Impact of dual Bt-transgenic maize (2A7) on soil microbial communities and enzyme activities: A comparative study with control variety Z58.

The impacts of transgenic crops on soil microbiology and fertility are critical in determining their biosafety. While transgenic crops can alter soil microbes, their effects are often context-dependent; therefore, the ecological importance of these changes remains a topic of ongoing research. Using high-throughput sequencing, we investigated the effects of Bacillus thuringiensis (Bt) maize expressing the mcry1Ab and mcry2Ab genes (2A7) on soil nutrient dynamics, as well as the diversity and function of soil microbial communities, including bacteria and fungi, within different soil compartments. Our findings revealed a plant-shaped rhizosphere (RS) microbial community as a result of the selective recruitment of microorganisms from the surrounding environment. The transgene insertion had a significant impact on the RS niche, and several species eventually became associated with Z58 and 2A7 plants. For example, Neocosmospora rubicola fungal and Pantoea dispersa bacterial microorganisms were significantly decreased in the dual Bt-transgenic 2A7 rhizosphere but enriched in the Z58 rhizospheres. The activity of soil enzymes such as urease, invertase, and alkaline phosphatase was boosted by Bt-transgenic 2A7. LefSe analysis identified significant bacterial and fungal biomarker species that were responsible for the differential effects of Bt-transgenic 2A7 and control Z58 within rhizosphere soils. Mantel analysis further demonstrated that the root exudates of 2A7 altered nutrient-acquisition enzymes by influencing biomarker taxa. PICRUSt2 functional characterization revealed a significantly higher abundance of the phosphate-starvation-inducible protein in control Z58 than in Bt-transgenic 2A7. Furthermore, taxonomy, alpha (Shannon diversity), and beta diversity analyses all revealed niche-driven microbial profile differentiation. Niche partitioning also had a significant impact on N- and P-related COGs as well. Our findings suggests that Bt-transgenic 2A7 modulates rhizosphere microbial communities by affecting biomarker taxa and soil enzyme activity. These findings will promote sustainable agriculture practices by advancing our knowledge of the ecological effects of Bt crops on soil microbial communities.

Mobility inhibition of arsenic in the soil: the role of green synthesized silica nanoparticles.

The studies showed the effectiveness of green-synthesized SiO2NPs in mitigating the toxicity of Arsenic. Density Functional Theory (DFT) is a computational method used to determine electronic structure, energy gap, and toxicity prediction. Experimentally, silicon nanoparticles of 0 (S0) and 100% v/v (S100) were applied to the surface of the soil. 150 mL of Arsenic trioxide was applied twice at a rate of 0 (As0) and 3.2 g/mL (As3.2) at an interval of three weeks. Green synthesized SiO2NPs possessed a higher chemical potential (µ) and electrophilicity index; consequently, charges could be transferred and easily polarized. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the green synthesized SiO2NPs enable them to donate electrons and complex with arsenic, reducing their bioavailability and toxicity. Evidence from the studies further showed that SiO2NPs had buffered the soil acidity and electric conductivity, posing a high binding site and reactivity with exchangeable cations and micronutrients due to their smaller energy gap. Furthermore, the catalytic activities of the soil enzymes dehydrogenase (DHA) and peroxidase (POD) were greatly increased, which enhanced the electrostatic interaction between the SiO2NPs and As.

Açai seed biochar improves soil quality and black pepper seedling development in the Amazon region.

Sustainable management of the Amazon rainforest is fundamental for supporting life on earth because of its crucial role in sequestering carbon. One of the species grown in the forest is açaí (Euterpe oleracea), which is an important food and income source for its inhabitant. The acai seed, resulting from the processing of the fruit, is a solid organic residue, which has been an agent of undesirable environmental impacts such as natural landscape modifications, clogging sewers and water courses, eutrophication of surface waters. In this research, we evaluated the use of wood chips as a source of energy in a rustic oven to produce acai biochar so that family farmers carry out sustainable management of the residue and use biochar to improve soil quality and produce seedlings of native plants to regenerate degraded forests. The experiment was conducted in Pará, Brazil, Amazon region, using a randomized complete block design. A factorial treatment structure was implemented consisting of four biochar particle sizes (3, 5, 7, and 12 mm), 4 application rates (4, 8, 16, and 32 t ha-1), and a biochar-free control, with 5 replications. The results showed that the methodology for biochar production was easy to apply and low cost, allowing its use by family farmers. The combination of biochar rate and particle size affected soil properties and the development of black pepper seedlings in different ways. The soil properties affected were water retention capacity, moisture, fluorescein diacetate hydrolysis and arylsulphatase activity. The growth parameters of the affected black pepper seedlings were height and root system development.

