Extracellular Enzyme Activities Research Articles

The expansion of evergreen and deciduous shrubs changed the chemical characteristics and biological community of alpine meadows soil

Global warming drives shrubs expansion. However, it is unclear how shrubs expansion affect the nutrients cycling, decomposer diversity and activity of alpine meadows. We selected two dominant shrub species in an alpine forest-Tundra ecotone on the eastern Tibetan Plateau: Rhododendron lapponicum (evergreen shrubs), and Sorbus rufopilosa (deciduous shrubs), the shrub-free tundra site as the control site. The fauna community diversity, microbial biomass, extracellular enzyme activity and enzyme stoichiometry of organic soil and mineral soil layer were determined to explore the effects of shrubs expansion. The soil total nitrogen, microbial biomass carbon and nitrogen, and some extracellular enzyme activity of the two shrubs were higher than those in CK. In addition, deciduous shrub expansion had a stronger effect on meadows ecosystem process than evergreen shrub expansion. However, both of them may alleviate the limitation of nitrogen and phosphorus in alpine meadows ecosystem, and the expansion of evergreen shrubs may also contribute to the accumulation of particulate organic matter. It is of great significance to probe the biogeochemical cycle of alpine meadows ecosystems under climate change.

Decreased Soil Microbial Nitrogen Under Vegetation ‘Shrubification’ in the Subarctic Forest–Tundra Ecotone: The Potential Role of Increasing Nutrient Competition Between Plants and Soil Microorganisms

The consequences of warming-induced ‘shrubification’ on Arctic soil carbon storage are receiving increased attention, as the majority of ecosystem carbon in these systems is stored in soils. Soil carbon cycles in these ecosystems are usually tightly coupled with nitrogen availability. Soil microbial responses to ‘shrubification’ may depend on the traits of the shrub species that increase in response to warming. Increase in deciduous shrubs such as Betula nana likely promotes a loss of soil carbon, whereas the opposite may be true if evergreen shrubs such as Empetrum hermaphroditum increase. We analyzed soil organic matter stocks and 13C NMR fractions, microbial CO2 respiration, biomass, extracellular enzyme activities (EEAs), and their association with shrub density in northern Sweden after 20 years of experimental warming using open top chambers (OTCs). Our study sites were located in a tundra heath that stores high soil carbon quantities and where the OTCs had increased deciduous shrubs, and in a mountain birch forest that stores lower soil carbon quantities and where the OTCs had increased evergreen shrubs. We predicted that organic matter stocks should be lower and respiration and EEAs higher inside the OTCs than untreated plots in the tundra, whereas no effect should be detected in the forest. Soil organic matter stocks and 13C NMR fractions remained unaffected at both sites. When expressed as per gram microbial biomass, respiration and EEAs for carbohydrate and chitin degradation were higher inside the OTCs, and contrasting our prediction, this effect was stronger in the forest. Unexpectedly, the OTCs also led to a substantially lower microbial biomass carbon and nitrogen irrespective of habitat. The decline in the microbial biomass counteracted increased activities resulting in no effect of the OTCs on respiration and a lower phenol oxidase activity per gram soil. Microbial biomass nitrogen correlated negatively with evergreen shrub density at both sites, indicating that ‘shrubification’ may have intensified nutrient competition between plants and soil microorganisms. Nutrient limitation could also underlie increased respiration per gram microbial biomass through limiting C assimilation into biomass. We hypothesize that increasing nutrient immobilization into long-lived evergreen shrubs could over time induce microbial nutrient limitation that contributes to a stability of accumulated soil organic matter stocks under climate warming.

Effects of 24 Years Different Straw Return on Soil Carbon, Nitrogen, Phosphorus, and Extracellular Enzymatic Stoichiometry in Dryland of the Loess Plateau, China

