Non-rhizosphere Soil Research Articles

Assessment of Ecological Recovery Potential of Various Plants in Soil Contaminated by Multiple Metal(loid)s at Various Sites near XiKuangShan Mine

Soil metal(loid) pollution is a threat to ecological and environmental safety. The vegetation recovery in mining areas is of great significance for protecting soil resources. In this study, (1) we first gathered four types of soils to analyse their contamination degree, including tailings mud (TM), wasteland soil (TS) very near TM, as well as non-rhizosphere soils of pepper (PF) and maize (MF) in a farmland downstream from the TM (about 5 km). Geo-accumulation and potential ecological risk indices indicated that the soil samples were mainly polluted by antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and copper (Cu) to different degrees. Leachates of TM resulted in increased Sb, As, and Cd accumulation in TS. (2) Then, we sampled six local plants growing in the TS to assess the possibilities of using these plants as recovery vegetation in TS, of which Persicaria maackiana (Regel) Nakai ex T. Mori absorbed relatively high Sb concentrations in the leaves and roots. (3) After that, we collected rhizosphere soil and tissue samples from eight crops on the above farmland to assess their capacities as recovering vegetation of contaminated farmland soil, of which the fruits of maize accumulated the lowest concentrations of most monitored metal(loid)s (except for Pb). Further, we compared the differences in the bacterial community structure of MF, PF, TM, and TS to assess capacities of cultivating pepper and maize to improve soil microbial community structure. The MF displayed the best characteristics regarding the following attributes: (1) the highest concentrations of OMs and total P; (2) the highest OTU numbers and diversity of bacteria; and (3) the lowest abundance of bacteria with potentially pathogenic and stress-tolerant phenotypes.

Variations of microbiota and metabolites in rhizosphere soil of Carmona microphylla at the co-contaminated site with polycyclic aromatic hydrocarbons and heavy metals.

Co-contamination with organic/inorganic compounds is common in industrial area and poses a great risk to local soil ecological environment. In this study, an operating ink factory site co-contaminated with polycyclic aromatic hydrocarbons (PAHs, mild to moderate pollution level) and heavy metals (HMs, heavy pollution level) was selected and screened for native vegetation, Carmona microphylla. High-throughput sequencing and metabolomics were mainly used to investigate the responses of soil bacteria and metabolites to the composite pollution and rhizosphere effect. As the results showed, among three pollution levels, a medium level of pollution was favorable to increase the richness and diversity of soil bacterial community, while high level of pollution greatly decreased special OTUs number. In addition, HMs were the most significant factors driving bacterial community structure, especially for Cd. The influence of medium molecular weight PAHs with 4 rings (MMW-PAHs) on dominant bacteria was greater than low molecular weight PAHs with 2-3 rings (LMW-PAHs) and high molecular weight PAHs with 5-6 rings (HMW-PAHs). Soil bacterial function was affected mainly by pollution level, but not rhizosphere effect, in which high pollution level changed α diversity and structure and composition of C- and N-cycling bacteria. Rhizosphere promoted network complexity by increasing the connection densities among bacterial communities, metabolites, soil properties and the involved number of metabolites. Compared to HMs, PAHs played a more important role in shaping bacterial community through affecting metabolites in non-rhizosphere soil, which was different from rhizosphere soil with a more significant effect of HMs than PAHs. Some key bacterial taxa have established resistance to HMs in rhizosphere soils, whereas they were sensitive to compound contamination in non-rhizosphere soils. Some key bacterial taxa are resistant to HMs in rhizosphere soils, whereas they are susceptible to complex contamination in non-rhizosphere soils, which could be a consequence of the rhizosphere by regulating soil metabolism. It also provides a valuable reference for how co-contaminants and rhizosphere effect shape together soil bacterial community through the changes of soil metabolites.

Soil microbial carbon use efficiency differs between mycorrhizal trees: insights from substrate stoichiometry and microbial networks.

