Extracellular Enzyme Activities Research Articles

Understanding phosphorus mobilization mechanisms in acidic soil amended with calcium-silicon-magnesium-potassium fertilizer

Calcium-silicon-magnesium-potassium fertilizer (CSMP) is usually used as an amendment to counteract soil acidification caused by historical excessive nitrogen (N) applications. However, the impact of CSMP addition on phosphorus (P) mobilization in acidic soils and the related mechanisms are not fully understood. Specifically, a knowledge gap exists with regards to changes in soil extracellular enzymes that contribute to P release. Such a knowledge gap was investigated by an incubation study with four treatments: i) initial soil (Control), ii) urea (60 mg kg−1) addition (U); iii) CSMP (1%) addition (CSMP) and iv) urea (60 mg kg−1) and CSMP (1%) additions (U + CSMP). Phosphorus mobilization induced by different processes was distinguished by biologically based P extraction. The Langmuir equation, K edge X-ray absorption near-edge structure spectroscopy, and ecoenzyme vector analysis according to the extracellular enzyme activity stoichiometry were deployed to investigate soil P sorption intensity, precipitation species, and microbial-driven turnover of organophosphorus. Results showed that CaCl2 extractable P (or citric acid extractable P) content increased by 63.4% (or 39.2%) in the soil with CSMP addition, compared with the study control. The accelerated mobilization of aluminum (Al)/iron (Fe)-bound P after CSMP addition, indicated by the reduction of the sum of FePO4·2H2O and AlPO4 proportion, contributed to this increase. The decrease of P sorption capacity can also be responsible for it. The CSMP addition increased enzyme extractable P in the soil nearly 7-fold and mitigated the limitations of carbon (C) and P for soil microorganisms (indicated by the enzyme stoichiometry and ecoenzyme vector analysis), suggesting that microbial turnover processes also contribute to P mobilization in amended acidic soil. These findings indicate that the P mobilization in CSMP amended acidic soil not only attributed to both decreasing P sorption capacity and dissolving phosphate precipitation, but also to the increase of the microbial turnover of the organophosphorus pool.

Pulsed inputs of high molecular weight organic matter shift the mechanisms of substrate utilisation in marine bacterial communities.

Heterotrophic bacteria hydrolyze high molecular weight (HMW) organic matter extracellularly prior to uptake, resulting in diffusive loss of hydrolysis products. An alternative 'selfish' uptake mechanism that minimises this loss has recently been found to be common in the ocean. We investigated how HMW organic matter addition affects these two processing mechanisms in surface and bottom waters at three stations in the North Atlantic Ocean. A pulse of HMW organic matter increased cell numbers, as well as the rate and spectrum of extracellular enzymatic activities at both depths. The effects on selfish uptake were more differentiated: in Gulf Stream surface waters and productive surface waters south of Newfoundland, selfish uptake of structurally simple polysaccharides increased upon HMW organic matter addition. The number of selfish bacteria taking up structurally complex polysaccharides, however, was largely unchanged. In contrast, in the oligotrophic North Atlantic gyre, despite high external hydrolysis rates, the number of selfish bacteria was unchanged, irrespective of polysaccharide structure. In deep bottom waters (> 4000 m), structurally complex substrates were processed only by selfish bacteria. Mechanisms of substrate processing-and the extent to which hydrolysis products are released to the external environment-depend on substrate structural complexity and the resident bacterial community.

Role of an arbuscular mycorrhizal fungus in vegetation restoration as indicated by bacterial diversity and microbial metabolic limitation in soil underlying moss biocrusts

