Topsoil Microbial Community Research Articles

Subtle changes in topsoil microbial communities of drained forested peatlands after prolonged drought.

A major consequence of anthropogenic climate change is the intensification and extension of drought periods. Prolonged drought can alter conditions in drained peatlands and cause disturbances in microbial communities in the topsoil layer of the peat. Varying environmental conditions throughout the growing season, such as the availability of organic matter and nutrients, temperature and water table, further impact these communities and consequently affect carbon and nutrient cycles. The impact of drought and new forestry practices is largely unknown in drained peatland forests. We examined how microbial communities change over a growing season in different harvesting intensities (continuous cover forestry, clear-cut and uncut) in a drained peatland site using bacterial 16S and fungal ITS2 rRNA analysis. We found seasonal differences in bacterial and fungal diversity and species richness, and subtle changes in microbial communities at the phylum and genus levels when comparing various environmental factors. Diversity, species richness and relative abundance differed in spring compared to summer and autumn. However, significant differences in the microbial community structure were not detected. Understanding the responses of microbial communities to disturbances like drought and other environmental factors provides new insights into the consequences of climate change on drained forested peatlands.

Microenvironment heterogeneity affected by anthropogenic wildfire-perturbed soil mediates bacterial community in Pinus tabulaeformis forests.

In recent years, the frequency and intensity of anthropogenic wildfires have drastically increased, significantly altering terrestrial ecosystems worldwide. These fires not only devastate vegetative cover but also impact soil environments and microbial communities, affecting ecosystem structure and function. The extent to which fire severity, soil depth, and their interaction influence these effects remains unclear, particularly in Pinus tabulaeformis forests. This study investigated the impact of wildfire intensity and soil stratification on soil physicochemical properties and microbial diversity within P. tabulaeformis forests in North China. Soil samples were collected from different fire severity zones (Control, Light, Moderate, High) and depths (topsoil: 0-10 cm; subsoil: 10-20 cm). Analyses included measurements of soil pH, organic carbon (SOC), total nitrogen (TN), and other nutrients. Microbial diversity was assessed using 16S rRNA gene sequencing. Our findings revealed significant variations in soil pH, SOC, TN, and other nutrients with fire severity and soil depth, profoundly affecting microbial community composition and diversity. Soil pH emerged as a critical determinant, closely linked to microbial α-diversity and community structure. We found that fire severity significantly altered soil pH (p = 0.001), pointing to noteworthy changes in acidity linked to varying severity levels. Topsoil microbial communities primarily differentiated between burned and unburned conditions, whereas subsoil layers showed more pronounced effects of fire severity on microbial structures. Analysis of bacterial phyla across different fire severity levels and soil depths revealed significant shifts in microbial communities. Proteobacteria consistently dominated across all conditions, indicating strong resilience, while Acidobacteriota and Actinobacteriota showed increased abundances in high-severity and light/moderate-severity areas, respectively. Verrucomicrobiota were more prevalent in control samples and decreased significantly in fire-impacted soils. Chloroflexi and Bacteroidota displayed increased abundance in moderate and high-severity areas, respectively. Correlation analyses illustrated significant relationships between soil environmental factors and dominant bacterial phyla. Soil organic carbon (SOC) showed positive correlations with total nitrogen (TN) and alkaline hydrolysable nitrogen (AN). Soil pH exhibited a negative correlation with multiple soil environmental factors. Soil pH and available phosphorus (AP) significantly influenced the abundance of the phylum Myxococcota. Soil water content (WC) significantly affected the abundances of Acidobacteriota and Actinobacteriota. Additionally, ammonium nitrogen (NH4 +-N) and nitrate nitrogen (NO3 --N) jointly and significantly impacted the abundance of the phylum Chloroflexi. This study highlights the significant long-term effects of anthropogenic wildfires on soil microenvironment heterogeneity and bacterial community structure in P. tabulaeformis forests in North China, 6 years post-fire. Our findings demonstrate that fire severity significantly influences soil pH, which in turn affects soil nutrient dynamics and enhances microbial diversity. We observed notable shifts in the abundance of dominant bacterial phyla, emphasizing the critical role of soil pH and nutrient availability in shaping microbial communities. The results underscore the importance of soil stratification, as different soil layers showed varying responses to fire severity, highlighting the need for tailored management strategies. Future research should focus on long-term monitoring to further elucidate the temporal dynamics of soil microbial recovery and nutrient cycling following wildfires. Studies investigating the roles of specific microbial taxa in ecosystem resilience and their functional contributions under varying fire regimes will provide deeper insights. Additionally, exploring soil amendments and management practices aimed at optimizing pH and nutrient availability could enhance post-fire recovery processes, supporting sustainable ecosystem recovery and resilience.

