Communities In Arable Soil Research Articles

Microbial response to antimony-arsenic distribution and geochemical factors at arable soil around an antimony mining site.

Antimony (Sb) mining often causes severe Sb pollution and associate arsenic (As) compound contamination. To further understand the interaction mechanism among soil microorganisms, heavy metal distribution, and geochemical factors, the effects of environmental factors on soil microbial communities under different levels of Sb-As co-contamination were studied in situ of Chashan antimony mine, Guangxi Province. The results showed that the range of Sb and As contents in soil were 1339.63-7762.28mg/kg and 2170.3-10,371.36mg/kg, respectively, and the residual fraction accounted for more than 98.0% with less than 2.0% of bioavailable fraction. Besides, the concentration of the two metals is both related to the distance to surface runoff. Different microbial communities in arable soils of each sample site were analyzed, which was significantly affected by soil environmental factors such as pH, ALN, AP, OM, Tot-Sb, Tot-As, Bio-As, and Bio-Sb. The phylum of Actinobacteria in sites 1, 4, and 5 was the most dominant and the phylum of Proteobacteria were the most dominant in sites 2 and 3. Moreover, the results of redundancy analysis (RDA), variation partition analysis (VPA), and Spearman correlation analyses demonstrated that microorganisms, heavy metal distribution, and geochemical factors interacted with each other and together shaped the microbial community. Our findings are beneficial for understanding the response of soil microorganisms to As-Sb distribution and geochemical factors in arable soils under Sb mining areas.

The effects of pollution by multiple metals derived from long-term smelting activities on soil mite communities in arable soils under different land use types in East China.

Soil pollution represents a threat to soil biodiversity and to soil and human health. However, many ecotoxicological issues, such as the impact of heavy metal pollution on the soil mite community and its spatial distribution in areas with complex environmental factors, are not fully understood. Here, an investigation was conducted in an arable area (about 11 km2) enclosed by surrounding mountains. The study area was contaminated with potentially toxic metals derived from copper smelting that was functioning for over 10years. The area comprised four land use types: woodlands, dry fields, paddy fields, and wastelands, and was divided into 141 study sites each with an area of 6.25ha. The soil metal (Cu, Zn, Pb, and Cd) contents, pH, and organic matter were determined and their distributions were established. Furthermore, soil mite (Acari) community properties (species richness, individual abundance, and Shannon-Wiener diversity index) were determined, and the distributions of total species number and abundance were ascertained. Soil metal pollution strongly reduced soil mite community, but the effects depended on mite groups or species and their sensitivity to different metals as well as land use types. CANOCO analysis revealed that the order Oribatida was more highly correlated with soil metal contents, whereas the other three orders responded to soil metal contents depending on land use types, mite properties, or metals. SADIE method indicated that the coordinate relationship between mite species number and metal concentration was more negative (4-25% of the study sites) than positive (4-12%). The metal pollution levels in the soil were evaluated by single and integrated pollution and ecological risk indices.

Impacts of coniferous bark-derived organic soil amendments on microbial communities in arable soil - a microcosm study.

A decline in the carbon content of agricultural soils has been reported globally. Amendments of forest industry side-streams might counteract this. We tested the effects of industrial conifer bark and its cascade process materials on the soil microbiome under barley (Hordeum vulgare L.) in clay and silt soil microcosms for 10 months, simulating the seasonal temperature changes of the boreal region. Microbial gene copy numbers were higher in clay soils than in silt. All amendments except unextracted bark increased bacterial gene copies in both soils. In turn, all other amendments, but not unextracted bark from an anaerobic digestion process, increased fungal gene copy numbers in silt soil. In clay soil, fungal increase occurred only with unextracted bark and hot water extracted bark. Soil, amendment type and simulated season affected both the bacterial and fungal community composition. Amendments increased bacteria originating from the anaerobic digestion process, as well as dinitrogen fixers and decomposers of plant cells. In turn, unextracted and hot water extracted bark determined the fungal community composition in silt. As fungal abundance increase and community diversification are related to soil carbon acquisition, bark-based amendments to soils can thus contribute to sustainable agriculture.