Mycorrhizosphere bacteria inhibit greenhouse gas emissions from microplastics contaminated soil by regulating soil enzyme activities and microbial community structure.

Microplastics (MPs) accumulation in terrestrial ecosystems can affect greenhouse gases (GHGs) production by altering microbial and soil structure. Presently, research on the MPs effect on plants is not consistent, and underlying molecular mechanisms associated with GHGs are yet unknown. For the first time, we conducted a microcosm study to explore the impact of MPs addition (Raw vs. aged) and Trichoderma longibrachiatum and Bacillus subtilis inoculation (Sole vs. combination) on GHGs emission, soil community structure, physiochemical properties, and enzyme activities. Our results indicated that the addition of aged MPs considerably enhanced the GHGs emissions (N2O (+16%) and CO2 (+21%), respectively), C and N cycling gene expression, microbial biomass carbon, and soil physiochemical properties than raw MPs. However, the soil microbial community structure and enzyme activities were enhanced in raw MPs added treatments, irrespective of the MPs type added to soil. However, microbial inoculation significantly reduced GHGs emission by altering the expression of C and N cycling genes in both types of MPs added treatments. The soil microbial community structure, enzymes activities, physiochemical properties and microbial biomass carbon were enhanced in the presence of microbial inoculation in both type of MPs. Among sole and combined inoculation of Trichoderma and Bacillus subtilis, the co-applied Trichoderma and Bacillus subtilis considerably reduced the GHGs emission (N2O (-64%) and CO2 (-61%), respectively) by altering the expression of C and N cycling genes regardless of MPs type used. The combined inoculation also enhanced soil enzyme activities, microbial community structure, physiochemical properties and microbial biomass carbon in both types of MPs treatment. Our findings provide evidence that polyethylene MPs likely pose a high risk of GHGs emission while combined application of Trichoderma and Bacillus subtilis significantly reduced GHGs emission by altering C and N cycling gene expression, soil microbial community structure, and enzyme activities under MPs pollution in a terrestrial ecosystem.

Imprint of clay mineralogy, sesquioxides, and crop residue addition for evaluation of soil organic carbon stability and associated microbial activity in dominant soil orders of Indian subcontinent.

The full behaviour of natural clay minerals in soil organic carbon (SOC) stabilization in the presence of oxides and external C inputs is yet unknown. Thus, an incubation experiment was conducted in a sand-clay mixture with different soil clay fractions (SCFs) obtained from Alfisol, Inceptisol, Mollisol, and Vertisol in the presence of wheat residues to compare their C stabilization capacity. The C mineralization rates were higher in 1:1 type dominated SCFs (Alfisol and Inceptisol) compared to 2:1 interstratified mineral dominated SCFs (Vertisol). Wheat residues as C source altered SCFs' abilities to stabilize SOC at only moderate dosages of application (3-12 g kg-1). C mineralization and microbial biomass carbon (MBC) fell by 40% and 30%, respectively, as the amount of clay increased from 7.5 to 40%. However, removing sesquioxides from the SCFs boosted C mineralization and MBC by 22% and 16-32%, respectively, which matched with higher enzymatic activities in the sand-clay mixture. The increased C stabilization capacity of Vertisol-SCF may be attributed to its greater specific surface area (SSA) (506 m2 g-1) and cation exchange capacity (CEC) [meq/100 g]. Regression analysis revealed that SSA, CEC, and enzymatic activity explained approximately 86% of total variations in C mineralization. This study highlighted the critical role of 2:1 expanding clay minerals and sesquioxides in greater stabilization of external C input compared to its 1:1 counterpart. It also implied that the role of mineralogy or texture and sesquioxides levels in different soils (Vertisol, Mollisol, Inceptisol, Alfisol) should be prioritized while adding crop residues to reduce C footprint and enhance sequestration.

Contamination risk by heavy metals and enzymatic stoichiometry in agricultural soils under intense use of pesticides.