Response of soil microbial communities to natural radionuclides along specific-activity gradients

Understanding the response of soil microbial community to abnormal natural radionuclides is important to maintain soil ecological function, but the underlying mechanism of tolerance and survival of microbes is poorly studied. The effects of natural radionuclides on the topsoil microbial communities in anomalous natural radiation area were investigated in this work, and it was found that microbial community composition was significantly influenced by the specific-activities of natural radionuclides. The results revealed that relative abundances of 10 major microbial phyla and genera displayed different patterns along specific-activity gradients, including decreasing, increasing, hump-shaped, U-shaped, and similar sinusoidal or cosine wave trends, which indicated that the natural radionuclides were the predominant driver for change of microbial community structure. At the phylum and genus level, microbial communities were divided into two special groups according to the tolerance to natural radionuclides, such as 238U and 232Th, including tolerant and sensitive groups. Taken together, our findings suggest that the high specific-activities of natural radionuclides can obviously drive changes in microbial communities, providing a possibility for future studies on the microbial tolerance genes and bioremediation strains.

Subsoiling tillage with straw incorporation improves soil microbial community characteristics in the whole cultivated layers: A one-year study

The subsoiling tillage managements have been recommended to remediate subsoil compaction and maintain crop production. These practices can improve soil properties and fertility due to soil loosening and straw incorporation, and further affect soil microbial community characteristics. However, the response of soil microbial community structure to subsoiling tillage managements is still poorly understood. The objective of this study was to examine the effects of tillage practices (conventional tillage, CT; subsoiling tillage, ST; subsoiling tillage with straw incorporation, STS) on soil microbial community characteristics. Topsoil (0–20 cm) and subsoil (20–35 cm) samples were taken from a 360–day in−situ field experiment in northeast China. Microbial community characteristics were determined by the phospholipid fatty acid (PLFA) method. The contents of subsoil bacterial PLFAs and fungal PLFAs were lower in the ST treatment than those in the other treatments within 60–360 days, and gram−positive (G+) bacteria were more abundant in the subsoil of ST treatment than those in the subsoil of STS treatment. In contrast to the other treatments, the STS treatment had the larger total PLFAs content and the higher ratio of fungal to bacterial PLFAs (F/B) in the subsoil during the whole incubation period, and fungi played a dominant role in straw degradation of subsoil. Compared with the other treatments, the STS treatment had a lower cyclopropyl to precursors (cy/pre) ratio in the subsoil on the 30th day, suggesting that the STS treatment provided more K2SO4−extractable organic carbon (EOC) and some available nutrients (nitrogen, potassium and phosphorous) for soil microbes. The STS treatment relative to the other treatments increased the bacterial PLFAs and fungal PLFAs contents in the topsoil, which were associated with the increase in the EOC/SOC ratio. Accordingly, STS practice had a great potential for improving subsoil and topsoil microbial community characteristics.

The effect of combined pollution by PAHs and heavy metals on the topsoil microbial communities of Spolic Technosols of the lake Atamanskoe, Southern Russia.