The role of mycorrhizal associations in controlling forest soil carbon storage remains under debate. This uncertainty is potentially due to an incomplete understanding of their influence on the free-living soil microbiome and its functions. In this study, rhizosphere and non-rhizosphere soils were collected from eight arbuscular mycorrhizal (AM) and seven ectomycorrhizal (ECM) tree species in a temperate forest. We employed high-throughput sequencing and 18O-H2O labeling to analyze the soil microbial community and carbon use efficiency (CUE), respectively. We find microbial respiration rates are higher in rhizosphere than that in non-rhizosphere soils for ECM trees, whereas microbial growth rates show no significant differences. Consequently, microbial CUE is lower in rhizosphere compared to non-rhizosphere soils for ECM trees. In addition, we find that non-rhizosphere soils from ECM trees exhibited higher CUE compared to those from AM trees. Furthermore, we observe that bacterial-fungal co-occurrence networks in ECM soils exhibit greater complexity relative to AM ones. Using random forest and structural equation modeling analyses, we find that microbial stoichiometric carbon/nitrogen imbalance and network complexity are key predictors of soil microbial CUE for AM and ECM trees, respectively. Our findings shed new light on the pivotal role of mycorrhizal associations in shaping free-living microbial communities and their metabolic characteristics in the studied soils. These insights are critical for predicting soil carbon sequestration in response to shifts in ECM and AM species within temperate forest under climate change.

Mechanisms activating trace heavy metals in the rhizosphere microenvironment of Amaranthus hypochondriacus L.

Soil heavy metal activation is closely related to rhizosphere soil pH, O2 and enzyme activity levels. In this study, we used laser ablation inductively coupled plasmamass spectrometry (ICPMS), planar optode (PO), soil in situ enzyme spectrum analysis, and the diffusive gradients in thin films (DGT) method to investigate heavy metal accumulation in Amaranthus hypochondriacus L. growing in polluted soil (Cd, Pb and Zn) and unpolluted soil, as well as dissolved oxygen (DO), pH, soil enzyme activity, and trace heavy metal dynamics in rhizosphere and nonrhizosphere soils. The results revealed that the growth of A. hypochondriacus was significantly inhibited under combined Cd, Pb, and Zn stress, with the most pronounced effects on root and branch biomass. Radial oxygen loss (ROL) and alkalization occurred in the roots of A. hypochondriacus, which were influenced primarily by root growth and environmental conditions. The enzyme activity patterns indicated that acid phosphatase (ACP), alkaline phosphatase (ALP), and β-glucosidase (BG) activities were primarily associated with the root system and that the activities of these enzymes were relatively low in nonrooted soil. Under heavy metal stress, the ACP, ALP and BG activities in the hotspots of soil increased. DO, pH, and soil enzyme activity were significantly correlated with the presence of heavy metals Cd, Pb, and Zn, influencing the mobilization mechanisms of trace metals in the rhizosphere. These findings lay the groundwork for understanding the impact of root-induced alterations in O2, pH, and soil enzyme activity on the mobility of trace heavy metals in soil.

Effects of Long-Term Soil Tillage Practices on Soil Organic C Accumulation Characteristics in Double-Cropped Rice Paddy

Unreasonable soil tillage measures have caused a sharp decline in the soil carbon (C) pool capacity of rice (Oryza sativa L.) paddy fields, have reduced soil fertility, and have threatened the safe production of rice. Based on long-term position–location experiments started in 2005, this paper systematically studied the effects of different soil tillage treatments (CT: no return of plowing straw to the field as control; CTS: return of plowing straw to the field; NTS: return of no-tillage straw to the field; RTS: return of rotary plowing straw to the field) on soil physical and chemical properties and soil organic carbon (SOC) accumulation characteristics in rice paddy fields, in order to clarify the impact of different long-term soil tillage measures on soil carbon cycle microecology in double-cropped rice paddy fields and provide a theoretical basis for soil SOC sequestration and the sustainable utilization of rice paddy fields in double-cropped rice paddy fields in southern China. The results were as follows: A total of 30.7–40.7% of the SOC stored in rice paddy fields was residue C derived from microorganisms, and 45.7–54.2% of SOC accumulation came from plant residue-derived C. Straw return treatments (CTS, RTS, and NTS) significantly increased soil lignin phenol content and promoted the accumulation of plant-derived SOC. Soil lignin phenol content in the RTS treatment was significantly higher than that in the CTS treatment (p < 0.05). Amino sugar content in rhizosphere soil was higher than that in non-rhizosphere soil. The measure of returning straw to the field increased amino sugar content in the rhizosphere and non-rhizosphere. C derived from plants was greater than that from microbial residues in double-cropped rice paddy fields in southern China. Hence, no-till/rotary tillage and straw return can improve the sequestration of soil SOC, which is of great significance for achieving “C neutrality” and alleviating the pressure on food security.