Exploring the biogeochemical cycle characteristics of soil carbon, nitrogen, and phosphorus in farmland in the dryland of the loess plateau can provide scientific basis and technical support for efficient crop production and sustainable land use. Here, based on a long-term (24 year) straw return field experiment in Shouyang, Shanxi province, the effects of different straw return regimes, i.e., straw mulching (SM), direct straw return (DS), animal-digested straw return (AS), and non-straw return (CK), on the stoichiometric ratio of soil elements and extracellular enzyme activities were studied. The vector angle and length were calculated to indicate the resource constraints faced by microorganisms. The vector angle was greater than 45° and less than 45°, indicating that microorganisms were limited by phosphorus and nitrogen, respectively. The greater the deviation from 45°, the greater the degree of limitation, and the longer the vector length, the more severely limited by carbon. The results showed that ① the soil C/N and C/P of long-term straw returning ranged from 9.81 to 14.28 and from 14.58 to 21.92, with the mean values of 12.36 and 17.51, respectively, which were 6.0% and 4.2% lower than that at the initial stage of the experiment. The soil N/P was distributed between 1.27 and 1.57, with an average of 1.42, which was 2.2% higher than that in the initial stage. The soil C/N and C/P ratios showed a trend of first decreasing and then increasing, the soil N/P ratio basically showed a flat trend, and there was no significant difference in soil element metering ratios between different straw returning treatments. ② Compared with the 24-year long-term non-straw return treatment, the activities of β-1,4-glucosidase (BG) and β-1,4-N-acetylglucosaminidase (NAG) in the soil of the long-term straw mulching treatment increased by 134.4% and 107.5% (P<0.05), the activities of BG and alkaline phosphatase (AP) in the soil of the long-term straw mulching treatment decreased by 59.3% and 59.5% (P<0.05), respectively, and the activities of NAG in the soil of the long-term straw mulching treatment increased by 102.8% (P<0.05). Under the long-term straw returning treatment, soil microorganisms were faced with carbon and phosphorus limitation as a whole. Long-term straw mulching aggravated microbial carbon limitation, and animal-digested straw return could alleviate the degree of carbon limitation. Compared with that in the 24-year long-term non-straw return treatment, soil EEAC/N could be significantly reduced by the animal-digested straw return treatment, and soil EEAC/P could be increased by the direct straw return treatment. The three straw returning methods had no significant indigenous effect on soil EEAN/P. The overall vector angle was greater than 45°, and the vector length increased by 3.8%-20.1% compared with that in the initial stage. ③ Correlation analysis showed that C and N inputs were significantly negatively correlated with BG activity; available nitrogen was significantly correlated with NAG activity, AP activity, and EEAC/N; C/P was significantly positively correlated with EEAC/N; there were significant correlations between N/P and NAG activity, AP activity, EEAC/N, and EEAC/P; and there was no significant correlation between EEAN/P and any environmental factors. In conclusion, the availability of soil nitrogen and phosphorus elements and N/P ratio had significant effects on soil extracellular enzyme activity and stoichiometric characteristics under different long-term straw returning treatments. In the future, more attention should be paid to the improvement of organic carbon and the promotion of nitrogen and phosphorus availability in farmland soil in soil-efficient cultivation and agricultural production activities.

Methylparaben toxicity and its removal by microalgae Chlorella vulgaris and Phaeodactylum tricornutum

The widespread occurrence of methylparaben (MPB) has aroused great concern due to its weak estrogenic endocrine-disrupting property and potential toxic effects. However, the degradation potential and pathway of MPB by microalgae have rarely been reported. Here, microalgae Chlorella vulgaris and Phaeodactylum tricornutum were used to investigate their responses, degradation potential and mechanisms towards MPB. MPB showed low-dose stimulation (by 86.02 ± 0.07% at 1 mg/L) and high-dose inhibition (by 60.17 ± 0.05% at 80 mg/L) towards the growth of C. vulgaris, while showed inhibition for P. tricornutum (by 6.99 ± 0.05%−20.14 ± 0.19%). The degradation efficiencies and rates of MPB were higher in C. vulgaris (100%, 1.66 ± 0.54–5.60 ± 0.86 day−1) than in P. tricornutum (4.3–34.2%, 0.04 ± 0.01–0.08 ± 0.00 day−1), which could be explained by the significantly higher extracellular enzyme activity and more fluctuation of the protein ratio for C. vulgaris, indicating a higher ability of C. vulgaris to adapt to pollutant stress. Biodegradation was the main removal mechanism of MPB for both the two microalgae. Furthermore, two different degradation pathways of MPB by the two microalgae were proposed. MPB could be mineralized and completely detoxified by C. vulgaris. Overall, this study provides novel insights into MPB degradation by microalgae and strategies for simultaneous biodegradation and detoxification of MPB in the environment.