The contamination with organic and inorganic pollutants changes significantly soil microbial community structure. These shifts indicate anthropogenic pressure and help to discover new possibilities for soil remediation. In this study, the microbial community structure of Spolic Technosols formed at the territory of a former industrial sludge reservoir near the Kamensk-Shakhtinsky (Southern Russia) was studied using a metagenomics approach. The studied soils contain high concentrations of heavy metals (HM) (up to 72,900mgkg-1) and 16 priority polycyclic aromatic hydrocarbons (PAHs) (up to 6670mgkg-1). Its microbial communities demonstrate an excellent adaptability level reflected in their complexity and diversity. As shown by the high values of alpha diversity indices (Shannon values up to 10.1, Chao1 values from 1430 to 4273), instead of decreasing quantitatively and qualitatively on the systemic level, microbial communities tend to undergo complex redistribution. Regardless of contamination level, the share of Actinobacteria and Proteobacteria was consistently high and varied from 20 to 50%. Following the results of the Mann-Whitney U test, there were significant changes of less abundant phyla. The abundance of oligotrophic bacteria from Gemmatimonadetes and Verrucomicrobia phyla and autotrophic bacteria (e.g., Nitrospira) decreased due to the high PAH's level. And abundance of Firmicutes and amoebae-associated bacteria such as TM6 and soil Chlamydia increased in highly contaminated plots. In the Spolic Technosols studied, the influence of factors on the microbial community composition decreased from PAHs concentration to soil characteristics (organic carbon content) and phylum-phylum interactions. The high concentrations of HMs influenced weakly on the microbial community composition.

Carbon Dynamics in Climate Smart Agriculture Precision Land Leveling Practices on Topsoil Microbial Community Changes and Soil Organic Carbon in Cereal Based Cropping Systems of Sub-Tropical India: A Review

The role of soil microorganisms in the biogeochemical process and nutrient cycling of soil is critical and is colossally impacted by agronomic management practices. In order to establish climate-smart precision land leveling practices in cereal based cropping systems, comprehension of the land bacterial local area and supplement nutrient dynamics under differentiating management practices is of most extreme significance. Climate smart agriculture (CSA) practices are gaining traction in subtropical India as a viable alternative to conventional cereal-based cropping systems for reversing natural resource depletion. Sustainable soil management alternatives that sequester carbon in the soil, reduce greenhouse gas (GHG) emissions and help intensify production, all while enhancing the natural resource base. Aggregate-associated soil organic carbon (SOC) contents in 0-15 cm depth were recorded highest SOC at 15-30 cm depth in Precision Land Leveling (PLL) systems as 9.4% for both M-P-MbPLL and M-W-MbPLL. Highest PON change in arable cropping system (30.9 & 40.1%) was found in O-W-Mb with precision land levelling plots followed by R-P-O with precision land levelling plots (26.1 & 35.8%) as compared to R-W and S-W system. The values of LFOC in surface soil were 194.7, 187.9, 176.2, 170.9, 168.5, 150.6, 132.8 and 123.8 mgkg−1 in R-P-O, R-C-O, M-W-Mb, O-W-Mb, M-P-Mb, R-P-Mb, R-W and S-W with precision land leveling treatments. Therefore, adopting Climate Smart Agriculture Precision Land leveling practices can dramatically boost system productivity in cereal-based cropping systems by improving SOC and soil biological quality. The overview literature accrued indicate that CSA based totally totally management has a remarkable impact on top soil resilience in phrases of relative abundances of bacterial groups, soil organic carbon & to be had plant nutrients and as a result may additionally play a vital function within the sustainability of the extensive cereal based cropping systems.