Natural compounds derived from Brassicaceae plants as an alternative to synthetic fungicides and their influence on soil fungus diversity.

The study aimed to develop a new formulation based on active substances of natural origin to protect plant seedlings against fungal pathogens, and to evaluate the effect of this formulation on fungal communities in arable soil. Coating seeds of common crop plants with a p-coumaric acid (p-CA)-based preparation resulted in a significant reduction in the growth of most of the tested pathogens. When applied to soil, both the p-CA-based formulation and Porter 250 EC had a similar overall effect on soil fungal communities and significantly altered the structure of fungal communities at all of the times examined. Shifts in the fungal community composition concerned less than 2% of the total number of amplicon sequence variants (ASVs). The strongest impact of the formulations on soil microbiota was recorded at the fourth week of treatment. Two ASVs assigned to Botrytis and Chromelosporium, known as plant pathogens, and an unidentified ASV from Diversisporales encompassing the arbuscular mycorrhizal fungi (AMF), were significantly depleted in soil samples treated with p-CA in comparison with Porter 250 EC. The p-CA-based preparation has the potential to be used as an alternative to synthetic fungicides. It shows a similar effect to Porter 250 EC on the organization of soil communities, determining changes in the character of the communities of fungi in general, at any given time. Moreover, p-CA caused a reduction in ASVs belonging to Botrytis and Chromelosporium (plant pathogens) and ASVs of Diversisporales (containing arbuscular mycorrhizal fungi) in comparison with the commercial compound that was analyzed. © 2022 Society of Chemical Industry.

Diversity of archaea and niche preferences among putative ammonia-oxidizing Nitrososphaeria dominating across European arable soils.

Archaeal communities in arable soils are dominated by Nitrososphaeria, a class within Thaumarchaeota comprising all known ammonia-oxidizing archaea (AOA). AOA are key players in the nitrogen cycle and defining their niche specialization can help predicting effects of environmental change on these communities. However, hierarchical effects of environmental filters on AOA and the delineation of niche preferences of nitrososphaerial lineages remain poorly understood. We used phylogenetic information at fine scale and machine learning approaches to identify climatic, edaphic and geomorphological drivers of Nitrososphaeria and other archaea along a 3000 km European gradient. Only limited insights into the ecology of the low-abundant archaeal classes could be inferred, but our analyses underlined the multifactorial nature of niche differentiation within Nitrososphaeria. Mean annual temperature, C:N ratio and pH were the best predictors of their diversity, evenness and distribution. Thresholds in the predictions could be defined for C:N ratio and cation exchange capacity. Furthermore, multiple, independent and recent specializations to soil pH were detected in the Nitrososphaeria phylogeny. The coexistence of widespread ecophysiological differences between closely related soil Nitrososphaeria highlights that their ecology is best studied at fine phylogenetic scale.

Saprotrophic fungal communities in arable soils are strongly associated with soil fertility and stoichiometry

The importance of soil saprotrophic fungi in agroecosystems is receiving increasing attention. However, the linkages between saprotrophic fungal communities and soil fertility and stoichiometry in agroecosystems are poorly understood. Here, four long-term field fertilization experiments with three treatments (i.e., no fertilizer (control), chemical nitrogen (N), phosphorus (P), and potassium (K) fertilizer (NPK), chemical combined with organic fertilizer (NPKM)) were performed to evaluate the associations of saprotrophic fungal communities with the soil fertility index (SFI) and stoichiometric carbon (C):N:P ratios. Long-term NPKM application increased the SFI by 57.66%–129.50% at the four sites, and the SFI was strongly correlated with the saprotrophic fungal community composition, which indicated that exogenous organic matter improved soil fertility to a large extent and stimulated the growth of saprotrophic fungi in arable soils. The soil C:P and N:P ratios were notably decreased in the fertilization treatment, indicated that P was sufficient. Further, the composition of saprotrophic fungi was significantly related to the C:N and N:P ratios, suggested that N status is an important factor for soil saprotrophic fungal communities. Our study provides empirical evidence that the saprotrophic fungal communities in arable soils are strongly associated with soil fertility and stoichiometry and offers guidance for improving soil fertility by regulating the saprophytic fungal community.