Self-Regulation of Soil Enzyme Activity and Stoichiometry under Nitrogen Addition and Plastic Film Mulching in the Loess Plateau Area, Northwest China

Soil extracellular enzyme activity (EA) and its eco-enzyme stoichiometric ratio (ES) are extremely sensitive to environmental change. This study aimed to clarify the change law of EA and ES in soil with different nitrogen addition levels under plastic film mulching, and to optimize the application amount of nitrogen fertilizer that was used. Based on the location experiment of plastic film mulching fertilization that has been ongoing since 2015, soil samples were collected from different depths (0–10 cm, 10–20 cm and 20–30 cm) during the harvest period of spring maize in October 2021. Four soil extracellular enzyme activities (β-1,4 glucosidase (βG), β-1, 4-N-acetylglucosidase (NAG), leucine aminopeptidase (LAP) and alkaline phosphatase (AP)) involved in soil carbon (C), nitrogen (N) and phosphorus (P) cycling at different nitrogen application levels (0, 90, 150, 225 and 300 kg·hm−2) were studied under two planting patterns of no plastic film mulching (LD) and plastic film mulching (PM). The latest discovery of this study is that the activities of soil EA involved in the cycling of soil carbon C, N and P are similar in different soil depths (0–10 cm, 10–20 cm and 20–30 cm). Both EC:P and EC:P in the soil in this area are less than 1:1, indicating that the soil is limited by N and P. Comprehensive analysis showed that a nitrogen application level of 225 kg·hm−2 was beneficial to the balance of soil nutrients and the improvement of soil EA at harvest. At the same time, PM can effectively improve the soil EA and is more conducive to the balance of soil nutrients. Redundancy analysis (RDA) showed that EA and ES were strongly correlated with pH, soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP). Most importantly, this study revealed that the activity of extracellular enzymes in arid and semi-arid areas was constantly self-regulated with the addition of nitrogen, which provided theoretical and technical support for the efficient use of nitrogen under the condition of plastic film mulching.

Characterization of fliR-deletion mutant ΔfliR from Vibrio alginolyticus and the evaluation as a live attenuated vaccine.

Vibrio alginolyticus is the common pathogen affecting various species of marine organisms. It has been demonstrated that fliR is a necessary virulence factor to adhere and infect their hosts for pathogenic bacteria. Frequent disease outbreaks in aquaculture have highlighted the necessity of developing effective vaccines. In the present study, in order to investigate the function of fliR in V.alginolyticus, the fliR deletion mutant ΔfliR was constructed and its biological properties were evaluated, additionally, the differences in gene expression levels between wild-type and ΔfliR were analyzed by transcriptomics. Finally, ΔfliR was used as a live attenuated vaccine to immunize grouper via the intraperitoneal route to evaluate its protective effect. Results show that fliR gene of V. alginolyticus was identified as being 783 bp in length, encoding 260 amino acids, and showing significant similarity to homologs of other Vibrio species. The fliR-deletion mutant ΔfliR of V. alginolyticus was successfully constructed, and its biological phenotype analysis showed no significant differences in growth capacity and extracellular enzyme activity compared to the wild-type. However, a substantial reduction of motility ability was detected in ΔfliR. Transcriptomic analysis revealed that the absence of fliR gene is responsible for a significantly decreased expression of flagellar genes, including flaA, flaB, fliS, flhB and fliM. The fliR-deletion mainly affects the related pathways involved in cell motility, membrane transport, signal transduction, carbohydrate metabolism, and amino acid metabolism in V. alginolyticus. The efficacy of ΔfliR as a candidate of live attenuated vaccine were evaluated by intraperitoneal injection in grouper. The ΔfliR provided the RPS (Relative protection rate) of 67.2% against V. alginolyticus in groupers. The ΔfliR efficiently stimulated antibody production with specific IgM still detected at 42d post-vaccination, and significantly elevated the activity of antioxidant enzymes like Catalase (CAT), Superoxide dismutase (SOD), and lactate dehydrogenase (LDH) in the serum. The higher expression levels of immune-related genes were observed in the immune tissues of inoculated grouper compared to the control. In conclusion, ΔfliR effectively improved the immunity of inoculated fish. The results suggest that ΔfliR is an effective live attenuated vaccine against vibriosis in in grouper.

Extracellular enzyme activity in the coastal upwelling system off Peru: a mesocosm experiment

