metals concentration in soils developed on a range of parent materials

This research was conducted to evaluate the utilization of magnetic susceptibility measurements in the assessment of metal concentrations in soils developed on a range of parent materials in northwestern Iran. Eighty surface soil samples were collected from eight parent rocks including ultrabasic rocks, basalt, andesite, granite, marl, limestone, Qom formation, and shale. The collected samples were assessed to determine magnetic susceptibility at low frequency (χlf) and concentrations of some metals comprising chromium (Cr), iron (Fe), copper (Cu), nickel (Ni), zinc (Zn), cobalt (Co), and manganese (Mn). The results showed that the highest levels of metals and χlf were observed in basic and ultrabasic soils. Strong positive correlations (P < 0.01) detected between χlf and Fe (0.87), Mn (0.78), Zn (0.74), Ni (0.90), Co (0.78), and Cr (0.90) in all samples indicated a potential for using magnetic susceptibility in semi-quantitative estimation of metal concentrations in soils of natural ecosystems. Multiple linear regression between metal contents and χlf showed that Ni, Zn, Mn, and Co could explain 77% of the total variance in χlf in the study area. K-means cluster analysis categorized the studied soils into three groups based on metals and χlf variability. Clustering of soils based on their parent rocks and use of further magnetic measures, i.e., saturation isothermal remanent magnetization (SIRM), isothermal remanent magnetization (IRM100mT) and natural remanent magnetization (NRM) are expected to improve the accuracy of metal concentration predictions in natural soils of the study area.

Biological properties of soils under the influence of agrotechnical factors

The results of comparison of the correlation matrices obtained for the investigated soils of natural ecosystems are presented, which showed the formation of their specific properties under the influence of abiotic and biotic factors. Uniqueness of each ecosystem has been confirmed. It has been mathematically proved that chernozems are more stable than gray forest soils, which are relatively easy to lose fertility due to anthropogenic impact, and also require ecologically stabilizing measures and protection for agricultural use.

Comparative Response of Indigenously Developed Bacterial Consortia on Progressive Degradation of Polyhydroxybutyrate Film Composites

The global demand of bioplastics has lead to an exponential increase in their production commercially. Hence, biodegradable nature needs to be evaluated in various ecosystems viz. air, water, soil and other environmental conditions to avoid the polymeric waste accumulation in the nature. In this paper, we investigated the progressive response of two indigenously developed bacterial consortia, i.e., consortium-I (C-I: Pseudomonas sp. strain Rb10, Pseudomonas sp. strain Rb11 and Bacillus sp. strain Rb18), and consortium-II (C-II: Lysinibacillus sp. strain Rb1, Pseudomonas sp. strain Rb13 and Pseudomonas sp. strain Rb19), against biodegradation behavior of polyhydroxybutyrate (PHB) film composites, under natural soil ecosystem (in net house). The biodegraded films recovered after 6 and 9 months of incubation were analyzed through Fourier transform infrared spectroscopy and scanning electron microscopy to determine the variations in chemical and morphological parameters (before and after incubation). Noticeable changes in the bond intensity, surface morphology and conductivity were found when PHB composites were treated with C-II. These changes were drastic in case of blends in comparison to copolymer. The potential isolates not only survived, but, also, there was a significant increase in bacterial diversity during whole period of incubation. To the best of our knowledge, it is the first report which described the biodegradation potential of Lysinibacillus sp. as a part of C-II with Pseudomonas sp. against PHB film composites.

Forecasting heavy metal pollution of soils in an administrative district of Belarus

