Soil Community Structure Research Articles

Impact of Combined Exposure to Glyphosate and Diquat on Microbial Community Structure and Diversity in Lateritic Paddy Soil

Microbial communities play crucial roles in the biogeochemical cycling of many important soil elements. Pesticides are known to affect non-targeted soil microorganisms. Glyphosate (GP) and diquat (DQ), two commonly used non-selective herbicides, often co-exist in lateritic paddy soil rich in iron/aluminum oxides. However, there is limited information on their co-impact on microbial community structure and diversity in this type of soil. Here, the short-term effects of combined exposure to GP and DQ on microbial diversity and community structure shifts were investigated in lateritic paddy soil from a tropical agricultural region (Hainan, China). The combined utilization dosages of two herbicides were set in three concentrations: low concentration (1 fold of the recommended dosage), medium concentration (10 fold of the recommended dosage) and high concentration (100 fold of the recommended dosage). The structure and diversity of microbial communities were determined via 16S rRNA and ITS gene high-throughput sequencing. The results revealed that Actinobacteria and Proteobacteria were the most sensitive microbial phyla to the combined exposure of GP and DQ in lateritic paddy soil. The combined exposure to GP and DQ increased the abundance of Actinobacteria but significantly inhibited that of Proteobacteria, especially at low and medium concentrations. Compared with CK, mixed herbicide (GP + DQ) had no adverse effects on the richness of bacteria and fungi communities as well as on the diversity of bacteria communities, but it significantly decreased the diversity of fungi communities at high concentrations within 28 days. However, the effects of combined exposure to GP and DQ on soil microbial richness and diversity were not significantly different from those of separate exposure of the two herbicides. In conclusion, the combined application of GP and DQ had no more adverse effects on soil microorganisms. Therefore, these two herbicides can be used reasonably in actual agricultural production.

Seasonality regulates the structure and biogeochemical impact of ectomycorrhizal fungal communities across environmentally divergent neotropical dry forests

Abstract Ectomycorrhizal (ECM) symbioses support forest functioning globally, yet both the structure and function of ECM fungal communities in seasonally dry neotropical forests (SDTFs), known for extreme heterogeneity in vegetation and edaphic properties, remain under characterized. Here, we evaluated the relative influences of seasonal versus spatial variation in ECM fungal community structure in soils from four environmentally divergent SDTFs. We also assessed the importance of biotic and abiotic drivers of SDTF ECM fungal community structure at regional scales, as well as ECM impacts on soil carbon (C) and nitrogen (N) cycling. ECM fungal frequency, relative abundance and richness all increased in the wet season, but spatial rather than seasonal effects explained more variation in community composition. Across the four SDTFs investigated, differences in tree communities drove ECM fungal community turnover more than geographic distances, site abiotic conditions or soil chemistry. Although soil moisture and ECM tree basal area were stronger predictors of soil biogeochemistry, incorporating ECM fungal community composition and relative abundance added explanatory power to models of soil C and N cycling in the wet season. Synthesis: Our results highlight the importance of seasonality and plant community composition in shaping different aspects of SDTF ECM fungal community structure and diversity as well as the potential for both the plant and fungal components of ECM symbioses to impact soil functioning across heterogenous SDTFs. Furthermore, our findings suggest that alterations in SDTF plant community composition due to climate or land‐use change will have important consequences for ECM fungal diversity and associated effects on soil biogeochemical cycling.

Precipitation Drives Soil Protist Diversity and Community Structure in Dry Grasslands.

