Soil Microbial Community Characteristics Research Articles

Understanding Responses of Soil Microbiome to the Nitrogen and Phosphorus Addition in Metasequoia glyptostroboides Plantations of Different Ages.

Nitrogen (N) and phosphorus (P) have significant effects on soil microbial community diversity, composition, and function. Also, trees of different life stages have different fertilization requirements. In this study, we designed three N additions and three P levels (5years of experimental treatment) at two Metasequoia glyptostroboides plantations of different ages (young, 6years old; middle mature, 24years old) to understand how different addition levels of N and P affect the soil microbiome. Here, the N fertilization of M. glyptostroboides plantation land (5years of experimental treatment) significantly enriched microbes (e.g., Lysobacter, Luteimonas, and Rhodanobacter) involved in nitrification, denitrification, and P-starvation response regulation, which might further lead to the decreasing in alpha diversity (especially in 6YMP soil). The P addition could impact the genes involved in inorganic P-solubilization and organic P-mineralization by increasing soil AP and TP. Moreover, the functional differences in the soil microbiomes were identified between the 6YMP and 24YMP soil. This study provides valuable information that improves our understanding on the effects of N and P input on the belowground soil microbial community and functional characteristics in plantations of different stand ages.

Dynamics of soil fertility and microbial community response to stocking density in rice-turtle co-culture

Co-culture modes of rice and aquatic animals as rice-crayfish, rice-fish and rice-turtle have expanded rapidly in paddy rice cultivation regions, due to its ecological efficiency, contributions to food security, food productivity and economic benefits. However, different co-culture strategies have great influences on rice or aquatic animal growth and related ecological benefits. In this study, we investigated the effect of turtle stocking density on the dynamics of paddy soil fertility and microbial community characteristics in a rice-turtle co-culture ecosystem. The Chinese soft-shell turtles (Pelodiscus sinensis) were allocated to experimental paddy fields at four gradient stocking densities ranging from 360 to 540 kg· ha−1. In comparison with conventional rice cultivation with a higher input rate of chemical fertilizer, rice yields were higher in the rice-turtle paddies. In addition, soil pH and organic matter were relatively stable in the rice-turtle mode, whereas both parameters decreased over time in conventional paddies. Stocking density significantly benefited soil fertility, with soil organic matter increasing in response to higher stocking density. Total soil nitrogen concentration was lower in the conventional rice cultivation and low stocking density co-culture groups, compared with the high stocking density groups. Furthermore, the soil microbial communities were also affected by turtle stocking density. Redundancy analysis showed that soil pH, organic matter and available potassium concentration were the major factors influencing the abundance of the dominant microbes. The findings revealed the responses of paddy soil fertility and microbial community characteristics in rice-turtle co-culture modes, which could help optimize the co-culture mode and provide a basis for soil nutrient management in such ecosystems.

Effects of biomass conditioner on soil nutrient and microbial community characteristics of alpine desertified grassland in northwest Sichuan, China

Biomass conditioner made from agricultural and animal husbandry waste for resource disposal could be used to improve desertified soil, which is one of the effective ways of ecological management on desertified grasslands in northwest Sichuan. To clarify the effects of different raw material conditioners on alpine desertified grassland in northwest Sichuan, we analyzed the effects of three conditioners on soil nutrients and microbial community characteristics. With no conditioner as the control (CK), three different biomass conditioners were set up with an application rate of 12 t·hm-2, including mushroom dregs (JZ), straw (JG) and biochar (SWT). The results showed that all biomass conditioners could significantly increase soil available nutrients and active organic carbon by 23.0%-521.6%. Among the three conditioners, JG had the best effect, with an improvement range for soil nutrient and organic carbon of 65.1%-521.6%. Because biomass conditioner was only applied in the first year, soil available nutrients and active organic carbon in the second year decreased by 4.5%-92.3% compared with that of the first year, while soil organic carbon and microbial biomass carbon content of the second year increased by 5.6%-458.0%. The biomass conditioners changed the relative abundance of the dominant bacteria in the microbial community. JG significantly affected bacterial flora, while JG and JZ affected fungal flora. Compared with CK, JG significantly reduced the diversity of soil bacteria and fungi. The Shannon index was decreased by 2.9% and 31.8%, while the Simpson index was increased by 175.0% and 320.9%, respectively. Results of the redundancy analysis showed that the contents of soil available nutrients and active organic carbon were important factors affecting microbial community composition. The contents of soil nitrate and microbial biomass carbon had greater impacts on bacterial community composition, explaining 65.9% of community variations. The contents of soil available potassium and microbial biomass carbon had a greater impact on fungal community composition, explaining 83.2% of community variation. According to the comprehensive comparison, straw conditioner could significantly increase soil available nutrients and active organic carbon, and benefit the growth of beneficial bacteria and fungi, which could be used as a promotion measure to improve soil quality of alpine desertified grassland in northwest Sichuan.