Soil contamination by heavy metals (HM) from pesticides poses a serious environmental threat, affecting sustainability and agricultural productivity. Soil enzymes are essential for biochemical reactions such as organic matter decomposition and nutrient cycling and are vital for maintaining soil health. However, the effects of HM on soil enzyme activity are not yet well understood. This study examined the impact of HM contamination on enzymatic stoichiometry in regions with intensive pesticide use. We selected flower cultivation areas with 5 years (CA1) and 10 years (CA2) of pesticide exposure and a native forest area (NFA) as a reference during the dry and rainy seasons. We measured Cd, Cu, Mn, Pb, and Zn levels and employed ecological risk indices to assess contamination levels. We also analyzed enzyme activities (arylsulfatase, ß-glucosidase, acid phosphatase, urease) and enzymatic stoichiometry. CA2 exhibited the highest concentrations of Cd, Cu, and Mn in both periods, while Zn was highest in both CA1 and CA2. CA2 had higher values for all indices, indicating significant contamination. Compared with NFA, arylsulfatase activity was lower in cultivated areas during both periods, suggesting decreased soil quality. We found negative correlations between Cu, Mn, Zn, and arylsulfatase, as well as a reduction in urease with Cd; these elements also increased microbial C limitation. Our findings show that continuous pesticide input increases HM levels and that enzyme activity and stoichiometry are effective bioindicator of soil contamination. This study underscores the urgent need for guidelines to protect soils from prolonged HM buildup.

Altered activities of extracellular soil enzymes by the interacting global environmental changes.

Soil enzymes are crucial in mediating ecosystems' responses to environmental drivers, so that the comprehension of their sensitivity to drivers of global change can help make predictions of future scenarios and design tailored interventions of biomanipulation. Drivers of global change usually act in combination of two or more, and indirect effects of one driver acting through modification of another one often occur, yet most of both manipulative and meta-analysis studies available tend to focus on the direct effect of one single driver on the activity of specific soil enzymes. One of the biggest challenges is, therefore, represented by the difficulty in assessing the interactions between different drivers, due to the complexity of disentangling the single direct effects from the indirect and combined ones. In this review, after elucidating the general mechanisms of soil enzyme production and activity regulation, we display the state-of-the-art knowledge on direct, indirect and combined effects of the main drivers of global change on soil enzyme activities, identify gaps in knowledge and challenges from research, plus we analyse how this can reverberate in the future of biomanipulation techniques for the improvement of ecosystem services. We conclude that qualitative but not quantitative outcomes can be predicted for some interactions such as warming + drought or warming + CO2 , while for other ones, the results are controversial: future basic research will have to center on this holistic approach. A general trend toward the overall increase of soil enzyme activities and acceleration of biogeochemical cycles will persist, until an inflection will be caused by factors such as future shifts in microbial communities and changes in carbon use efficiency. Applied research will develop toward the refinement of "in situ" analytical systems for the study of soil enzyme activities and the support of bioengineering for the better tailoring of interventions of biomanipulation.

Comparative study on plant growth-promoting bacterial inoculation by irrigation and spraying for promoting Bidens pilosa L. phytoremediation of cadmium-contaminated soil.

A field study was conducted to compare FM-1 inoculation by irrigation and spraying for promoting Bidens pilosa L. phytoremediation of cadmium (Cd)-contaminated soil. Cascading relationships between bacterial inoculation by irrigation and spraying and soil properties, plant growth-promoting traits, plant biomass and Cd concentrations in Bidens pilosa L. were explored based on the partial least squares path model (PLS-PM). The results indicated that inoculation with FM-1 not only improved the rhizosphere soil environment of B. pilosa L. but also increased the Cd extracted from the soil. Moreover, Fe and P in leaves play vital roles in promoting plant growth when FM-1 is inoculated by irrigation, while Fe in leaves and stems plays a vital role in promoting plant growth when FM-1 is inoculated by spraying. In addition, FM-1 inoculation decreased the soil pH by affecting soil dehydrogenase and oxalic acid in cases with irrigation and Fe in roots in cases with spraying. Thus, the soil bioavailable Cd content increased and promoted Cd uptake by Bidens pilosa L. To address Cd-induced oxidative stress, Fe in leaves helped to convert GSH into PCs, which played a vital role in ROS scavenging when FM-1 was inoculated by irrigation. The soil urease content effectively increased the POD and APX activities in the leaves of Bidens pilosa L., which helped alleviate Cd-induced oxidative stress when FM-1 was inoculated by spraying. This study compares and illustrates the potential mechanism by which FM-1 inoculation can improve the phytoremediation of Cd-contaminated soil by Bidens pilosa L., suggesting that FM-1 inoculation by irrigation and spraying is useful in the phytoremediation of Cd-contaminated sites.

