Soil Parameters Drive the Structure, Diversity and Metabolic Potentials of the Bacterial Communities Across Temperate Beech Forest Soil Sequences

Association between Soil Physicochemical Properties and Bacterial Community Structure in Diverse Forest Ecosystems

Although the importance of the soil bacterial community for ecosystem functions has long been recognized, there is still a limited understanding of the associations between its community composition, structure, co-occurrence patterns, and soil physicochemical properties. The objectives of the present study were to explore the association between soil physicochemical properties and the composition, diversity, co-occurrence network topological features, and assembly mechanisms of the soil bacterial community. Four typical forest types from Liziping Nature Reserve, representing evergreen coniferous forest, deciduous coniferous forest, mixed conifer-broadleaf forest, and its secondary forest, were selected for this study. The soil bacterial community was analyzed using Illumina MiSeq sequencing of 16S rRNA genes. Nonmetric multidimensional scaling was used to illustrate the clustering of different samples based on Bray-Curtis distances. The associations between soil physicochemical properties and bacterial community structure were analyzed using the Mantel test. The interactions among bacterial taxa were visualized with a co-occurrence network, and the community assembly processes were quantified using the Beta Nearest Taxon Index (Beta-NTI). The dominant bacterial phyla across all forest soils were Proteobacteria (45.17%), Acidobacteria (21.73%), Actinobacteria (8.75%), and Chloroflexi (5.06%). Chao1 estimator of richness, observed ASVs, faith-phylogenetic diversity (faith-PD) index, and community composition were distinguishing features of the examined four forest types. The first two principal components of redundancy analysis explained 41.33% of the variation in the soil bacterial community, with total soil organic carbon, soil moisture, pH, total nitrogen, carbon/nitrogen (C/N), carbon/phosphorous (C/P), and nitrogen/phosphorous (N/P) being the main soil physicochemical properties shaping soil bacterial communities. The co-occurrence network structure in the mixed forest was more complex compared to that in pure forests. The Beta-NTI indicated that the bacterial community assembly of the four examined forest types was collaboratively influenced by deterministic and stochastic ecological processes.

Reforestation of Cunninghamia lanceolata changes the relative abundances of important prokaryotic families in soil

Over the past decades, many forests have been converted to monoculture plantations, which might affect the soil microbial communities that are responsible for governing the soil biogeochemical processes. Understanding how reforestation efforts alter soil prokaryotic microbial communities will therefore inform forest management. In this study, the prokaryotic communities were comparatively investigated in a secondary Chinese fir forest (original) and a reforested Chinese fir plantation (reforested from a secondary Chinese fir forest) in Southern China. The results showed that reforestation changed the structure of the prokaryotic community: the relative abundances of important prokaryotic families in soil. This might be caused by the altered soil pH and organic matter content after reforestation. Soil profile layer depth was an important factor as the upper layers had a higher diversity of prokaryotes than the lower ones (p < 0.05). The composition of the prokaryotic community presented a seasonality characteristic. In addition, the results showed that the dominant phylum was Acidobacteria (58.86%) with Koribacteraceae (15.38%) as the dominant family in the secondary Chinese fir forest and the reforested plantation. Furthermore, soil organic matter, total N, hydrolyzable N, and NH 4 + - N were positively correlated with prokaryotic diversity (p < 0.05). Also, organic matter and NO 3 - - N were positively correlated to prokaryotic abundance (p < 0.05). This study demonstrated that re-forest transformation altered soil properties, which lead to the changes in microbial composition. The changes in microbial community might in turn influence biogeochemical processes and the environmental variables. The study could contribute to forest management and policy-making.

Tracing the pathways by which flood duration impacts soil bacteria through soil properties and water-extractable dissolved organic matter: A soil column experiment

Soil microbial communities control biogeochemical processes, nutrient cycling, and organic carbon storage and release in wetlands, which are influenced by flooding. To predict soil nutrient function in wetland ecosystems, understanding the effect of flooding on soil biogeochemical cycling and energy flux, including soil properties, dissolved organic matter (DOM), and microbial communities is essential. This study investigated how different flood durations (1, 3, 8, 16, and 30 d) affect the interactions between physicochemical properties and bacterial communities in a river wetland. The DOM composition was measured using ultraviolet/visible spectrophotometry coupled with fluorescence spectroscopy, and the bacterial communities were identified using 16S rRNA sequencing. Simpson's diversity index varied from 0.92 to 0.94, indicating high bacterial diversity throughout the treatments; the highest and lowest bacterial diversities were found at 1 and 8 flooding days, respectively. The abundance of Desulturomonadales, Clostridiales, Bacteroidales, and Gaiellales was positively correlated with pH, electrical conductivity, water-extractable dissolved organic carbon (WEOC), and water-extractable total dissolved nitrogen (TDN) but negatively correlated with dissolved oxygen (DO) and soil organic matter (SOM), suggesting complex interactions among these factors in response to flooding. Structural equation model revealed that flooding directly increased TDN but indirectly increased WEOC through increasing soil pH; and directly decreased DO and SOM, leading to decreases in total protein-like fraction. Three significant pathways were identified, showing the impacts of flooding on bacterial diversity: (1) flood duration decreased DO, resulting in decreased bacterial diversity; (2) flood duration decreased SOM, leading to increased bacterial diversity; and (3) flood duration decreased DO and SOM, leading to increased bacterial diversity via decreased total protein-like fraction. This study indicated that prolonged flooding has both positive and negative impacts on bacterial diversity, depending on environmental factors. It highlights the importance of flooding in shaping soil bacterial communities, with implications for nutrient cycling and carbon storage in wetlands.

Soil Bacterial Assemblage Across a Production Landscape: Agriculture Increases Diversity While Revegetation Recovers Community Composition

Aboveground ecological impacts associated with agricultural land use change are evident as natural plant communities are replaced with managed production systems. These impacts have been extensively studied, unlike those belowground, which remain poorly understood. Soil bacteria are good candidates to monitor belowground ecological dynamics due to their prevalence within the soil system and ability to survive under harsh and changing conditions. Here, we use soil physicochemical assessment and 16S rRNA gene sequencing to investigate the soil physical and bacterial assemblage changes across a mixed-use agricultural landscape. We assess soil from remnant vegetation (Eucalyptus mallee), new and old vineyards, old pasture, and recently revegetated areas. Elevated concentrations of nitrogen (NO₃^-) and plant-available (Colwell) phosphorus were identified in the managed vineyard systems, highlighting the impact of agricultural inputs on soil nutrition. Alpha diversity comparison revealed a significant difference between the remnant mallee vegetation and the vineyard systems, with vineyards supporting highest bacterial diversity. Bacterial community composition of recently revegetated areas was similar to remnant vegetation systems, suggesting that bacterial communities can respond quickly to aboveground changes, and that actions taken to restore native plant communities may also act to recover natural microbial communities, with implications for soil and plant health. Findings here suggest that agriculture may disrupt the correlation between above- and belowground diversities by altering the natural processes that otherwise govern this relationship (e.g. disturbance, plant production, diversity of inputs), leading to the promotion of belowground microbial diversity in agricultural systems.