Contamination characteristics of heavy metals and enrichment capacity of native plants in soils around typical coal mining areas in Gansu, China

Exploitation of mineral resources is a vital backbone of a country’s socio-economic development. However, the coal exploration would cause ecological and environmental problems such as pollutions of water, soils and atmosphere. Especially, the pollution of heavy metals of soil has become increasingly severity. Plant enrichment and tolerance to heavy metals are crucial for the phytoremediation of coal gangue mountain. In phytoremediation, phytostabilization which can reduce the metal contamination of soil by uptake and burn-off of heavy metals with highly accumulating plants, is one of the most effective techniques of eco-remediation treatment. In present work, heavy metals contamination of soil and plants in the Yaojie mining which located in arid and semi-arid area of northwest China were investigated through field investigation. To identify the suitable plants for the remediation and ecological reclamation of heavy metal contaminated soil in typical mining area, the contamination characteristics of heavy metals in the above-ground parts of 27 native plants and their surrounding non-rhizosphere soils were analyzed. After eliminated by wet digestion and high-pressure closed digestion, the mass fractions of Zinc (Zn), cadmium (Cd), chromium (Cr) and copper (Cu) were determined with inductively coupled plasma emission spectrometer, and the contents of Hydrargyrum (Hg) and Arsenic (As) were analyzed with atomic fluorescence spectrophotometer. The Nemerow pollution index showed that in the surrounding soil, the pollution index of heavy metal was 6.32, which reached the extreme severe pollution level. Among the 6 heavy metals, the most severe contamination being Hg (Pi = 8.50) and had particularly strong Coefficient of variation (CV = 105.8%), which is more likely to be caused by anthropogenic activities. In the aboveground parts of 27 plants, except for Zn, other metals exceeded the standard level, and the exceedance rates in descending order were As, Hg, Cr, Cd, and Cu. The most severe exceedance of As was found in C. virgata, which was as high as 19.20, and the average exceedance rate of As in all plants was 2.79. Bioconcentration Factor (BCF) was utilized as an indicator of the enrichments of various metals in 27 plants. The maximum value of BCF for As and Hg in C. virgata were 1.52 and 2.50, Cr and Cu in X. sibiricum were 0.72 and 2.32, Cd and Zn in S. glauca were 3.33 and 1.82. As revealed, except Cr, all the BCF of other metals are greater than 1, indicating that the three plants exhibited a strong accumulation capacity of heavy metal and are potential candidate pioneer species for the removal of heavy metals from the contaminated soil in the Yaojie mining area. This study provides a basis for plant selection for ecological restoration of contaminated soils in arid and semi-arid regions.

Effect of biodegradable microplastics and Cd co-pollution on Cd bioavailability and plastisphere in soil-plant system