The Impact of Permethrin and Cypermethrin on Plants, Soil Enzyme Activity, and Microbial Communities.

Pyrethroids are insecticides most commonly used for insect control to boost agricultural production. The aim of the present research was to determine the effect of permethrin and cypermethrin on cultured and non-cultivated bacteria and fungi and on the activity of soil enzymes, as well as to determine the usefulness of Zea mays in mitigating the adverse effects of the tested pyrethroids on the soil microbiome. The analyses were carried out in the samples of both soil not sown with any plant and soil sown with Zea mays. Permethrin and cypermethrin were found to stimulate the multiplication of cultured organotrophic bacteria (on average by 38.3%) and actinomycetes (on average by 80.2%), and to inhibit fungi growth (on average by 31.7%) and the enzymatic activity of the soil, reducing the soil biochemical fertility index (BA) by 27.7%. They also modified the number of operational taxonomic units (OTUs) of the Actinobacteria and Proteobacteria phyla and the Ascomycota and Basidiomycota phyla. The pressure of permethrin and cypermethrin was tolerated well by the bacteria Sphingomonas (clone 3214512, 1052559, 237613, 1048605) and Bacillus (clone New.ReferenceOTU111, 593219, 578257), and by the fungi Penicillium (SH1533734.08FU, SH1692798.08FU) and Trichocladium (SH1615601.08FU). Both insecticides disturbed the growth and yielding of Zea mays, as a result of which its yield and leaf greenness index decreased. The cultivation of Zea mays had a positive effect on both soil enzymes and soil microorganisms and mitigated the anomalies caused by the tested insecticides in the microbiome and activity of soil enzymes. Permethrin decreased the yield of its aerial parts by 37.9% and its roots by 33.9%, whereas respective decreases caused by cypermethrin reached 16.8% and 4.3%.

Response of Carrot (Daucus carota L.) to Multi-Contaminated Soil from Historic Mining and Smelting Activities.

A pot experiment was undertaken to investigate the effect of Cd, Pb and Zn multi-contamination on the physiological and metabolic response of carrot (Daucus carota L.) after 98 days of growth under greenhouse conditions. Multi-contamination had a higher negative influence on leaves (the highest Cd and Zn accumulation) compared to the roots, which showed no visible change in terms of anatomy and morphology. The results showed the following: (i) significantly higher accumulation of Cd, Zn, and Pb in the multi-contaminated variant (Multi) compared to the control; (ii) significant metabolic responses-an increase in the malondialdehyde content of the Multi variant compared to the control in the roots (by 20%), as well as in the leaves (by 53%); carotenoid content in roots decreased by 31% in the Multi variant compared with the control; and changes in free amino acids, especially those related to plant stress responses. The determination of hydroxyproline and sarcosine may reflect the higher sensitivity of carrot leaves to multi-contamination in comparison to roots. A similar trend was observed for the content of free methionine (significant increase of 31% only in leaves); (iii) physiological responses (significant decreases in biomass, changes in gas-exchange parameters and chlorophyll a); and (iv) significant changes in enzymatic activities (chitinase, alanine aminopeptidase, acid phosphatase) in the root zone.

Mechanisms of combined bioremediation by phosphate-solubilizing fungus and plants and its effects on cadmium contamination in phosphate-mining wastelands.