We tested the dynamical model of migration based on balance equations, for a predictive assessment of soil pollution by heavy metals: lead, cadmium, zinc and copper, at the level of an administrative district. As the main input components of the balance, we took into account the flows of metals caused by atmospheric depositions, weathering of parent materials and input with fertilizers (on agricultural lands); the expenditure part of the balance is described by flows of metals with the infiltration subsurface flow and consumption for buildup of the vegetation biomass or the removal with the harvest. It is found that given the continuation of the existing level of loads (scenario 1), for the calculated period (40 years) in the soils of natural ecosystems the concentrations of the four elements can decrease substantially or remain at the previous level. Changes will make up 0.2–0.8% for lead, 0.5–5 for cadmium, 0.8–4 for copper, and 0.3–1.5% for zinc of their total content levels in the soil. In the soils of agricultural lands, provided that the aforementioned conditions are observed, the total content of lead will increase by 5–6.5%, cadmium by 1–1.2%, copper by 2.1–3, and zinc by 12.5–16.5%. It is determined that with an increase in the flow of atmospheric deposition (scenario 2), for 40 years the soils of natural ecosystems will retain a minor negative balance of cadmium (0.001–0.004 mg/kg of the soil); for lead the negative balance in forest ecosystems will change to a minor positive balance (0.09–0.18 mg/kg of the soil), and the removal of zinc and copper will retain its previous level. In the soils of agricultural lands, with a simultaneous increase of the rates of application of organic fertilizers by 20%, the total concentrations of lead for the calculated period can increase by 7.1–9.6%, cadmium by 7–8.5, copper by 5.2–7.8, and zinc by 18.2–24.2%.

Mechanisms responsible for high N2O emissions from subarctic permafrost peatlands studied via stable isotope techniques

AbstractRecent field studies have shown that there are habitats in the subarctic tundra emitting N2O at exceptionally high rates. In this study, stable isotope techniques were applied to characterize the processes responsible for these high N2O emissions which have been found from bare peat surfaces in permafrost peatlands. The results include the first data on the nitrogen and oxygen isotopic composition of N2O emitted from arctic tundra. The emission‐weighted average δ15Nbulk value for N2O of −13.0‰ ± 2.0‰ (mean ± SD; n = 8) from the bare peat surfaces falls within the range of the emission‐weighted average values from other natural ecosystems but is distinct from those for managed/agricultural ecosystems. This implies that if in the future, a smaller rate in the overall decreasing trend of δ15Nbulk N2O tropospheric isotopic composition is found, it cannot be attributed only to agricultural N2O emission reductions from mitigation actions but also to soils in natural ecosystems that may be emitting more N2O to the atmosphere due to warmer conditions. The site preference (SP) values from emitted N2O range from −30‰ to 58‰, indicating a temporal shift of microbial production and consumption of N2O during the sampling period. Soil emission SP data suggest that the N2O emission in subarctic tundra are more likely to be produced by nitrifier denitrification in the drier study year, but due to variable published SP values for N2O production processes in soils, this interpretation has to be taken with caution. According to SP values at depth, denitrification was the main N2O production pathway. To better address the usefulness of SP in partitioning microbial mechanisms in soils, further studies in soils mesocosms are required.

The role of the structure to provide biogeocenotic soil functions

There is a presentation of analysis of the structural state role in the manifestation of biogeocenotic soil functions, which are due to their physical, chemical and biochemical, physical-chemical, information, integrity properties. The main role in the formation of the structure of living space manifests itself in existence, due to the presence in soil aggregates of different sizes and structures, of numerous and diverse ecological niches for soil organisms. The participation of structure in providing housing and shelter is evident in its impact on the majority of soil conditions. The role of the structure in the manifestation of the support is associated with fixing function in plants through the soil root system, as well as with structural features of the surface soil, which is used by animals when moving. The participate of structure in preservation of plant seeds, eggs and larvae of animal is due to the formation of aggregated soil optimal living conditions for living organisms. The structure plays an important role in realization of the soil nutrients and source connections, as plants are able to obtain only minerals in dissolved form and the optimal conditions for this can provide only soil with qualitative waterproof structure. The structure also participates in the formation of a depot of nutrients, energy and moisture, most of which are found in soil and aggregates that can be made available to living organisms after their destruction. The role of the of structure in providing stimulator function and inhibitor of biochemical processes is evident in the formation of a kind of the medium through which the interaction of the root systems of plants, as well as providing conditions for humification and mineralization of soil organic matter. The influence of the structure on the sorption of particulate material coming from the atmosphere is evident in its involvement in the formation of structural units of the soil. The role of the structure in the sorption of fine soil microorganisms living in the soil is due to the fact that this process is largely determined by the shape of aggregates, mineral composition and organic matter, which are included in their composition. The features of the structure to provide a signal function to the seasonal biological processes are related to the determining the influence of the aggregate composition of the soil at its thermal regime, which mainly depends on all biological processes in the soil. The role of the structure in the regulation of number and composition of the ecological community is due to the existence of the relationship between aggregate soil composition and characteristics of ecological community that exists on it. Participation in the launch of some of the structures of succession occurs mainly at the sharp deterioration of the structural state of the soil, which may be associated with the processes of water and wind erosion. The role of the structure to provide a «memory» of biogeocoenosis is explained by quite stable structural state of the natural ecosystems of the soil in the absence of catastrophic processes, which is able to store information about the features of the state of other components of biogeocoenosis. Participation of the structure in the transformation of matter and energy entering biogeocoenosis is due to the constant transformation of minerals, grain size elements, organic matter and other constituent parts of the soil in the process of aggregation. The role of the structure in the display of the sanitary function is due to the fact that there is a degradation of organic residues and metabolic products of living organisms in the soil, its antiseptic properties is best evident only in well-structured soil. The value of the structure in the function of the protective screen and buffer biogeocenotic screen provision is most fully shown in the soils of natural ecosystems with a favorable and stable structural state, due to which ecosystems are protected from mechanical destruction under the influence of various factors – water, wind, gravity force. Despite the cited aspects of the role of structure manifestation in providing biogeocenotic soil functions there is a need for further detailed research in this area.