Warmer winters result in reshaping of the European beech forest soil microbiome (bacteria, archaea and fungi)-With potential implications for ecosystem functioning

In temperate regions, climate warming alters temperature and precipitation regimes. During winter, a decline in insulating snow cover changes the soil environment, where especially frost exposure can have severe implications for soil microorganisms and subsequently for soil nutrient dynamics. Here, we investigated winter climate change responses in European beech forests soil microbiome. Nine study sites with each three treatments (snow exclusion, insolation, and ambient) were investigated. Long-term adaptation to average climate was explored by comparing across sites. Triplicated treatment plots were used to evaluate short-term (one single winter) responses. Community profiles of bacteria, archaea and fungi were created using amplicon sequencing. Correlations between the microbiome, vegetation and soil physicochemical properties were found. We identify core members of the forest-microbiome and link them to key processes, for example, mycorrhizal symbiont and specialized beech wood degraders (fungi) and nitrogen cycling (bacteria, archaea). For bacteria, the shift of the microbiome composition due to short-term soil temperature manipulations in winter was similar to the community differences observed between long-term relatively cold to warm conditions. The results suggest a strong link between the changes in the microbiomes and changes in environmental processes, for example, nitrogen dynamics, driven by variations in winter climate.

Fungal–Bacterial Networks in the Habitat of SongRong (Tricholoma matsutake) and Driving Factors of Their Distribution Rules

Soil origin, mycorrhizal plant partners and environmental factors affect the growth and development of SongRong (Tricholoma matsutake). In order to clarify the relationships of fungi–bacteria networks and various influence factors in the habitat of SongRong, we chose three collection sites with a Quercus mongolica pure forest (plot A without SongRong was used as the control sample site), Q. mongolica mixed Rhododendron dauricum (plot B) and Q. mongolica mixed with R. dauricum and Pinus densiflora (plot C). By using high-throughput sequencing, we obtained a total of 4930 fungal and 55501 bacterial amplicon sequence variants (ASVs) based on internally transcribed spacer ribosomal RNA (ITS rRNA) and 16S ribosomal RNA (16S rRNA) sequencing via the Illumina NovaSeq platform. In the habitat soil of SongRong (plot B and plot C), alpha or beta diversity and species compositions of fungi and bacteria were different from plot A. The fungal–bacterial networks follow the selection rule that few dominant genera account for the greater relative abundance. Forest types, but not the host itself, drove the fungal–bacterial networks of the forest soil, and soil physicochemical characteristics and texture affected their abundance. The abundance of Tricholoma was affected by the fungal and bacterial abundance in the habitat.

Tree Cover Species Modify the Diversity of Rhizosphere-Associated Microorganisms in Nothofagus obliqua (Mirb.) Oerst Temperate Forests in South-Central Chile

Chilean native forests have been subjected to several types of disturbances, with one of them being the replacement by exotic species. Pinus radiata D. Don is a widespread exotic tree that forms extensive plantations in southern Chile. It covers extended areas, affecting the landscape, biodiversity, and ecosystem services associated with native forest ecosystems. Although advances in assessing the impact of exotic plant species have been conducted, few studies have focused on the alteration of soil microorganisms. This study aimed to characterize the rhizosphere bacterial and fungal communities associated with the tree species Nothofagus obliqua inside a native forest stand and within a P. radiata plantation growing nearby. We used a 16S rRNA gene and ITS region metabarcoding approach. Using bioinformatics, diversity indices, relative abundance, preferential taxa, and predicted functions and guilds were estimated. The β-diversity analysis showed that both factors, the type of soil (rhizosphere or bulk soil) and the type of site (native forest or P. radiata plantation), were significant, with the site explaining most of the variation among bacterial and fungal communities. Proteobacteria and Basidiomycota were the most abundant bacterial and fungal phyla in both types of soil and sites. Similarly, bacteria showed similar abundant taxa at the family level, independent of the soil type or the site. The main fungal taxa associated with native forests were Tricholomataceae and Cantharellales, whereas in P. radiata plantations, Russulaceae and Hyaloscyphaceae were the most abundant families. The main bacteria functional groups were chemoheterotrophy and aerobic chemoheterotrophy, without significant differences between the type of soil or sites. Overall, these results demonstrate that the composition and diversity of bacterial and fungal communities associated with native N. obliqua forest are influenced by the surrounding forest, and mainly depend on the site’s characteristics, such as the lignin-rich wood source. These results improve our understanding of the impact of native forest replacement on soil microbial communities, which can alter microbial-related soil ecosystem services.

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

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.

Variations in bacterial and archaeal community structure and diversity along the soil profiles of a peatland in Southwest China

As bacteria and archaea are key components in the ecosystem, information on their dynamics in soil profiles is important for understanding the biogeochemical cycles in peatlands. However, little is known about the vertical distribution patterns of bacteria and archaea in the Bitahai peatland, or about their relationships with soil chemical properties. Here, bacterial and archaeal abundance, diversity, and composition of the Bitahai peatlands at 0-100 cm soil depths were analyzed by sequencing of 16S rRNA genes (Illumina, MiSeq). Soil pH, total C, N, and P concentrations and stoichiometric ratios were also estimated. The results revealed that total C and total N contents, as well as C:P and N:P ratios, significantly increased with increasing peatland soil depths, while total P decreased. The top three dominant phyla were Proteobacteria (39.64%), Acidobacteria (12.93%), and Chloroflexi (12.81%) in bacterial communities, and were Crenarchaeota (58.67%), Thaumarchaeota (14.34%), and Euryarchaeota (10.82%) in archaeal communities in the Bitahai peatland, respectively. The total relative abundance of methanogenic groups and ammonia-oxidizing microorganisms all significantly decreased with soil depth. Both bacterial and archaeal diversities were significantly affected by the soil depth. Soil C, N, and P concentrations and stoichiometric ratios markedly impacted the community structure and diversity in archaea, but not in bacteria. Therefore, these results highlighted that the microbial community structure and diversity depended on soil depth for the Bitahai peatlands, and the factors affecting bacteria and archaea in the Bitahai peatlands were different.

Pollution impact on microbial communities composition in natural and anthropogenically modified soils of Southern Russia

Metagenomic studies of soil microbocenoses are extremely relevant nowadays. The study of pollution impact on soil microbiomes is of particular interest. The structure of microbial communities in soils with different levels of pollution by polycyclic aromatic hydrocarbons (PAHs) and potentially toxic elements (PTEs) was studied. High bacterial biodiversity was found in all the studied soil samples, but its lowest values are found in soil samples taken on the territory of technogenically polluted Lake Atamanskoye. Assessment of soil pollution showed the highest content of polycyclic aromatic hydrocarbons (PAHs) and potentially toxic elements (PTEs) for the soils Lake Atamanskoye. The high content of pollutants negatively affects the abundance of representatives of the phyla Actinobacteria, Planctomycetes, Verrucomicrobia, and Nitrospirae. Such phyla as Proteobacteria, Candidate Divisions TM7, OD1, WPS-2, Chlamydiae, Cyanobacteria are characterized by positive direct correlation with the content of pollutants, especially with PAHs. A cooperative effect of decrease in the number of Actinobacteria and Proteobacteria with an increase in Armatimonadetes probably corresponds to PTEs contamination. The proportion of Candidate Division OD1, Chlamydiae, Cyanobacteria, and Candidate Division WPS-2 was increased in the soil microbiome under the influence of severe combined pollution. Pollutants negatively affect the abundance of dominant unclassified_o__Gaiellales and unclassified_o__WD2101 genera. Iamia, Salinibacterium, Arthrobacter, Kaistobacter, Thiobacillus genera are characterized by a low abundance, but they are presumably the most resistant to soil pollution. It was revealed that the level of soil pollution largely determines the composition and diversity of bacterial communities in the soils of the studied territories. Operating taxonomic units have been established that have prognostic value for assessing the state, level of soil pollution, and their biological safety.