Arbuscular mycorrhizal (AM) fungi contribute to the revegetation of degraded ecosystems such as coal mining areas and may indirectly affect the development of biological soil crusts (biocrusts). However, bacterial diversity and microbial nutrient cycling in the soil underlying biocrusts are seldom considered when assessing ecological restoration effects. Bacterial community composition was quantified and compared using 16S rRNA gene sequencing, metabolic limitation of microbes via extracellular enzymatic stoichiometry and their association with carbon use efficiency (CUE) in soil underlying moss biocrusts in vegetated areas inoculated with an AM fungus or uninoculated and in uninoculated unvegetated areas. The AM fungal inoculum significantly influenced bacterial community composition and diversity, extracellular enzyme activities and CUE in soil underlying moss biocrusts mainly by affecting soil nutrients. Correlation analysis revealed that Actinobacteria, Armatimonadetes, Bacteroidetes, Chlorobi, Cyanobacteria, Saccharibacteria, and Verrucomicrobia were positively correlated with soil nutrients carbon (C), nitrogen (N) and phosphorus (P). A vector analysis of extracellular enzyme activity indicates that soil microbial communities underlying moss biocrusts were limited by P but microbial communities in areas inoculated with the AM fungus had the lowest relative P limitation. The alleviation of microbial P limitation increased the microbial CUE and bacterial phylum community and alpha diversity, leading to an increase in subsoil C content underlying moss biocrusts. This indicates that microbial communities in soil underlying moss biocrusts under in restoration areas containing the AM fungus were more stable under environmental stress, and the inclusion of AM fungal inoculation may be recommended as the preferred option for ecosystem restoration in arid and semi-arid coal mining areas.

Evaluation of farmland soil health and optimization of evaluation system under different green manure applications in a semi‐arid irrigation area

AbstractHealthy soil is essential for maintaining food security and enhancing ecosystem functions. Green manure application improves soil fertility and is an alternative to chemical fertilizers; however, research on optimizing soil health assessment systems and providing comprehensive and accurate information for local farmland green manure management models remains limited. In this study, we used maize and potato intercropped with green manure farmland in the main crop production area of a semi‐arid irrigation area in Northwest China as the research object, integrated the regional soil environment characteristics, and used principal component analysis and other methods to establish a minimum index data set including physicochemical, biological, and yield indices. A soil health assessment system applicable to the study region was constructed and optimized by drawing the scoring curve. The results showed that green manure treatment exerted a positive effect on the soil bulk density, nutrient content, extracellular enzyme activity, and the yield of maize and potato fields. This evaluation method showed that both green manure treatments could improve the soil health index of two major crop fields, with scores of 6.9 (3.7–8.6) and 6.2 (4.5–7.0) for maize and potato farmland, respectively, with a greater positive effect caused on maize. This evaluation system can not only reflect the soil conditions of farmland accurately given the application of green manure in the semi‐arid irrigation areas of northwest China but also provide reference for the promotion of organic fertilizers such as green manure and the resolution of regional soil health differences.

Stochastic processes dominated the soil bacterial community assemblages along an altitudinal gradient in boreal forests

Soil bacteria, as integral components of the soil microbial community, play pivotal roles in biogeochemical cycles and ecosystem functions in boreal forests. The altitudinal patterns of soil bacteria have been widely reported, but their community assembly is uncertain. Here, we investigated the soil bacterial community attributes (diversity, taxonomic and functional composition, and bacterial interactions) and ecological processes associated with community assembly on Mt. Oakley in the northern Greater Khingan Mountains via Illumina MiSeq sequencing and functional annotation tools. The alpha diversity indices of the soil bacteria exhibited a progressively decreasing trend with increasing altitude across seasons. The relative abundance of the dominant bacterial taxa was more sensitive to altitude than to season. More complex (more nodes and links) bacterial interactions were detected at the lowest and highest altitudinal sites, as well as in September. The variations in the taxonomic and functional compositions of the soil bacteria induced by altitude were mainly driven by the variations in soil pH and extracellular enzyme activities. Stochastic (dispersal limitation and drift) processes largely controlled the soil bacterial community assemblages across spatiotemporal scales. The community assemblages of soil bacteria were affected by altitude-induced changes in the taxonomic composition and functional groups. Collectively, our results have significant implications for understanding bacterial biogeography and community assembly mechanisms along altitudinal gradients in boreal forest ecosystems.