Disentangling relationships between plant diversity and decomposition processes under forest restoration

SummaryBiodiversity has been elucidated to be one of the major factors sustaining ecosystem functioning. The vast majority of studies showing a relationship between biodiversity and ecosystem functioning have come from experiments, and this knowledge has not yet been applied to most real‐world cases of conservation and management. This is especially true in forest ecosystems, characterized by the dominance of long‐lived organisms (trees) and high levels of structural complexity and environmental heterogeneity.To apply biodiversity–function relationships to actual forest management, there are several issues to be considered. These include employing a cross‐taxon perspective, as some functions (e.g. soil biogeochemical processes) cannot be maintained by a narrow set of organisms, as is usually the case with experimental systems. More specifically, although the interaction between above‐ and below‐ground diversity is important for many functions in forests, there are few studies that evaluated the roles of diversity in both subsystems in a manner that could be informative in practice.To evaluate the roles of above‐ and below‐ground diversity to support natural soil ecosystem functions, we conducted a decomposition experiment in the northern forests of Japan, which are currently under restoration management. The restoration area consists of mosaics of different vegetation types by various revegetation activities and establishment of ungulate exclosures. Using structural equation modelling and linear mixed‐effects models, we assessed direct and indirect pathways from diversity to functions by focusing on both of taxonomic and functional diversity indices. To put our findings into practice, we utilized a trait‐based approach, which provides a link between the functional consequences of human influences and ecosystem structure.We found little direct effects of tree diversity on below‐ground functions such as decomposition rate and litter stabilization. However, once the diversities of understorey herbaceous plants and soil fungi were considered as a possible mediating explanatory factor, we found a significant effect of tree diversity to indirectly support these functions by supporting these other types of biodiversity. Particularly, we found that the models based on functional trait diversity, rather than on taxonomic species richness, best explained the variation in below‐ground processes.Synthesis and applications. Forest restoration in the northern forests of Japan has had no explicit objective to restore soil functions. Nevertheless, afforestation, and the associated increase in tree diversity as a measure of forest restoration, was, although often unintentionally, proven effective for the maintenance of multiple ecosystem functions, such as soil biogeochemical processes. This finding suggests a great potential for management to make local tree assemblages functionally dissimilar and diverse for the sake of supporting and enhancing fundamental ecosystem functions in forests.

Adaptations of enchytraeids to single and combined effects of physical and chemical stressors