PGPR in Agriculture: A Sustainable Approach to Increasing Climate Change Resilience

Growing environmental concerns are potentially narrowing global yield capacity of agricultural systems. Climate change is the most significant problem the world is currently facing. To meet global food demand, food production must be doubled by 2050; over exploitation of arable lands using unsustainable techniques might resolve food demand issues, but they have negative environmental effects. Current crop production systems are a major reason for changing global climate through diminishing biodiversity, physical and chemical soil degradation, and water pollution. The over application of fertilizers and pesticides contribute to climate change through greenhouse gas emissions (GHG) and toxic soil depositions. At this crucial time, there is a pressing need to transition to more sustainable crop production practices, ones that concentrate more on promoting sustainable mechanisms, which enable crops to grow well in resource limited and environmentally challenging environments, and also develop crops with greater resource use efficiency that have optimum sustainable yields across a wider array of environmental conditions. The phytomicrobiome is considered as one of the best strategies; a better alternative for sustainable agriculture, and a viable solution to meet the twin challenges of global food security and environmental stability. Use of the phytomicrobiome, due to its sustainable and environmentally friendly mechanisms of plant growth promotion, is becoming more widespread in the agricultural industry. Therefore, in this review, we emphasize the contribution of beneficial phytomicrobiome members, particularly plant growth promoting rhizobacteria (PGPR), as a strategy to sustainable improvement of plant growth and production in the face of climate change. Also, the roles of soil dwelling microbes in stress amelioration, nutrient supply (nitrogen fixation, phosphorus solubilization), and phytohormone production along with the factors that could potentially affect their efficiency have been discussed extensively. Lastly, limitations to expansion and use of biobased techniques, for instance, the perspective of crop producers, indigenous microbial competition and regulatory approval are discussed. This review largely focusses on the importance and need of sustainable and environmentally friendly approaches such as biobased/PGPR-based techniques in our agricultural systems, especially in the context of current climate change conditions, which are almost certain to worsen in near future.

Agricultural management practices influence the soil enzyme activity and bacterial community structure in tea plantations

BACKGROUND

The soil quality and health of the tea plantations are dependent on agriculture management practices, and long-term chemical fertilizer use is implicated in soil decline. Hence, several sustainable practices are used to improve and maintain the soil quality. Here, in this study, changes in soil properties, enzymatic activity, and dysbiosis in bacterial community composition were compared using three agricultural management practices, namely conventional (CA), sustainable (SA), and transformational agriculture (TA) in the tea plantation during 2016 and 2017 period. Soil samples at two-months intervals were collected and analyzed.

RESULTS

The results of the enzyme activities revealed that acid phosphatase, arylsulfatase, β-glucosidase, and urease activities differed considerably among the soils representing the three management practices. Combining the redundancy and multiple regression analysis, the change in the arylsulfatase activity was explained by soil pH as a significant predictor in the SA soils. The soil bacterial community was predominated by the phyla Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, and Bacteroidetes in the soil throughout the sampling period. Higher Alpha diversity scores indicated increased bacterial abundance and diversity in the SA soils. A significant relationship between bacterial richness indices (SOBS, Chao and ACE) and soil pH, K and, P was observed in the SA soils. The diversity indices namely Shannon and Simpson also showed variations, suggesting the shift in the diversity of less abundant and more common species. Furthermore, the agricultural management practices, soil pH fluctuation, and the extractable elements had a greater influence on bacterial structure than that of temporal change.

CONCLUSIONS

Based on the cross-over analysis of the bacterial composition, enzymatic activity, and soil properties, the relationship between bacterial composition and biologically-driven ecological processes can be identified as indicators of sustainability for the tea plantation.

Bioprospecting of Beneficial Bacteria Traits Associated With Tomato Root in Greenhouse Environment Reveals That Sampling Sites Impact More Than the Root Compartment

Tomato is subject to several diseases that affect both field- and greenhouse-grown crops. To select cost-effective potential biocontrol agents, we used laboratory throughput screening to identify bacterial strains with versatile characteristics suitable for multipurpose uses. The natural diversity of tomato root-associated bacterial communities was bioprospected under a real-world environment represented by an intensive tomato cultivation area characterized by extraseasonal productions in the greenhouse. Approximately 400 tomato root-associated bacterial isolates, in majority Gram-negative bacteria, were isolated from three compartments: the soil close to the root surface (rhizosphere, R), the root surface (rhizoplane, RP), and the root interior (endorhizosphere, E). A total of 33% of the isolates produced siderophores and were able to solubilize phosphates and grow on NA with 8% NaCl. A total of 30% of the root-associated bacteria showed antagonistic activity against all the tomato pathogens tested, i.e., Clavibacter michiganesis pv. michiganensis, Pseudomonas syringae pv. tomato, Pseudomonas corrugata and Xanthomonas euvesicatoria pv. perforans, and Fusarium oxysporum f. sp. lycopersici. We found that the sampling site rather than the root compartment of isolation influenced bacterial composition in terms of analyzed phenotype. This was demonstrated through a diversity analysis including general characteristics and PGPR traits, as well as biocontrol activity in vitro. Analysis of 16S rRNA gene (rDNA) sequencing of 77 culturable endophytic bacteria that shared multiple beneficial activity revealed a predominance of bacteria in Bacillales, Enterobacteriales, and Pseudomonadales. Their in vitro antagonistic activity showed that Bacillus species were significantly more active than the isolates in the other taxonomic group. In planta activity against phytopathogenic bacteria of a subset of Bacillus and Pseudomonas isolates was also assessed.

Key soil parameters affecting the survival of Panax notoginseng under continuous cropping

Negative plant-soil feedbacks lead to the poor growth of Panax notoginseng (Sanqi), a well-known herb in Asia and has been used worldwide, under continuous cropping. However, the key soil parameters causing the replant problem are still unclear. Here we conducted a field experiment after 5-year continuous cropping. Sanqi seedlings were cultivated in 7 plots (1.5 m × 2 m), which were randomly assigned along a survival gradient. In total, 13 important soil parameters were measured to understand their relationship with Sanqi’s survival. Pearson correlation analysis showed that 6 soil parameters, including phosphatase, urease, cellulase, bacteria/fungi ratio, available N, and pH, were all correlated with Sanqi’s survival rate (P < 0.05). Principal component analysis (PCA) indicated that they explained 61% of the variances based on the first component, with soil pH being closely correlated with other parameters affecting Sanqi’s survival. The optimum pH for Sanqi growth is about 6.5, but the mean soil pH in the study area is 5.27 (4.86–5.68), therefore it is possible to ameliorate the poor growth of Sanqi by increasing soil pH. This study may also help to reduce the replant problem of other crops under continuous cropping since it is widespread in agricultural production.