Protists are essential components of soil microbial communities, mediating nutrient cycling and ecosystem functions in terrestrial ecosystems. However, their distribution patterns and driving factors, particularly, the relative importance of climate, plant and soil factors, remain largely unknown. This limits our understanding of soil protist roles in ecosystem functions and their responses to climate change. This is particularly a concern in dryland ecosystems where soil microbiomes are more important for ecosystem functions because plant diversity and growth are heavily constrained by environmental stresses. Here, we explored protist diversity and their driving factors in grassland soils on the Tibetan Plateau, which is a typical dryland region with yearly low temperatures. Soil protist diversity significantly decreased along the gradient of meadow, steppe, and desert. Soil protist diversity positively correlated with precipitation, plant biomass and soil nutrients, but these correlations were changed by grazing. Structural equation and random forest models demonstrated that precipitation dominated soil protist diversity directly and indirectly by influencing plant and soil factors. Soil protist community structure gradually shifted along meadow, steppe and desert, and was driven more by precipitation than by plant and soil factors. Soil protist community compositions were dominated by Cercozoa, Ciliophora and Chlorophyta. In particular, Ciliophora increased but Chlorophyta decreased in relative abundance along the gradient of meadow, steppe and desert. These results demonstrate that precipitation plays more important roles in driving soil protist diversity and community structure than plant and soil factors, suggesting that future precipitation change profoundly alters soil protist community and functions in dry grasslands.

Litter inputs exert greater influence over soil respiration and its temperature sensitivity than roots in a coniferous forest in north-south transition zone

The changes in carbon inputs of litter and roots to forest soils caused by climate change will result in a serious cascade effect on soil respiration and its temperature sensitivity (Q10). To differentiate and quantify the effects of surface litter and living roots on soil respiration and Q10, and further explore the role of abiotic factors and microbial properties on soil respiration and Q10, a short-term (two years) detritus input and removal treatment experiment was conducted in a coniferous forest of central China. Soil temperature, soil moisture, C/N, microbial biomass and community composition were analyzed to explore the drive mechanisms of soil respiration and Q10 in response to carbon inputs. The results showed that litter addition increased soil respiration by 22 %, while litter or roots removal did not affect soil respiration, which might be ascribed to the “priming effects” mediated by fresh plant litter. We also found that litter addition increased Q10, while litter removal decreased Q10. Litter addition significantly enhanced the microbial biomass for any single functional group and altered soil microbial community composition. Structural equation model further proved that microbial biomass and community composition exerted stronger impacts on Q10 than do soil abiotic factors. Soil moisture, microbial biomass and community structure were main factors in predicting soil respiration. The study highlights the important role of litter inputs compared with living roots in carbon cycling in short-term and deepens our understanding on the complex relationships among soil respiration, soil micro-environment and microbial community composition.

Effects of mushroom-tobacco rotation on microbial community structure in continuous cropping tobacco soil.

Rotation is an effective strategy for controlling crop diseases and improving plant health. However, the effect of a mushroom-tobacco rotation on the composition and structure of microbial communities in continuous cropping soil is unclear. This study analysed the structure and function of soil bacterial and fungal communities using Illumina MiSeq high-throughput 16S rRNA gene sequencing. The results showed that the physicochemical properties (organic matter, available nitrogen, available phosphorus, and available potassium) and enzymatic activity (phosphatase, catalase, urease and invertase activity) in the rotation treatments (Y1, M1, Y2 and M2) were significantly higher than those in the control (continuous cropping) treatment (CK) and reached peak values in the M2 treatment. PCA showed that the soil microbial community structure in each rotation treatment was different from that in the control. The dominant bacterial phyla of the different soil treatments were Proteobacteria and Actinobacteriota, and the dominant fungal phyla of the different soil treatments were Ascomycota and Basidiomycota. The M2 rotation significantly reduced the relative abundance of harmful fungi (Penicillium and Gibberella) compared to the other treatments. RDA showed that the most abundant bacterial taxa were negatively correlated with pH and positively correlated with physicochemical properties. However, the most abundant fungal taxa were positively correlated with pH and negatively correlated with physicochemical properties. The mushroom-tobacco rotation can effectively maintain the ecological balance of the substrate microbial environment, and provide a more effective way to prevent the continuous cropping of tobacco.