Climate changes are expected to be greatest in the polar and temperate areas, where predictions point to an increase in freeze–thaw events and changes in precipitation, evaporation, and salinity patterns. These events will therefore affect biological activity of the soil compartment that may result in large impacts in ecosystem functioning and dynamics therein. This concern becomes even more important when considering the presence of contaminants due to intense anthropogenic activity, which may lead to synergistic or antagonistic effects and increase or decrease the impact on natural ecosystems. This paper reviews the effect of physical and chemical stressors on enchytraeids, with special emphasis on Enchytraeus albidus because most relevant studies have involved this species. E. albidus is a freeze-tolerant and euryhaline organism and several studies suggest that the absence of salinity may have important (negative) consequences not only for their freeze tolerance ability but also for their reproduction and capacity to deal with the presence of contaminants, such as metals and fungicides. Single and joint effects of constant freezing or freeze–thaw cycles and surfactants, such as 4-nonylphenol, affected negatively E. albidus freeze tolerance by decreasing the levels of cryoprotectants, membrane fluidity and interfering with cellular energy allocation. Because enchytraeids are of ecological significance in many important habitats along the Artic and cold-temperate environments, a reduction in abundance may result in disturbances of the decomposition processes in soils. The knowledge of the biological, physiological, and biochemical limits of enchytraeids to combined effect of physical and chemical stressors are crucial to provide a scientific basis for improving the setting of safety factors when extrapolating from controlled (and optimal) laboratory conditions to natural soil ecosystems. Therefore, there is a need to expand and evolve experiments that more realistically mimic the situation in the field, where interactions between factors are highly relevant. The synergistic or antagonistic interactions identified in the present review may also represent a stepping stone in the evaluation and possible inclusion of natural factors, like cold and salinity, in standardized enchytraeid test guidelines and consequently in risk assessment of chemicals.

Effect of organic and conventional practices on carbon-substrate utilisation by the soil microbial community in a ‘Cripps Pink’/M7 apple orchard

Changes in microbial community metabolic profiles potentially can be used to identify differences in soil characteristics caused by dissimilar orchard floor management practices. The impacts of orchard floor management practices on the microbial community metabolic diversity (CMD) were examined in apple orchard soils subjected to two conventional (CON) and three organic (ORG) orchard floor management practices. The CMD, as indicated by carbon (C) substrate utilisation (BIOLOG™ system), was determined in composite soil samples (0–15 cm) from the tree rows. The CON treatments reduced, and ORG treatments increased, C-source utilisation and, hence, CMD. Among the CON treatments, C-source utilisation in summer was favoured by winter cover crops in work rows, controlled with herbicide in spring, compared to uncontrolled weed-covered work rows. Orchard soils under ORG regimes more closely resembled soils of natural ecosystems in that they were better able to sustain CMD, and possibly afford a better option to sustain critical ecosystem functions than under CON management, which relies heavily on synthetic agrochemical usage.

Adaptation of Bacillus subtilis carbon core metabolism to simultaneous nutrient limitation and osmotic challenge: a multi‐omics perspective

SummaryThe Gram‐positive bacterium Bacillus subtilis encounters nutrient limitations and osmotic stress in its natural soil ecosystem. To ensure survival and sustain growth, highly integrated adaptive responses are required. Here, we investigated the system‐wide response of B. subtilis to different, simultaneously imposed stresses. To address the anticipated complexity of the cellular response networks, we combined chemostat experiments under conditions of carbon limitation, salt stress and osmoprotection with multi‐omics analyses of the transcriptome, proteome, metabolome and fluxome. Surprisingly, the flux through central carbon and energy metabolism is very robust under all conditions studied. The key to achieve this robustness is the adjustment of the biocatalytic machinery to compensate for solvent‐induced impairment of enzymatic activities during osmotic stress. Specifically, increased production of several enzymes of central carbon metabolism compensates for their reduced activity in the presence of high salt. A major response of the cell during osmotic stress is the production of the compatible solute proline. This is achieved through the concerted adjustment of multiple reactions around the 2‐oxoglutarate node, which drives metabolism towards the proline precursor glutamate. The fine‐tuning of the transcriptional and metabolic networks involves functional modules that overarch the individual pathways.

Attractions of nematodes to yeasts are influenced by both nematodes and yeasts

Both yeasts and nematodes are significant components of the soil biomass and biodiversity and fulfil a wide variety of ecological functions. However, relatively little is known about the interactions between yeasts and nematodes, including the potential use of yeasts by nematodes as a food source and potential diseases that these yeasts can cause in nematodes. To begin investigating their ecological relationships, we tested the in vitro attractive ability of representative yeast species on nematodes. A total of 15 yeast strains belonging to six species were assayed for their attraction abilities towards two nematode species. Our results suggest that nematodes are able to distinguish between their microbial food source and yeast pathogens. Furthermore, our analyses demonstrated that host nematodes, yeast species, and in some cases yeast strains all contributed to the variation in attraction abilities. We hypothesize that volatile and/or diffusible organic compounds released from the yeasts are involved in attracting the nematodes. These results suggest the attraction and consumption interaction between soil yeasts and nematodes may be common in the environment. These interactions may be significant in regulating the populations of both the yeasts and their nematode hosts in natural soil ecosystems. The data presented here could also help to develop nematode-based model systems for studying fungal pathogenesis.