Changes of bacterial community in arable soil after short-term application of fresh manures and organic fertilizer

ABSTRACT The application of animal manure is highly recommended in agricultural production. However, the effect of different kinds of manures on bacterial community in farmland still remains unclear. In this study, a short-term field experiment was conducted to investigate the rapid effects of pig manure (PM), chicken manure (CM) and organic fertilizer (OF, composted by pig manure) application on soil physicochemical properties and soil bacterial community. The results showed that the application of CM and OF significantly increased soil bacterial richness (p < 0.05), mainly correlated with the increase of soil total nitrogen. Compared with CM and PM, OF had the greatest disturbance to soil bacterial structure. And total phosphorus showed the highest correlation with bacterial community. Meanwhile, the application of OF reduced the relative abundance of Actinobacteria, the organic matter synthetic bacteria, and Nitrospirae, the nitrifying bacteria, by 17.18% and 40.00%, respectively. 16S functional prediction analysis results shows that the application of OF increased the relative abundance of genes encoding Ribulose-1,5-bisphosphate carboxylase/oxyg (RuBsiCO), the genes involved in soil Calvin cycling, by 20.51%, and increased the relative abundance of genes encoding nitrous-oxide reductase by 44.86%. In conclusion, Short-term application of OF had greater disturbance to soil bacteria than CM and PM, and it had a significant influence on soil functional bacteria and genes involved in soil carbon and nitrogen cycling.

Oribatida (Acari) communities in arable soils formed under waterlogged conditions: the influence of a soil moisture gradient

Oribatid mites make up a dominant group of soil mesofauna. These microarthropods are quite rarely researched in heavy clay soils, and their seasonal dynamics has never been studied thoroughly during the year in such an environment. The research was conducted in 1994–1995 at three sites along a small-scale moisture gradient, with the aim of describing the influence of different moisture conditions on this soil mesofaunal group and evaluating their seasonal dynamics regarding temperature and soil humidity fluctuations. The study area was characterized by a land depression in a field with clay soil, where waterlogged periods occurred, in the Eastern Slovak Lowland (Slovakia). The investigations were based on 24,890 oribatid adults from 72 species. The mean abundance and total species richness of Oribatida increased with increasing soil moisture towards the lower part of the land depression. The abundance and number of species reached a maximum at the bottom site (ca. 8000 ind.m−2 and 59 species) and was two-fold greater than at the summit site. The mean oribatid abundance and the mean species richness between the sites were compared, and significant differences were found on almost all sampling occasions, but the patterns of changes along the moisture gradient differed between study years. The seasonal fluctuations of oribatid abundance within the sites showed a pattern with spring and autumn maxima and a summer minimum only at moist depression bottom. Seasonal changes in the oribatid community composition were more pronounced at sites with lower soil moisture. Specific communities consisting of hygrophilous or eurytopic species and located at the bottom and slope sites of the depression clearly differed from those of the summit site, where xerotolerant species predominated. Ordination analysis confirmed the influence of temperature and precipitation on the species community composition. The bottom and slope site communities were dominated by the species combination of hygrophilous Microppia minus, Oxyoppia europaea and hygrotolerant Oppiella nova, while at the summit site these mites were replaced by more xerotolerant species: Ramusella insculpta, Oppiella obsoleta and Tectocepheus velatus.