Sampling period and disease severity of bacterial wilt significantly affected the bacterial community structure and functional prediction in the sesame rhizosphere soil

The changes in the structure and function of bacterial communities present in the rhizosphere soils are of great significance for disease control in sesame, but it remains unclear to date. The present study explored the effects of five sampling periods (F0, day 0 after the first flowering; F11; F21; F32; F48) and three disease severities (H0, healthy; D5, moderate diseased; D9, serious diseased) on the structure and function using high throughput sequencing. The results indicated that the values of the Obs, Shannon, Chao1, and ACE first increased and then decreased in the D5 and D9 groups as plants matured, while an increasing trend was observed in the H0 group. The relative abundances of Actinobacteria and Proteobacteria demonstrated a trend from lower values to increased values and then again to lower values in the later sampling period. In the D9 group, Ralstonia experienced a significant 2.15-fold increase during the F0 period, while Gemmatimonas and Streptomyces demonstrated significant increases of 0.65 and 0.30 percentage points, respectively, in the D9 group during the F11 and F21 periods compared to H0. The predominant phyla in the H0 group during the F0 and F11 periods were p_Verrucomicrobiota and p_Firmicutes, respectively. In the D5 group during the F11 period, there were notable increases in xenobiotics biodegradation and metabolism (7.72%) and amino acid metabolism (0.80%) compared to H0, while nucleotide metabolism, replication and repair, and translation experienced significant decreases of 1.85%, 2.16%, and 1.64%, respectively. This critical period preceding the final flowering influenced the structure and function of bacterial communities in the sesame rhizosphere soil. The available potassium and boron exhibited a significant negative correlation with the phyla Proteobacteria and Crenarchaeota, while these phyla were significantly positively correlated with the genera Sphingomonas, Ramlibacter, and Gemmatimonas in the rhizosphere soil, and Carbohydrate_Metabolism and Cell_Motivity of the bacterial functions. The findings contribute to the understanding of the temporal dynamics of microbial communities and their functions in sesame rhizosphere soil, and their response mechanisms to bacterial wilt severity.

Effects of nitrogen and phosphorus additions on CH4 flux in wet meadow of Qinghai-Tibet Plateau

Methane (CH4) is a critical greenhouse gas, and wetlands are the largest natural emitters of CH4. Owing to global climate change and the intensification of anthropogenic activities, the input of exogenous nutrients such as nitrogen (N) and phosphorus (P) into wetland ecosystems has increased, which may significantly affect nutrient cycling and CH4 fluxes from wetlands. However, the environmental and microbial effects of the addition of N and P on CH4 emissions from alpine wetlands have not been thoroughly examined. We conducted a two-year field experiment with N and P addition to examine its impact on CH4 emissions from wetlands on the Qinghai-Tibet Plateau (QTP). The treatments comprised a blank control (CK), N addition (15 kg N ha−1 yr−1, N15), P addition (15 kg P ha−1 yr−1, P15), and NP co-addition (15 kg NP ha−1 yr−1, N15P15). We measured CH4 flux, soil environmental factors, and microbial community structure for each treatment plot. The results showed that the CH4 emissions of N and P addition were higher than CK. Specifically, the CH4 fluxes of N15, P15, and N15P15 treatments were 0.46 mg CH4 m−2 h−1, 4.83 mg CH4 m−2 h−1, and 0.95 mg CH4 m−2 h−1 higher than the CK. Additionally, the CH4 fluxes of N15P15 treatments was 3.88 mg CH4 m−2 h−1 lower than the P15 and 0.49 mg CH4 m−2 h−1 higher than the N15. This finding indicated that the CH4 flux in the alpine wetland soil was more sensitive to the addition of P. N and P addition increased not only soil organic carbon content (P < 0.05) but also the relative abundance of Chloroflexi and Actinobacteria in the soil, which may be the main reason for the promotion of CH4 emissions. Therefore, our results indicate that N and P addition can change the microbial abundance and community structure of wetland soil, and the distribution of soil carbon, promote CH4 emissions, and ultimately affect the carbon sink function of wetland ecosystems.

