Extracellular Enzyme Activities Research Articles

Long-term fertilization affects microbial necromass accumulation by regulating nutrient and enzymatic stoichiometry in a calcareous Fluvisol

Microbial necromass accumulation through rhizodeposition plays a critical role in increasing the stable soil organic carbon pool, which is greatly affected by fertilization. However, the legacy effects of long-term fertilization on microbial necromass accumulation remain unclear. Here, we selected a calcareous Fluvisol treated with no fertilizer (Ctrl), P and K fertilizers (PK), N and K fertilizers (NK), and N, P and K fertilizers (NPK) for 34 years and conducted a 12-week microcosm experiment with simulated daily rhizodeposition to disentangle the legacy effects of long-term fertilization on microbial necromass accumulation. We measured soil C, N and P contents and C-, N- and P-acquiring extracellular enzyme activities and analyzed phospholipid fatty acids (PLFAs) and amino sugars to indicate microbial biomass and necromass, respectively. We found that compared with the Ctrl and NK treatments, the PK and NPK treatments significantly decreased the C:N and C:P ratios and the net accumulation of microbial necromass but significantly increased the ratios of C- to N- and C- to P-acquiring enzyme activities and the fungal PLFAs abundance in soils. The net accumulation of microbial necromass was positively correlated with soil nutrient stoichiometry (mainly the C:N and C:P ratios) but negatively correlated with soil enzymatic stoichiometry (mainly the ratios of C- to N- and C- to P-acquiring enzyme activities) and the fungal to bacterial PLFA ratio. Taken together, these results suggest that long-term fertilization has legacy effects on microbial necromass accumulation and that fertilization-induced changes in nutrient and enzymatic stoichiometry regulate microbial necromass accumulation through rhizodeposition in the calcareous Fluvisol.

Microbial community and enzyme activity respond differently to seasonal and edaphic factors in forest and grassland ecosystems

Although microbial community and function patterns have been extensively studied, little is known about whether the patterns are consistent in different ecosystems and how they are influenced by seasonality or other environmental factors. To test the driving factors of microbial communities and potential functions, we collected soil samples from five forests (mixed broadleaved-Korean pine forest, mixed pine and oak forest, deciduous broadleaved mixed forest, subtropical evergreen broad-leaved forest and tropical rainforest) and three grassland ecosystems (meadow steppe, semi-arid grassland and arid grassland) across China in three seasons (spring, summer and autumn). Microbial diversity based on the sequencing of 16S rRNA gene for bacteria and internal transcribed spacer (ITS) genes for fungi were measured, and potential functions represented by soil extracellular enzyme activities (EEAs) were analyzed. The results found that soil EEAs were significantly higher in summer than in spring and autumn, and both bacterial and fungal richness indices showed greater seasonal fluctuations than the diversity. Fungal richness indices were highest in summer in both forest and grassland ecosystems, while the lowest were observed in spring for forest and in autumn for grassland, respectively. In addition, fungal communities were closely related to ecosystem types, while bacterial communities were not significantly different across ecosystems and exhibited a broader habitat niche breadth, but the relative abundance of dominant bacterial phyla showed stronger correlations with environmental variables (including climate, soil properties and nutrients) in grassland than in forest ecosystems. The decoupling of microbial community and EEAs was observed in both forest and grassland ecosystems, indicating the function redundancy of soil microorganisms. The present study provided crucial information about the effects of ecosystem types, seasonality and edaphic factors on soil microbial communities and EEAs, and could advance the understanding of soil potential function responses to environmental changes.

WITHDRAWN:Evaluation of extracellular enzymatic activity in the Aburrá-Medellín tropical river in Colombia as a response to variations in water quality and flow regime, in an urbanized basin

WITHDRAWN:Evaluation of extracellular enzymatic activity in the Aburrá-Medellín tropical river in Colombia as a response to variations in water quality and flow regime, in an urbanized basin

Impact of residual antibiotics on microbial decomposition of livestock manures in Eutric Regosol: Implications for sustainable nutrient recycling and soil carbon sequestration