Biochar-amended coastal wetland soil enhances growth of Suaeda salsa and alters rhizosphere soil nutrients and microbial communities

Biochar has the potential to improve soil properties and increase plant productivity. However, due to the different types of soil, plants, and environmental factors, the impact of biochar is likely to vary. We explored the impacts of biochar prepared from an invasive plant Spartina alterniflora on plant performance and soil characteristics in a simulated coastal wetland ecosystem. We investigated the impact of three application ratios (control, 1%, and 5%; weight ratio) of biochar on the germination and growth of a native plant Suaeda salsa, the nutrient content and microbial community characteristics of the rhizosphere soil under three flooding treatments (no flooding, episodic flooding, and continuous flooding). Biochar application had no impact on seed germination of S. salsa, but promoted its seedling growth (biomass, height, root length) and nitrogen content. Biochar application also enhanced soil nutrient content and affected soil microbial community characteristics. Seed germination and seedling growth of S. salsa were sensitive to flooding and were the best under episodic flooding. Notably, flooding inhibited the impact of biochar on S. salsa and rhizosphere soil. In conclusion, biochar can positively affect the growth of S. salsa and improve the quality of rhizosphere soil, especially under no flooding. Our findings highlight the possibility of applying biochar for the restoration of S. salsa in coastal wetlands.

Soil microbial community characteristics in a vineyard ten years after fumigation

AbstractCalifornia is the number one producer of grapes in the United States. Soil fumigation has been used to control soilborne pests and pathogens. However, fumigants can potentially have a negative impact on native soil microbial populations. Given the roles of microorganisms in the soil system, it is important to assess the long‐term impact of fumigation on soil microbial communities, which is currently lacking. The objective of this research was to study the long‐term impact of microbial communities in grapevine (Vitis vinifera L.) replanting situations after fumigation. Soil treatments included methyl bromide (MeBr), Telone C35, InLine, a nonfumigated control, and a mustard (Sinapis alba L.) cover crop in two side‐by‐side field experiments fumigated in 2007 and 2008. Microbial community biomass in 2017 and 2018 did not differ between fumigated and nonfumigated plots at the 0‐ to 30‐cm depth. However, plots with shank‐injected MeBr and Telone C35 applied in 2008 showed significantly reduced microbial biomass in 2018 at deeper depths than subsurface drip‐applied InLine plots. The results show the impact of fumigation on bacterial communities; however, the impact on fungal and arbuscular mycorrhizal fungi (AMF) communities was not evident after 10 years. Furthermore, the effect of depth was apparent on bacterial communities compared with fungal and AMF communities. The data suggest that deep‐rooted grapevines influenced fungal populations, which probably supplied labile C in fumigated and nonfumigated plots. Future research needs to focus collectively on the long‐term effects of fumigation on fruit quality and yield in vineyards, and on soil microbial communities.