Biodegradable plastics (BPs) are regarded as ecomaterials and are emerging as a substitute for traditional non-degradable plastics. However, the information on the interaction between biodegradable microplastics (BMPs) and cadmium (Cd) in agricultural soil is still limited. Here, lettuce plants were cultured in BMPs (polylactic acid (PLA) MPs and poly(butylene-adipate-co-terephthalate) (PBAT) MPs) and Cd co-polluted soil for 35 days. The results show that diffusive gradient in thin films technique (DGT) but not diethylenetriaminepentaacetic acid (DTPA) extraction method greatly improved the prediction reliability of Cd bioavailability in non-rhizosphere soil treated with BMPs (R2 = 0.860). BMPs increased the Cd bioavailability in non-rhizosphere soil indirectly by decreasing soil pH, cation exchange capacity (CEC), and dissolved organic carbon (DOC), rather than by directly adsorbing Cd on their surface. PLA MPs incubated in rhizosphere soil showed more considerable degradation with extremely obvious cavities and the fracture of ester functional groups on their surface than PBAT MPs. BMPs could provide ecological niches to colonize and induce microorganisms associated with BMPs’ degradation to occupy a more dominant position. In addition, Cd only affected the composition and function of microbial communities in soil but not on BMPs. However, co-exposure to BMPs and Cd significantly reduced the degrees of co-occurrence network of fungal communities on PLA MPs and PBAT MPs by 37.7% and 26.7%, respectively, compared to single exposure to BMPs.

Cadmium availability in rhizosphere and non-rhizosphere soils in cacao farms in Santander, Colombia

Current research has highlighted the need to understand the factors influencing cadmium (Cd) availability in cacao-growing soils to elucidate its presence in cacao beans (the raw material for chocolate). Although literature about this topic is increasing, few report the importance of rhizosphere soils on Cd dynamics. This study aimed to understand the changes in available Cd and its association with soil properties (pH, pseudo-total Cd, available Cd (Cd-DTPA), Ca, Mg, K, Na, soil organic carbon, P, Zn, urease activity, exchangeable acidity, and cation exchange capacity) considering rhizosphere and non-rhizosphere soils. Both soil types (51 samples of each, 102 in total) were collected from two Colombian cacao farms. The medians of pseudo-total Cd (1.86 mg kg−1) and Cd-DTPA (0.76 mg kg−1) were, respectively, about threefold and fourfold higher in rhizosphere compared to non-rhizosphere soils. Principal component analysis showed a clear distinction between rhizosphere and non-rhizosphere soils based on differences in soil properties, which explained the observed changes in available Cd when comparing both soil types. Soil organic carbon and Zn were important drivers of available Cd in rhizosphere soils. Spatial distribution analysis revealed a tendency of available Cd to cluster in rhizosphere soils, and indicated hotspots within each farm. These findings highlight the importance of rhizosphere soils for Cd diagnosis and monitoring, and for improving knowledge about Cd dynamics in the soil-Theobroma cacao L. system.

Soil organic carbon sources exhibit different patterns with stand age in rhizosphere and non-rhizosphere soils

The sources of soil organic carbon (SOC) determine its stability and dynamics. However, in the soil’s active zone − rhizosphere, the sources and regulatory mechanisms of SOC are still unclear, and the rhizosphere and non-rhizosphere soils may exhibit variations depending on stand age. We collected rhizosphere and non-rhizosphere soils from a typical subtropical evergreen broadleaf forest (Castanopsis hystrix plantations) at six distinct stand age in the South Subtropical region, using soil amino sugars and lignin phenols content to characterize microbial-derived carbon and plant-derived carbon, respectively. The results indicated that the SOC sources varied significantly in rhizosphere soils while remained stable in non-rhizosphere soils. Soil amino sugars content in rhizosphere soils was higher than non-rhizosphere soils and increased with stand age, leading to the rhizosphere effect on soil amino sugars content significantly increased with stand age. Soil lignin phenols content in rhizosphere soils was initially lower than that in non-rhizosphere soils at 6–––10 stand age, but it increased significantly over time, resulting in a significantly increased in the rhizosphere effect on soil lignin phenols content with stand age. Further analysis revealed that the SOC sources were jointly regulated by stand age and rhizosphere effect during forest restoration, in which the fungal and bacterial phospholipid fatty acids were key factors to drive the variation in soil amino sugars while litter C:N ratio and fine root biomass accounted for the patterns of soil lignin phenols. Therefore, we found significant differences in the patterns and driving factors of SOC sources between rhizosphere and non-rhizosphere soils with stand age, emphasizing the importance of considering the rhizosphere effect when studying soil carbon dynamics during forest restoration.