The land application of livestock manure has been widely acknowledged as a beneficial approach for nutrient recycling and environmental protection. However, the impact of residual antibiotics, a common contaminant of manure, on the degradation of organic compounds and nutrient release in Eutric Regosol is not well understood. Here, we studied, how oxytetracycline (OTC) and ciprofloxacin (CIP) affect the decomposition, microbial community structure, extracellular enzyme activities and nutrient release from cattle and pig manure using litterbag incubation experiments. Results showed that OTC and CIP greatly inhibited livestock manure decomposition, causing a decreased rate of carbon (28%–87%), nitrogen (15%–44%) and phosphorus (26%–43%) release. The relative abundance of gram-negative (G-) bacteria was reduced by 4.0%–13% while fungi increased by 7.0%–71% during a 28-day incubation period. Co-occurrence network analysis showed that antibiotic exposure disrupted microbial interactions, particularly among G- bacteria, G+ bacteria, and actinomycetes. These changes in microbial community structure and function resulted in decreased activity of urease, β-1,4-N-acetyl-glucosaminidase, alkaline protease, chitinase, and catalase, causing reduced decomposition and nutrient release in cattle and pig manures. These findings advance our understanding of decomposition and nutrient recycling from manure-contaminated antibiotics, which will help facilitate sustainable agricultural production and soil carbon sequestration.

Comparative study of virulence factors, pathogenicity and genetic diversity of Acidovorax avenae subsp. avenae, the causal agent of red stripe disease in sugarcane

AbstractAcidovorax avenae subsp. avenae (Aaa) is the causal agent of red stripe in sugarcane, a disease characterized by two forms: leaf stripe and top rot. Despite the importance of this disease, little is known about Aaa infection mechanisms, and studies of virulence factors (VFs) have not been reported. Previous analysis of Aaa isolates obtained from sugarcane fields in Tucumán, Argentina, suggested that pathogenicity was not related to genetic groups determined by rep‐PCR analysis. Therefore, the aims of this work were to analyse VFs produced by Aaa strains from different genetic groups and to evaluate the association among VFs, between VFs and Aaa pathogenicity and between VFs and Aaa genetic diversity. Bacterial motility (sliding, swimming and twitching), extracellular enzyme activities (proteases, amylases and endoglucanases), H2O2‐mediated oxidative stress, cell adhesion and exopolysaccharide (EPS) production were assayed in 14 Aaa isolates from different genetic groups. Pearson's correlation analysis and principal component analysis (PCA) were performed. For each VF analysed, values were variable presenting quantitative traits among the strains. Significant correlations were observed among the VFs, though no clear trend was identified between them and the pathogenicity or genetic group. Results reinforce the idea that a single VF does not account for the infection outcome, but a more complex process occurs where the interplay among VFs must be considered. The results of this study are crucial because they provide insight into the infection mechanism of this bacterium.

Soil extracellular enzyme activity reflects the change of nitrogen to phosphorus limitation of microorganisms during vegetation restoration in semi-arid sandy land of northern China

Soil extracellular enzyme activity (EEA) and enzyme stoichiometry are indicators of soil nutrient availability and microbial substrate limitation. However, the patterns in soil enzyme activities and stoichiometry, and their key drivers remain unclear during vegetation restoration in degraded sandy land. Here, soil ecosystems at five restoration stages of degraded sandy land were selected for investigation and we quantified the microbial nutrient limitation using EEA stoichiometry. The average C:N:P ratio for the nutrient-acquisition enzymes was 1:0.88:0.86, which differed from the global ratio of 1:1:1, indicating stronger microbial C limitation than N or P limitation. With vegetation restoration, the enzyme N:P ratio decreased, but the angle term used in vector analysis increased, indicating that the restored grassland transitioned from N-restricted (angle < 45°) to P-restricted (angle > 45°). Plant C inputs increased the soil nutrient content and significantly decreased the microbial C and N limitation but increased P limitation due to nutrient competition between plants and soil microorganisms. Decreased soil water levels caused by vegetation transpiration may have shifted the microbial limitation from N to P. The decreased fungi:bacteria ratio strengthened the microbial C and N or P limitations. On the basis of these findings, as measures to alleviate the associated nutrient limitations, we would recommend supplementation with phosphorus in the potential and slight stages of rocky desertification and the supplementary application of nitrogen in the moderate and severe stages during the restoration of degraded sandy ecosystems.