Illumina MiSeq sequencing investigation on the contrasting rhizosphere soil bacterial community structures in tea orchard soil under different content of aluminium

The rhizosphere of grown tea (Camellia sinensis (L.) O. Kuntze) becomes acidic, and aluminium (Al) toxicity has been identified as a key constraint on plant development in acidic soils. The current study investigated the composition and functions of rhizosphere bacteria as well as soil enzyme activity under different Al stress conditions. The effect of soil pH, soil enzyme activities, the diversity and structure of the rhizosphere bacterial population under various Al concentrations were studied by the pot experiment. All analyses demonstrated that substantial alterations in the activity of soil enzymes and the composition of the bacterial communities in the rhizosphere could only be seen under conditions of extreme Al stress. Soil enzymes were more concentrated in Al concentrations of 100, 150 and 250 µM, respectively. More than 82,000 valid reads were obtained for each replicate, and the abundance of certain genera in the aluminium treated groups were greater than the control group. Lower Al stress attracted Al-tolerant bacteria such as Burkholderia to increase Al stress resistance. These findings revealed that soil enzyme activities and the structure of the rhizosphere bacterial population in tea orchard soil provided tolerance or resistance capability to tea plants for their development under Al stress.

Effects of biochar amendment on bacterial communities and their function predictions in a microplastic-contaminated Capsicum annuum L. soil

Microplastics (MPs) have been confirmed as a novel type of environmental pollutant. They have long-term existence in the soil environment and threaten the soil ecological environment system. Biochar soil amendment is capable of enhancing the water and nutrient holding capacity and improving the soil structure and quality of terrestrial ecosystems. However, the effect of biochar amendment on bacterial community in MPs-contaminated soil–plant system remain unclear, in particular the prediction of bacterial function of these systems. In this study, the effects of biochar amendment on the bacterial community structure of MPs-contaminated soil were investigated through different treatments at three pepper growth stages, and the bacterial function of MPs-contaminated soil was predicted. As indicated by the results of this study, biochar amendment led to the increased species evenness and richness of bacterial community in MPs-contaminated soil, the enhanced relative abundance of MPs-contaminated tolerant bacteria (e.g., Proteobacteria, Acidobacteria, Actinobacteria, and Bacteroidetes), as well as the improved relative abundance of Massilia, Lysobacter, and Terrimonas. Furthermore, soil total phosphorus (TP), soil organic carbon (SOC), NH4+-N, NO3−-N, and pH served as the main factors for the composition of soil bacterial community, as revealed by the result of Pearson correlation analysis and redundancy analysis. Bacterial genera Massilia, Lysobacter, and Terrimonas significantly affected the growth indicator of pepper. PICRUSt functional prediction suggested that the bacterial community of MPs-contaminated soil primarily comprised four level-1 functional layers and 16 level-2 functional layers, and the active soil bacterial community was identified in Metabolism, Genetic information processing, as well as Cellular processes. Biochar amendment enhanced the abundance of genes correlated with Amino acid metabolism and Carbohydrate metabolism of bacteria in MPs-contaminated soil, thus facilitating the nitrogen and phosphorus metabolism cycle of MPs-contaminated soil plants. Our results confirmed that biochar amendment increase the beneficial bacteria in MPs-contaminated soil, more significantly facilitate the nitrogen and phosphorus metabolism cycle within MPs-contaminated soil plants, while effectively expediting the growth of plants in MPs-contaminated soil. This study provides more insights into the correlation of plant and bacterial communities in response to biochar amendment in MPs-contaminated soil system.

Responses of soil fauna community under changing environmental conditions

Soil faunas account for 23% of known animal species and play a crucial role in ecosystem processes such as mineralizing nutrients, regulating microbial community composition, forming soil aggregates, and enhancing primary productivity. However, due to global climate change, population density, community composition, and distribution patterns of soil fauna vary. Understanding the responses of soil fauna to major environmental change facilitate the conservation of biodiversity. Therefore, a review work of recent researches for analysing the effects of key environmental factors on soil fauna, such as warming, drought, food quality, and soil physical-chemical properties was studied. For most species, warming may exert a positive effect on their abundance and population development, however, it can inhibit the survival and reproduction of hibernating species. Drought leads to low soil porosity and water holding capacity, which reduces soil fauna population and changes their community composition. Drought also can reduce the coverage of flora and alter microclimate of the soil surface, which in turn indirectly reduces fauna abundance. Climate warming and elevated atmospheric carbon dioxide can reduce litter quality, which will force soil fauna to change their dietary choices (from higher-quality foods to poor quality foods) and reduce reproduction for survival. However, it is still predicted that enhanced species richness of plant (or litter) mixtures will positively affect soil fauna diversity. Habitat loss caused by the deterioration of soil physical-chemical property is primary factor affecting soil fauna. We mainly discuss the threats of increased salinity (a major factor in arid land) to soil fauna and their potential responses to anthropogenic disturbance in saline soils. The increase in soil salinity can override other factors that favour habitat specialists, leading to negative effects on soil fauna. Moreover, we find that more studies are needed to explore the responses of soil fauna in saline soils to human activities. And the relationship of important ecological processes with soil fauna density, community structure, and diversity needs to be redefined.