Effect of stand age on soil microbial communities of a plantation Ormosia hosiei forest in southern China

Changes in soil environmental factors and microbial communities of a precious tree species (Ormosia hosiei) plantation with different forest ages are still unclear. Obtaining this information can provide a theoretical basis for scientific forest management. Ormosia hosiei plantations of varying ages (7, 20, and 45 years old) were targeted in Zhejiang Province, China. We collected surface soil (0–20 cm) and analysed the diversity and structural characteristics of soil microbial communities by high-throughput sequencing. Redundancy analysis (RDA) and Spearman correlation analysis revealed soil environmental factors that cause differences in the microbial communities. The soil bacterial community diversity was not significantly affected by stand age, while the Chao and Ace indexes of the fungal community at 20 and 45 years were markedly higher than those at 7 years. The abundance of Proteobacteria in the 45 years was lower than those at 7 and 20 years, while the abundance of Actinobacteria at 7 years was lower than those at 20 and 45 years, and the abundance of Basidiomycota gradually increased with increasing stand age. The RDA and correlation analysis indicated that the soil microbial biomass carbon (MBC), bulk density (SBD), total porosity (STP), and total potassium (TK) were key factors that affected the bacterial communities and had a significant correlation with Actinobacteria. Soil temperature (T), available phosphorus (AP) and forest litter (FL) affected the fungal communities and had a significant correlation with Basidiomycota. In conclusion, forest age did not affect bacterial diversity, but the soil fungal community of the O. hosiei plantation in the middle-aged forest (20 years old) had the highest diversity; there were obvious differences in the composition and structure of soil microorganisms between different forest ages, which may be attributed to the phyla present (e.g., Proteobacteria, Actinobacteria, and Basidiomycota), which may be caused by differences in T, SBD, STP, AP, TK, MBC, and FL.

Intertillage during Natural Farming Rice Paddy Production Negatively Impacted the Microbial Abundances in Soils but Not Diversities

In natural farming rice paddies, intertillage (tillage between rows, during rice growth period) is often performed mainly to remove weeds without the use of chemicals. Also, the intertillage disturbs soil surfaces, potentially impacting the characteristics of soil microbial communities, such as their diversity and abundance. Natural farming systems aim to maintain biodiversity, but it remains unclear whether the intertillage impacts soil microbes in rice paddies. Thus, this study aimed to understand to what extent “five times intertillage” treatment (5T) influences soil bacterial abundance and community structures compared with no tillage (NT), under a natural farming rice paddy system. Soils were sampled at rice proximity, soil surface, and 10 cm depth in a natural farming rice paddy, during the early to late vegetative phase (June to July), in Hokkaido, Japan. The 16S rRNA community structures and abundance were analyzed by next generation sequencing (NGS) and quantitative PCR, respectively. We observed that NT had significantly higher bacterial abundances at the soil surface than 5T. However, there were no clear differences between 5T and NT, regarding the bacterial community structures, including their diversity indices. Instead, the sampling timings markedly impacted the bacterial community structures for the rice proximity and soil surface, showing increasing diversity indices at the late vegetative stage, compared to the early vegetative stage, suggesting the interaction between the crop growth and bacterial communities. In this study, we did not observe the significant difference between the rice yield from NT (2.3 ± 0.7 t·ha−1) and 5T plots (2.7 ± 0.9 t·ha−1); however, the 5T might have negatively impacted soil bacterial abundances but not the community structure of the bacteria.

Variation of subtropical forest soil microbial biomass and soil microbial community functional characteristics along an urban-rural gradient