Extracellular polymeric substances are closely related to land cover, microbial communities, and enzyme activity in tropical soils

Extracellular polymeric substances (EPS) form the main matrix of microbial biofilms and play a crucial role in maintaining microbial life. However, factors influencing EPS concentration and production in soil are poorly understood. Here we show that EPS are closely related to microbial communities and nutrient acquisition in tropical forest and cropland soils with varying iron-aluminum-manganese concentrations and total reserve in base cations. We found under homogenized moisture and temperature conditions that EPS concentration and production efficiency (i.e., EPS per unit of microbial biomass) depend more on land cover than on geochemical soil properties. EPS concentration and production efficiency were higher in cropland than in forest soil and were related to the higher relative abundance of microbial sequences identified as Paenibacillaceae, Ramlibacter, Chaetosphaeria, Burkholderiaceae, and Xanthobacteraceae, pointing to potential EPS producers. In contrast, lower EPS concentration in forest soil was related to the higher relative abundance of microbial sequences associated with e.g., Gemmatimonas and Massilia, suggesting potential EPS degradation. We also found that EPS production efficiency was positively related to microbial investment in nutrient acquisition, implying that EPS production likely follows the same principles as extracellular enzyme activity. That is, EPS production may increase when resources are scarce to facilitate nutrient acquisition, and decrease when resources are abundant. Overall, microbial community composition and resource demand seem to control EPS degradation and accumulation in tropical soils, which could influence microbially-driven carbon and nutrient cycling.

Response of soil extracellular enzyme activity and stoichiometry to short-term warming and phosphorus addition in desert steppe.

Phosphorus (P) is regarded as one of the major limiting factors in grassland ecosystems. Soil available phosphorus deficiency could affect soil extracellular enzyme activity, which is essential for microbial metabolism. Yet it is still unclear how soil available phosphorus affects soil extracellular enzyme activity and microbial nutrient limitation of desert steppe in the context of climate warming. This study carried out a short-term open-top chambers (OTCs) experiment in a desert steppe to examine the effects of warming, P addition, and their interaction on soil properties, the activities of soil extracellular enzymes, and stoichiometries. The findings demonstrated that soil acquisition enzyme stoichiometry of C: N: P was 1.2:1:1.5 in this experiment region, which deviated from the global mean scale (1:1:1). Warming increased soil AN (ammonium nitrogen and nitrate nitrogen) contents and decreased microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN). Phosphorus addition raised soil available phosphorus and microbial biomass phosphorus (MBP) contents. Soil extracellular enzyme activities and stoichiometries in desert steppe are largely impacted by soil AN, MBC: MBP, and MBN: MBP. These results revealed that the changes of soil available nutrients and stoichiometries induced by short-term warming and P addition could influence soil microbial activities and alleviate soil microbial carbon and phosphorus limitation. Our findings highlight that soil available phosphorus played a critical role in regulating soil extracellular enzyme activity and microbial nutrient limitation of desert steppe. Further research on soil microbial communities should explore the microbiological mechanisms underlying these findings.

Nitrogen deposition raises temperature sensitivity of soil organic matter decomposition in subtropical forest

Subtropical ecosystems are strongly affected by nitrogen (N) deposition, impacting soil organic matter (SOM) availability and stocks. Here we aimed to reveal the effects of N deposition on i) the structure and functioning of microbial communities and ii) the temperature sensitivity (Q10) of SOM decomposition. Phosphorus (P) limited evergreen forest in Guangdong Province, southeastern China, was selected, and N deposition (factor level: N (100 kg N ha−1 y−1 (NH4NO3)) and control (water), arranged into randomized complete block design (n = 3)) was performed during 2.5 y. After that soils from 0 to 20 cm were collected, analyzed for the set of parameters and incubated at 15, and 25, and 35 °C for 112 days. N deposition increased the microbial biomass N and the content of fungal and Gram-positive bacterial biomarkers; activities of beta-glucosidase (BG) and acid phosphatase (ACP) also increased showing the intensification of SOM decomposition. The Q10 of SOM decomposition under N deposition was 1.66 and increased by 1.4 times than under control. Xylosidase (BX), BG, and ACP activities increased with temperature under N but decreased with the incubation duration, indicating either low production and/or decomposition of enzymes. Activities of polyphenol-(PPO) and peroxidases (POD) were higher under N than in the control soil and were constant during the incubation showing the intensification of recalcitrant SOM decomposition. At the early incubation stage (10 days), the increase of Q10 of CO2 efflux was explained by the activities of BX, BQ, ACP, and POD and the quality of the available dissolved organic matter pool. At the later incubation stages (112 days), the drop of Q10 of CO2 efflux was due to the depletion of the labile organic substances and the shift of microbial community structure to K-strategists. Thus, N deposition decoupled the effects of extracellular enzyme activities from microbial community structure on Q10 of SOM decomposition in the subtropical forest soil.