An estimate of the global sink for nitrous oxide in soils

A literature survey of studies reporting nitrous oxide uptake in the soils of natural ecosystems is used to suggest that the median uptake potential is 4 μg m(-2) h(-1). The highest values are nearly all associated with soils of wetland and peatland ecosystems. Globally, the consumption of nitrous oxide in soils is not likely to exceed 0.3 TgN yr(-1), indicating that the projected sink is not more than 2% of current estimated sources of N(2)O in the atmosphere.

Changes of Soil Bacterial Diversity as a Consequence of Agricultural Land Use in a Semi-Arid Ecosystem

Natural scrublands in semi-arid deserts are increasingly being converted into fields. This results in losses of characteristic flora and fauna, and may also affect microbial diversity. In the present study, the long-term effect (50 years) of such a transition on soil bacterial communities was explored at two sites typical of semi-arid deserts. Comparisons were made between soil samples from alfalfa fields and the adjacent scrublands by two complementary methods based on 16S rRNA gene fragments amplified from total community DNA. Denaturing gradient gel electrophoresis (DGGE) analyses revealed significant effects of the transition on community composition of Bacteria, Actinobacteria, Alpha- and Betaproteobacteria at both sites. PhyloChip hybridization analysis uncovered that the transition negatively affected taxa such as Acidobacteria, Chloroflexi, Acidimicrobiales, Rubrobacterales, Deltaproteobacteria and Clostridia, while Alpha-, Beta- and Gammaproteobacteria, Bacteroidetes and Actinobacteria increased in abundance. Redundancy analysis suggested that the community composition of phyla responding to agricultural use (except for Spirochaetes) correlated with soil parameters that were significantly different between the agricultural and scrubland soil. The arable soils were lower in organic matter and phosphate concentration, and higher in salinity. The variation in the bacterial community composition was higher in soils from scrubland than from agriculture, as revealed by DGGE and PhyloChip analyses, suggesting reduced beta diversity due to agricultural practices. The long-term use for agriculture resulted in profound changes in the bacterial community and physicochemical characteristics of former scrublands, which may irreversibly affect the natural soil ecosystem.

A real-scale soil phytoremediation

In the present investigation, a phytoremediation process with a combination of different plant species (Populus nigra (var.italica), Paulownia tomentosa and Cytisus scoparius), and natural growing vegetation has been proposed at real-scale (10.000m(2)) to bioremediate and functionally recover a soil historically contaminated by heavy metals and hydrocarbons. In the attempts to assess both effectiveness and evolution of the remediation system towards a natural soil ecosystem, besides the pollution parameters, also parameters describing the efficiency of the microbiological components (enzyme activities), were investigated. In 3years, the total content of hydrocarbons and heavy metals in soil decreased with time (40% and 20-40%, respectively), reaching concentrations under the limit of National legislation and making the site suitable for environmental reusing. The reduction in pollutants was probably the reason of the increase in dehydrogenase (indicator of overall microbial activity), β-glucosidase and phosphatase activities, enzymes related to C and P cycles, respectively. However, this trend was obviously due also to the increase of chemical nutrients, acting as substrate of these enzymes. Moreover, a phytotest carried out with Raphanus sativus, showed, after 3years, a significant increase in percentage of plant growth, confirming a reduction in soil toxicity and an improvement in soil nutritional state. Therefore, this phytoremediation system seems very promising to perform both decontamination and functional recovery of a polluted soil at real-scale level.