Lasting effect of repeated application of organic waste products on microbial communities in arable soils

Using organic waste products (OWP) in agriculture makes it possible to increase productivity with less use of mineral fertilizers. However, the lasting effect on soil microbial communities of an OWP application repeated over several years needs further investigation. In the present study, soils were sampled from two long-term field experiments: QualiAgro and Colmar (France), where different types of OWP characterized by more or less stable organic matter had been applied for more than 10 years, and were compared to a control treatment. At QualiAgro, the carbon inputs due to OWP application were greater (∼4 t C ha−1 every two years) than at Colmar (∼1.7 t C ha−1 every two years). On both sites, soil samples were taken more than six months after the last OWP input. At QualiAgro, soil organic carbon, N and P2O5 concentrations, pH, and CEC were increased by repeated OWP inputs, as compared to the control. Soil microbial community parameters were also lastingly affected by OWP application. A 50% increase in microbial biomass was observed with OWP with the most stable organic matter contents. The prokaryotic community structure was influenced: directly by the OWP applied, and indirectly by soil properties changes. Soil pH appeared as a major driver for structure of the soil prokaryotic community. Fungal community structure was only directly influenced by the OWP applied. Contrastingly, at Colmar, OWP application had no impact on soil chemical characteristics or microbial communities’ parameters. This was probably due to the smaller amount of OWP applied than at QualiAgro, and/or a longer delay between the OWP application and soil sampling. Altogether, our results show that, depending on its type, the applied OWP could produce a lasting increase in soil microbial biomass and shape microbial community structure.

Cropping history shapes fungal, oomycete and nematode communities in arable soils and affects cavity spot in carrot

Fungal, nematode and oomycete communities in arable soil serve diverse ecological functions. However, little is known about the dynamics among these three taxonomic groups. In order to identify the driving factors and networks shaping these communities, and the influence of communities on the development of carrot cavity spot, we collected soil samples from more than sixty fields in which carrot was planned as the next crop, and analyzed the microbial communities using metabarcoding. Crop grown before sampling was best in explaining variation in community composition, but also soil type was shaping fungal and nematode communities, but not oomycete communities. Network analysis revealed that correlations between taxa within taxonomic groups were mostly positive whereas negative correlations dominated between taxa across the different taxonomic groups. Pythium intermedium and P. irregulare from soil samples were found to be associated with cavity spot disease in carrot, and were also found in the lesions of cavity spot. Our study demonstrate that previous crop and soil type significantly affect microbial communities and the development of symptoms of cavity spot in carrot. We also found that differences in co-occurrences within and between taxonomic groups exist.

Subsoil arbuscular mycorrhizal fungal communities in arable soil differ from those in topsoil

Arbuscular mycorrhizal fungi are recognized as important drivers of plant health and productivity in agriculture but very often existing knowledge is limited to the topsoil. With growing interest in the role of subsoil in sustainable agriculture, we used high-throughput Illumina sequencing on a set of samples encompassing drilosphere, rhizosphere and bulk soil, in both top- and subsoil. Our results show subsoil AMF communities harbor unique Operational Taxonomic Units (OTUs) and that both soil depths differ in community structure both at the OTU and family level. Our results emphasize the distinctness of subsoil AMF communities and the potential role of subsoil as a biodiversity reservoir.

High-throughput sequencing technology reveals that continuous cropping of American ginseng results in changes in the microbial community in arable soil

BackgroundAmerican ginseng (Panax quinquefolius L.) is renowned worldwide for its eutherapeutic effects. The replantation of American ginseng usually fails due to problems associated with continuous cropping. An imbalance in the microbial community is thought to be responsible for this, but the overall changes in microbial communities under a continuous cropping system are unclear.MethodsThis study used quantitative polymerase chain reaction combined with high-throughput sequencing methods to confirm changes in a microbial community under continuous cropping of American ginseng.ResultsCopy numbers of bacteria and fungi significantly declined by 47.7 and 45.5%, respectively, upon American ginseng cropping over 3 years. A total of 66,391 classified sequences were obtained from high-throughput sequencing analyses of 16S and 18S rRNA in six soil samples. A decline in bacterial diversity and an increase in fungal diversity were observed in the continuous cropping soils of American ginseng compared to those of traditional crops. Compared with soils used for traditional crops, the relative abundance of bacterial and fungal groups changed in soils subjected to continuous cropping with American ginseng.ConclusionsOur results revealed that the diversity and composition of soil bacterial and fungal communities changed in the continuous cropping of American ginseng compared to those of traditional crops. Those data provided comprehensive insight into microbial communities at the agro-ecosystem scale and contributed to the understanding of micro-ecological environments in the rhizosphere of medicinal plants.