Abstract. The Peruvian upwelling system is a highly productive ecosystem with a large oxygen minimum zone (OMZ) close to the surface. In this work, we carried out a mesocosm experiment off Callao, Peru, with the addition of water masses from the regional OMZ collected at two different sites simulating two different upwelling scenarios. Here, we focus on the pelagic remineralization of organic matter by the extracellular enzyme activity of leucine aminopeptidase (LAP) and alkaline phosphatase activity (APA). After the addition of the OMZ water, dissolved inorganic nitrogen (N) was depleted, but the standing stock of phytoplankton was relatively high, even after N depletion (mostly &gt; 4 µg chlorophyll a L−1). During the initial phase of the experiment, APA was 0.6 nmol L−1 h−1 even though the PO43- concentration was &gt; 0.5 µmol L−1. Initially, the dissolved organic phosphorus (DOP) decreased, coinciding with an increase in the PO43- concentration that was probably linked to the APA. The LAP activity was very high, with most of the measurements in the range of 200–800 nmol L−1 h−1. This enzyme hydrolyzes terminal amino acids from larger molecules (e.g., peptides or proteins), and these high values are probably linked to the highly productive but N-limited coastal ecosystem. Moreover, the experiment took place during a rare coastal El Niño event with higher than normal surface temperatures, which could have affected enzyme activity. Using a nonparametric multidimensional scaling analysis (NMDS) with a generalized additive model (GAM), we found that biogeochemical variables (e.g., nutrient and chlorophyll-a concentrations) and phytoplankton and bacterial communities explained up to 64 % of the variability in APA. The bacterial community best explained the variability (34 %) in LAP. The high hydrolysis rates for this enzyme suggest that pelagic N remineralization, likely driven by the bacterial community, supported the high standing stock of primary producers in the mesocosms after N depletion.

Evaluation of drought-tolerant endophytic fungus Talaromyces purpureogenus as a bioinoculant for wheat seedlings under normal and drought-stressed circumstances.

The present work is aimed to hypothesize that fungal endophytes associated with wheat (Triticum aestivum L.) plants can play a variety of roles in biotechnology including plant growth. Out of 67 fungal isolates, five maximum drought-tolerant isolates were used to check their various plant growth-promoting traits, antioxidants, and antifungal activities under secondary screening. Fungal isolate #8TAKS-3a exhibited the maximum drought tolerance capacity and potential to produce auxin, gibberellic acid, ACC deaminase, phosphate, zinc solubilization, ammonia, siderophore, and extracellular enzyme activities followed by #6TAKR-1a isolate. In terms of antioxidant activities, #8TAKS-3a culture also showed maximum DPPH scavenging, total antioxidant, and NO-scavenging activities. However, #6TAKR-1a exhibited maximum total flavonoid content, total phenolic content, and Fe-reducing power and also the highest growth inhibition of Aspergillus niger (ITCC 6152) and Colletotrichum sp. (ITCC 6152). Based on morphological characters and multi-locus phylogenetic analysis of the nuc rDNA internal transcribed spacer region (ITS1-5.8S-ITS2 = ITS), β-tubulin (TUB 2), and RNA polymerase II second largest subunit (RPB2) genes, potent fungal isolate #8TAKS-3a was identified as Talaromyces purpureogenus. Under the in vitro conditions, T. purpureogenus (#8TAKS-3a) was used as a bioinoculant that displayed a significant increase in various physio-biochemical growth parameters under normal and stressed conditions (p < 0.05). Our results indicate that drought stress-tolerant T. purpureogenus can be further used for field testing as a growth promoter.

Impacts of microplastics and heavy metals on the earthworm Eisenia fetida and on soil organic carbon, nitrogen, and phosphorus

Microplastics (MPs) are increasingly being studied because they have become ubiquitous in aquatic and terrestrial environments. However, little is known about the negative effects of co-contamination by polypropylene microplastic (PP MPs) and heavy metal mixtures on terrestrial environment and biota. This study assessed the adverse effects of co-exposure to PP MPs and heavy metal mixture (Cu2+, Cr6+, and Zn2+) on soil quality and the earthworm Eisenia fetida. Soil samples were collected in the Dong Cao catchment, near Hanoi, Vietnam, and analyzed for changes in extracellular enzyme activity and carbon, nitrogen, and phosphorus availability in the soil. We determined the survival rate of earthworms Eisenia fetida that had ingested MPs and two doses of heavy metals (the environmental level - 1 × - and its double - 2 ×). Earthworm ingestion rates were not significantly impacted by the exposure conditions, but the mortality rate for the 2 × exposure conditions was 100%. Metal-associated PP MPs stimulated the activities of β-glucosidase, β-N-acetyl glucosaminidase, and phosphatase enzymes in soil. Principle component analysis showed that these enzymes were positively correlated with Cu2+ and Cr6+ concentrations, but negatively correlated with microbial activity. Zn2+ showed no correlation with soil extracellular enzyme activity or soil microbial activity. Our results showed that co-exposure of earthworms to MPs and heavy metals had no impact on soil nitrogen and phosphorus but caused a decrease in total soil carbon content, with a possible associated risk of increased CO2 emissions.

Isolation, functional evaluation of probiotic properties and molecular identification of strains isolated from Iranian poultry's gut.