Seasonal effects of river flow on microbial community coalescence and diversity in a riverine network

Terrestrial microbial communities may take advantage of running waters and runoff to enter rivers and mix with aquatic microorganisms. However, the environmental factors governing the interchange of the microbial community within a watercourse and its surrounding environment and the composition of the resulting community are often underestimated. The present study investigated the effect of flow rate on the mixing of water, soil, sediment and biofilm at four sites along the Lancang River and one branch of the river in winter and summer and, in turn, the resultant changes in the microbial community within each habitat. 16S rRNA gene-based Illumina high-throughput sequencing illustrated that bacterial communities were apparently distinct among biofilm, water, soil and sediment. Biofilms had the lowest richness, Shannon diversity and evenness indices compared with other habitats, and those three indices in all habitats increased significantly from winter to summer. SourceTracker analysis showed a significant coalescence between the bacterial communities of sediment, water and biofilm samples at lower flow rates. Additionally, the proportion of Betaproteobacteria in sediment and biofilms increased with a decrease in flow rate, suggesting the flow rate had a strong impact on microbial community composition and exchange among aquatic habitats. These results were further confirmed by a Mantel test and linear regression analysis. Microbial communities in all samples exhibited a significant but very weak distance-decay relationship (r = 0.093, P = 0.024). Turbidity played a much more important role on water bacterial community structure in summer (i.e. rainy season) (BIOENV, r = 0.92). Together, these results suggest that dispersal is an important factor affecting bacterial community structure in this system.

Salinity and nutrient modulate soil bacterial communities in the coastal wetland of the Yellow River Delta, China

The Yellow River Delta is the largest and youngest estuarine and coastal wetland in China and is experiencing the most active interactions of seawater and freshwater in the world. Bacteria played multifaceted influence on soil biogeochemical processes, and it was necessary to investigate the intermodulation between the soil factors and bacterial communities. Soil samples were collected at sites with different salinity degree, vegetations, and interference. The sequences of bacilli were tested using 16S rRNA sequencing method and operational taxonomic units were classified with 97% similarity. The soil was highly salinized and oligotrophic, and the wetland was nitrogen-restricted. Redundancy analysis suggested that factors related with seawater erosion were principal to drive the changes of soil bacterial communities and then the nutrient level and human disturbance. A broader implication was that, in the early succession stages of the coastal ecosystem, seawater erosion was the key driver of the variations of marine oligotrophic bacterial communities, while the increasing nutrient availability may enhance in the abundance of the riverine copiotrophs in the late stages. This study provided new insights on the characteristics of soil bacterial communities in estuarine and coastal wetlands.

Variation of rhizosphere microbial community in continuous mono-maize seed production

Soil microbe is crucial to a healthy soil, therefore its diversities and abundances under different conditions are still need fully understand.The aims of the study were to characterize the community structure and diversity of microbe in the rhizosphere soil after continuous maize seed production, and the relationship between the disease incidence of four diseases and the variation of the rhizosphere microbe. The results showed that different fungal and bacterial species were predominant in different cropping year, and long-term maize seed production had a huge impact on structure and diversity of soil microbial. Ascomycota and Mortierellomycota were the dominant fungal phyla and Mortierella and Ascomycetes represented for a large proportion of genus. A relative increase of Fusarium and Gibberella and a relative decrease of Mortierella, Chrysosporium, Podospora, and Chaetomium were observed with the increase of cropping year. Pathogenic Fusarium, Curvularia, Curvularia-lunata, Cladosporium, Gibberella-baccata, and Plectosphaerellaceae were over-presented and varied at different continuous cropping year, led to different maize disease incidence. Proteobacteria and Actinobacteria ranked in the top two of all bacterial phyla, and genus Pseudarthrobacter, Roseiflexus and RB41 dominated top 3. Haliangium and Streptomyces decreased with the continuous cropping year and mono-cropping of maize seed production increased disease incidence with the increase of cropping year, while the major disease was different. Continuous cropping of maize seed production induced the decrease of protective microbe and biocontrol genera, while pathogenic pathogen increased, and maize are in danger of pathogen invasion. Field management show great effects on soil microbial community.

Soil Enzyme Activity and Microbial Metabolic Function Diversity in Soda Saline–Alkali Rice Paddy Fields of Northeast China

Western Jilin province has the most serious area of soda salinization in Northeast China, which affects and restricts the sustainable development of agriculture. The effects of physico-chemical properties of rhizosphere and non-rhizosphere soil on soil microbial diversity and enzyme activities (polyphenol oxidase, catalase, invertase, amylase) were evaluated in typical soda saline-alkali paddy field. Community-level physiological profile (CLPP) based on Biolog-ECO plates was used to assess the functional diversity of soil microorganisms. Exchangeable sodium percentage (ESP) and pH were negative correlated with the microbial activity (AWCD), soil enzyme activities (amylase, sucrose, and catalase, except for polyphenol oxidase) in rice rhizosphere and non-rhizosphere soil (P < 0.05). The indexes of microbial diversity in rice rhizosphere soil were significantly higher than that of non-rhizosphere soil. The utilization of amino acids by rice rhizosphere microorganisms was relatively high, while non-rhizosphere soil had relatively high utilization of carboxylic acid, phenolic acid, and amine. Among the selected physico-chemical properties, soil organic carbon (SOC) and soil water content (SWC) had the greatest influence on the variation of microbial diversity indexes and enzyme activities in rhizosphere soil. ESP and pH showed a significant positive correlation with carbon source utilization, especially for amine (AM) and phenolic acid (PA) carbon source utilization (P < 0.05) by means of RDA, and the utilization rate of AM and PA carbon sources by rice rhizosphere and non-root soil microorganisms was P1 < P2 < P3.

Plant Genotype Influences Physicochemical Properties of Substrate as Well as Bacterial and Fungal Assemblages in the Rhizosphere of Balsam Poplar

Abandoned unrestored mines are an important environmental concern as they typically remain unvegetated for decades, exposing vast amounts of mine waste to erosion. Several factors limit the revegetation of these sites, including extreme abiotic and unfavorable biotic conditions. However, some pioneer tree species having high levels of genetic diversity, such as balsam poplar (Populus balsamifera), can naturally colonize these sites and initiate plant succession. This suggests that some tree genotypes are likely more suited for acclimation to the conditions of mine wastes. In this study, we selected two contrasting mine waste storage facilities (waste rock from a gold mine and tailings from a molybdenum mine) from the Abitibi region of Quebec (Canada), on which poplars were found to have grown naturally. First, we assessed in situ the impact of vegetation presence on each mine waste type. The presence of balsam poplars improved soil health locally by modifying the physicochemical properties (e.g., higher nutrient content and pH) of the mine wastes and causing an important shift in their bacterial and fungal community compositions, going from lithotrophic communities that dominate mine waste environments to heterotrophic communities involved in nutrient cycling. Next, in a greenhouse experiment we assessed the impact of plant genotype when grown in these mine wastes. Ten genotypes of P. balsamifera were collected locally, found growing either at the mine sites or in the surrounding natural forest. Tree growth was monitored over two growing seasons, after which the effects of genotype-by-environment interactions were assessed by measuring the physicochemical properties of the substrates and the changes in microbial community assembly. Although substrate type was identified as the main driver of rhizosphere microbiome diversity and community structure, a significant effect due to tree genotype was also detected, particularly for bacterial communities. Plant genotype also influenced aboveground tree growth and the physicochemical properties of the substrates. These results highlight the influence of balsam poplar genotype on the soil environment and the potential importance of tree genotype selection in the context of mine waste revegetation.