Tillage Practice Impacts on the Carbon Sequestration Potential of Topsoil Microbial Communities in an Agricultural Field

Soil microorganisms are the core force driving the conversion of plant residues into soil organic carbon (SOC). Identifying the changes in soil microorganism responses to tillage practices is a key step in understanding the SOC sequestration potential. The aim of this study is to assess the impacts of different tillage practices on microbial communities and functions in agricultural soils. A field experiment involving no tillage (NT), rotary tillage (RT), and deep tillage (DT) in winter wheat-summer maize double cropping was performed to determine the structure of the microbial community and its functions using metagenomics. We found that tillage practices changed the composition of soil microbial communities and their functions related to the C cycle. The relative abundance of fungi in DT was significantly higher than that of the NT and RT treatments and primarily facilitated the growth of the fungi community. Moreover, DT treatment increased the relative abundance of genes involved in carbohydrate transport and metabolism genes and carbohydrate metabolism pathway genes, in addition to those encoding carbohydrate-binding modules. Therefore, we concluded that DT increases the transformation potential of straw-C to SOC in the North China Plain where large amounts of wheat and maize straw are returned to the field every year.

Topsoil microbial community structure responds to land cover type and environmental zone in the Western Pacific region

Soil encompasses diverse microbial communities that are essential for fundamental ecosystem functions such as biogeochemical cycling. To better understand underlying biogeochemical processes, it is necessary to know the structure of soil archaeal and bacterial communities and their responses to edaphic and climate variables within and across various land cover types (LCTs) and environmental zones (ENZs). Here we sampled eighty-nine sites across five ENZs and four LCTs within the Western Pacific region. Through leveraging the second-generation sequencing of topsoil samples, we showed that α-diversity (taxonomic diversity) of archaea strongly varied within LCTs, whereas bacterial α-diversity was significantly controlled by both LCT and ENZ. Soil archaea and bacteria showed global niche differentiation associated with contrasting diversity responses to latitude and differential responses of microbial diversity patterns to edaphic and climate variables within LCTs and ENZs. In contrast to α-diversity, microbial β-diversity (the compositional dissimilarity between sites) was majorly governed by ENZs, particularly for archaea (P < 0.01). Our results highlight the importance of LCTs and ENZs for understanding soil microbial contributions to nutrient dynamics and ecosystem resilience under land-use intensification and climate change.

Altered microbial structure and function after thermokarst formation.

Permafrost thaw could induce substantial carbon (C) emissions to the atmosphere, and thus trigger a positive feedback to climate warming. As the engine of biogeochemical cycling, soil microorganisms exert a critical role in mediating the direction and strength of permafrost C-climate feedback. However, our understanding about the impacts of thermokarst (abrupt permafrost thaw) on microbial structure and function remains limited. Here we employed metagenomic sequencing to analyze changes in topsoil (0-15cm) microbial communities and functional genes along a permafrost thaw sequence (1, 10, and 16years since permafrost collapse) on the Tibetan Plateau. By combining laboratory incubation and a two-pool model, we then explored changes in soil labile and stable C decomposition along the thaw sequence. Our results showed that topsoil microbial α-diversity decreased, while the community structure and functional gene abundance did not exhibit any significant change at the early stage of collapse (1year since collapse) relative to non-collapsed control. However, as the time since the collapse increased, both the topsoil microbial community structure and functional genes differed from the control. Abundances of functional genes involved in labile C degradation decreased while those for stable C degradation increased at the late stage of collapse (16years since collapse), largely driven by changes in substrate properties along the thaw sequence. Accordingly, faster stable C decomposition occurred at the late stage of collapse compared to the control, which was associated with the increase in relative abundance of functional genes for stable C degradation. These results suggest that upland thermokarst alters microbial structure and function, particularly enhances soil stable C decomposition by modulating microbial functional genes, which could reinforce a warmer climate over the decadal timescale.

Native broadleaf tree species stimulate topsoil nutrient transformation by changing microbial community composition and physiological function, but not biomass in subtropical plantations with low P status