The use of probiotics as an alternative to antibiotics in poultry diets has attracted a lot of interest recently. In this context, the determination of probiotic characteristics was evaluated on several isolates obtained from Iranian poultry's gut. Probiotic characteristics such as hemolysis activity, acid, bile, gastric juice tolerate, in vitro adhesion assay, cell surface properties (hydrophobicity, auto-aggregation and co-aggregation) and antibiotic susceptibility test were evaluated. Finally, selected isolates identified molecularly after temperature-salt tolerance and extracellular enzyme activity (amylase, protease and cellulose). Out of 362 strains isolated from native poultry in three geographical regions of Iran, nine strains (belong to Bacillus sp., Enterococcus sp., Pediococcus sp., Lactobacillus sp., Kluyveromyces sp.) showed resistance against gastrointestinal physiological conditions, desirable surface properties, ability to adhere to epithelial intestine cell line and antibiotic susceptibility. Also, these strains were discovered to be temperature-salt tolerant but, only a small number of them were able to produce hydrolase enzymes. According to the results, the selected strains can be introduced as native probiotic candidates for utilization in novel poultry feeds.

Penicillium citrinum, a Drought-Tolerant Endophytic Fungus Isolated from Wheat (Triticum aestivum L.) Leaves with Plant Growth-Promoting Abilities.

Endophytic fungi have recently garnered significant attention as next-generation bioinoculants due to their plausible role in ameliorating abiotic and biotic stresses. This adaptation is achieved via various signalling molecules and mechanisms established by these symbionts with their hosts. The present study screened 61 endophytic isolates of culturable mycobiome associated with wheat variety PBW725 during their crop cycle. Three endophytic isolates exhibited a minimum reduction in their growth and maximum biomass production during the drought stress developed using polyethylene glycol 6000. Further, these isolates also exhibited plant growth promoting properties by virtue of the production of indole acetic acid, gibberellic acid and ammonia. These isolates also exhibited the propensity to solubilise phosphate and zinc, produce siderophores and further exhibit extracellular enzymatic activities, contributing to plants' adaptability to abiotic stresses. The best isolate amongst the three was #5TAKL-3a, identified as Penicillium citrinum based on multilocus phylogenetic analysis. The isolate as a bioinoculant enhances various biochemical and physiological properties in planta. Hence our studies indicate that Penicillium citrinum #5TAKL-3a is a potential candidate bioinoculant for field trials to improve the adaptability of the wheat plant under drought stress.

Ecoenzymatic stoichiometry reveals soil P limitation under biochar addition in a reclaimed mine area in Shanxi Province, China

Extracellular enzymatic activity plays an important role in carbon (C), nitrogen (N), and phosphorous (P) cycling, and consequently, serves as an indicator for soil function. However, microbial activities are inhibited in degraded lands due to nutrition limitations, which pose a challenge to ecological management. We investigated the effects of maize biochar addition (1, 3, and 5%) on soil and enzyme stoichiometries in a post‐mining area in Shanxi province. The results showed that soil organic C and total N increased significantly with increasing biochar addition, leading to significant increases in soil C:P (by 157.9%) and N:P (by 76.1%) under 5% of addition. Biochar addition stimulated enzyme activities significantly, and the maximum of enzyme activities occurred in treatment of 5% addition. Soil enzyme C:N increased significantly following biochar addition, while enzyme C:P and N:P decreased at 5% biochar addition. Vector analysis indicated that microbial activity tended to be limited by soil N before addition, whereas it was limited by P availability at high biochar addition. This was mainly because that biochar addition could promote sorption of P and lower P bioavailability in soil. Our research suggested that biochar application could substantially improve soil nutrition status and microbial activity in infertile land, however, it would likely result in imbalances between substrate stoichiometry and microbial demand. The result might provide a reference for the management of biochar application during soil restoration.

PacC mediated ammonia synthesis contributes to the pathogenicity of Trichothecium roseum by regulating reactive oxygen species and extracellular enzymes