Urban soil quality deteriorates even with low heavy metal levels: An arthropod-based multi-indices approach.

Urban-induced habitat conversion drastically changes soil life in a variety of ways. Soil sealing, human disturbance, habitat fragmentation, industrial and vehicular pollution are the main causes of urban soil degradation. Soil arthropods, as one of the most abundant and diverse group of soil fauna, are involved in many soil processes that are of great importance in maintaining soil health and multifunctionality. Nevertheless, soil quality is still mainly characterized by physical, chemical, and microbiological parameters. Here, we assessed and compared the biological soil quality in woody (REF: reference forest, REM: remnant forest) and nonwoody (TURF: public turfgrass, and RUD: ruderal habitat) types of urban green spaces along a disturbance and management intensity gradient in the Budapest metropolitan area (Hungary), using community metrics and soil arthropod-based indicators. Vegetation cover and landscape characteristics of study sites were quantified through vegetation and urbanization indices, respectively. Basic soil properties, total and bioavailable concentrations of the main heavy metals (Cd, Co, Hg, Ni, Zn) were also measured. Acari, Collembola, and Hymenoptera (mainly Formicidae) were the most abundant groups. Litter-dweller taxa, particularly Protura, proved to be the most sensitive to urban disturbance. Representatives of Hemiptera, Diptera, Symphyla, and Pauropoda were common in low densities. The taxonomic diversity of soil arthropod assemblages in nonwoody and woody habitats was similar. Although the integrated faunal indices showed no differences among soil habitat types, they provided different responses and, consequently, different information. Our findings demonstrated that the biological quality and arthropod community structure of soils were strongly impacted by soil C/N and heavy metal contamination. We found that low and moderate levels of pollution have adverse effects on edaphic fauna, suggesting biological degradation of soils, even below pollution limits. Nevertheless, more disturbed urban green spaces have been shown to play a significant role in maintaining belowground biodiversity, thereby soil functions.

Safe Rice Production in Cd-Contaminated Paddy Soil: Strategy and Environmental Implications

This field study explored safe rice production in Cd-contaminated red paddy soil by application of the combined Si-/Se- containing foliar inhibitors (Si or Se) and the mixture amendments of quicklime (Q), polyacrylamide (A), or/and sepiolite (S) at low (1) and high (2) application rates. The results showed that all treatments increased soil pH and decreased total P and soil organic matter (excluding QSe2). With the increasing application rates, QAS significantly decreased the available Cd because of the enhanced stabilization, while QSi and QSe significantly increased the available Cd because of the inhibited plant uptake. After remediation, QA1, QSi2, and QSe2 most effectively decreased the uptake Cd by rice to meet the threshold of National Food Safety Standard of China. The treatments excluding Q1, QA1, QSi1, and QSi2 did not dramatically change the bacterial community structure in soil. Collectively, QSe2 was recommended for remediating Cd-contaminated red paddy soil.