Chlamydiae in the Environment

Chlamydiae have been known for more than a century as major pathogens of humans. Yet they are also found ubiquitously in the environment where they thrive within protists and in an unmatched wide range of animals. This review summarizes recent advances in understanding chlamydial diversity and distribution in nature. Studying these environmental chlamydiae provides a novel perspective on basic chlamydial biology and evolution. A picture is beginning to emerge with chlamydiae representing one of the evolutionarily most ancient and successful groups of obligate intracellular bacteria.

Effects of simulated warming on bacterial diversity and abundance in tropical soils from East Malaysia using open top chambers

The effects of global warming are increasingly evident, where global surface temperatures and atmospheric concentration of carbon dioxide have increased in past decades. Given the role of terrestrial bacteria in various ecological functions, it is important to understand how terrestrial bacteria would respond towards higher environmental temperatures. This study aims to determine soil bacterial diversity in the tropics and their response towards in situ warming using an open-top chamber (OTC). OTCs were set up in areas exposed to sunlight throughout the year in the tropical region in Malaysia. Soil samples were collected every 3 months to monitor changes in bacterial diversity using V3-V4 16S rDNA amplicon sequencing inside the OTCs (treatment plots) and outside the OTCs (control plots). After 12 months of simulated warming, an average increase of 0.81 to 1.15 °C was recorded in treatment plots. Significant changes in the relative abundance of bacterial phyla such as Bacteroidetes and Chloroflexi were reported. Increases in the relative abundance of Actinobacteria were also observed in treatment plots after 12 months. Substantial changes were observed at the genus level, where most bacterial genera decreased in relative abundance after 12 months. This study demonstrated that warming can alter soil bacteria in tropical soils from Kota Kinabalu.

Comparative study of neighboring Holm oak and olive trees-belowground microbial communities subjected to different soil management

It is well-known that different plant species, and even plant varieties, promote different assemblages of the microbial communities associated with them. Here, we investigate how microbial communities (bacteria and fungi) undergo changes within the influence of woody plants (two olive cultivars, one tolerant and another susceptible to the soilborne fungal pathogen Verticillium dahliae, plus wild Holm oak) grown in the same soil but with different management (agricultural versus native). By the use of metabarcoding sequencing we determined that the native Holm oak trees rhizosphere bacterial communities were different from its bulk soil, with differences in some genera like Gp4, Gp6 and Solirubrobacter. Moreover, the agricultural management used in the olive orchard led to belowground microbiota differences with respect to the natural conditions both in bulk soils and rhizospheres. Indeed, Gemmatimonas and Fusarium were more abundant in olive orchard soils. However, agricultural management removed the differences in the microbial communities between the two olive cultivars, and these differences were minor respect to the olive bulk soil. According to our results, and at least under the agronomical conditions here examined, the composition and structure of the rhizospheric microbial communities do not seem to play a major role in olive tolerance to V. dahliae.

Effects of biochar particle size and concomitant nitrogen fertilization on soil microbial community structure during the maize seedling stage

Biochar is widely used as a soil amendment, either alone or in association with fertilizer. However, the effects of biochar particle size on the soil microbial community are largely unclear. Biochar was divided into two groups according to diameter sizes: < 1 mm and 2.5-5 mm (labeled as CB1 and CB5, respectively). A pot experiment was established in which maize (Zea maize L.) was treated with CB1, CB5, and/or external nitrogen (N, NH₄NO₃). At the end of the seedling period (45 days), analyses of soil microbial community structure and other soil and crop properties were conducted. The biochar (regardless of N addition) enhanced microbial biomass and activity. CB1 had a stronger capacity than CB5 to modify soil microbial community structure by promoting soil microbial groups (e.g., fungi, Gram-negative bacteria), which is likely due to CB1 undergoing a series of more intense processes (e.g., nutrient release, mineralization) than CB5. However, this difference was diminished or disappeared when N was added, mainly due to the masking effect of soil acidification that was induced by N fertilization. Collectively, fine biochar has a stronger effect on soil microbial community than coarse biochar. Particle size only affects soil microbial community structure when biochar is applied alone; it has no effect when biochar is applied in association with chemical N fertilizer, at least during the seedling period. The relationship between particle size and soil microbial community needs to be considered when using biochar for soil amendment.

A microcosm approach highlights the response of soil mineral weathering bacterial communities to an increase of K and Mg availability

The access and recycling of the base cations are essential processes for the long-lasting functioning of forest ecosystems. While the role of soil bacterial communities has been demonstrated in mineral weathering and tree nutrition, our understanding of the link between the availability of base cations and the functioning of these communities remains limited. To fill this gap, we developed a microcosm approach to investigate how an increase in key base cations (potassium or magnesium) impacted the taxonomic and functional structures of the bacterial communities. During a 2-month period after fertilization with available potassium or magnesium, soil properties, global functions (metabolic potentials and respiration) as well as mineral weathering bioassays and 16S rRNA amplicon pyrosequencing were monitored. Our analyses showed no or small variations in the taxonomic structure, total densities and global functions between the treatments. In contrast, a decrease in the frequency and effectiveness of mineral weathering bacteria was observed in the fertilized treatments. Notably, quantitative PCR targeting specific genera known for their mineral weathering ability (i.e., Burkholderia and Collimonas) confirmed this decrease. These new results suggest that K and Mg cation availability drives the distribution of the mineral weathering bacterial communities in forest soil.

Restriction of plant roots in boreal forest organic soils affects the microbial community but does not change the dominance from ectomycorrhizal to saprotrophic fungi

Boreal forest soils store significant amounts of carbon and are cohabited by saprotrophic and ectomycorrhizal fungi (ECM). The ‘Gadgil effect’ implies antagonistic interactions between saprotrophic fungi and ECM. Plant photosynthates support the competitive fitness of the ECM, and may also shape the soil bacterial communities. Many ‘Gadgil effect’ experiments have focused on litter layer (OL) or have litter and root-fragments present, and thus possibly favor the saprotrophs. We compared how the restriction of plant roots and exudates affect soil microbial community structures in organic soil (mixed OF and OH). For this, we established a 3-yr field experiment with 3 different mesh treatments affecting the penetration of plant roots and external fungal hyphae. Exclusion of plant photosynthates induced modest changes in both fungal and bacterial community structures, but not to potential functionality of the microbial community. The microbial community was resilient towards rather short-term disturbances. Contrary to the ‘Gadgil effect’, mesh treatments restricting the entrance of plant roots and external fungal hyphae did not favor saprotrophs that originally inhabited the soil. Thus, we propose that different substrate preferences (fresh litter vs. fermented or humified soil), rather than antagonism, maintain the spatial separation of saprotrophs and mycorrhizal fungi in boreal forest soils.