Alterations in the composition and metabolite profiles of the saline-alkali soil microbial community through biochar application

Saline-alkali soil poses significant chanllenges to sustainable development of agriculture. Although biochar is commonly used as a soil organic amendment, its microbial remediation mechanism on saline-alkali soil requires further confirmation. To address this, we conducted a pot experiment using cotton seedlings to explore the potential remediation mechanism of rice straw biochar (BC) at three different levels on saline-alkaline soil. The results showed that adding of 2% biochar greatly improved the quality of saline-alkaline soil by reducing pH levels, electrical conductivity (EC), and water-soluble ions. Moreover, biochar increased the soil organic matter (SOM), nutrient availability and extracellular enzyme activity. Interestingly, it also reduced soil salinity and salt content in various cotton plant tissues. Additionally, biochar had a notable impact on the composition of the microbial community, causing changes in soil metabolic pathways. Notably, the addition of biochar promoted the growth and metabolism of dominant salt-tolerant bacteria, such as Proteobacteria, Bacteroidota, Acidobacteriota, and Actinobacteriota. By enhancing the positive correlation between microorganisms and metabolites, biochar alleviated the inhibitory effect of salt ions on microorganisms. In conclusion, the incorporation of biochar significantly improves the soil microenvironment, reduces soil salinity, and shows promise in ameliorating saline-alkaline soil conditions.

The silicon regulates microbiome diversity and plant defenses during cold stress in Glycine max L.

With climate change, frequent exposure of bioenergy and food crops, specifically soybean (Glycine max L.), to low-temperature episodes is a major obstacle in maintaining sustainable plant growth at early growth stages. Silicon (Si) is a quasi-essential nutrient that can help to improve stress tolerance; however, how Si and a combination of cold stress episodes influence plant growth, plant physiology, and microbiome diversity has yet to be fully discovered. The soybean plants were exposed to cold stress (8-10°C) with or without applying Si, and the different plant organs (shoot and root) and rhizospheric soil were subjected to microbiome analysis. The plant growth, physiology, and gene expression analysis of plant defenses during stress and Si were investigated. We showed that cold stress significantly retarded soybean plants' growth and biomass, whereas, Si-treated plants showed ameliorated negative impacts on plant growth at early seedling stages. The beneficial effects of Si were also evident from significantly reduced antioxidant activities - suggesting lower cold-induced oxidative stress. Interestingly, Si also downregulated critical genes of the abscisic acid pathway and osmotic regulation (9-cis-epoxy carotenoid dioxygenase and dehydration-responsive element binding protein) during cold stress. Si positively influenced alpha and beta diversities of bacterial and fungal microbiomes with or without cold stress. Results showed significant variation in microbiome composition in the rhizosphere (root and soil) and phyllosphere (shoot) in Si-treated plants with or without cold stress exposures. Among microbiome phyla, Proteobacteria, Bacteroidota, and Ascomycota were significantly more abundant in Si treatments in cold stress than in control conditions. For the core microbiome, we identified 179 taxa, including 88 unique bacterial genera in which Edaphobacter, Haliangium, and Streptomyces were highly abundant. Enhanced extracellular enzyme activities in the cold and Si+cold treatments, specifically phosphatase and glucosidases, also reflected the microbiome abundance. In conclusion, this work elucidates cold-mediated changes in microbiome diversity and plant growth, including the positive impact Si can have on cold tolerance at early soybean growth stages - a step toward understanding crop productivity and stress tolerance.

Analyzing soil enzymes to assess soil quality parameters in long-term copper accumulation through a machine learning approach