Owing to uncontrolled mining activities and lack of ecological protection measures, phosphate-mining wastelands are contaminated with the heavy metal Cd. In this study, Penicillium oxalicum strain ZP6, a Cd-resistant phosphate-solubilizing fungus, was used in combination with the fast-growing, high-biomass plant Brassica juncea L. to enhance Cd remediation in phosphate-mining wastelands. Further, the bioremediation mechanisms were explored and elucidated. In pot experiments, strain ZP6 and Brassica juncea L. alone were significantly effective in removing Cd from phosphate-mining wastelands; however, their combination was more effective, exhibiting a high removal rate of 88.75%. The presence of phosphorite powder increases soil-enzyme activity, promotes plant growth, and reduces the bioaccumulation and translocation factors. However, Cd-inhibited plant growth and chlorophyll content increased malondialdehyde accumulation, which was alleviated by inoculation with strain ZP6. The results from the study indicate that bioremediation using a combination of strain ZP6 and plants is a restoration strategy with appreciable potential to resolve Cd contamination in phosphate-mining wastelands.

An insight to rhizosphere bacterial community composition and structure of consecutive winter-initiated sugarcane ratoon crop in Southern China.

BACKGROUND: Ratooning in sugarcane is a crucial strategy for ensuring the long-term sustainability of the sugarcane industry. Knowledge gap relating to the interaction between rhizosphere microbiome and ratooning crop, particularly the impact of different sugarcane cultivars on the rhizosphere microbiome in consecutive ratooning, requires additional research. The response of two different sugarcane cultivars, viz ZZ-1 and ZZ-13, were evaluated in consecutive ratooning towards the rhizosphere microbial community and cane morphological characters. RESULTS: Significant changes in the rhizosphere microbiome were observed in the second ratooning over the years. Several important genera were observed in high abundance during the second ratooning, including Burkholderia, Sphingomonas, Bradyzhizobium, and Acidothermus. Cultivar ZZ-13 caused more alterations in the rhizosphere microbiome than ZZ-1, resulting in a more favorable rhizosphere environment for sugarcane growth. The genotypes also varied in terms of nutrients and enzyme activity over the years. There were significant differences between the genotypes and year for number of stalks and yield was significant for genotypes, years and genotype × year. CONCLUSION: This finding will help to understand thorough interactions between rhizosphere microorganisms and ratoon sugarcane and lay the foundation for promoting and maximizing yield as far as possible. In the future, this work can serve as guidance in sugarcane husbandry, mainly in Guangxi, China.

Soil enzymes as indicators of soil function: A step toward greater realism in microbial ecological modeling.

Soil carbon (C) and nitrogen (N) cycles and their complex responses to environmental changes have received increasing attention. However, large uncertainties in model predictions remain, partially due to the lack of explicit representation and parameterization of microbial processes. One great challenge is to effectively integrate rich microbial functional traits into ecosystem modeling for better predictions. Here, using soil enzymes as indicators of soil function, we developed a competitive dynamic enzyme allocation scheme and detailed enzyme-mediated soil inorganic N processes in the Microbial-ENzyme Decomposition (MEND) model. We conducted a rigorous calibration and validation of MEND with diverse soil C-N fluxes, microbial C:N ratios, and functional gene abundances from a 12-year CO2  × N grassland experiment (BioCON) in Minnesota, USA. In addition to accurately simulating soil CO2 fluxes and multiple N variables, the model correctly predicted microbial C:N ratios and their negative response to enriched N supply. Model validation further showed that, compared to the changes in simulated enzyme concentrations and decomposition rates, the changes in simulated activities of eight C-N-associated enzymes were better explained by the measured gene abundances in responses to elevated atmospheric CO2 concentration. Our results demonstrated that using enzymes as indicators of soil function and validating model predictions with functional gene abundances in ecosystem modeling can provide a basis for testing hypotheses about microbially mediated biogeochemical processes in response to environmental changes. Further development and applications of the modeling framework presented here will enable microbial ecologists to address ecosystem-level questions beyond empirical observations, toward more predictive understanding, an ultimate goal of microbial ecology.

Commonwealth of Soil Health: How Do Earthworms Modify the Soil Microbial Responses to CeO2 Nanoparticles?