Genotypes and virulence-related activities of Candida albicans derived from oral cavity of patients in Hokkaido

ObjectiveThis study aimed to elucidate the difference in virulence of Candida albicans derived from oral candidiasis and non-oral candidiasis patients, and its genotype differences in Hokkaido to obtain a clue of a platform to develop new approaches for diagnosis and treatment. DesignC. albicans strains were collected from patients who visited the Hokkaido University Hospital Dental Center. Each strain was examined to i) identify the Candida albicans genotype by PCR, ii) measure the strain’s extracellular secretory enzyme activity, iii) determine the strain’s ability to induce the production of interleukin-8, and iv) determine the strain’s ability to induce cell death. ResultsCertain virulence-related protease activities and cytotoxicity were higher in strains derived from patients with oral candidiasis compared with strains derived from patients without oral candidiasis. This is the first report on genotypes and the virulence-related activities, such as some protease secretion, IL-8 induction and cytotoxicity of C. albicans in Hokkaido. ConclusionsThe virulence-related activities of the fungal strain may influence the pathogenesis of oral candidiasis, such as production of secreted aspartyl protease and cytotoxicity. In addition, C. albicans genotype C may be important for pathogenicity in Hokkaido, because the ratio of genotype C was increased in strains derived from oral candidiasis patients.

N2-Fixing Tree Species Help to Alleviate C- and P-Limitation in Both Rhizosphere and Non-Rhizosphere Soils in the Eucalyptus Plantations of Subtropical China

The extracellular enzyme activity (EEA) and enzymatic stoichiometry (EES) of soil are useful indicators of shifts in soil nutrition and microbial resource requirements. Nevertheless, it is uncertain how the limitation of soil microbial nutrients is altered by a Eucalyptus plantation mixed with a N2-fixing tree species. Our study examined the microbial nutrient limitation in two plantations: a pure Eucalyptus plantation (PP) and a mixed plantation (Eucalyptus and Erythrophleum fordii, MP) in rhizosphere and non-rhizosphere soils, beginning with two indicators, soil EEA and EES. In this study, the soil EEA was considerably (p < 0.05) greater in the MP contrasted to the PP, and the enzyme C:N:P ratios of the PP (1.12:1:1.10) and MP (1.07:1:1.08) both diverged from the global average EEA (1:1:1), and the deviation degree of the PP was greater. The results of the vector analysis demonstrated that the vector angle (VA) and vector length (VL) were considerably (p < 0.05) smaller in the MP contrasted to the PP. In comparison to the PP, the MP had a considerably (p < 0.05) poorer carbon quality index (CQI). Additionally, both microbial and soil properties have a considerable impact on soil EEA and EES, according to variance partitioning analysis (VPA) and redundancy analysis (RDA). In summary, our results show that the restriction of microorganisms on C and P in rhizosphere soils is usually weaker than that in non-rhizosphere soils and that the addition of N2-fixing tree species to Eucalyptus plantations can lessen but not completely remove the restriction of soil microorganisms on C and P. Future management practices involving mixed plantations with N2-fixing trees species could help decrease microbial nutrient limitation and promote sustainable plantations.