Rhizosphere Shifts: Reduced Fungal Diversity and Microbial Community Functionality Enhance Plant Adaptation in Continuous Cropping Systems.

Continuous cropping problems constitute threats to perennial plant health and survival. Soil conditioners have the potential to enhance plant disease resistance in continuous cropping systems. However, how microbes and metabolites of the rhizosphere respond to soil conditioner addition remains largely unknown, but this knowledge is paramount to providing innovative strategies to enhance plant adaptation in continuous cropping systems. Here, we found that a biochar conditioner significantly improved plant survival rates in a continuous cropping system. The biochar-induced rhizosphere significantly alters the fungal community, causing a decline in fungal diversity and the downregulation of soil microbial community functionality. Specifically, the biochar-induced rhizosphere causes a reduction in the relative abundance of pathogenic Fusarium sp. and phenolic acid concentration, whose variations are the primary causes of continuous cropping problems. Conversely, we observed an unexpected bacterial diversity increase in rhizospheric and non-rhizospheric soils. Our research further identified key microbial taxa in the biochar-induced rhizosphere, namely, Monographella, Acremonium, Geosmithia, and Funneliformis, which enhance soil nutrient availability, suppress Fusarium sp., mitigate soil acidification, and reduce phenolic acid concentrations. Collectively, we highlight the critical role of regular microbial communities and metabolites in determining plant health during continuous cropping and propose a synthetic microbial community framework for further optimizing the ecological functions of the rhizosphere.

Microbial necromass accrual from newly added labile and native soil carbon in the rhizosphere vs. non-rhizosphere of broadleaved and coniferous trees

Microbe-mediated carbon (C) transformation plays a crucial role in the accumulation of soil organic C (SOC). However, microbial conversion efficiency of newly-added labile C and native SOC to necromass remain under-investigated. Here we collected the rhizosphere and non-rhizosphere soils under broadleaved and coniferous trees of varying nutrient availability, and conducted an 80-day soil incubation with 13C-labelled glucose to evaluate ‘microbial C pump’ (MCP) capacity (new C-derived biomass and necromass), phospholipid fatty acids (PLFAs)-based C use efficiency (i.e., new C-derived PLFAs relative to respiration, referred as CUE′ to differentiate from microbial biomass C-based CUE) and amino sugar (reflecting necromass) accumulation efficiency (AAE; new C-derived amino sugars relative to respiration). We found that MCP capacity, microbial AAE and CUE′ had different variation patterns and influencing factors. The amount of added glucose played a decisive role in determining MCP capacity. The key predictors of AAE were the ratio of inorganic nitrogen (N) to added glucose (reflecting N limitation) and bacterial PLFAs, while ratios of fungi to bacteria and C to N were important for predicting CUE′. Furthermore, we found that glucose addition stimulated microbial transformation of native SOC into necromass in C- but not N-limited soils (with a high AAE) without invoking a priming effect, potentially enhancing microbe-mediated SOC sequestration. These findings suggest that the efficiency of microbial necromass accumulation is strongly influenced by N availability and decoupled from biomass synthesis, highlighting nutrient regulations on SOC sequestration via plant–microbe interactions. We argue that AAE is a more reliable indicator to assess the efficiency of MCP fueled by labile C.

Characteristics of Bacterial Communities in Rhizosphere and Non-Rhizosphere Soil of the Relict Plant Diplandrorchis sinica S. C. Chen

Characteristics of Bacterial Communities in Rhizosphere and Non-Rhizosphere Soil of the Relict Plant Diplandrorchis sinica S. C. Chen

Soil metabolic processes influenced by rice roots co-regulates the environmental evolution of antibiotic resistome