Soil microorganisms, which are sensitive to environmental changes, affect soil nutrient cycling and play an important role in the biogeochemical cycling. To understand the changes of soil microorganisms in subtropical forest across the urban-rural environmental gradient, we analyzed the differences in soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial community functional diversitiy in Dashu Mountain National Forest Park (urban forest), Zipeng Mountain National Forest Park (suburban forest) in Hefei and Wanfo Mountain(rural forest) in Luan City. Results showed that soil MBC followed an order of rural natural forest (115.07 mg·kg-1) > suburban forest (101.68 mg·kg-1) > urban forest (82.73 mg·kg-1), soil MBN followed an order of rural natural forest (57.73 mg·kg-1) > urban forest (31.57 mg·kg-1) > suburban forest (29.01 mg·kg-1), soil microbial metabolic activities (AWCD), McIntosh index (U) were shown as rural natural forest > suburban forest > urban forest. The main carbon sources used by soil microbial communities in those forests were carboxylic acids, amino acids and carbohydrates, with weak utilization capacity for polyamines and polyphenols. The utilization capacity of soil microorganisms to amino acids, carboxylic acids, polymers and polyphenols followed the order of rural natural forest > suburban forest > urban forest. There were significant spatial variations in the functional characteristics of soil microbial communities under urban-rural environmental gradient, with Tween 80 and β-methyl-D-Glucoside being the characteristic carbon sources as the influencing factors. Soil pH was significantly positively correlated with the microbial McIntosh index and AWCD value, while soil ammonium nitrogen (NH4+-N) showed a significant positive correlation with microbial Shannon diversity index and AWCD value. There was a negative correlation between the microbial Simpson index and soil nitrate nitrogen (NO3--N). Soil pH, NH4+-N and NO3--N were the main factors affecting diversity index of microbial communities. The results suggested that there were significant differences in microbial community characteristics of forest soil in urban-rural environmental gradient forests, and that the metabolic potential and functional diversity of soil microbial community in urban forests were weaker than that of natural forests.

Litter decomposition, microbial community dynamics and their relationships under seasonal snow cover

Under global climate change, changes in seasonal snow cover patterns significantly affect surface material cycling and microbial community composition. High-throughput sequencing and litter decomposition experiments were employed to study the relationships between soil microbial community characteristics and litter decomposition levels for different snow cover periods and thicknesses. The mass loss of litter was approximately 25–28%, the decomposition coefficient (k) was between 0.277 and 0.322, and k was significantly (p < 0.05) higher under thick snow cover than under no snow cover. Decomposition period significantly affected the observed species number and Shannon and phylogenetic diversity (PD) indices (p < 0.01) of the prokaryote and fungus communities. Snow cover thickness significantly affected the observed species number and Shannon and PD indices of prokaryotes. Prokaryote alpha diversity was significantly (p < 0.05) higher in the deep-freeze period and middle of the growing season than in the freeze-thaw period, and diversity was significantly (p < 0.05) higher under thick snow cover than under no snow cover during the freeze-thaw period. Fungal diversity was significantly (p < 0.05) greater in the middle of the growing season than in the freeze-thaw period and late growing season. The effect of prokaryote diversity on litter properties was greater than that of fungal diversity. Our findings reveal a significant impact of seasonal snowfall on soil microbial communities and variation in the relationships between various properties with changing snow cover thickness. This study provides important data for understanding the impact of winter environmental changes on microbial diversity, material cycling and other ecological processes under global climate change.

Comparison of soil microbial community between reseeding grassland and natural grassland in Songnen Meadow

Microorganisms have important ecological functions in ecosystems. Reseeding is considered as one of the main strategies for preventing grassland degradation in China. However, the response of soil microbial community and diversity to reseeding grassland (RG) and natural grassland (NG) remains unclear, especially in the Songnen Meadow. In this study, the soil microbial community compositions of two vegetation restoration types (RG vs NG) were analyzed using a high-throughput sequencing technique. A total of 23,142 microbial OTUs were detected, phylogenetically derived from 11 known bacterial phyla. Soil advantage categories included Proteobacteria, Acidobacteria, Actinobacteria, and Bacteroidetes, which together accounted for > 78% of the all phyla in vegetation restoration. The soil microbial diversity was higher in RG than in NG. Two types of vegetation restoration had significantly different characteristics of soil microbial community (P < 0.001). Based on a molecular ecological network analysis, we found that the network in RG had a longer average path distance and modularity than in NG network, making it more resilient to environment changes. Meanwhile, the results of the canonical correspondence analysis and molecular ecological network analysis showed that soil pH (6.34 ± 0.35 in RG and 7.26 ± 0.28 in NG) was the main factor affecting soil microbial community structure, followed by soil moisture (SM) in the Songnen meadow, China. Besides, soil microbial community characteristics can vary significantly in different vegetation restoration. Thus, we suggested that it was necessary and reasonable for this area to popularize reseeding grassland in the future.