Land use alters arbuscular mycorrhizal fungal communities and their potential role in carbon sequestration on the Tibetan Plateau

Loss of belowground biodiversity by land-use change can have a great impact on ecosystem functions, yet appropriate investigations remain rare in high-elevation Tibetan ecosystems. We compared arbuscular mycorrhizal (AM) fungal communities in arable soils with those in native forest and grassland in southeast Tibet and investigated their potential contribution to carbon sequestration. The AM fungi were abundant and diverse. AM fungal diversity was significantly higher in grassland than in forest or arable land. Significant differences in AM fungal community composition were found among different land use types. The relative abundance of operational taxonomic units (OTUs) in forest and grassland were positively related to glomalin-related soil protein (GRSP), soil organic carbon, macroaggregates, and the unprotected and physically protected carbon, while the AM fungal community in arable soils was dominated by a few OTUs which were positively linked to soil pH. Changes in GRSP content were closely related to water-stable macroaggregates and carbon storage in grassland and forest soils but not in arable soil. Given the inevitable trend toward agricultural management this study emphasizes the need to implement effective agricultural practices that can enhance AM fungal activity to maintain soil quality and carbon sequestration for the sustainable development of this fragile ecosystem.

Endospores, prokaryotes, and microbial indicators in arable soils from three long-term experiments

Management impacts on microbial communities in arable soil may influence soil quality and fertility. We examined the composition of the prokaryotic community in soils maintained under specific treatments for 24–118 years at Askov Experimental Station, Denmark. The experiments involved nutrient addition (unfertilized, mineral fertilizer, cattle manure), straw disposal (no straw, 8 t straw ha−1 year−1), and soil texture (5–18 % clay). Domain- and phylum-assigned cells were quantified by 16S ribosomal RNA (rRNA) gene analysis and endospores by analysis of dipicolinic acid (DPA). Amino sugars (glucosamine, galactosamine, and muramic acid) were assayed as microbial source indicators. Severe nutrient depletion reduced cell numbers and increased endospore abundance; straw disposal slightly increased both prokaryote and endospore numbers. Nutrient source (animal manure or mineral fertilizer) and soil texture had a little effect on cell and endospore numbers. With the notable exception of unfertilized soil, the ratio of endospores to total cells was similar across all treatments. The 16S rRNA gene analysis showed dominance of Bacteria over Archaea, the latter accounting for 0.2–8.4 % of total genes. Archaeal abundance differed a little among treatments. Firmicutes made up 0.2–1.2 % of the bacterial 16S rRNA genes. The numbers of Firmicutes were lower in unfertilized than in fertilized soil and decreased with decreasing soil clay content; straw treatment and nutrient source had a little effect. Amino sugar ratios suggested a dominance of fungi over bacteria, but the concentrations of microbial indicators and soil organic C were closely correlated, indicating that the amino sugar ratios represented a historical fingerprint (legacy effect) of the impact of management on the microbial community. Our results show that it takes extreme management to distort the general structure of prokaryotic communities in temperate arable soils.

Response of rhizosphere microbial community structure and diversity to heavy metal co-pollution in arable soil.

Due to the emerging environmental issues related to heavy metals, concern about the soil quality of farming lands near manufacturing district is increasing. Investigating the function of soil microorganisms exposed to long-term heavy metal contamination is meaningful and important for agricultural soil utilization. This article studied the potential influence of several heavy metals on microbial biomass, activity, abundance, and community composition in arable soil near industrial estate in Zhuzhou, Hunan province, China. The results showed that soil organic contents (SOC) were significantly positive correlated with heavy metals, whereas dehydrogenase activity (DHA) was greatly depressed by the heavy metal stress. Negative correlation was found between heavy metals and basal soil respiration (BSR), and no correlation was found between heavy metals and microbial biomass content (MBC). The quantitative PCR (QPCR) and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis could suggest that heavy metal pollution has significantly decreased abundance of bacteria and fungi and also changed their community structure. The results could contribute to evaluate heavy metal pollution level in soil. By combining different environmental parameters, it would promote the better understanding of heavy metal effect on the size, structure, and activity of microbial community in arable soil.