Plant root activities lead to significant differences in metabolites between the rhizosphere and non-rhizosphere soil, profoundly affecting microbial distribution. However, how this process drives the migration and propagation of manure-derived antibiotic resistance genes (ARGs) in farmland ecosystems remains unclear. Herein, we used a rice pot microcosm experiment to explore the characteristics of antibiotic resistome and bacterial communities in rhizosphere and non-rhizosphere soils and the driving effects of rhizosphere metabolites on ARG propagation. The results showed significant differences in some ARGs and bacterial diversity in rhizosphere and non-rhizosphere soils with varied differential ARGs between different growth stages of rice (P < 0.05). The biosynthesis of secondary metabolites and glutathione metabolism were found to be the main pathways affecting ARG differences in rhizosphere and non-rhizosphere soils under manure application. Structural equation modeling (SEM) analysis further indicated that ARG distribution differences between rhizosphere and non-rhizosphere soils were mainly regulated by differential metabolites, which influenced the ARG distribution by altering the succession of soil microbial communities. These results demonstrate the role of differential metabolites resulting from rice root activities in co-regulating ARG distribution, providing new insights into the regulatory mechanisms of soil ARG dynamics in paddy fields.

Distribution and characterization of endophytic and rhizosphere bacteriome of below-ground tissues in Chinese fir plantation.

Plantations of Chinese fir, a popular woody tree species, face sustainable issues, such as nutrient deficiency and increasing disease threat. Rhizosphere and endophytic bacteria play important roles in plants' nutrient absorption and stress alleviation. Our understanding of the microbiome structure and functions is proceeding rapidly in model plants and some crop species. Yet, the spatial distribution and functional patterns of the bacteriome for the woody trees remain largely unexplored. In this study, we collected rhizosphere soil, non-rhizosphere soil, fine root, thick root and primary root samples of Chinese fir and investigated the structure and distribution of bacteriome, as well as the beneficial effects of endophytic bacterial isolates. We discovered that Burkholderia and Paraburkholderia genera were overwhelmingly enriched in rhizosphere soil, and the abundance of Pseudomonas genus was significantly enhanced in fine root. By isolating and testing the nutrient absorption and pathogen antagonism functions of representative endophytic bacteria species in Pseudomonas and Burkholderia, we noticed that phosphorus-solubilizing functional isolates were enriched in fine root, while pathogen antagonism isolates were enriched in thick root. As a conclusion, our study revealed that the endophytic and rhizosphere environments of Chinese fir hold distinct structure and abundance of bacteriomes, with potential specific functional enrichment of some bacterial clades. These findings assist us to further study the potential regulation mechanism of endophytic functional bacteria by the host tree, which will contribute to beneficial microbe application in forestry plantations and sustainable development.

Revealing the characteristics of myxobacterial communities in rhizosphere and non-rhizosphere soils of halophytic plants following wetland degradation using high-throughput sequencing

Myxobacteria represent a distinct group in soil microbial communities, with their predatory capabilities playing a vital role in regulating and stabilizing these communities. However, the characteristics of myxobacterial communities in the soils of Karelinia caspia (KC), a halophytic plant growing in degraded wetlands, remain unclear. In this study, we investigated myxobacterial communities in rhizosphere and non-rhizosphere soils from nine KC’ sampling sites in saline-alkaline land formed after wetland degradation using high-throughput sequencing. A total of 486 myxobacterial ASVs were identified from both rhizosphere and non-rhizosphere soil samples, comprising 2.68% of the total bacterial community. The dominant genera at the genus level were Unclassified_g_bacteriap25 and Haliangium. FAPROTAX functional predictions indicated that myxobacteria in rhizosphere soils performed various ecological functions, such as predation, organic matter decomposition, and cellulose degradation, while in non-rhizosphere soils, they primarily displayed predatory functions. The high proportion of unclassified functions suggests that many aspects of myxobacteria in soil remain unexplored. Correlation analysis showed that electrical conductivity, soil moisture, and total nitrogen significantly affected myxobacterial diversity and abundance. Co-occurrence network analysis revealed multiple associations between myxobacteria and other bacterial groups, highlighting their crucial role in maintaining the dynamic equilibrium of soil bacterial communities. These findings deepen our understanding of the relationship between microbial community dynamics and environmental factors, laying a strong foundation for future research in soil microbial ecology and conservation strategies.