Impact of Maize–Mushroom Intercropping on the Soil Bacterial Community Composition in Northeast China

Conservative agricultural practices have been adopted to improve soil quality and maintain crop productivity. An efficient intercropping of maize with mushroom has been developed in Northeast China. The objective of this study was to evaluate and compare the effects of planting patterns on the diversity and structure of the soil bacterial communities at a 0–20 cm depth in the black soil zone of Northeast China. The experiment consisted of monoculture of maize and mushroom, and intercropping in a split-plot arrangement. The characteristics of soil microbial communities were performed by 16S rRNA gene amplicom sequencing. The results showed that intercropping increased soil bacterial richness and diversity compared with maize monoculture. The relative abundances of Acidobacteria, Chloroflexi, Saccharibacteria and Planctomycetes were significantly higher, whereas Proteobacteria and Firmicutes were lower in intercropping than maize monoculture. Redundancy analysis suggested that pH, NO3−-N and NH4+-N contents had a notable effect on the structure of the bacterial communities. Moreover, intercropping significantly increased the relative abundance of carbohydrate metabolism pathway functional groups. Overall, these findings demonstrated that intercropping of maize with mushroom strongly impacts the physical and chemical properties of soil as well as the diversity and structure of the soil bacterial communities, suggesting this is a sustainable agricultural management practice in Northeast China.

Response differences between soil fungal and bacterial communities under opencast coal mining disturbance conditions

Despite significant progress in understanding the effect of disturbances on microbial communities, little research has been performed to systematically assess the stability of bacterial and fungal communities in response to environmental changes associated with opencast coal mining. To address this research gap, in this study, we investigated the characteristics of soil microbial communities along the distance gradient in the Shengli east#2 opencast coal mine using Illumina MiSeq high-throughput sequencing. Through phylogenetic analysis and community heat map approaches, we observed that the structure of bacterial and fungal communities was altered by an opencast coal mining disturbance and that microorganisms associated with coal degradation and pollutant detoxification were enriched. LEfSe analysis and molecular ecological networks revealed that the fungal community was more stable than the bacterial community, as it exhibited more biomarkers and a more connected and complex ecological network despite having a lower species diversity. Redundancy analysis showed that soil enzymes among total environmental factors were consistently and tightly aggregated, suggesting that soil enzymes may be key drivers associated with microbial community stability. In summary, our findings provide innovative information for the ecological restoration of mining areas in the future.

Revealing the Impact of the Environment on Cistanche salsa: From Global Ecological Regionalization to Soil Microbial Community Characteristics.

To understand the regulatory relationship between the environment and Cistanche salsa, here we integrated the macro- and microdimension methods. From a macroperspective, the MaxEnt model indicated that countries along the Belt and Road Initiative, such as China, Egypt, and Libya, were particularly suitable for growth of C. salsa from ancient times (Last Glacial Maximum and mid-Holocene) to the future (2050 and 2070). The Jackknife test revealed that precipitation is an important ecological factor that affects C. salsa's distribution. From a microperspective, 16S rRNA amplicon sequencing data showed that the soil microbial communities of three ecotypes (desert-steppe, grassland, and gravel-desert) were significantly different (p < 0.001). Core microbiome analysis demonstrated that the bacterial genera Arthrobacter, Sphingomonas, and Bacillus were enriched core taxa of C. salsa. LEfSe and random forest were used to excavate the Gillisia (desert-steppe), Flavisolibacter (grassland), and Variibacter (gravel-desert) as biomarkers that can distinguish among microbial communities from the three ecotypes. The prediction profile showed that the metabolic function of the microbial community was enriched in metabolic pathways and environmental information processing. Correlation analyses revealed that the altitude, precipitation of the warmest quarter (bio18), mean diurnal range (bio2), and mean temperature of the warmest quarter (bio10) were important ecological factors that affect the composition of soil microbial communities. This work provided new insights into the regulatory relationship among the suitable distribution of C. salsa, soil microbial communities, and ecological drivers. Moreover, it deepened the understanding of the interaction between desert plants and ecological factors in arid environments.