Soil ecotoxicological assays on nanoparticles (NPs) have mainly investigated single components (e.g., plants, fauna, and microbes) within the ecosystem, neglecting possible effects resulting from the disturbance of the interactions between these components. Here, we investigated soil microbial responses to CeO2 NPs in the presence and absence of earthworms from the perspectives of microbial functions (i.e., enzyme activities), the community structure, and soil metabolite profiles. Exposure to CeO2 NPs (50, 500 mg/kg) alone decreased the activities of enzymes (i.e., acid protease and acid phosphatase) participating in soil N and P cycles, while the presence of earthworms ameliorated these inhibitory effects. After the CeO2 NP exposure, the earthworms significantly altered the relative abundance of some microbes associated with the soil N and P cycles (Flavobacterium, Pedobacter, Streptomyces, Bacillus, Bacteroidota, Actinobacteria, and Firmicutes). This was consistent with the pattern found in the significantly changed metabolites which were also involved in the microbial N and P metabolism. Both CeO2 NPs and earthworms changed the soil bacterial community and soil metabolite profiles. Larger alterations of soil bacteria and metabolites were found under CeO2 NP exposure with earthworms. Overall, our study indicates that the top-down control of earthworms can drastically modify the microbial responses to CeO2 NPs from all studied biological aspects. This clearly shows the importance of the holistic consideration of all soil ecological components to assess the environmental risks of NPs to soil health.

Comparison of bacterial diversity, root exudates and soil enzymatic activities in the rhizosphere of AVP1-transgenic and nontransgenic wheat (Triticum aestivum L.).

AIMS: Soil microbial communities are among the most diverse communities that might be affected due to transgenic crops. Therefore, risk assessment studies on transgenes are essentially required as any adverse effects may depend not only on the specific gene and crop involved but also on soil conditions. METHODS AND RESULTS: The present study deals with the comparison of bacterial populations, root exudates and activities of soil enzymes in nontransgenic and AVP1-transgenic wheat rhizosphere, overexpressing vacuolar H + pyrophosphatase for salinity and drought stress tolerance. Amounts of organic acids and sugars produced as root exudates and activities of dehydrogenase, phosphatase and protease enzymes in soil solution showed no significant differences in AVP1-transgenic and nontransgenic wheat rhizosphere, except for urease and phenol oxidase activities. The higher copy number of nifH gene showed the abundance of nitrogen-fixing bacteria in the rhizosphere of AVP1-transgenic wheat compared with nontransgenic wheat. nifH gene sequence analysis indicated the common diazotrophic genera Azospirillum, Bradyrhizobium, Rhizobium and Pseudomonas in AVP1-transgenic and nontransgenic wheat except for Zoogloea detected only in nontransgenic wheat. Using 454-pyrosequencing of 16S rRNA gene from soil DNA, a total of 156, 282 sequences of 18 phyla were obtained, which represented bacterial (128,006), Archeal (7928) and unclassified (21,568) sequences. Proteobacteria, Crenarchaeota and Firmicutes were the most abundant phyla in the transgenic and nontransgenic wheat rhizosphere. Further comparison of different taxonomic units at the genus level showed similar distribution in transgenic and nontransgenic wheat rhizospheres. CONCLUSION: We conclude that the AVP1 gene in transgenic wheat has no apparent adverse effects on the soil environment and different bacterial communities. However, the bacterial community depends on several other factors, not only genetic composition of the host plants. SIGNIFICANCE OF THE STUDY: The present research supports introduction and cultivation of transgenic plants in agricultural systems without any adverse effects on indigenous bacterial communities and soil ecosystems.

Harnessing rhizobacteria to fulfil inter-linked nutrient dependency on soil and alleviate stresses in plants.

Plant rhizo-microbiome comprises complex microbial communities that colonize at the interphase of plant roots and soil. Plant growth-promoting rhizobacteria (PGPR) in the rhizosphere provide important ecosystem services ranging from the release of essential nutrients for enhancing soil quality and improving plant health to imparting protection to plants against rising biotic and abiotic stresses. Hence, PGPR serve as restoring agents to rejuvenate soil health and mediate plant fitness in the facet of changing climate. Though it is evident that nutrient availability in soil is managed through inter-linked mechanisms, how PGPR expedite these processes remain less recognized. Promising results of PGPR inoculation on plant growth are continually reported in controlled environmental conditions, however, their field application often fails due to competition with native microbiota and low colonization efficiency in roots. The development of highly efficient and smart bacterial synthetic communities by integrating bacterial ecological and genetic features provides better opportunities for successful inoculant formulations. This review provides an overview of the interplay between nutrient availability and disease suppression governed by rhizobacteria in soil followed by the role of synthetic bacterial communities in developing efficient microbial inoculants. Moreover, an outlook on the beneficial activities of rhizobacteria in modifying soil characteristics to sustainably boost agroecosystem functioning is also provided.