Understanding the interaction between soil ORP and enzyme activity: How does wetland type affect constructed wetland performance for the advanced treatment of swine wastewater?

Constructed wetlands (CWs) are widely used for the advanced treatment of swine wastewater. Wetland type is the most critical parameter for engineering applications; therefore, the performance of horizontal/vertical subsurface flow CWs (HSFCWs and VSFCWs) was explored over one year of operation. The effects of five antibiotics (40 μg/L each), copper (Cu, 1.0 mg/L), and their combination on CW performance and soil oxidation–reduction potential (ORP) and enzyme activity were investigated. The annual removal efficiencies of HSFCWs and VSFCWs for total organic carbon (TOC), nitrogen, and phosphorus were 72.03 %–84.49 % and 87.15 %–90.72 %, for antibiotics were 91.35 %–99.52 % and 87.33 %–99.57 %, and for Cu were 97.37 %–97.44 % and 95.52 %–96.85 %, respectively. The CWs removed antibiotics through substrate adsorption, plant absorption, and biodegradation. Total antibiotic residues in HSFCW and VSFCW soils ranged from 6.29 to 17.31 and 24.57 to 589.07 μg/kg, respectively, and enrofloxacin and roxithromycin posed medium and high risks in VSFCW non-rhizosphere soil. The amount of residual antibiotics in Phragmites australis parts was in the order of fibrous roots > rhizomes > aboveground. ORP and enzyme activities were greater in rhizosphere soil than in non-rhizosphere soil and greater in the VSFCWs than in the HSFCWs. CW performance and soil enzyme activities decreased under the stress of antibiotics and coexistence of antibiotics and Cu. These findings advance our knowledge of CW design, elucidate the unique advantages of CWs, and offer efficient operation strategies for swine wastewater advanced treatment, helping researchers recognize the adverse effects of antibiotics on CWs.

The Combination of Biochar and Phosphorus-Containing Materials Can Effectively Enhance the Remediation Capacity of Amaranth on Cadmium-Contaminated Soil and Improve the Structure of Microbial Communities

Cadmium (Cd) pollution in soil has become a huge problem for agricultural production in China and even the world. Passivation and phytoremediation are two important remediation technologies for Cd pollution. In this study, the cadmium-contaminated and phosphorus-poor farmland soil around a mining area in Huainan was taken as the research object, and the remediation effect of biochar and phosphorus-containing materials on soil cadmium pollution was discussed. The results showed that the combined application of biochar and phosphorus-containing materials significantly reduced the pH of non-rhizosphere soil and rhizosphere soil, and increased the content of soil dissolved organic carbon (DOC). The combined application of biochar and phosphorus-containing materials significantly reduced soil pore water Cd and soil available Cd. In addition, both a single application of biochar and synergistic application of biochar and phosphorus-containing materials significantly increased the biomass of aboveground and underground parts of amaranth and soil urease and catalase activities. Phosphorus application reduced the bioavailability of Cd in soil. With the increase in phosphorus application, the content of available Cd in soil decreased significantly, and there was a certain negative correlation between Cd content and phosphorus content in plants. The abundance of beneficial microorganisms such as Ochrobactrum, Anaerolinea, Achromobacter, and Cellvibrio in soil was significantly increased after the synergistic application of biochar and phosphorus-containing materials.

Impacts of shifting from single-species pine forests to distinct agroforestry models on soil fertility, exchangeable cations, and microbial functions