Soil contamination by agrochemicals is a big concern for soil health and ecosystem functioning. This is especially true for non-degradable substances like heavy metals (HM) that, because of their long-term use, are reaching significant values today due to soil accumulation. Among agrochemicals, copper (Cu) has been important in fighting fungal diseases on perennial crops for centuries.Laboratory experiments can be useful to understand the highest potential toxic effect of Cu but need to reflect what happens with long-term application in a dynamic and living agroecosystem. This study uses multivariate data analysis and machine learning to investigate long-term Cu accumulation on soil quality parameters, especially soil extracellular enzymatic activities. We collected soil samples from 21 apple orchards in South Tyrol, Italy. The orchards had different concentrations of Cu. We took 315 samples in total and analyzed them for various soil properties. We also measured the concentrations of elements in apple leaves and the activities of soil extracellular enzymes. We depicted the effect of Cu on several enzymatic activities, shedding light on the effect of Cu on the soil microbial communities functionality. Our results show that Cu concentrations in the study area affect only phosphatase activity, showing effects above 60 mg kg−1 of available Cu. Protease activity was positively correlated with Cu, while soil organic matter and management mainly influenced the carbon (C) cycle enzymes. Phosphatase decrease could be of concern for the potential disruption of the Phosphorus (P) cycle in the soil and plays a role in plant nutrition, as seen by P concentration in apple trees' leaves.We demonstrated how machine learning can help interpret complex and multivariate environmental data and overcome some downsides of traditional statistical models.

Engineering the Tat-secretion pathway of Bacillus licheniformis for the secretion of cytoplasmic enzyme arginase.

The industrial bacterium Bacillus licheniformis has long been used as a microbial factory for the production of enzymes due to its ability to secrete copious amounts of native extracellular proteins and its generally regarded as safe (GRAS) status. However, most attempts to use B. licheniformis to produce heterologous and cytoplasmic enzymes primarily via the general secretory (Sec) pathway have had limited success. The twin-arginine transport (Tat) pathway offers a promising alternative for the extracellular export of Sec-incompatible proteins because it transports full, correctly folded proteins. However, compared to the Sec pathway, the yields of the Tat pathway have historically been too low for commercial use. To improve the export efficiency of the Tat pathway, we identified the optimal Tat-dependent signal peptides and increased the abundance of the Tat translocases, the signal peptidase (SPase), and the intracellular chaperones. These strategic modifications significantly improved the Tat-dependent secretion of the cytoplasmic enzyme arginase into the culture medium using B. licheniformis. The extracellular enzymatic activity of arginase showed a 5.2-fold increase after these modifications. Moreover, compared to the start strain B. licheniformis 0F3, the production of extracellular GFP was improved by 3.8 times using the strategic modified strain B. licheniformis 0F13, and the extracellular enzymatic activity of SOX had a 1.3-fold increase using the strain B. licheniformis 0F14. This Tat-based production chassis has the potential for enhanced production of Sec-incompatible enzymes, therefore expanding the capability of B. licheniformis as an efficient cellular factory for the production of high-value proteins. KEY POINTS: • Systematic genetic modification of Tat-pathway in B. licheniformis. • Significant enhancement of the secretion capacity of Tat pathway for delivery the cytoplasmic enzyme arginase. • A new platform for efficient extracellular production of Sec-incompatible enzymes.

Exploring the hidden treasures: Deep-sea bacterial community structure in the Bay of Bengal and their metabolic profile

Deep sea bacterial communities demonstrate remarkable adaptability to high-pressure environments coupled with low temperatures which has sparked curiosity about their diversity and exceptional metabolic pathways. Additionally, bacteria in the deep sea exert a substantial influence over various biogeochemical processes. To date, we have relatively very little information about the deep-sea bacterial communities and, they remain largely unexplored. We investigated the variability in the physicochemical conditions, heavy metals and their influence on deep-sea bacterial community structure across three different depths in the Bay of Bengal. The structural and metabolic diversity of deep-sea sediment microbial communities were examined through culture-based sequencing of 16S rRNA genes, ecto-enzymatic studies, and community-level physiological profiling. Bacillota was the most dominant phylum representing 61% of the cultured bacterial isolates, while the remaining belonged to Actinomycetota and Pseudomonodata. Five potential novel species belonging to the genera Fictibacillus, Lysinibacillus, Salinicola, Robertmurraya and Blastococcus were identified. The extracellular enzymatic activity was positive for >50% of the bacterial isolates, wherein the genera Bacillus and Micromonospora exhibited versatile profiles. High metabolic diversity was recorded through the carbon substrate utilization profiles indicating that microbial communities are active participants in biogeochemical cycles in the deep sea. The most prominently utilized carbon substrates were α-cyclodextrin, glucose-1-phosphate, D-xylose, glycogen, and 2-hydroxy benzoic acid which serve as organic substrates for microbial metabolism, facilitating the decomposition of organic matter and, recycling carbon in deep-sea ecosystems. Multivariate statistical analyses confirmed that the environmental variables had a profound influence on the bacterial community. The findings shed light on spatial variability in the bacterial community structure, enzyme activity and metabolic profiles, and enhance our understanding of Bay of Bengal deep-sea sedimentary microbial ecology.