Traits of dominant species and soil properties co-regulate soil microbial communities across land restoration types in a subtropical plateau region of Southwest China

Soil microbial community is essential for maintaining and improving ecosystem functioning in ecological restoration practice and is intimately linked with the plant community. However, little is known on how soil microbial communities respond to the functional characteristics of plant communities. Here we investigated the changes in plant community functional attributes, soil properties, and soil microbial community characteristics of four land restoration (vegetation) types in a subtropical plateau region. The relative contributions of soil abiotic properties and plant community functional attributes to variation in microbial community composition and function were then assessed. We found that plant community attributes, soil properties, and the soil microbial communities differed significantly among land restoration types, and the plant functional traits of dominant species and soil properties jointly determined soil microbial community structure and functions. Specifically, soil microbial community structure was significantly linked to the community-weighted mean (CWM) of plant functional traits, soil water content, and soil organic carbon. Soil microbial carbon-metabolic functions were tightly correlated with the CWM of leaf dry matter content, specific leaf area, and specific root length. Variance partitioning also revealed that the CWM of plant functional traits and soil variables cooperatively explained 67% and 64% variation in soil microbial community structure and carbon-metabolic functions. Meanwhile, significant correlations were found between variation in microbial community composition and carbon-metabolic functions. In conclusion, our observations demonstrate that soil microbial community characteristics were governed by dominant species in plant communities across land restoration types, mainly due to differences in plant functional traits and soil resource driven by plant traits.

Effects of Crop Rotation and Biocontrol Amendments on Rhizoctonia Disease of Potato and Soil Microbial Communities

Rotation crops and biocontrol amendments were investigated for suppression of Rhizoctonia solani on potato (Solanum tuberosum) and their interactive effects on soil microbial communities. Greenhouse trials were conducted to evaluate selected rotation crops, including barley, common and “Lemtal” ryegrass, clover, potato, and combinations of barley with ryegrass or clover, for their effects on populations of R. solani and Rhizoctonia disease. Potato and clover preceding potato resulted in higher disease severity than most other rotations, whereas ryegrass reduced stem canker severity. In addition, all ryegrass treatments resulted in substantially higher populations of R. zeae. Field trials evaluating selected biocontrol treatments in combination with different rotations were conducted at two locations in Maine. Potatoes were treated with the biocontrol organisms Laetisaria arvalis, Trichoderma virens, or Bacillus subtilis and planted following rotation crops of barley and ryegrass, barley and clover, or potato. The barley/ryegrass rotation significantly reduced incidence and severity of stem canker and increased tuber yield at one location. Efficacy of the biocontrol treatments varied by rotation and location, with L. arvalis and T. virens reducing black scurf in some rotations and increasing some aspects of tuber yield at one location. Soil microbial community characteristics differed among rotation crops and biocontrol treatments. Significant crop by biocontrol interactions were observed demonstrating the complex interactions among rotation crops, biocontrol treatments, and soil microbial communities, as well as indicating that biocontrol can be enhanced within beneficial rotations.

Characteristics of soil microbial and nematode communities under artificial Medicago sativa grasslands with different cultivation years in semi-arid region of Loess Plateau, Northwest China