An inventory of global N2O emissions from the soils of natural terrestrial ecosystems

Abstract We develop an inventory of global N2O emissions from natural ecosystem soils using an artificial neural network approach and field observational data of N2O fluxes. We estimate that the global soil N2O source strength from natural ecosystems is 3.37 Tg (1 Tg = 1012 g) N per year with an uncertainty ranging from 1.96 to 4.56 Tg N per year in 2000. While our global estimate is lower than other existing estimates, the spatial patterns of our simulated N2O emissions agree with other existing studies. There was a large spatial and seasonal variability in the soil N2O emissions due to the variation in soil type, vegetation and climate conditions. Consistent with other studies, we confirm that warm and moist tropical soils are the major source of atmospheric N2O. As a result of the low temperatures, the high latitude ecosystems have significantly low emission rates and contribute little (less than 0.10 Tg N per year) to the global N2O source. The simulated annual global N2O emissions are found to be most sensitive to variation in precipitation. This study uses the most current available data for N2O fluxes and their associated environmental variables to quantify the global N2O emissions, and provides an independent global inventory of this important trace gas, which will facilitate future studies of atmospheric chemistry and climate feedbacks at the global scale.

Electronic Nose Technology to Measure Soil Microbial Activity and Classify Soil Metabolic Status

AbstractThe electronic nose (E-nose) is a sensing technology that has been widely used to monitor environments in the last decade. In the present study, the capability of an E-nose, in combination with biochemical and microbiological techniques, of both detecting the microbial activity and estimating the metabolic status of soil ecosystems, was tested by measuring on one side respiration, enzyme activities and growth of bacteria in natural but simplified soil ecosystems over 23 days of incubation through traditional methodologies, and on the other side VOCs and/or gases evolution in their headspace during the same period through the E-nose. Both kinds of measurements, i.e. biochemical-microbiological and sensorial, succeeded in discriminating between inoculated and non-inoculated microcosms and in distinguishing different phases of bacterial growth and activity during the incubation. E-nose responses were highly and significantly correlated with all catalytic activities, respiration and different phases of bacterial growth. Hence, the E-nose was proved able to detect microbial activity in natural soil ecosystems. The metabolic status of these soil ecosystems was calculated on the base of some of the parameters previously tested in order to obtain a metabolic index (MI), ranging between 0 and 1. These MIs were then grouped into 3 classes, corresponding to a low, medium and high metabolic status. All the other measures were used as a multi-type data set in a partial least square discriminant analysis to generate a model capable of classifying the soil microcosms at different sampling dates according to the 3 classes of MIs. The resulting outcomes confirmed that the E-nose technology combined with both metabolic and biomass parameters can altogether represent reliable indicators of the metabolic status of soil ecosystems.

Medium pH, carbon and nitrogen concentrations modulate the phosphate solubilization efficiency of Penicillium purpurogenum through organic acid production

To study phosphate solubilization in Penicillium purpurogenum as function of medium pH, and carbon and nitrogen concentrations. Tricalcium phosphate (CP) solubilization efficiency of P. purpurogenum was evaluated at acid or alkaline pH using different C and N sources. Glucose- and (NH(4) )(2) SO(4) -based media showed the highest P solubilization values followed by fructose. P. purpurogenum solubilizing ability was higher in cultures grown at pH 6·5 than cultures at pH 8·5. Organic acids were detected in both alkaline and neutral media, but the relative percentages of each organic acid differed. Highest P release coincided with the highest organic acids production peak, especially gluconic acid. When P. purpurogenum grew in alkaline media, the nature and concentration of organic acids changed at different N and C concentrations. A factorial categorical experimental design showed that the highest P-solubilizing activity, coinciding with the highest organic acid production, corresponded to the highest C concentration and lowest N concentration. The results described in the present study show that medium pH and carbon and nitrogen concentrations modulate the P solubilization efficiency of P. purpurogenum through the production of organic acids and particularly that of gluconic acid. In the P solubilization optimization studies, glucose and (NH(4) )(2) SO(4) as C and N sources allowed a higher solubilization efficiency at high pH. This organism is a potentially proficient soil inoculant, especially in P-poor alkaline soils where other P solubilizers fail to release soluble P. Further work is necessary to elucidate whether these results can be extrapolated to natural soil ecosystems, where different pH values are present. Penicillium purpurogenum could be used to develop a bioprocess for the manufacture of phosphatic fertilizer with phosphate calcium minerals.