Tree Species Shape Soil Bacterial Community Structure and Function in Temperate Deciduous Forests

Amplicon-based analysis of 16S rRNA genes and transcripts was used to assess the effect of tree species composition on soil bacterial community structure and function in a temperate deciduous forest. Samples were collected from mono and mixed stands of Fagus sylvatica (beech), Carpinus betulus (hornbeam), Tilia sp. (lime), and Quercus sp. (oak) in spring, summer, and autumn. Soil bacterial community exhibited similar taxonomic composition at total (DNA-based) and potentially active community (RNA-based) level, with fewer taxa present at active community level. Members of Rhizobiales dominated at both total and active bacterial community level, followed by members of Acidobacteriales, Solibacterales, Rhodospirillales, and Xanthomonadales. Bacterial communities at total and active community level showed a significant positive correlation with tree species identity (mono stands) and to a lesser extent with tree species richness (mixed stands). Approximately 58 and 64% of indicator operational taxonomic units (OTUs) showed significant association with only one mono stand at total and active community level, respectively, indicating a strong impact of tree species on soil bacterial community composition. Soil C/N ratio, pH, and P content similarly exhibited a significant positive correlation with soil bacterial communities, which was attributed to direct and indirect effects of forest stands. Seasonality was the strongest driver of predicted metabolic functions related to C fixation and degradation, and N metabolism. Carbon and nitrogen metabolic processes were significantly abundant in spring, while C degradation gene abundances increased from summer to autumn, corresponding to increased litterfall and decomposition. The results revealed that in a spatially homogenous forest soil, tree species diversity and richness are dominant drivers of structure and composition in soil bacterial communities.

Sedimentary Marl mudstone as a substrate in a xeric environment revealed by microbiome analysis

The sedimentary Marl mudstone soil is composed primarily of CaCO₃, and is an important pedologic and geomorphologic element known as Marl, extensively dispersed in slopes and ridges in the northern Negev Desert, Israel. The wide Marl soil-layer areas are barren, with well-developed streamsides and no perennial vegetation cover. Soil systems in the Negev Desert have been widely studied, yet very little information was collected on Marl soils, and even less on the microbiome present in the Negev. Thus, an evaluation of the microbial-community inhabitants in a Marl soil layer was conducted in an attempt to distinguish between Marl with surface green mat and bare Marl soil layer. Our objective was to investigate the microbiome and abiotic components of the upper layer (0-5 cm) of Marl and Marl-with-green-mat soil collected in the Negev Desert. Plate-counting enabled the estimation of fungal and bacterial population size, while nested polymerase chain reaction (nPCR) and Ion Torrent sequencing were used to analyze biological diversity. The results indicate significant differences in microbial biomass and microbial-community diversity between Marl and Marl-green mat, despite similar pH levels. Further study is needed to enhance understanding of the activity of the biotic components and their contribution to slope stabilization.

Soil parameters, land use, and geographical distance drive soil bacterial communities along a European transect

To better understand the relationship between soil bacterial communities, soil physicochemical properties, land use and geographical distance, we considered for the first time ever a European transect running from Sweden down to Portugal and from France to Slovenia. We investigated 71 sites based on their range of variation in soil properties (pH, texture and organic matter), climatic conditions (Atlantic, alpine, boreal, continental, Mediterranean) and land uses (arable, forest and grassland). 16S rRNA gene amplicon pyrosequencing revealed that bacterial communities highly varied in diversity, richness, and structure according to environmental factors. At the European scale, taxa area relationship (TAR) was significant, supporting spatial structuration of bacterial communities. Spatial variations in community diversity and structure were mainly driven by soil physicochemical parameters. Within soil clusters (k-means approach) corresponding to similar edaphic and climatic properties, but to multiple land uses, land use was a major driver of the bacterial communities. Our analyses identified specific indicators of land use (arable, forest, grasslands) or soil conditions (pH, organic C, texture). These findings provide unprecedented information on soil bacterial communities at the European scale and on the drivers involved; possible applications for sustainable soil management are discussed.

Native soils with their microbiotas elicit a state of alert in tomato plants

Several studies have investigated soil microbial biodiversity, but understanding of the mechanisms underlying plant responses to soil microbiota remains in its infancy. Here, we focused on tomato (Solanum lycopersicum), testing the hypothesis that plants grown on native soils display different responses to soil microbiotas. Using transcriptomics, proteomics, and biochemistry, we describe the responses of two tomato genotypes (susceptible or resistant to Fusarium oxysporum f. sp. lycopersici) grown on an artificial growth substrate and two native soils (conducive and suppressive to Fusarium). Native soils affected tomato responses by modulating pathways involved in responses to oxidative stress, phenol biosynthesis, lignin deposition, and innate immunity, particularly in the suppressive soil. In tomato plants grown on steam-disinfected soils, total phenols and lignin decreased significantly. The inoculation of a mycorrhizal fungus partly rescued this response locally and systemically. Plants inoculated with the fungal pathogen showed reduced disease symptoms in the resistant genotype in both soils, but the susceptible genotype was partially protected from the pathogen only when grown on the suppressive soil. The 'state of alert' detected in tomatoes reveals novel mechanisms operating in plants in native soils and the soil microbiota appears to be one of the drivers of these plant responses.

Long-Term Nitrogen Fertilization Elevates the Activity and Abundance of Nitrifying and Denitrifying Microbial Communities in an Upland Soil: Implications for Nitrogen Loss From Intensive Agricultural Systems

The continuous use of nitrogen (N) fertilizers to increase soil fertility and crop productivity often results in unexpected environmental effects and N losses through biological processes, such as nitrification and denitrification. In this study, multidisciplinary approaches were employed to assess the effects of N fertilization in a long-term (~20 years) field experiment in which a fertilizer gradient (0, 200, 400, and 600 kg N ha⁻¹ yr⁻¹) was applied in a winter wheat-summer maize rotation cropping system in the North China Plain, one of the most intensive agricultural regions in China. The potential nitrification/denitrification rates, bacterial community structure, and abundances of functional microbial communities involved in key processes of the N cycle were assessed during both the summer maize (SM) and winter wheat (WW) seasons. Long-term N fertilization resulted in a decrease in soil pH and an increase in soil organic matter (OM), total N and total carbon concentrations. Potential nitrification/denitrification and the abundances of corresponding functional N cycling genes were positively correlated with the fertilization intensity. High-throughput sequencing of the 16S rRNA gene revealed that the increased fertilization intensity caused a significant decrease of bacterial diversity in SM season, while changed the microbial community composition such as increasing the Bacteroidetes abundance and decreasing Acidobacteria abundance in both SM and WW seasons. The alteration of soil properties markedly correlated with the variation in microbial structure, as soil pH and OM were the most predominant factors affecting the microbial structure in the SM and WW seasons, respectively. Furthermore, consistently with the results of functional gene quantification, functional prediction of microbial communities based on 16S rRNA sequence data also revealed that the abundances of the key nitrificaiton/denitrification groups were elevated by long-term N inputs. Taken together, our results suggested that soil microbial community shifted consistently in both SM and WW seasons toward a higher proportion of N-cycle microbes and exhibited higher N turnover activities in response to long-term elevated N fertilizer. These findings provided new insights into the molecular mechanisms responsible for N loss in intensively N fertilized agricultural ecosystems.