The Pal signaling pathway plays an important role in the adaptation of pathogenic fungi to environmental pH fluctuations and consists of PalA, PalB, PalC, PalF, PalI, PalH and Pac C in filamentous fungi. As a key regulator of the Pal signaling pathway, the transcription factor PacC is involved in the regulation of ammonia synthesis, extracellular enzyme activity and pathogenicity of fungi. However, the effect of PacC on the Pal signaling pathway and the production of reactive oxygen species (ROS) in fungi is unknown. It is also unclear whether PacC is involved in the synthesis and transport of ammonia, the alkalinization of environmental pH and the regulation of extracellular enzyme gene expression in Trichothecium roseum. In this study, the wild-type strain, ΔPacC mutant and ΔPacC-C complement strains of T. roseum were used as material to analyze the role of TrPacC in the Pal pathway, ammonia accumulation and environmental pH regulation. Meanwhile, the effect of TrPacC on the pathogenicity of T. roseum was investigated by determining the production of ROS and the expression of extracellular enzyme genes. The results showed that deletion of TrPacC enhanced the pH signal perception and transduction by upregulating the expression of TrPalF and TrPalH, but downregulated the expression of TrPalC, TrPalA and TrPalB, which are involved in PacC activation. Deletion of TrPacC inhibited ammonia synthesis and secretion by downregulating the expression of TrGDH2, TrAMET, TrMEPB and TrGLT1, resulting in reduced ammonia accumulation and attenuated alkalization ability at ambient pH in vivo and in vitro. Deletion of TrPacC also reduced superoxide anion and hydrogen peroxide levels by downregulating TrNoxA expression, but had no significant effect on TrNoxB expression. In addition, deletion of TrPacC downregulated the expression of TrPG, TrPMG, TrPME, TrPL, TrPAL and TrCx and inhibited the lesion expansion of T. roseum on muskmelon and apple fruit. Taken together, deletion of TrPacC attenuated the pathogenicity of T. roseum in muskmelon and apple fruit by reducing the accumulation of ammonia and ROS and inhibiting the expression of extracellular enzyme genes.

Antagonistic, plant growth promoting and extracellular hydrolytic enzyme activity of fungal endophytes of Dioscorea bulbifera L.

Fungal endophytes can be considered as a new source of biological control and plant growth promoting agents. Moreover, the huge repertoire of extracellular enzymes produced by them has great biotechnological importance in medicine, agriculture and industry. The current study aimed at the assessment of plant growth promotion and biocontrol potential of endophytic fungal isolates associated with Dioscorea bulbifera L. for efficiently improved plant growth and protection of hosts from various infections. Overall, the experimental work revealed significant results where, 81% of the endophytic fungal isolates exhibited biocontrol potential against atleast one or more bacterial pathogens. The endophytic fungal isolate ARW2 (Clonostachys pseudochroleucha) was found to be highly effective against Gram positive bacteria whereas N4 (Parathyridaria percutanea) and H1B (Curvularia lunata) were effective against Gram negative bacteria. 52% of the endophytic fungal isolates were found to possess strong inhibition potential against fungal pathogens. H22 (F. proliferatum) and G8 (F. equiseti) demonstrated strong inhibition potential with percent inhibition ranging from 50 to 70%. The plant growth promoting activity of endophytic fungal isolates depicted that 52%, 27% and 2% isolates were capable of siderophore production, phosphate solubilisation and HCN production respectively. A quantitative estimation of IAA production revealed that almost all the isolates were producing IAA ranging from 1.2 to 200 μg/mL. Further assessment of extracellular enzymatic potential revealed that 37.5%, 31%, 18%, 12.5% and 4% of the endophytic fungal isolates exhibited activity positive results for amylase, lipolytic, protease, cellulolytic and chitinase activity, respectively. Our results indicate that these endophytic fungal isolated can be a promising source for future applications in medicine, agriculture and industry.

Shifting relationships between SOC and molecular diversity in soils of varied carbon concentrations: Evidence from drained wetlands

The molecular diversity of soil organic matter (SOM) is considered to be a critical factor influencing soil organic carbon (SOC) persistence, and is found to show a positive relationship with SOC in many upland soils with relatively low SOC concentrations. However, the SOM diversity-SOC relationship remains under-investigated in high-SOC soils such as wetlands, which exhibit divergent SOC accumulation mechanisms compared to upland soils and may induce contrasting shifts in SOM composition during drainage-induced SOC changes. Here we utilized three contrasting wetlands (i.e., two fens and a bog) that encompassed a wide SOC range and experienced decades of artificial drainage to investigate shifts in SOM diversity after drainage. The molecular diversity of SOM was assessed based on SOM pyrolysis products using pyrolysis–gas chromatography-mass spectrometry, and its influencing factors (including plant inputs, soil minerals, and extracellular enzyme activity, etc.) were evaluated. We observed divergent responses of SOM diversity to long-term drainage in the investigated wetlands. While SOM diversity increased with SOC concentration in the low-SOC (i.e., ≤ 60 mg g−1 soil) fen after drainage, it did not change in high-SOC (i.e., > 60 mg g−1 soil) wetlands after drainage regardless of SOC variations. While plant inputs (e.g., root mass) drove SOC accumulation in these wetlands, microbial processing rather than plant inputs dominated increases in SOM diversity, thereby resulting in the decoupling of SOC concentration and SOM diversity in high-SOC soils. These findings suggest that SOC and SOM diversity had a non-linear relationship in divergent soils. In organic-rich soils such as peatlands, SOM diversity did not increase with SOC accumulation after drainage, in contrast to low-SOC soils. Our study provides a novel, molecular diversity-based perspective on understanding wetland SOC stability in the context of drainage caused by increasing human activity and/or climate changes.