Microbial communities and their associated enzyme activities affect carbon (C), nitrogen (N), and phosphorus (P) metabolism in soils. We used phospholipid fatty acids (PLFAs) analysis and extracellular enzyme activity assays to evaluate the effects on topsoil microbial community and nutrient transformation of converting Chinese fir (CF) plantations to native broadleaf (Castanopsis hystrix [CH] and Mytilaria laosensis [ML]) plantations in this study. We found that CH and ML plantations had significantly higher soil organic C (SOC), total N (TN), NH4+-N, soil C/N ratios (C/Nsoil), soil C/P ratios (C/Psoil) and soil N/P ratios (N/Psoil) but significantly lower total P (TP) compared to CF plantations. A distinct shift in soil microbial community composition, but not microbial biomass was evident 23 years after stand conversion. Redundancy analysis (RDA) showed that soil microbial community composition was substantially influenced by litterfall mass (LF), TP, N/Psoil, SOC, fine root biomass (FR), C/Nsoil, TN, litter C/N ratios (C/Nlitter), and C/Psoil; of these, LF appeared to be the primary driver of differences in soil microbial community composition (p < 0.05). In addition, the total activity of hydrolytic enzymes involved in C metabolism (β-glucosidase and cellobiohydrolase), N metabolism (N-acetyl-glucosaminidase), and P metabolism (acid phosphatase) increased significantly in the two native broadleaf plantations, whereas the total activity of oxidase (phenol oxidase) decreased significantly. Furthermore, the change trends of specific enzyme activity (i.e., enzymes per unit microbe) were similar to total enzyme activity. The dynamics of soil microbial enzymatic activity after stand conversion provide a functional link between changes in microbial community composition and soil nutrient transformation. Our findings suggest a mechanism in native, non-N2-fixing broadleaf tree species that stimulates soil nutrient transformation in subtropical planted forests with low P via increases in the quantity and quality of litter and the physiological function per unit of microbial biomass.

Monitoring Soil Microorganisms with Community-Level Physiological Profiles Using Biolog EcoPlates™ in Chaohu Lakeside Wetland, East China

Under the circumstance of wetland degradation, we used Biolog EcoPlatesTM method to investigate the impact of ecological restoration on the function of topsoil microbial communities by monitoring their metabolic diversity around Chaohu lakeside wetland. Four restoration patterns were selected, including reed shoaly land (RL), poplar plantation land (PL), abandoned shoaly grassland (GL) and cultivated flower land (FL). The result showed a rapid growth trend at the initial stage of incubation, following the fastest change rate at 72 h in both dormant and growing seasons. The Average Well Color development (AWCD) values of RL pattern was the highest at the detection points of each culture time, while the GL were the lowest. The calculation of diversity indicators also displayed significant lower McIntosh index in dormant season and Shannon-Wiener index in growing season in GL than in the others (P < 0.05). Carbohydrates and carboxylic acids were found to be the main substrates used in dormant season, whereas amino acids, polymers and phenolic acids were increasingly utilized by the microbial communities in growing season. We observed soil total potassium as the key factor that significantly affected the utilization efficiency of different carbon sources in both seasons (P < 0.05).

Differences in the Cyanobacterial Community Composition of Biocrusts From the Drylands of Central Mexico. Are There Endemic Species?

In drylands worldwide, biocrusts, topsoil microbial communities, are prevalent, contributing to the biostabilization of soils and allowing the subsequent establishment and growth of vascular plants. In early successional biocrusts, cyanobacteria are the first dominant colonizers of bare ground, largely determining their functioning. However, there are large gaps in our knowledge of the cyanobacterial diversity in biocrusts, particularly in understudied geographic regions, such as the tropical latitudes. We analyzed the diversity of the cyanobacteria inhabiting the biocrusts of semideserts from Central Mexico in two localities belonging to the same desert system (Chihuahuan Desert) that are separated by a cordillera that crosses the center of Mexico. Morphological identification of the cyanobacteria was carried out after cultivation in parallel with the direct observation of the environmental samples and was supported by genetic characterization through analysis of the 16S rRNA gene of the isolated strains and by next-generation sequencing of the soil samples. Taxonomic assignment revealed a clear dominance of heterocystous cyanobacteria at one of the studied locations (Actopan, Hidalgo state). Although heterocystous forms were abundant at the other location (Atexcac, Puebla state), almost a third of the cyanobacterial phylotypes were represented by unicellular/colonial cyanobacteria, mostly Chroococcidiopsis spp. Only 28.4% of the phylotypes were found to be common to both soils. Most of the other taxa, however, were biocrust-type specific, and approximately 35% of the phylotypes were found to be unique to the soil they were collected in. In addition, differences in the abundances of the shared cyanobacteria between the locations were also found. These differences in the cyanobacterial distribution were supported by the distinct responses of the isolated strains representative of the sites to extreme heat and desiccation in bioassays. Some cyanobacteria with high abundance or only present at the hottest Actopan site, such as Scytonema hyalinum, Scytonema crispum, Nostoc commune, Nostoc sp., and Calothrix parietina, survived extreme heat and desiccation. However, Tolypothrix distorta and Chroococcidiopsis spp. were clearly sensitive to these extreme conditions in relation to their lower abundances at Actopan as opposed to Atexcac. Since novel biocrust-associated phylotypes were also found, the emergence of endemic cyanobacterial taxa is discussed.