Soil extracellular enzyme stoichiometry reveals the nutrient limitations in soil microbial metabolism under different carbon input manipulations

Changes in the quality and quantity of litter and root inputs due to climate change and human activities can influence below-ground biogeochemical processes in forest ecosystems. However, it is unclear whether and how much aboveground litter and root inputs affect soil microbial metabolism and nutrient limitation mechanisms. In this study, according to a 4-years field manipulation experiment, litter and root manipulations (control (CK), double litter input (DL), no litter (NL), no root (NR), and no inputs (NI)) were set up to analyze the extracellular enzyme activities and stoichiometric ratios characteristics of 0–10 cm and 10–20 cm soils, explore the metabolic limitations of microorganisms, and clarify the main driving factors restricting nutrient limitation. The results showed that the enzyme activities associated with the C cycling (β-1,4-glucosidase (BG), cellulose disaccharide hydrolase (CBH)) and N cycling (β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP)) in DL treatment were significantly higher than those in NR treatment. Moreover, enzyme activities related to P cycling are significantly higher in comparison to other treatments. The acid phosphatase (AP), which is related to the P cycle, showed the highest activity under NR treatment. In addition, there was no significant difference in soil microbial metabolic limitation by the different carbon inputs, which did not change the original nutrient limitation pattern. The main drivers of microbial nutrient metabolic limitation included soil physicochemical properties, soil total nutrients, and available nutrients, among which soil SWC and pH presented the greatest influence on microbial C limitation and soil total nutrients showed the greatest influence on microbial N limitation. Changes in soil carbon input altered soil extracellular enzyme activities and their stoichiometric ratios by affecting soil physicochemical properties, total nutrients. This study provides data for the understanding of material cycling in forest ecosystems under environmental change.

Crop residue heterogeneity: Decomposition by potential indigenous ligno-cellulolytic microbes and enzymatic profiling

The continuous depletion of fossil resources, energy-crisis and environmental pollution has gained popularity for careful selection of suitable microbial consortium to efficiently decompose crop residue and facilitate nutrient cycling. While crop residue is commonly incorporated into soil, the impact of the heterogeneity of residue on decomposition and biological mechanisms involved in extracellular carbon (C) cycle related enzyme activities remain not fully understood. To address this problem, an incubation study was conducted on chemical heterogeneity of straw and root residue with indigenous ligno-cellulolytic microbial consortium on extracellular enzymes as their activity is crucial for making in-situ residue management decisions under field condition. The activity of extracellular enzymes in different substrates showed differential variation with the type of enzyme and ranged from 16.9 to 77.6 µg mL−1, 135.7 to 410.8 µg mL−1, 66.9 to 177.1 µg mL−1 and 42.1 to 160.9 µg mL−1 for cellulase, xylanase, laccase and lignin peroxidase, respectively. Extracellular enzyme activities were sensitive to heterogeneity of biochemical constituent's present in straw and root residues and enhanced the decomposition processes with indigenous ligno-cellulolytic microbial consortium (Bacillus altitudinis, Streptomyces flavomacrosporus and Aspergillus terreus). Correlation matrix elucidated A. terreus and B. altitudinis as potential indigenous ligno-cellulolytic microbial inoculant influencing soil enzymatic activity (p < 0.001). This research work demonstrates a substantial impact of chemically diverse crop residues on the decomposition of both straw and root. It also highlights the pivotal role played by key indigenous decomposers and interactions between different microorganisms in governing the decomposition of straw and root primarily through release of extracellular enzymes. Consequently, it is novel bio-emerging strategy suggested that incorporation of the crop residues under field conditions should be carried out in conjunction with the potential indigenous ligno-cellulolytic microbial consortium for efficient decomposition in a short period of time under sustainable agriculture system.