Responses of Bacterial Communities in Arable Soils in a Rice-Wheat Cropping System to Different Fertilizer Regimes and Sampling Times

Soil physicochemical properties, soil microbial biomass and bacterial community structures in a rice-wheat cropping system subjected to different fertilizer regimes were investigated in two seasons (June and October). All fertilizer regimes increased the soil microbial biomass carbon and nitrogen. Both fertilizer regime and time had a significant effect on soil physicochemical properties and bacterial community structure. The combined application of inorganic fertilizer and manure organic-inorganic fertilizer significantly enhanced the bacterial diversity in both seasons. The bacterial communities across all samples were dominated by Proteobacteria, Acidobacteria and Chloroflexi at the phylum level. Permutational multivariate analysis confirmed that both fertilizer treatment and season were significant factors in the variation of the composition of the bacterial community. Hierarchical cluster analysis based on Bray-Curtis distances further revealed that bacterial communities were separated primarily by season. The effect of fertilizer treatment is significant (P = 0.005) and accounts for 7.43% of the total variation in bacterial community. Soil nutrients (e.g., available K, total N, total P and organic matter) rather than pH showed significant correlation with the majority of abundant taxa. In conclusion, both fertilizer treatment and seasonal changes affect soil properties, microbial biomass and bacterial community structure. The application of NPK plus manure organic-inorganic fertilizer may be a sound fertilizer practice for sustainable food production.

Impact of poplar on soil organic matter quality and microbial communities in arable soils

Poplars grown in short rotation coppice on agricultural land are a promising bioenergy crop. This study aimed to evaluate the soil organic matter (SOM) quality and viable microbial consortium under six-years-old poplar (Populus maximowiczii) and under wheat (Triticum aestivum) at a test site in central Germany. The SOM molecular composition and stability was determined by pyrolysis-field ionization mass spectrometry (Py-FIMS). The microbial consortium was assessed in terms of microbial phospholipid fatty acid (PLFA) profiles. Py-FIMS and the PLFAs agreed in showing crop-specific differences in the SOM quality and in the associated microbial communities. Higher proportions of carbohydrates, long-chained fatty acids, sterols and suberins at the expense of N-containing compounds under poplar than under wheat were associated with lower concentrations of microbial PLFAs in the organic matter. A higher ratio of total fungal to bacterial (f/b) PLFAs, a lower ratio of Gram-positive to Gram-negative bacterial PLFAs and lower biomass of arbuscular mycorrhizal fungi in the organic matter were revealed under poplar than under wheat. Lower N- and increased C-availability in the SOM promoted fungal vs. bacterial colonization, increased the SOM stability by a lower decomposability and caused SOM accumulation under poplar.

Mineral fertilizer alters cellulolytic community structure and suppresses soil cellobiohydrolase activity in a long-term fertilization experiment

Nutrient inputs to soil can alter mineralization of organic matter and subsequently affect soil carbon levels. To understand how elemental interactions affect the biogeochemistry and storage of soil C, we examined soils receiving long-term applications of mineral fertilizer and manure-containing fertilizers. As cellulose is the dominant form of carbon entering arable soils, cellulolytic communities were monitored through enzymatic analysis, and characterization of the abundance (real-time PCR) and diversity (terminal restriction fragment length polymorphism, T-RFLP) of fungal cellobiohydrolases (cbhI) genes. The data showed that long-term mineral fertilization increased soil organic C and crop productivity, and reduced soil heterotrophic respiration and cellobiohydrolases (CBH) activity. Correspondingly, the diversity and community structure of cellulolytic fungi were substantially altered. The variation in cellulolytic fungi is mainly attributable to shifts in the proportion of Eurotiomycetes. In addition, CBH activity was significantly correlated with the diversity and community structure of cellulolytic fungi. These results suggest that enhanced C storage by mineral fertilizer addition occurs not only from extra organic carbon input, but may also be affected through the cellulose decomposing community in arable soil.