Exclusion of small mammals and lagomorphs invasion interact with human-trampling to drive changes in topsoil microbial community structure and function in semiarid Chile

Species losses and additions can disrupt the relationship between resident species and the structure and functioning of ecosystems. Persistent human-trampling, on the other hand, can have similar effects through the disruption of biocrusts on surface soils of semiarid systems, affecting soil stability and fixation of carbon and nitrogen. Here, we tested the interactive and synergistic impacts of the exclusion of native mammalian herbivores and the effects of introduced lagomorphs in a semiarid thorn scrub ecosystem, where soils were subjected to two different trampling intensities (i.e., trampled and non-trampled). We postulated that because of their differential habitat use and fossorial activities, with respect to native small mammals, lagomorphs would have strong negative effects on soil structure, biocrust cover, and biocrust bacterial community structure. Our expectations were that changes in biocrust cover in response to trampling where native mammals were excluded, but exotic lagomorphs were present, will spread their impacts on soil chemical and physical features. To test our hypotheses, we measured changes in soil biogeochemical properties in four experimental plots where lagomorphs (L)/small mammals (SM) were experimentally manipulated to exclude them from the plots (−), or let them be present (+). The experimental combinations monitored were: -L/+SM, -L/-SM, +L/+SM, and +L/-SM. Results showed that human-trampling disturbance interacted with the loss of native small mammals and the presence of non-native lagomorphs to cause large changes on biological (i.e., biocrust cover, bacterial and nifH genes abundance), physical (i.e., soil moisture and soil stability) and chemical (i.e., TC and TN) soil features. The relative impacts of trampling disturbance on biological and physicochemical features were strongly influenced by the presence of non-native lagomorphs. For example, larger decreases in biocrust cover and bacterial abundance were observed in treatments without lagomorphs (-L/+SM; -L/-SM). In turn, losses of biocrust cover, in addition to trampling, determined decreases in soil stability in all treatments. These results suggest that non-native lagomorphs surpass the effects of the loss of native small mammals in reducing soil quality and productivity. Therefore, human-trampling has the potential to convert low disturbed soils, as those observed in non-trampled soils in treatments -L/+SM, -L/-SM into poor soils with low biocrusts cover and concomitant low stability, as observed in +L/+SM; +L/-SM treatments. These findings agree with previous observations that different components of global change act in synergic ways in fragile, water-limited environments. Because biological invasions and soil surface disturbance are becoming widespread in dryland regions globally, understanding the long-term consequences of these interactions is essential.

Large Blooms of Bacillales (Firmicutes) Underlie the Response to Wetting of Cyanobacterial Biocrusts at Various Stages of Maturity.