Multi-year and multi-site effects of recurrent glyphosate applications on the wheat rhizosphere microbiome.

Glyphosate (N-(phosphonomethyl)glycine) is broad-spectrum herbicide that is extensively used worldwide, but its effects on the soil microbiome are inconsistent. To provide a sound scientific basis for herbicide re-review and registration decisions, we conducted a four-year (2013-2016) study in which we consecutively applied glyphosate to a wheat (Triticum aestivum L.)-field pea (Pisum sativum L.)-canola (Brassica napus L.)-wheat crop rotation at five sites in the Canadian prairies. The glyphosate rates were 0, 1, 2, 4 and 8 kg ae ha-1, applied pre-seeding and post-harvest every year. The wheat rhizosphere was sampled in the final year of the study and analysed for microbial biomass C (MBC), the composition and diversity of the microbiome, and activities of ß-glucosidase, N-acetyl-ß-glucosiminidase, acid phosphomonoesterase and arylsulphatase. Glyphosate did not affect MBC, the composition and diversity of prokaryotes and fungi, and the activities of three of the four enzymes measured in the wheat rhizosphere. The one effect of glyphosate was a wave-like response of N-acetyl-ß-glucosaminidase activity with increasing application rates. The experimental sites had much greater effects, driven by soil pH and organic C, on the soil microbiome composition and enzyme activities than glyphosate. Soil pH was positively correlated with the relative abundance of Acidobacteriota but negatively correlated with that of Actinobacteriota and Basidiomycota. Soil organic C was positively correlated with the relative abundances of Proteobacteriota and Verrucomicrobiota, but negatively correlated with the relative abundance of Crenachaeota. The activity of acid phosphomonoesterase declined with increasing relative abundance of Acidobacteriota, but increased with that of Actinobacteriota and Basidiomycota. The activity of N-acetyl-ß-glucosaminidase also increased with increasing relative abundance of Actinobacteriota but decreased with that of Mortierellomycota. ß-glucosidase activity also decreased with increasing relative abundance of Mortierellomycota. The core fungal species observed in at least 90% of the samples were Humicola nigrescens, Gibberella tricincta and Giberella fujikuroi. Therefore, this multi-site study on the Canadian prairies revealed no significant effects of 4-year applications of glyphosate applied at different rates on most soil microbial properties despite differences in the properties among sites. However, it is important to keep evaluating glyphosate effects on the soil microbiome and its functioning because it is the most widely used herbicide worldwide.

Effect of biochar on immobilization remediation of Cd⁃contaminated soil and environmental quality.

PURPOSE: Field experiments were conducted to explore the remediation effects of ordinary biochar and PEI-modified biochar on the Cd-contaminated yellow brown soil, and the improvement of soil environment quality in southern Shaanxi province, so as to provide theoretical basis and technical support for in-situ remediation of Cd-contaminated soil in southern Shaanxi province. RESULTS AND DISCUSSION: Biochar applied in soil could increase the soil pH value, EC, ECEC, and SOC, and improve the soil physical and chemical properties to a certain extent. Biochar in soil could change the chemical form of Cd in soil, effectively passivate Cd in soil and reduce its bio-availability. Biochar could enhance the activities of catalase, urease, alkaline phosphatase and sucrase in soil to different degrees, and the four soil enzymes could be used as indicators of passivation effects of soil Cd by biochar. With biochar treatment, soil aggregates MWD and GMD increased to different degrees, so biochar could enhance soil stability. The biochar could decrease the content of Cd in different parts of wheat, the content of Cd in wheat grains had a highly significant positive correlation with the available content of Cd in soil, and highly significant or significant negative correlations with pH, SOC, EC, ECEC, and the activities of phosphatase, urease and sucrase in soil. Compared with ordinary biochar, the passivation effect of PEI-modified biochar on Cd was more significant. CONLUSIONS: The results of the study indicated that ordinary biochar and PEI-modified biochar could passivate the Cd in soil, and remediate Cd-contaminated soil, and improve the soil environmental quality effectively, compared with ordinary biochar, the PEI-modified biochar produced batter.

Effects of heavy metals on microorganisms and enzymes in soils of lead-zinc tailing ponds.