Land Use and Local Conditions Effects on Extracellular Enzyme Activity of Actinobacteria Strains

Purpose: Evaluate how land use and local conditions affects extracellular enzyme activity of actinobacterial strains isolated from soils in the Brazilian Semi-arid Northeast region. Theoretical framework: The study is framed within soil microbial ecology and environmental microbiology, examining how environmental factors shape the diversity and function of soil bacteria. Method: Soil samples were collected along transects from 3 conservation units into surrounding areas with different land uses. Actinobacteria were isolated and identified morphologically. Extracellular enzyme activities were measured and compared between land uses and locations. Results: The study found considerable actinobacterial diversity, with Streptomyces as the most abundant genus. Amylase, cellulase and xylanase activities varied between locations and land uses. Multivariate analysis revealed heterogeneity in the functional diversity of actinobacterial communities related to land use. Conclusions: Both land use and minor local distinctions can strongly influence the metabolic potential and ecosystem functions of actinobacterial populations in semi-arid environments. Originality/value: Provides new insights into actinobacterial ecology in Brazilian semi-arid soils, showing land use and local conditions strongly influence bacterial community distribution.

No‐till marginally mitigates the impact of harvesting corn stover on soil microbial parameters

AbstractHarvesting corn stover can negatively impact soil chemical and physical properties, but less is known regarding its effects on soil microbiology. We evaluated the impact of corn (Zea mays L.) stover removal level (SRL) on soil microbial biomass (MB) and extracellular enzyme activities (EEAs) in irrigated, continuous corn located in eastern Nebraska. Soil fatty acid‐methyl esters (FAMEs) and EEA of eight soil enzymes were measured over 2 years, 0‐ to 20‐cm soil depth, under conventional disk tillage (CT) and no‐till (NT) under three SRLs. Soil chemical properties were measured as explanatory variables for changes in soil microbial communities and their enzymatic potential. Potential EEA of all enzymes decreased with stover removal and tillage. Soil bacterial biomass (BB) and fungal biomass (FB) decreased with SRL, while mycorrhizal biomass was unresponsive. Impacts of tillage on MB groups varied by year; however, FB was consistently higher under CT. At all growth stages, NT with all stover retained, a “soil conservation target” had distinct soil enzyme and bacterial FAME profiles compared to CT across all SRLs and to NT under high and sometimes moderate SRLs. Principal component analysis of soil properties was dominated by SRL with EEAs, BB, soil organic matter (SOM), water‐extractable carbon, and H3A‐extractable potassium being positively correlated to stover retention. Reduced input of microbial substrates also led to a loss of fine particulate organic matter, an indicator correlated to stable macroaggregation. Because NT partially ameliorated the negative impact of stover removal on BB, SOM fractions, and soil enzymes critical to nutrient cycling, pairing NT with stover removal may be more sustainable in the long term.

Changes in Soil Properties and Enzyme Stoichiometry in Three Different Forest Types Changed to Tea Plantations

Understanding the characteristics and driving factors of soil carbon, nitrogen, phosphorus, and enzyme stoichiometry during land use/cover change is of great significance for assessing microbial nutrient restriction and sustainable land development during the process. China, the world’s largest tea producer, is witnessing a significant expansion of tea plantations into previously forested areas. We performed field sampling in three forest types with the area partially converted to tea plantations in Wuyishan National Park. We examined the changes in soil carbon (TC), nitrogen (TN), phosphorus (TP), and three kinds of extracellular enzyme activities, β-glucosidase (BG), β-n-acetylglucosidase (NAG), and acid phosphatase (ACP). By analyzing the enzyme stoichiometric ratio, vector length (VL), and vector angle (VA), the relative nutrient limitations of soil microorganisms were explored. The results showed that soil TC and TN decreased significantly (p < 0.05), TP increased significantly, and soil carbon (C):nitrogen (N), carbon (C):phosphorus (P), and nitrogen (N):phosphorus (P) ratios decreased significantly after the conversion of forest land to tea plantation. Soil BG, NAG, and ACP contents decreased significantly (p < 0.05). There were no significant differences in enzyme carbon:nitrogen ratios (EC/N), enzyme carbon:phosphorus ratios (EC/P), enzyme nitrogen:phosphorus ratios (EN/P), VL, or VA (p > 0.05). Through the analysis of soil enzyme stoichiometry, it was found that forest soil was generally limited by P, which was, to some extent, relieved after the conversion to tea plantation. Redundancy analysis showed that TC, TN, and the C:N ratio were the main factors influencing enzyme activity and stoichiometry. These results indicated that land use/cover change had significant effects on soil nutrient status, enzyme activity, and stoichiometry. Soil enzyme activity is very sensitive to the changes in soil nutrients and can reflect the restriction of soil nutrients more accurately.