Effects of biochar addition on aeolian soil microbial community assembly and structure

The effects of biochar on soil improvement have been widely confirmed, but its influence on soil microorganisms is still unclear. Elucidating the complex relationship and the community assembly processes of microorganisms under biochar addition is important to understand the ecological effects of this substance. We performed a one-time addition of biochar on aeolian soils and planted maize (Zea mays L.) continuously for 7 years. Afterwards, soil samples were collected, and the 16S/ITS rRNA gene sequencing technology was used to study changes in microbial community structure, network characteristics, and community assembly processes in the aeolian soils. We found that biochar addition significantly increased the maize yield and changed the soil microbial community composition (β-diversity), but had no significant effect on the microbial α-diversity. The addition of 31.5-126.0 Mg ha-1 of biochar led to a reduction of the rhizosphere bacterial network's edge number, average degree, and robustness, but had no significant effect on the fungal network properties. The bacterial community was controlled by deterministic processes, while fungi were mainly controlled by stochastic processes. The addition of 126.0 Mg ha-1 of biochar led to a transformation of the bacterial community's assembly processes from deterministic to stochastic. These results indicate that the stability of the rhizosphere bacterial community's complex network in aeolian soils diminishes under biochar addition, together changed the bacterial community's assembly processes. Fungi can instead effectively resist the environmental changes brought by biochar addition, and their network remains unchanged. These findings help clarify the effect of biochar addition on microbial interaction and assembly processes in aeolian soils characteristic of arid regions. KEY POINTS: • Biochar addition led to changes in the microbial community composition • Biochar addition reduced the network's stability of rhizosphere bacteria • Biochar addition changed the processes of the bacterial community assembly.

Prokaryotic diversity and community structure in the rhizosphere of Lantana weed (Lantana camara L.).

Lantana weed (Lantana camara L.) is among the most noxious weeds in the world. Keeping in mind its invasive behavior and great ecological tolerance, it becomes imperative to analyze the structure and function of associated microbiome. In this perspective, Illumina-based metagenome sequencing was performed to gain a better understanding of prokaryotic diversity and community structure in the rhizosphere soil of L. camara L. The organic carbon, nitrogen, phosphorus, and potassium contents in the rhizosphere soil were 0.91% (± 0.21%); 280 Kg ha-1 (± 4.02 Kg ha-1), 54.5 Kg ha-1 (± 3.12 Kg ha-1), and 189 Kg ha-1 (± 6.11 Kg ha-1), respectively. The metagenome analysis revealed the existence of 41 bacterial and 2 archaeal phyla, with only 12 showing ≥1% abundances. Pseudomonadota was the dominant phylum with 31.3% abundance, followed by Actinomycetota (20.9%). Further, 54 different genera were identified with the highest abundance of Devosia (2.8%). The PICRUSt analysis predicted various functional traits in the soil metagenome, with general cellular functions dominating, followed by stress tolerance. Moreover, 10% of the functions were associated with nitrogen fixation, phosphate solubilization, and potassium mobilization. In conclusion, the present study revealed the existence of diverse prokaryotic communities in the rhizosphere of the L. camara L. which was primarily associated with stress response and plant growth promotion. To the best of our knowledge, this study documents for the first time the L. camara L. microbiome. Furthermore, the identified genera can be explored for agricultural needs in future.

Response of rice yield to organic amendments was regulated by soil chemical properties, microbial functional genes and bacterial community rather than fungal community

Integrated fertilization using mineral fertilizer and organic amendments is common practices for sustainable crop production. However, the impacts of different organic amendments on soil chemical properties, function genes, and microbial community, as well as their contribution to rice yield have not been well illustrated. In this study, soil chemical properties, microbial diversity, community structure and stability, and functional genes were evaluated after 10 years of fertilization. Compared with the mineral fertilizer regime, the integrated addition of mineral fertilizer and organic amendments improved soil fertility and increased the grain yield by 0.32 %–11.45 %, in terms of five-year average yield. Bacterial diversity and microbial community stability were significantly improved by organic amendments (p < 0.05). Additionally, organic amendments significantly reshaped the microbial community and increased the relative abundance of beneficial bacteria and fungi, as well as suppressed the growth of plant pathogenic fungi (p < 0.05). Besides, multiple functional genes were upregulated by organic amendments, and had significant relationships with grain yield. Soil chemical properties explained most of the variation in grain yield. PLS-PM result further revealed that functional genes and bacterial community (diversity, composition, and stability), rather than fungal community, which were positively affected by fertilization and soil chemical properties, had a strong influence on grain yield. Overall, organic amendments strongly improved soil chemical properties and function and regulated bacterial community, thus enhancing rice yield.