The establishment of Medicago sativa artificial grasslands is an important practice of grassland vegetation restoration in the Loess Plateau. Understanding community characteristics of soil microbes and nematodes can provide important information for evaluating and controlling ecolo-gical and environmental effects of vegetation restoration. In this study, we used M. sativa artificial grasslands with four different cultivation years (1, 2, 6 and 12 years) in southern Ningxia mountainous region, with a farmland and a natural grassland as control, to explore changing trends of the two biological communities during artificial grassland restoration in semi-arid region of the Loess Plateau. The results showed that: 1) After the conversion of farmland to M. sativa grassland, Chao1, ACE and Shannon diversity indices of soil bacterial community increased firstly and then decreased, which reached the maximum after six years of M. sativa grassland establishment. For soil fungal community, Shannon diversity index was lower in 6 and 12 year-old M. sativa grasslands than in the other two artificial grasslands, and the community composition differed across restoration years. 2) With the increases of restoration years, the abundance of soil nematodes showed a similar changing trend with Shannon diversity index of bacterial community. The composition of nematode community did not greatly differ between the 6-year-old M. sativa grassland and farmland, while that in 12-year-old artificial grassland was more similar to that in natural grassland. The proportion of bacterivorous and plant-feeding nematodes, as well as plant parasitic index and nematode channel index of nematode community,were increased, while the proportion of fungivores and omnivores-predators and maturity index were decreased. 3) During the restoration, changes in soil organic carbon, total nitrogen and available phosphorus greatly affected soil microbial community, which could further influence soil nematode community. There were significant correlations between dominant microbial phyla and trophic groups of soil nematodes, implying the possible effects of soil microbes on nematode community. In M. sativa artificial grassland with different establishment years, changes in plant biomass and diversity might significantly affect soil nematode and microbial communities through affecting their food conditions.

Spatial distribution of phthalate esters and the associated response of enzyme activities and microbial community composition in typical plastic-shed vegetable soils in China.

The widespread use of phthalate esters (PAEs) in plastic products has made them ubiquitous in environment. In this study, 93 soil samples were collected in 31 plastic-sheds from one of China's largest vegetable production bases, Shouguang City, Shandong Province, to investigate the pollution characteristics and composition of PAEs in soils. Eleven PAEs were detected in the soil samples with the total concentration of 756-1590μgkg-1 dry soil. Di (2-ethylhexyl) phthalate (DEHP), bis (2-n-butoxyethyl) phthalate (DBEP), di-isobutyl phthalate (DiBP) and di-n-butyl phthalate (DBP) were the main pollutants with the highest concentrations. Moreover, soil properties, including pH, total organic carbon (TOC), soil enzyme activities, and soil microbial community characteristics, were monitored to explore the associated formation mechanisms. The concentration of PAEs in the plastic-shed vegetable soils was regionalized and the contamination degree in different regions was related to soil microbial characteristics and soil enzyme activities. Phthalate ester is positively correlated with catalase and sucrase, and negatively correlated with dehydrogenase and urease. Furthermore, some tolerant and sensitive bacteria were selected, which possibly could be used as potential indicators of PAE contamination in soil. Dimethyl phthalate (DMP) and DBP also had greater effects on the soil microbial community than other PAEs. The results will provide essential data and support the control of PAEs in plastic-shed vegetable soils in China.

Long term effects of management practice intensification on soil microbial community structure and co-occurrence network in a non-timber plantation

Intensive forest plantation management practices, such as use of inorganic chemical fertilizer and herbicides improve productivity, however, their environmental impacts on plantation soil microbial communities and its interaction pattern remain unclear. In this study, we investigated associations between management practice intensities (nutrient-herbicide, nutrient-mowing and manure-mowing), environmental factors including plant coverage, pH, exchangeable calcium (Ca2+), aluminium ion (Al3+), total organic carbon (TOC), C to N ratio (C/N) and soil moisture (SM), and microbial community structure in Chinese hickory (Carya cathayenses) plantations cultivated on two soil types (calcareous and yellow soils). Our results demonstrated that long-term management practices with different intensities significantly changed certain soil environmental factors, and revealed a significant impact on both α and β-diversity of soil bacterial and fungal communities. Specifically, significant higher values of plant coverage, pH, Ca2+, TOC, C/N and SM and lower value of Al3+ were observed under manure-mowing management. Calcareous soil showed significantly higher pH, Ca2+ and TN contents and lower AP values than yellow soil across all three operating intensities. The bacterial community structure was different between the calcareous and yellow soil, but there was no difference for the fungi. Edaphic properties such as pH, Ca2+, TOC and TN were shown to play crucial roles in microbial community structuring, while vegetation-associated factors (vegetation coverage and Al3+) were correlated with fungal community structure. The complexity of microbe co-occurrence network decreased as management practice intensified. The keystone taxa including Bradyrhizobium, Reyranella and Phaselicystis in bacterial network and Rhizophydium and Microascales in fungal network were only observed under manure-mowing, with ecological functions mainly involved in organic carbon degradation and nitrogen fixation. Our results provide insight into the interactions between management practice intensities and soil microbial community characteristics and have implications for the optimization of sustainable forestry management practices and maintenance of microbial diversity and network complexity in over-managed forest plantations.