Effect of raw material and application rate of biogas slurry on Cucumber growth, Fusarium wilt suppression, and soil properties

With the popularization and application of biogas engineering, byproduct biogas slurry has excellent application potential as organic liquid fertilizer, while its source and application rate significantly affect its effect. Irrational application of biogas slurry, can reduce crop yields and cause environmental problems such as soil salinization and diffuse source pollution. In this study, the impact of different types of biogas slurry from various materials (i.e., pig manure, chicken manure, vinasse, and kitchen waste) and their required application rates on the growth and incidence of cucumber were investigated by analyzing the dry weight of cucumber, soil chemical properties, soil extracellular enzyme activity, and the incidence of cucumber wilt disease. The results showed that the effects of the four selected types of biogas slurry on cucumber growth and disease were similar. It was shown that 3% was the most suitable application rate considering the dry weight of cucumber plants and the incidence of wilt disease. At this application rate, it was achievable to increase soil pH, soil AN, AK, Olsen P content, and enzyme activities without increasing the risk of salinization. In summary, despite different sources, biogas slurry showed the best growth promotion and disease suppression ability in 3% (v/w) application, without the risk of soil salinization.

Depth profiles of biological aerated contactors: Characterizing microbial activity treating reduced contaminants

The biological treatment process consisting of an aerated contactor and filter is effective for groundwaters containing elevated ammonia and other reduced contaminants, including iron, manganese, arsenic, and methane. Depth profiles characterizing microbial activity across aerated contactors are lacking. A 1-year pilot study comparing gravel- and ceramic-packed contactors was conducted, and media depth profile samples were collected at the conclusion of the study. Media and water samples also were collected from pilot-scale aerated contactors at 4 other water systems. Water quality, media surface metals concentrations, and a suite of biofilm parameters were analyzed. Media surface metals concentrations were greatest at the influent end. ATP concentrations, extracellular polymeric substances, and extracellular enzyme activities tended to be similar across depth. Bacteria and functional genes involved in contaminant oxidation co-occurred and tended to decrease across depth, but were not correlated to the media metals concentration. Microbial community composition changed with depth, and the diversity either decreased or remained similar. The microbial activity profiles through aerated contactors differed from what is typically reported for groundwater biofilters, suggesting that the different reactor flow and dissolved oxygen profiles impacted the microbial community.

An extracellular glucose sensor for substrate-dependent secretion and display of cellulose-degrading enzymes.

The efficient hydrolysis of lignocellulosic biomass into fermentable sugars is key for viable economic production of biofuels and biorenewable chemicals from second-generation feedstocks. Consolidated bioprocessing (CBP) combines lignocellulose saccharification and chemical production in a single step. To avoid wasting valuable resources during CBP, the selective secretion of enzymes (independent or attached to the surface) based on the carbon source available is advantageous. To enable enzyme expression and secretion based on extracellular glucose levels, we implemented a G-protein-coupled receptor (GPCR)-based extracellular glucose sensor; this allows the secretion and display of cellulases in the presence of the cellulosic fraction of lignocellulose by leveraging cellobiose-dependent signal amplification. We focused on the glucose-responsiveness of the HXT1 promoter and engineered PHXT1 by changing its core to that of the strong promoter PTHD3 , increasing extracellular enzyme activity by 81%. We then demonstrated glucose-mediated expression and cell-surface display of the β-glucosidase BglI on the surface of Saccharomyces cerevisiae. The display system was further optimized by re-directing fatty acid pools from lipid droplet synthesis toward formation of membrane precursors via knock-out of PAH1. This resulted in an up to 4.2-fold improvement with respect to the baseline strain. Finally, we observed cellobiose-dependent signal amplification of the system with an increase in enzymatic activity of up to 3.1-fold when cellobiose was added.