ABSTRACTBiological soil crusts (biocrusts) account for a substantial portion of primary production in dryland ecosystems. They successionally mature to deliver a suite of ecosystem services, such as carbon sequestration, water retention and nutrient cycling, and climate regulation. Biocrust assemblages are extremely well adapted to survive desiccation and to rapidly take advantage of the periodic precipitation events typical of arid ecosystems. Here we focus on the wetting response of incipient cyanobacterial crusts as they mature from “light” to “dark.” We sampled a cyanobacterial biocrust chronosequence before (dry) and temporally following a controlled wetting event and used high-throughput 16S rRNA and rRNA gene sequencing to monitor the dynamics of microbial response. Overall, shorter-term changes in phylogenetic beta diversity attributable to periodic wetting were as large as those attributable to biocrust successional stage. Notably, more mature crusts showed significantly higher resistance to precipitation disturbance. A large bloom of a few taxa within the Firmicutes, primarily in the order Bacillales, emerged 18 h after wetting, while filamentous crust-forming cyanobacteria showed variable responses to wet-up across the successional gradient, with populations collapsing in less-developed light crusts but increasing in later-successional-stage dark crusts. Overall, the consistent Bacillales bloom accompanied by the variable collapse of pioneer cyanobacteria of the Oscillatoriales order across the successional gradient suggests that the strong response of few organisms to a hydration pulse with the mortality of the autotroph might have important implications for carbon (C) balance in semiarid ecosystems.

Soil microbial beta-diversity is linked with compositional variation in aboveground plant biomass in a semi-arid grassland

Exploring biodiversity linkages between aboveground and belowground biota is a core topic in ecology, and can have implications on our understanding of ecosystem process stability. Yet, this topic still remains underexplored. Here, we explored diversity linkages, in terms of both alpha- and beta- diversity, between plant and top soil microbial communities in a semi-arid grassland ecosystem. Soil microbial community structure was assessed based on both 16S rRNA and functional genes, and plant community composition was evaluated by traditional “species composition” and a newly-defined “biomass composition”, which includes the information on the biomass of each species. The bacterial alpha-diversity, expressed as the richness and Shannon diversity of 16S rRNA genes, was significantly correlated with plant species richness and Shannon diversity, whereas the alpha-diversity of microbial functional genes showed marginal association with total plant biomass. Microbial beta-diversity, evaluated by 16S rRNA genes, showed close relationship with plant beta-diversity estimated by both “species composition” and “biomass composition”, while the microbial beta-diversity based on functional genes was only associated with the compositional variation in aboveground plant biomass. These results showed that the differences in metabolic potential of soil microbial communities, which is closely related with ecosystem functions, can be better predicted by the variation of plant-derived resources returned to soil, than merely by the species composition of the macro-organism communities.

Elevated Air Humidity Changes Soil Bacterial Community Structure in the Silver Birch Stand.

Soil microbes play a fundamental role in forest ecosystems and respond rapidly to changes in the environment. Simultaneously with the temperature increase the climate change scenarios also predict an intensified hydrological cycle for the Baltic Sea runoff region. The aim of this study was to assess the effect of elevated air humidity on the top soil microbial community structure of a silver birch (Betula pendula Roth.) stand by using a free air humidity manipulation facility (FAHM). The bacterial community structures of bulk soil and birch rhizosphere were analyzed using high-throughput sequencing of bacteria-specific16S rRNA gene fragments and quantification of denitrification related genes. The increased air humidity altered both bulk soil and rhizosphere bacterial community structures, and changes in the bacterial communities initiated by elevated air humidity were related to modified soil abiotic and biotic variables. Network analysis revealed that variation in soil bacterial community structural units is explained by altered abiotic conditions such as increased pH value in bulk soil, while in rhizosphere the change in absorptive root morphology had a higher effect. Among root morphological traits, the absorptive root diameter was strongest related to the bacterial community structure. The changes in bacterial community structures under elevated air humidity are associated with shifts in C, N, and P turnover as well as mineral weathering processes in soil. Increased air humidity decreased the nir and nosZ gene abundance in the rhizosphere bacterial community. The potential contribution of the denitrification to the N2O emission was not affected by the elevated air humidity in birch stand soil. In addition, the study revealed a strong link between the bacterial community structure, abundance of denitrification related genes, and birch absorptive root morphology in the ecosystem system adaptation to elevated air humidity.