Shifts in characteristics of the plant-soil system associated with flooding and revegetation in the riparian zone of Three Gorges Reservoir, China

The operation of the Three Gorges Reservoir (TGR), the largest hydropower dam in the world, has triggered a dramatic shift in the flooding regimes of sites upstream of the reservoir. Little is known about how disrupted flooding regimes and consequent management approaches might affect the ecological and biogeochemical characteristics of riparian ecosystems. In this study, we evaluated the effects of disruptions to natural flooding regime on basic soil properties, soil nutrient and heavy metal levels, and key characteristics of riparian plant and soil microbial communities. To do this, we used an elevational gradient that encompassed four flooding duration zones (0 (i.e., control), 169, 237, 286 days of flooding per year on average). The disrupted flooding regimes were associated with levels of soil total N and P that were on average 17% and 24% lower, respectively, than those in the non-flooded areas. On the other hand, the concentrations of heavy metals (Hg, Pb, Cu, Zn and Mn) were higher in flood-affected areas than in the non-flooded areas. Increased flooding frequency was also associated with lower plant diversity and species richness relative to non-flooded areas. Thus, disruption of the natural flooding regime had strong and often negative consequences for the ecological and biogeochemical properties of the riparian ecosystems in our study. There was some evidence that riparian plant communities were able to partially recover from prior flooding during a single growing season, even after nine years of repeated flooding, and these recovery trajectories were associated with shifts in soil chemical properties during the same period. However, revegetation efforts had few effects on ecosystem properties or their recovery trajectories following flooding events, suggesting that natural regeneration could be a useful option for the management of these sites. We conclude that the unnatural flooding regimes associated with large scale reservoir development are likely to have profound impacts on the structure and functioning of riparian ecosystems, and these will pose a considerable challenge for environmental management and biodiversity conservation.

Linking rhizosphere soil biochemical and microbial community characteristics across different land use systems in mountainous region in Northeast India

In Northeast India, widely practiced shifting cultivation practice created various land uses associated with altered soil biochemical and microbial attributes. The present study aimed to analyze soil biochemical and microbial characteristics in rhizosphere using Illumina paired-end sequencing in five dominant land uses (Oil Palm Plantation, OPP; Bamboo Forest, BF; Rubber Plantation, RP; Fallow Land, FL and Natural Forest, NF) of Mizoram, Northeast India. The soils of different land uses were strongly acidic (pH ranged from 4.4–5.3) in nature reflecting the dominance of acidophilic soil microbes (e.g. Acidobacteria, Proteobacteria and Verrucomicrobia) and majority of unassigned bacteria accounting >50% of all sequences. NF soil showed high organic carbon and total nitrogen (TN), however, levels of available phosphorous (Pavail), microbial biomass carbon, ammonium and nitrate nitrogen, and rates of N-mineralization (N-min) were considerably high in BF. Basal soil respiration significantly (p < .05) varied across land uses with maximum in RP and minimum in BF. Species diversity estimator showed highest bacterial diversity in BF (pH 5.3) and lowest in FL (pH 4.4). Acidobacteria were dominant in NF which declined with land use changes due to increase in soil pH. Soil pH was the strongest predictor variable explaining 96% variability of microbial diversity (R2-predicted, 78%), however, it explained 99% variability (R2-predicted, 99%) in combination with Pavail and TN. High N-min rate in BF soil was corresponded with maximum abundance of Nitrospirae. The study indicated that the changing land use patterns in this region are intertwined with changing soil biochemical and bacterial community structure.