Structural Characteristics and Assembly Mechanisms of Soil Microbial Communities under Water-Salt Gradients in Arid Regions.

Exploring the structural characteristics of arid soil microbial communities and their assembly mechanisms is important for understanding the ecological characteristics of arid zone soils and promoting ecological restoration. In this study, we used Illumina high-throughput sequencing technology to study soils in the arid zone of the Lake Ebinur basin, determined the differences among soil microbial community structures in the study area under different water-salt gradients, and investigated the effects of environmental factors on microbial community structure and assembly mechanisms. The results show the following: the microbial community alpha diversity exhibited a significantly higher low water-salt gradient (L) than high water-salt gradient (H) and medium water-salt gradient (M). The pH was most strongly correlated with soil microbial community structure, where the alpha diversity indices of the bacterial community and fungal community were significantly negatively correlated with pH, and the Bray-Curtis distance of bacterial community was significantly positively correlated with pH (p < 0.05). The complexity of bacterial community co-occurrence networks showed a significantly higher L than H and M, and the complexity of fungal community co-occurrence network showed a significantly lower L than H and M. The cooperative relationship of H and M in the co-occurrence networks was stronger than that of the L, and the key species of the microbial co-occurrence network were different under different water-salt gradients. Stochastic processes dominated the assembly mechanism of the microbial community structure of soil, and the explanation rates of deterministic and stochastic processes were different under different water-salt gradients, with the highest explanation rate of stochastic processes on the L accounting for more than 90%. In summary, the soil microbial community structure and assembly mechanisms significantly differed across water-salt gradients, and these findings can help provide a reference for further research on soil microbiology in arid zones.

Bacterial Communities Structure and Diversity in Rhizosphere Soil of Dominant Plants in Riparian Wetlands of Reservoir in Zhejiang Province, China

Soil bacterial play special roles in the maintenance and stabilization of wetland ecosystem. To investigate bacterial community structure and diversity in rhizosphere soils of four dominant plants in riparian wetlands of mountain reservoir in Zhejiang province, the V4+V5 areas of 16S rDNA gene of bacteria were sequenced and analyzed by the Illumina HiSeq 2500 high-throughput sequencing technology. The results indicated that 27 phylums, 70 classes, 144 orders, 218 families, and 370 genuses of bacteria were achieved, with Proteobacteria, Acidobacteria,Actinobacteria and Bacteroidetes being the dominant phylum and Gammaproteobacteria, Deltaproteobacteria, Acidobacteria, Actinobacteria, Betaproteobacteria and Thermoleophilia being the main class in the soils of riparian wetlands in this areas. The Shannon index and chao1 index of the rhizosphere soil bacteria of Salix babylonica were 8.64 and 585.58, respectively, which were the highest among the four plants, and that of Pterocarya stenoptera were the lowest, with 7.71 and 289.63, respectively. Soil pH, total nitrogen and organic matter were the main factors affecting the soil bacterial community structure in the soil rhizosphere of four dominant plants species in wetlands of riparian zone of reservoir in Zhejiang province.

Enhanced bioremediation of triclocarban-contaminated soil by Rhodococcus rhodochrous BX2 and Pseudomonas sp. LY-1 immobilized on biochar and microbial community response.

Triclocarban (TCC), an emerging organic contaminant (EOC), has become a severe threat to soil microbial communities and ecological security. Here, the TCC-degrading strain Rhodococcus rhodochrous BX2 and DCA-degrading strain Pseudomonas sp. LY-1 (together referred to as TC1) were immobilized on biochar to remove TCC and its intermediates in TCC-contaminated soil. High-throughput sequencing was used to investigate the microbial community structure in TCC-contaminated soil. Analysis of co-occurrence networks was used to explore the mutual relationships among soil microbiome members. The results showed that the immobilized TC1 significantly increased the removal efficiency of TCC from 84.7 to 92.7% compared to CK (no TC1 cells on biochar) in 10 mg/L TCC liquid medium. The utilization of immobilized TC1 also significantly accelerated the removal of TCC from contaminated soil. Microbial community analysis revealed the crucial microorganisms and their functional enzymes participating in TCC degradation in soil. Moreover, the internal labor division patterns and connections of TCC-degrading microbes, with a focus on strains BX2 and LY-1, were unraveled by co-occurrence networks analysis. This work provides a promising strategy to facilitate the bioremediation of TCC in soil, which has potential application value for sustainable biobased economies.