Taking the soil around the lead-zinc tailings pound in the upper reaches of the Hanjiang River in Shaanxi Province as the research object, with tailings pond as the center, seven different belt zones were divided outwards, the contents of Pb, Cu, Zn, V, Ni, Cd in soil were analyzed, as well as soil basic respiration (SBR), microbial biomass carbon (MBC), microbial metabolic quotient (MMQ), and the activities of catalase, urease, cellulase, invertase and neutral phosphatase were also determined. The purpose was to reveal the intrinsic relationship between soil microbial, enzyme activities and heavy metal pollution, and to establish the characterization system of enzyme activities, soil heavy metal pollution degree, as well as microbial parameters. The results showed that: (1) The potential ecological risk index of six heavy metals was ranked as Cd > Cu > Pb > Ni > Zn > V. Cd was a high potential ecological risk, Cu was a medium potential ecological risk, and Zn, Pb, V and Ni were low potential ecological risk. The comprehensive evaluation result of Hakanson's potential ecological hazard index showed that, Zone I was of high potential risk level, Zone II, III and IV were of medium risk level, and Zone V, VI and VII were of low level. (2) Microbial biomass carbon (MBC) had a significant negative correlation or extremely significant negative correlation with 6 heavy metals, and microbial metabolic quotient (MMQ) had a significant positive correlation or extremely significant positive correlation with 6 heavy metals. MBC and MMQ were effective microbiological indexes to measure the quality status of soil, while SBR was not. (3) Catalase, cellulase, sucrase and neutral phosphatase activity had significant negative correlation with the contents of 6 heavy metals, and they could replicate the pollution degree of substantial metals in the soil. However, urease had no significant correlation with the contents of 6 heavy metals, which could not reflect the pollution degree of soil heavy metals.

Calcite in combination with olive pulp biochar reduces Ni mobility in soil and its distribution in chili plant.

The presence of Ni above the permissible limit in agriculture soils poses negative effects on soil health, crop quality, and crop productivity. Surprisingly, the usage of various organic and inorganic amendments can reduce Ni mobility in the soil and its distribution in the crops. A pot experiment was conducted to elucidate the effects of olive pulp biochar (BR), calcite (CAL), and wheat straw (WS), as sole amendments and their mixtures of 50:50 ratio, added to Ni polluted soil on Ni mobility in the soil, Ni immobilization index (Ni - IMi), soil enzymatic activities, Ni distribution in parts of chili plant, Ni translocation factor and bioaccumulation factor in fruit, plant growth parameters and oxidative stress encountered by the plants. Outcomes of this pot experiment revealed that amendments raised soil pH, improved soil enzymatic activities, values of Ni - IMi, while significantly reduced bioavailable Ni fraction in the post-harvest soil. However, the highest activities of acid phosphatase, urease, catalase, and dehydrogenase by 50, 70, 239, and 111%, respectively, improvement in Ni - IMi up to 60% while 60% reduction in the bioavailable Ni fraction was observed in BR + CAL treatment, compared to control was noted. Among all amendments, the top most reduction in Ni concentrations in shoots, roots, fruit, Translocation Factor (TF), and Bioaccumulation Factor (BAF) values of fruit by 72%, 36%, 86%, 72%, and 86%, in BR + CAL treatment, compared to control. Moreover, the plants growing on BR + CAL amended Ni contaminated soil showed the topmost improvement in plant phonological parameters while encountered the least oxidative stress. Such findings refer to the prospective usage of BR + CAL at 50:50 ratio than BR, CAL, WS alone, and BR + WS as well as WS + CAL for reducing Ni mobility in the soil, improving Ni - IMi, soil enzymatic activities, plant phonological and oxidative stress while reducing Ni distribution in plant parts. Novelty statementIn this experiment, it was hypothesized that amending Ni polluted soil with olive pulp biochar (BR), CAL, and WS as alone soil amendments and their combinations at 50:50 ratios can reduce Ni bioavailability in soil, Ni distribution in chili plant and oxidative stress encountered by the plants. Moreover, these amendments may improve, soil enzymatic activities, Ni immobilization index, plant phenological traits. Therefore, it was aimed to undertake useful scientific planning and research, to restore and rehabilitate the dwellings, biological resources and to minimize the sufferings of the peoples in nutrient-poor Ni contaminated soils, by improving soil health and chili productivity.