Impact of soil pedogenesis on the diversity and composition of fungal communities across the California soil chronosequence of Mendocino

Understanding how soil pedogenesis affects microbial communities and their in situ activities according to ecosystem functioning is a central issue in soil microbial ecology, as soils represent essential nutrient reservoirs and habitats for the biosphere. To address this question, soil chronosequences developed from a single, shared mineralogical parent material and having the same climate conditions are particularly useful, as they isolate the factor of time from other factors controlling the character of soils. In our study, we considered a natural succession of uplifted marine terraces in Mendocino, CA, ranging from highly fertile in the younger terrace (about 100,000 years old) to infertile in the older terraces (about 300,000 years old). Using ITS amplicon pyrosequencing, we analysed and compared the diversity and composition of the soil fungal communities across the first terraces (T1 to T3), with a specific focus in the forested terraces (T2 and T3) on soil samples collected below trees of the same species (Pinus muricata) and of the same age. While diversity and richness indices were highest in the grassland (youngest) terrace (T1), they were higher in the older forested terrace (T3) compared to the younger forested terrace (T2). Interestingly, the most abundant ectomycorrhizal (ECM) taxa that we found within these fungal communities showed high homology with ITS Sanger sequences obtained previously directly from ECM root tips from trees in the same study site, revealing a relative conservation of ECM diversity over time. Altogether, our results provide new information about the diversity and composition of the fungal communities as well as on the dominant ECM species in the soil chronosequence of Mendocino in relation to soil age and ecosystem development.

Bacterial and Fungal Community Composition and Functional Activity Associated with Lake Wetland Water Level Gradients

The water regime is often the primary force driving the evolution of freshwater lakes, but how soil microbes responded to this process is far from understood. This study sampled wetland soils from a shallow lake that experienced water regime changes, Poyang Lake of China, to explore the features of bacterial and fungal community in response to water level changes. The soil physicochemical properties, T-RFLP based community structures and soil activities (including basal respiration, microbial biomass and enzymes) were all determined. Soil microbial eco-function was captured by testing the carbon metabolism with Biolog-Ecoplate. The results showed remarkable influence of the water level gradients on the soil physicochemical properties, microbial community structures and soil activities. However, the carbon utilization profile exhibited weak connections with the environmental variables and microbial community structures (p > 0.05). The microbial activities were significantly correlated with both bacterial and fungal community structures. Our results also emphasized the ascendant role of the deterministic process in the assemblages of microbial community structures and functions in wetland. In conclusion, this study revealed the discrepancy between community structures and eco-functions in response to water level gradients, and a relatively stable eco-function helped to maintain the ecosystem function of wetland from a long-term perspective.

Exploring Viral Diversity in a Unique South African Soil Habitat

The Kogelberg Biosphere Reserve in the Cape Floral Kingdom in South Africa is known for its unique plant biodiversity. The potential presence of unique microbial and viral biodiversity associated with this unique plant biodiversity led us to explore the fynbos soil using metaviromic techniques. In this study, metaviromes of a soil community from the Kogelberg Biosphere Reserve has been characterised in detail for the first time. Metaviromic DNA was recovered from soil and sequenced by Next Generation Sequencing. The MetaVir, MG-RAST and VIROME bioinformatics pipelines were used to analyse taxonomic composition, phylogenetic and functional assessments of the sequences. Taxonomic composition revealed members of the order Caudovirales, in particular the family Siphoviridae, as prevalent in the soil samples and other compared viromes. Functional analysis and other metaviromes showed a relatively high frequency of phage-related and structural proteins. Phylogenetic analysis of PolB, PolB2, terL and T7gp17 genes indicated that many viral sequences are closely related to the order Caudovirales, while the remainder were distinct from known isolates. The use of single virome which only includes double stranded DNA viruses limits this study. Novel phage sequences were detected, presenting an opportunity for future studies aimed at targeting novel genetic resources for applied biotechnology.

Different impacts of manure and chemical fertilizers on bacterial community structure and antibiotic resistance genes in arable soils

Both manure and chemical fertilizers are widely used in modern agriculture. However, the impacts of different fertilizers on bacterial community structure and antibiotic resistance genes (ARGs) in arable soils still remain unclear. In this study, high-throughput sequencing and quantitative PCR were employed to investigate the bacterial community structure, ARGs and mobile genetic elements (MGEs) influenced by the application of different fertilizers, including chemical fertilizers, piggery manure and straw ash. The results showed that the application of fertilizers could significantly change the soil bacterial community and the abundance of Gaiella under phylum Actinobacteria was significantly reduced from 12.9% in unfertilized soil to 4.1%-7.4% in fertilized soil (P < 0.05). It was also found that the application of manure could cause a transient effect on soil resistome composition and the relative abundance of ARGs increased from 7.37 ppm to 32.10 ppm. The abundance of aminoglycoside, sulfonamide and tetracycline resistance genes greatly increased after manure fertilization and then gradually returned to normal levels with the decay of some intestinal bacteria carrying ARGs. In contrast, the application of chemical fertilizers and straw ash significantly changed the bacterial community structure but exerted little effect on soil resistome. Overall, the results of this study illustrated the different effects of different fertilizers on the soil resistome and revealed that the changes of soil resistome induced by manure application mainly resulted from alteration of bacteria community rather than the horizontal gene transfer.

Bacterial microbiomes of individual ectomycorrhizal Pinus sylvestris roots are shaped by soil horizon and differentially sensitive to nitrogen addition

Plant roots select non-random communities of fungi and bacteria from the surrounding soil that have effects on their health and growth, but we know little about the factors influencing their composition. We profiled bacterial microbiomes associated with individual ectomycorrhizal Pinus sylvestris roots colonized by different fungi and analyzed differences in microbiome structure related to soils from distinct podzol horizons and effects of short-term additions of N, a growth-limiting nutrient commonly applied as a fertilizer, but known to influence patterns of carbon allocation to roots. Ectomycorrhizal roots growing in soil from different horizons harboured distinct bacterial communities. The fungi colonizing individual roots had a strong effect on the associated bacterial communities. Even closely related species within the same ectomycorrhizal genus had distinct bacterial microbiomes in unfertilized soil, but fertilization removed this specificity. Effects of N were rapid and context dependent, being influenced by both soil type and the particular ectomycorrhizal fungi involved. Fungal community composition changed in soil from all horizons, but bacteria only responded strongly to N in soil from the B horizon where community structure was different and bacterial diversity was significantly reduced, possibly reflecting changed carbon allocation patterns.