Coupling changes of soil functional gene abundances and extracellular enzyme activities across the diagnostic horizons of agricultural Isohumosols

Soil functional microbial taxa and extracellular enzymes are involved in a variety of biogeochemical cycling processes. Although many studies have revealed the vertical change patterns of microbial communities along soil profile, the general understanding of the coupling changes in the functional gene abundances (FGAs) and extracellular enzyme activities (EEAs) in soil profiles is still limited, which hinders us from revealing soil ecosystem processes. Herein, we comparatively investigated the FGAs and EEAs in the diagnostic horizons of soil profiles obtained from Ustic and Udic Isohumosols in northeast China based on quantitative real-time PCR (qPCR) and standard fluorometric techniques, respectively. Results showed that the distribution patterns of both FGAs and EEAs were significantly distinguished by two suborders of Isohumosols, and were also separated from A- to C-horizons. Additionally, the variations of EEAs and FGAs were greater in Udic Isohumosols compared to Ustic Isohumosols along soil profile, and greater changes were observed in C- than in A-horizons. The both FGAs and EEAs correspondently decreased along the soil profiles. However, when normalized by soil organic carbon, the specific EEAs were significantly increased in deep soil horizons, suggesting that microorganisms will input more resources to the production of enzymes to ensure microbial nutrient requirements under resource scarcity. More importantly, we revealed that soil microbial nutrient demands were limited by carbon and phosphorus, and the limitation significantly increased along soil profiles with a greater carbon limitation observed in Ustic Isohumosols than that in Udic Isohumosols. Overall, our findings provided solid evidences to link between FGAs, EEAs, and microbial nutrient limitations, which would be helpful for a better understanding of the ecosystem processes in the soil profile.

Effects of different sizes of polystyrene micro(nano)plastics on soil microbial communities

Micro(nano)plastic (MNP) pollution in soil environments is a major concern, but the effects of different sizes of MNPs on soil microbial communities, which are crucial in nutrient cycling, has not been well investigated. In this study, we aimed to determine the effects of polystyrene (PS) MNPs of different sizes (0.05-, 0.5-, and 5-μm) on soil microbial activity and community composition. Changes in inorganic N concentration, microbial biomass, and extracellular enzyme activities were determined in soils treated with 100 and 1000 μg PS MNPs g−1 soil during a 40-d incubation experiment. Soil microbial biomass was significantly lowered when soils were treated with 0.5- or 5-μm MNPs at 100 and 1000 μg PS MNPs g−1 soil. NH4+ concentration was higher in soils treated with 5-μm MNPs at 100 and 1000 μg g−1 soil than in the control soils at day 1, suggesting that MNPs inhibited the soil nitrification in short term. In contrast, extracellular enzyme activity was not altered by MNPs. The composition of microbial communities analyzed by Illumina MiSeq sequencing changed; particularly, the relative abundance of several bacteria related to N cycling, such as the genus Rhizomicrobium belonging to Alphaproteobacteria was decreased by 0.5- and 5-μm MNPs. Our study shows that the size of MNPs is an important factor that can determine their effects on soil microbial communities. Therefore, the size effects need to be considered in assessing the environmental impacts of MNPs.

Development of a Multicomponent Microbiological Soil Inoculant and Its Performance in Sweet Potato Cultivation.