Changes in the composition and diversity of topsoil bacterial, archaeal and fungal communities after 22 years conventional and no-tillage managements in Northern China

ABSTRACTA comprehensive comparison about microbial community (bacterial, archaeal and fungal) response to different tillage managements in Northern China remain little studied, in this study we compared no-tillage (NT) versus conventional tillage (CT) management on topsoil microbial community diversity and composition in field experiment. We found that NT practice significantly increased the soil moisture content (SMC), bulk density, stocks of soil organic carbon (SOC), total nitrogen (TN), and microbial biomass carbon and nitrogen (P < 0.05). Moreover, higher levels of bacterial and archaeal alpha diversity were observed in NT relative to CT while unexpectedly, there was no significant difference found in fungal diversity between two treatments. The most pronounced shifts in the composition of the different microbial groups were found for the archaeal community, which followed by bacterial and fungal. NT practice markedly enhanced abundances of Proteobacteria (belongs to bacteria) phyla, Thaumarchaeota phyla (belongs to archaea) and Glomeromycota phyla (belongs to fungi). Redundancy analysis revealed that the factor that most closely correlated with bacterial, archaeal and fungal composition were SMC, TN and SOC, respectively. Considering NT enhanced both microbial composition and C storage in topsoil, we suggest that NT offers significant promise to improve topsoil health in this region.

Notice of Retraction: Electrical Power Generation with Himalayan Mud Soil using Microbial Fuel Cell

Topsoil microbial community primarily consists of bacteria species that can generate electricity if a microbial fuel cell is incorporated with it. Since such electron producing bacteria are abundant in nature, microbial fuel cells can be considered as clean source of electricity generation and a prospect for renewable energy growth. Here, the authors have shown experiments with a real microbial fuel cell, investigating electrical power production from it using the Himalayan top soil of Dehradun in Uttarakhand, India. At the smallest level it can help remote rural areas to power lamps or other less energy intensive devices. Using a setup that includes anode, cathode, and related electrical fittings this work has utilized these bacteria over time and observe the power they produce; also the addition of nutrients to the soil which increases the rate of power production has also been experimented. The setup brings together the concept of energy, electronics and microbiology under one framework and is in line with issues relating to climate change, energy security and sustainability. An attempt has been made to explore the spectrum of scenarios and speculating the possibility of generating renewable power using the Himalayan top soil.

The role of the exopolysaccharides in enhancing hydraulic conductivity of biological soil crusts

Biological soil crusts (BSCs) are highly specialized topsoil microbial communities commonly found in arid and semiarid environments, permeated by a polymeric matrix of polysaccharides. BSCs can in principle influence edaphic properties such as texture, pore formation and water retention, which in turn determine water distribution and biological activity in dry lands. This paper investigates the influence of biotic and abiotic factors on BSC hydraulic conductivity, a parameter gauging the ease with which water can move through the pore spaces. Texture, phototroph abundance, microbial composition, and extracellular carbohydrate content were considered as potentially relevant parameters in a correlational study of BSC samples that spanned 1.5 orders of magnitude in hydraulic conductivity. A newly developed, non-destructive extraction method enabled us to directly quantify the specific role of extracellular polysaccharides on soil permeability on a variety of samples. Hydraulic conductivity showed a strongest correlation with texture (positive with sand content, negative with silt and clay). A weaker negative correlation with carbohydrate content, especially with polysaccharides having a molecular weight < 100 kDa, was also detected. In multiple regression analyses texture (silt content) was sufficient to explain most of the variation in hydraulic conductivity However, experimental removal of polymeric carbohydrates, resulted invariably in a substantial decrease in hydraulic conductivity for any given sample (between 1.7 and 3.3 fold). Our results suggest that while soil texture determines overall hydraulic conductivity in BSCs, the presence of exopolysaccharides can significantly enhance it, likely by conferring a spongy structure to a BSC thus increasing the number of waterways within it.