Taxonomic and functional shifts in the beech rhizosphere microbiome across a natural soil toposequence

It has been rarely questioned as to whether the enrichment of specific bacterial taxa found in the rhizosphere of a given plant species changes with different soil types under field conditions and under similar climatic conditions. Understanding tree microbiome interactions is essential because, in contrast to annual plants, tree species require decades to grow and strongly depend on the nutritive resources of the soil. In this context, we tested using a natural toposequence the hypothesis that beech trees select specific taxa and functions in their rhizosphere based on the soil conditions and their nutritive requirements. Our 16S rRNA gene pyrosequencing analyses revealed that the soil type determines the taxa colonizing the beech rhizosphere. A rhizosphere effect was observed in each soil type, but a stronger effect was observed in the nutrient-poor soils. Although the communities varied significantly across the toposequence, we identified a core beech rhizosphere microbiome. Functionally, GeoChip analyses showed a functional redundancy across the toposequence, with genes related to nutrient cycling and to the bacterial immune system being significantly enriched in the rhizosphere. Altogether, the data suggest that, regardless of the soil conditions, trees enrich variable bacterial communities to maintain the functions necessary for their nutrition.

Ericoid Roots and Mycospheres Govern Plant-Specific Bacterial Communities in Boreal Forest Humus

In this study, the bacterial populations of roots and mycospheres of the boreal pine forest ericoid plants, heather (Calluna vulgaris), bilberry (Vaccinium myrtillus), and lingonberry (Vaccinium vitis-idaea), were studied by qPCR and next-generation sequencing (NGS). All bacterial communities of mycosphere soils differed from soils uncolonized by mycorrhizal mycelia. Colonization by mycorrhizal hyphae increased the total number of bacterial 16S ribosomal DNA (rDNA) gene copies in the humus but decreased the number of different bacterial operational taxonomic units (OTUs). Nevertheless, ericoid roots and mycospheres supported numerous OTUs not present in uncolonized humus. Bacterial communities in bilberry mycospheres were surprisingly similar to those in pine mycospheres but not to bacterial communities in heather and lingonberry mycospheres. In contrast, bacterial communities of ericoid roots were more similar to each other than to those of pine roots. In all sample types, the relative abundances of bacterial sequences belonging to Alphaproteobacteria and Acidobacteria were higher than the sequences belonging to other classes. Soil samples contained more Actinobacteria, Deltaproteobacteria, Opitutae, and Planctomycetia, whereas Armatimonadia, Betaproteobacteria, Gammaproteobacteria, and Sphingobacteriia were more common to roots. All mycosphere soils and roots harbored bacteria unique to that particular habitat. Our study suggests that the habitation by ericoid plants increases the overall bacterial diversity of boreal forest soils.

Forest Soil Bacteria: Diversity, Involvement in Ecosystem Processes, and Response to Global Change

The ecology of forest soils is an important field of research due to the role of forests as carbon sinks. Consequently, a significant amount of information has been accumulated concerning their ecology, especially for temperate and boreal forests. Although most studies have focused on fungi, forest soil bacteria also play important roles in this environment. In forest soils, bacteria inhabit multiple habitats with specific properties, including bulk soil, rhizosphere, litter, and deadwood habitats, where their communities are shaped by nutrient availability and biotic interactions. Bacteria contribute to a range of essential soil processes involved in the cycling of carbon, nitrogen, and phosphorus. They take part in the decomposition of dead plant biomass and are highly important for the decomposition of dead fungal mycelia. In rhizospheres of forest trees, bacteria interact with plant roots and mycorrhizal fungi as commensalists or mycorrhiza helpers. Bacteria also mediate multiple critical steps in the nitrogen cycle, including N fixation. Bacterial communities in forest soils respond to the effects of global change, such as climate warming, increased levels of carbon dioxide, or anthropogenic nitrogen deposition. This response, however, often reflects the specificities of each studied forest ecosystem, and it is still impossible to fully incorporate bacteria into predictive models. The understanding of bacterial ecology in forest soils has advanced dramatically in recent years, but it is still incomplete. The exact extent of the contribution of bacteria to forest ecosystem processes will be recognized only in the future, when the activities of all soil community members are studied simultaneously.

Chemical treatment of contaminated sediment for phosphorus control and subsequent effects on ammonia-oxidizing and ammonia-denitrifying microorganisms and on submerged macrophyte revegetation

In this work, sediments were treated with calcium nitrate, aluminum sulfate, ferric sulfate, and Phoslock®, respectively. The impact of treatments on internal phosphorus release, the abundance of nitrogen cycle-related functional genes, and the growth of submerged macrophytes were investigated. All treatments reduced total phosphorus (TP) and soluble reactive phosphorus (SRP) in interstitial water, and aluminum sulfate was most efficient. Aluminum sulfate also decreased TP and SRP in overlying water. Treatments significantly changed P speciations in the sediment. Phoslock® transformed other P species into calcium-bound P. Calcium nitrate, ferric sulfate, and Phoslock® had negative influence on ammonia oxidizers, while four chemicals had positive influence on denitrifies, indicating that chemical treatment could inhibit nitrification but enhance denitrification. Aluminum sulfate had decreased chlorophyll content of the leaves of submerged macrophytes, while ferric sulfate and Phoslock® treatment would inhibit the growth of the root. Based on the results that we obtained, we emphasized that before application of chemical treatment, the effects on submerged macrophyte revegetation should be taken into consideration.

Driving forces of soil bacterial community structure, diversity, and function in temperate grasslands and forests

Soil bacteria provide a large range of ecosystem services such as nutrient cycling. Despite their important role in soil systems, compositional and functional responses of bacterial communities to different land use and management regimes are not fully understood. Here, we assessed soil bacterial communities in 150 forest and 150 grassland soils derived from three German regions by pyrotag sequencing of 16S rRNA genes. Land use type (forest and grassland) and soil edaphic properties strongly affected bacterial community structure and function, whereas management regime had a minor effect. In addition, a separation of soil bacterial communities by sampling region was encountered. Soil pH was the best predictor for bacterial community structure, diversity and function. The application of multinomial log-linear models revealed distinct responses of abundant bacterial groups towards pH. Predicted functional profiles revealed that differences in land use not only select for distinct bacterial populations but also for specific functional traits. The combination of 16S rRNA data and corresponding functional profiles provided comprehensive insights into compositional and functional adaptations to changing environmental conditions associated with differences in land use and management.

Specific impacts of beech and Norway spruce on the structure and diversity of the rhizosphere and soil microbial communities

The impacts of plant species on the microbial communities and physico-chemical characteristics of soil are well documented for many herbs, grasses and legumes but much less so for tree species. Here, we investigate by rRNA and ITS amplicon sequencing the diversity of microorganisms from the three domains of life (Archaea, Bacteria and Eukaryota:Fungi) in soil samples taken from the forest experimental site of Breuil-Chenue (France). We discovered significant differences in the abundance, composition and structure of the microbial communities associated with two phylogenetically distant tree species of the same age, deciduous European beech (Fagus sylvatica) and coniferous Norway spruce (Picea abies Karst), planted in the same soil. Our results suggest a significant effect of tree species on soil microbiota though in different ways for each of the three microbial groups. Fungal and archaeal community structures and compositions are mainly determined according to tree species, whereas bacterial communities differ to a great degree between rhizosphere and bulk soils, regardless of the tree species. These results were confirmed by quantitative PCR, which revealed significant enrichment of specific bacterial genera, such as Burkholderia and Collimonas, known for their ability to weather minerals within the tree root vicinity.