The cultivation and consumption of sweet potato (Ipomoea batatas) are increasing globally. As the usage of chemical fertilizers and pest control agents during its cultivation may lead to soil, water and air pollution, there is an emerging need for environment-friendly, biological solutions enabling increased amounts of healthy crop and efficient disease management. Microbiological agents for agricultural purposes gained increasing importance in the past few decades. Our goal was to develop an agricultural soil inoculant from multiple microorganisms and test its application potential in sweet potato cultivation. Two Trichoderma strains were selected: Trichoderma ghanense strain SZMC 25217 based on its extracellular enzyme activities for the biodegradation of plant residues, and Trichoderma afroharzianum strain SZMC 25231 for biocontrol purposes against fungal plant pathogens. The Bacillus velezensis strain SZMC 24986 proved to be the best growth inhibitor of most of the nine tested strains of fungal species known as plant pathogens, therefore it was also selected for biocontrol purposes against fungal plant pathogens. Arthrobacter globiformis strain SZMC 25081, showing the fastest growth on nitrogen-free medium, was selected as a component with possible nitrogen-fixing potential. A Pseudomonas resinovorans strain, SZMC 25872, was selected for its ability to produce indole-3-acetic acid, which is among the important traits of potential plant growth-promoting rhizobacteria (PGPR). A series of experiments were performed to test the selected strains for their tolerance to abiotic stress factors such as pH, temperature, water activity and fungicides, influencing the survivability in agricultural environments. The selected strains were used to treat sweet potato in two separate field experiments. Yield increase was observed for the plants treated with the selected microbial consortium (synthetic community) in comparison with the control group in both cases. Our results suggest that the developed microbial inoculant has the potential to be used in sweet potato plantations. To the best of our knowledge, this is the first report about the successful application of a fungal-bacterial consortium in sweet potato cultivation.

Contributions of plant litter to soil microbial activity improvement and soil nutrient enhancement along with herb and shrub colonization expansions in an arid sandy land

Shrubs and herbs are two important types of vegetation that play a pivotal role in combating land desertification in arid sandy land. Yet, the effects of plant litter on sandy soil microbial activities and soil nutrients during the shrub and herb colonization process are still unclear. Here, contributions of plant litter to soil microbial activity improvement and soil nutrient enhancement along herb and shrub colonization expansion interfaces were studied in an arid sandy landscape. Plant litter mass, soil water content, pH, nutrient content, extracellular enzyme activities, and microbial community structure (taxon composition, α-diversity, β-diversity, and co-occurrence pattern) of soils at depths of 0–10 cm were examined relative to the colonization processes of shrubs and herbs (shrub and herb vegetation → sand-shrub and sand-herb interface → a sand dune) in an arid sandy land. We found that the processes of both herb and shrub colonization significantly increased litter cumulative mass at the soil surface to soil depths of 5 cm, and shrub colonization contributed several folds more litter than herb colonization. Plant litter input significantly decreased soil pH, accelerated soil extracellular enzyme activities, increased abundances of some microbial phyla (Actinobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, Patescibacteria, Armatimonadetes, Ascomycota, Moritierellomycota, and Chytridiomycota), enhanced both prokaryotic and fungal α-diversities, altered both prokaryotic and fungal communities, and promoted complexity of microbial networks during both herb and shrub colonization. As a result, microorganisms actively participated in litter decomposition and soil nutrient enhancement. Nevertheless, shrub colonization process exhibited greater potential in nutrient input than herb colonization process due to its greater plant litter input, though both colonization played a comparable role in accelerating soil enzyme activity and improving soil microbial community diversity and co-occurrence. Therefore, xeromorphic shrubs are still more important plants than herbs should be used for vegetation construction and ecological restoration in arid sandy land.

Mycoremediation with Agaricus bisporus and Pleurotus ostreatus growth substrates versus phytoremediation with Festuca rubra and Brassica sp. for the recovery of a Pb and γ-HCH contaminated soil

Mycoremediation with mushroom growth substrates can be used for the recovery of mixed contaminated soils due to the benefits derived from the physicochemical characteristics of the substrates, the activity of extracellular enzymes secreted by the fungi, and the presence of the fungal mycelia. The objective of this work was to assess the potential of Agaricus bisporus and Pleurotus ostreatus growth substrates (inoculated mushroom substrates vs. spent mushroom substrates) for the mycoremediation of soils co-contaminated with lead and lindane (γ-HCH). We compared the efficiency of these mycoremediation strategies with the phytoremediation with Brassica spp. Or Festuca rubra plants, in terms of both reduction in contaminant levels and enhancement of soil health. An enhanced soil health was achieved as a result of the application of mycoremediation treatments, compared to phytoremediation and control (untreated) treatments. The application of P. ostreatus inoculated substrate led to the most significant reduction in γ-HCH concentration (up to 88.9% compared to corresponding controls). In the presence of inoculated mushroom substrate, P. ostreatus fruiting bodies extracted more Pb than Brassica spp. Or F. rubra plants. Mycoremediation with P. ostreatus growth substrates appears a promising strategy for the recovery of the health of soils co-contaminated with Pb and γ-HCH.