Mulch-derived microplastic aging promotes phthalate esters and alters organic carbon fraction content in grassland and farmland soils

Agricultural plastic mulch is a major microplastics (MPs) source in terrestrial ecosystems. However, knowledge about the aging characteristics of mulch-derived MPs entering natural and agricultural soils and their effects on phthalate esters (PAEs) and organic carbon fractions is still limited. Black (contains black masterbatches) and white polyethylene (PE) and biodegradable (Bio, Poly propylene carbonate and Polybutylene adipate terephthalate synthetic material (PPC+PBAT)) mulch-derived MPs, at 0.3% (w/w) dose, were added to grassland and farmland soils for eight-week incubation. Microplastic (MP) aging degree was explored by quantifying the carbonyl index (CI). The soil PAEs and organic carbon fractions were also analyzed. After incubation, black and white PE-MP aged greater in farmland than in grassland. PAEs accumulated highest in PE-MP treatment (5.27–6.41 mg kg−1) followed by Bio-MP (1.88–2.38 mg kg−1). Soil organic carbon (SOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) were reduced by 5.3%–8.2%, 31.8%–41.6%, and 39.7%–63.0%, dissolved organic carbon (DOC) was increased by 10.1%–27.6% in grassland containing MP compared to control. MPs’ aging degree promoted PAEs content or altered nutrients, then regulated soil microbial biomass and extracellular enzyme activity directly or indirectly, ultimately affecting SOC. Environmental implicationMicroplastics are persistent environmental pollutants that gradually undergo surface aging in response to extracellular enzymes secreted by microorganisms. As microplastics age, their surface roughness and functional groups change; thus, organochemical contaminants gradually leach out. Therefore, this study analyzed the aging of mulch film-derived microplastics under the action of diverse microorganisms in farmland and grassland soils and the effect on plasticizer and organic carbon fractions. The results proved that polyethylene microplastic aging degree was highest in farmland soil. Besides, biodegradable microplastic caused lower contamination of phthalate esters than polyethylene, but they affected soil carbon balance in grassland and farmland soils. Statement of environmental implicationThis study highlights that MPs affect organic carbon fractions by influencing the PAEs, available nutrients, and extracellular enzyme activity.

Regulation of straw decomposition and its effect on soil function by the amount of returned straw in a cool zone rice crop system

The degradation process of returned straw in rice fields can improve soil organic matter and promote sustainable agriculture. The degradation process of returned straw is a humification process as well as a mineralization process involving microorganisms and enzymes. However, the degradation process of returned straw, the effect on straw decomposing microorganisms and the regulatory mechanism on potential functionality under cool climate flooding conditions are currently unknown.For this purpose, we investigated the biodegradation of straw from a biodegradation point of view at 20, 40, 71, 104, and 137 d after return under conventional (130 kg hm−2), 1/3 straw return (2933 kg hm−2), 2/3 straw return (5866 kg hm−2), and full straw return (8800 kg hm−2) applications in cool climate rice fields.. The test found Paludibacteraceae and Archaeaceae were the dominant bacteria for straw degradation, and their relative abundance was highest when 2/3 of straw was returned to the field. The straw degradation extracellular enzyme activity was higher in the late return period (104 d). At this time, the potential functionality of the soil differed significantly among the different return amounts, with the best extracellular enzyme activity and potential functionality at the 2/3 straw return amount. Therefore, the optimal amount of rice straw returned to the field is 5866 kg hm−2 at the current conventional N application rate (130 kg hm−2) in the cold zone.

Biodegradation of Glyphosate in Aqueous Medium by Strain JAN3 Aspergillus tubingensis isolated from Agricultural Soil

The use of glyphosate has raised a major concern among researchers around the world because of its adverse effects and toxic nature. In the present study, the enrichment technique was used to isolate the strain JAN3 Aspergillus tubingensis from agricultural soil. The ability of the isolate to utilize glyphosate as the sole carbon and energy source was evaluated using HPLC and FTIR. The results revealed that the strain JAN3 could mineralize 96% of glyphosate within 5 days of incubation. The infrared spectrum of standard glyphosate when compared to degradation by strain Aspergillus tubingensis showed the absence of peak for major functional groups which could be due to the breakdown of the compound into simpler structures. IR spectra of the degraded sample showed the presence of an aldehyde group and carboxylic acid which confirmed that glyphosate was mineralized by the strain JAN3. The degradation results were further fitted into different kinetic models and the results showed that the reaction followed pseudo first order kinetics. The extracellular enzymatic activity was analysed during glyphosate degradation. The results of the study highlight that the strain Aspergillus tubingensis may have the potential to mineralize high concentrations of the herbicide in the contaminated areas.