The transition from monoculture to mixed-species agroforestry systems affects soil organic matter and microbial activity. However, the specific dynamics of these changes, particularly within medicinal plant-based agroforestry, remain underexplored. This study investigates the impact of monoculture Pine (Pinus massoniana) forests and four agroforestry models: (M1) Pinus massoniana and Alpina oxyphylla, (M2) Pinus massoniana and Ficus simplicissima, (M3) Pinus massoniana and Amomum villosum, and (M4) Pinus massoniana and Curcuma longa on soil properties and microbial activity in rhizosphere and non-rhizosphere environments. Our results showed significantly higher pH (4.80) and total nitrogen (N) content (1.77 g kg−1) in the rhizosphere of model (M4) compared to (CK). Total organic carbon (TOC) and carbon fractions (POC, DOC, and MBC) also differed significantly across monoculture and agroforestry models, with highest TOC concentrations (31.70 g kg⁻1) in rhizosphere of CK. Exchangeable cations, including Ca2⁺, and Mg2⁺ were significantly higher in the rhizosphere of agroforestry models compared to CK, particularly in M4, where Ca2⁺ was recorded at 12.03 cmol kg−1 with the highest percent base saturation (PBS) at 90.17%. Enzymes leucine aminopeptidase and polyphenol oxidase varied significantly, with higher activity in the rhizosphere of agroforestry models and greater activity in non-rhizosphere of monoculture. Soil microbial respiration (MRes) revealed substantial differences, with an average 17% decrease in rhizosphere soil for models M2 and M4 and a 20.83% reduction in non-rhizosphere soil for model M1 compared to CK. Generalized Linear Model (GLM) demonstrated a significant positive correlation between TOC and MRes (R2 = 0.885, p < 0.01), indicating that higher TOC levels are linked with increased MRes. In conclusion, model M4 most effectively enhanced soil fertility and nutrient availability followed by the other agroforestry models tested. This suggests that integrating medicinal plants into agroforestry systems is a viable strategy for improving ecosystem functioning compared to monoculture practices.

The effects of irrigation on the survival of Clostridium sporogenes in the phyllosphere and soil environments of lettuce

This study aimed to address the gap in knowledge regarding the fate of foodborne pathogens within agro-ecosystems. It specifically focused on the surrogate microorganism Clostridium sporogenes, which was introduced into lettuce-producing environments via surface and spray irrigation methods, respectively. The concentration of C. sporogenes in the rhizosphere, phyllosphere, and non-rhizosphere soil was quantified by quantitative polymerase chain reaction (qPCR) over a 42-day trial. The surface irrigation method exhibited a more noticeable contamination effect on the soil environments, compared to the phyllosphere. The results indicated a noticeable increase in C. sporogenes concentrations during the initial 22 days, with a 10.4-fold rise (0.39–4.05 log copy numbers/g soil) in the rhizosphere and 1.9-fold increase (2.97–5.59 log copy numbers/g soil) in the non-rhizosphere. However, concentrations in both soil environments subsequently decreased, falling below the initial inoculum concentration by the end of the trial. In contrast, the spray irrigation method resulted in most of the contamination being localised on the lettuce phyllosphere, with a high C. sporogenes concentration of 9.09 log copy numbers/g leaves on day 0. This concentration exponentially decreased to a minimal 0.019 log copy numbers/g leaves by day 32. Although concentrations in both soil environments decreased over time, trace concentrations of C. sporogenes were detectable at the end of the trial, posing a potential hazard to the microbiological safety of postharvest produce. These findings shed light on the dynamics of C. sporogenes in agro-ecosystems and underscore the importance of irrigation practices that ensure the safety of those who consume fresh produce.

Exploring microbial diversity and function in companion planting systems of white clover and orchard grass

Companion planting of white clover (Trifolium repens L.) with orchard grass (Dactylis glomerata L.), a famous hay grass, improves the forage quality of orchard grass. Microbiome profiling techniques can reveal the specific role of white clover companion planting with orchard grass. This study aimed to explore the microbiome distribution and gene functions of rhizosphere and non-rhizosphere soil via companion planting systems of white clover and orchard grass. From metagenomics sequencing analysis, we confirmed the significant role of white clover on soil environment modeling during companion planting with orchard grass. Twenty-eight biomarkers of rhizosphere soil organisms were identified during companion planting, including Proteobacteria, Betaproteobacteria, Flavobacteriia, and Caulobacterales. The number of gene functions of nitrogen and carbon fixation in companion planting was higher than that in single plants, indicating new functional flora for companion planting. We characterized specific rhizosphere effects, typical biomarker flora, and potential regulatory mechanisms for white clover-related companion planting by metagenomics analyses.