Moderate Nitrogen Reduction Increases Nitrogen Use Efficiency and Positively Affects Microbial Communities in Agricultural Soils

Excessive nitrogen fertilizer usage in agricultural often leads to negative ecological and production gains. Alterations in the physical and chemical properties and microbial community structure of agricultural soils are both the cause and consequence of this process. This study explored the perturbation of soil properties and microorganisms in agricultural soils by different nitrogen levels. Soil total nitrogen, total phosphorus, and total potassium decreased in the shallow soil layer with decreasing nitrogen. Changes in nitrogen affected soil organic matter, pH, bulk density, and water content. However, a moderate reduction in nitrogen did not cause significant yield loss; the increased nitrogen use efficiency was the main reason, attributed to the available phosphorus and potassium. Short-term changes in nitrogen had limited effects on soil microbial community structure. Bacteria were more susceptible to perturbation by nitrogen changes. Nitrogen reduction increased the relative abundance of MND1 (1.21%), RB41 (1.96%), and Sphingomonas (0.72%) and decreased Dongia (0.3%), Chaetomium (0.41%), and Penicillium (0.5%). Nitrogen reduction significantly increased the bacteria functional composition of aerobic ammonia oxidation (4.20%) and nitrification (4.10%) and reduced chemoheterotrophy (2.70%) and fermentation (4.08%). Available phosphorus specifically drove bacterial community structure variation in the shallow soil layers of moderate nitrogen reduction treatments. Steroidobacter, RB41, Gemmatimonas, Ellin6067, Haliangium, and Sphingomonas were the main component nodes in this community structure. These results provide insights into the study of nitrogen and microorganisms in agricultural soils.

Long-term different fertilization regimes impact on the fate of root-derived C and microbial community structure in paddy soil

It is known that fertilization pattern could alter soil nutrient and organic matter status. However, it is still unclear how photosynthesized C is distributed in rice–rhizosphere soil-microbial system and its influencing factors due to fertilization pattern and subsequent changes in soil fertility. This study examined the allocation of rice photosynthetic C in rice–rhizosphere soil–microbial systems and the changes in microbial community under three long-term fertilizer regimes. Rice was grown in soils with 8-year history of no fertilizer, inorganic fertilizer (NPK) or NPK fertilizer plus cattle manure (NPK + CM), and was pulse–labelled with 13CO2 at rice tillering stage. The results showed that 13C incorporation in rice-rhizosphere soil system was the highest in the NPK + CM treatment, increased by 489% and 28.9% compared to unfertilized control and the NPK alone. In the >2 mm aggregate fraction, the 13C enrichment was higher in NPK + CM compared to no-fertilized control and NPK treatments. Total PLFA and PLFA groups contents in all aggregate size fractions were the greatest in the NPK + CM treatment. Partial least squares path modelling analysis revealed that microbial community in large macroaggregate (>2 mm) was significantly (P < 0.05) affected by root properties, while soil fertility had a significant (P < 0.01) impact on microbial community in microaggregate (<0.25 mm). The redundancy analysis showed that soil parameters except soil alkali-hydro nitrogen (AN) significantly impacted the soil microbial communities. Through canonical variation partitioning analysis, soil available K was the most important factor leading to variance (11.4%) in microbial community composition. On the other hand, soil pH significantly (P < 0.05) affected the distribution of 13C in microbe community. More than 20% of 13C was incorporated into G– and G+ bacteria across all treatments. Overall, it was observed the NPK fertilizer plus cattle manure treatment was most conducive to retain C from root exudates in the rice-rhizosphere soil-microbial system.