Effects of elevated atmospheric CO 2 and N fertilization on abundance, diversity and C-isotopic signature of collembolan communities in arable soil

Rising atmospheric CO 2 concentrations are expected to have marked impacts on the carbon (C) turnover in agro-ecosystems through increased plant photosynthetic rates, leading to an enhanced biomass, and wider plant C/N ratios. Through increased carbon allocation below-ground, as well as through changed litter quality, CO 2 enrichment will indirectly affect soil faunal communities. In the present study we investigated how elevated atmospheric CO 2 and two different levels of N fertilization may affect abundance and diversity of collembolans, as important catalysts in decomposition processes, within an agro-ecosystem under winter wheat cultivation. The investigations were carried out in 2002 within a field experiment using the “Free Air CO 2 Enrichment” technique (FACE) at the Federal Agricultural Research Centre (Braunschweig, Germany). Stable C-isotopic analysis of collembolans, soil, and crops gave insight into C translocation. During our investigations δ 13C values of all components analysed were significantly more negative under FACE compared to ambient air conditions. Stable C-isotopic signatures of collembolans were similar to those of soil under ambient air, but in between those of soil and roots under elevated CO 2 conditions. Our results revealed significant effects of both treatments (CO 2 enrichment and N fertilization) on density and species diversity of collembolans. Overall, collembolans were stimulated under elevated CO 2 conditions, showing an increased abundance of more than 50% (11 240 ind m −2) as well as a higher biodiversity (Shannon Weaver index = 2.5; evenness = 0.75) compared to ambient air conditions (7520 ind m −2; Shannon Weaver index = 2.2; evenness = 0.72). With regard to N supply, a decrease of about 20–30% under CO 2 enrichment and 45–55% under ambient air conditions in collembolan abundance with no alteration in diversity was recorded under reduced N fertilization. The observed impacts were species-specific.

Activity and Composition of the Denitrifying Bacterial Community Respond Differently to Long-Term Fertilization

The objective of this study was to explore the long-term effects of different organic and inorganic fertilizers on activity and composition of the denitrifying and total bacterial communities in arable soil. Soil from the following six treatments was analyzed in an experimental field site established in 1956: cattle manure, sewage sludge, Ca(NO3)2, (NH4)2SO4, and unfertilized and unfertilized bare fallow. All plots but the fallow were planted with corn. The activity was measured in terms of potential denitrification rate and basal soil respiration. The nosZ and narG genes were used as functional markers of the denitrifying community, and the composition was analyzed using denaturing gradient gel electrophoresis of nosZ and restriction fragment length polymorphism of narG, together with cloning and sequencing. A fingerprint of the total bacterial community was assessed by ribosomal intergenic spacer region analysis (RISA). The potential denitrification rates were higher in plots treated with organic fertilizer than in those with only mineral fertilizer. The basal soil respiration rates were positively correlated to soil carbon content, and the highest rates were found in the plots with the addition of sewage sludge. Fingerprints of the nosZ and narG genes, as well as the RISA, showed significant differences in the corresponding communities in the plots treated with (NH4)2SO4 and sewage sludge, which exhibited the lowest pH. In contrast, similar patterns were observed among the other four treatments, unfertilized plots with and without crops and the plots treated with Ca(NO3)2 or with manure. This study shows that the addition of different fertilizers affects both the activity and the composition of the denitrifying communities in arable soil on a long-term basis. However, the treatments in which the denitrifying and bacterial community composition differed the most did not correspond to treatments with the most different activities, showing that potential activity was uncoupled to community composition.