Changes in soil organic carbon and microbial community in saline soil following different forms of straw incorporation

AbstractStraw has been commonly incorporated into soil to increase soil organic carbon (SOC) content. However, the response and mechanism of organic carbon transformation following the addition of different forms of straw to saline soil to have not been fully evaluated. Thus, in our study, chopped wheat straw, granular wheat straw and wheat straw biochar were used as exogenous organic amendments. The carbon‐to‐nitrogen ratio of each form of straw was adjusted to 25:1. Under the same amount of carbon input, the three forms of straw were added to saline soil for a one‐year incubation experiment. The research focused on studying the changes in SOC transformation, enzyme activity, and microbial community structure. At the end of incubation, both granular and biochar straw treatments had significantly increased SOC relative to the unamended control, with extent of SOC increase greater in the biochar straw treatment. The biochar straw treatment also had significantly higher dissolved organic carbon than the other treatments at end of the incubation. The enzyme activity of β‐cellobiohyrolase (CBH) was the highest in the granular straw treatment, which was increased by 71.9% compared with the chopped straw treatment (p &lt; 0.05). The cumulative carbon mineralization amount (Cum C) in the granular straw treatment was the highest, which was increased by 757.4% and 21.3% compared with the biochar straw and chopped straw treatments, respectively (p &lt; 0.05). The Mantel test analysis further revealed significant correlations between soil bacterial community and SOC content in soils treated with different straw incorporation forms, as well as between fungal community and extracellular enzyme activities. We assumed that a possible reason for the high SOC mineralization amount in the granular straw treatment was changing the structure of the Bacteroidota in the bacterial phylum and Blastocladiomycota in the fungal phylum. Based on these findings, it is believed that adding biochar can increase the SOC content, but its utilization by microorganisms is limited. However, applying granular straw will not have a negative impact on its use as a microbial carbon source, thereby promoting carbon transformation. Therefore, in future research aimed at enhancing soil fertility in saline soil regions, the adoption of granular straw as an agricultural practice is recommended and should be promoted.

Subsoil SOC increased by high C:N ratio straw application with optimized nitrogen supplementation

AbstractThe application of straw and nutrients to agricultural subsoils is of significant interest to enhance carbon (C) sequestration and soil fertility. However, little research has explored the effect straw application on microbial stoichiometry, soil organic carbon (SOC) mineralization and accumulation and their relationships, in subsoil. In order to address these knowledge gaps, we examined the soil characteristics (organic carbon mineralization, available nutrient contents and microbial stoichiometric ratio) under straw addition (maize leaf and stem) with and without nitrogen (N) supplementation (no addition, 30 mg N kg−1 dry soil−1, 60 mg N kg−1 dry soil−1) during an 80‐day incubation experiment. The microbial stoichiometric ratio imbalance (C:N and C:Phosphorus (P)) and extracellular enzyme stoichiometry were measured as indicators of the systematic relationship between soil resource availability and the mineralization of organic carbon. Our study demonstrated that the addition of straw significantly enhanced CO2 emissions and led to an increase in the C:N imbalance, while simultaneously decreasing microbial carbon use efficiency (CUE). In addition, stem addition showed 5.6% lower CUE, but 8.2% higher SOC compared with leaf addition. We also found that nitrogen addition to subsoil alleviated microbial nitrogen limitation. 60 mg N kg−1 dry soil rates of nitrogen application had a positive effect on reducing C:N imbalance and promoting the accumulation of SOC. Extracellular enzyme activity and microbial stoichiometric ratio were the most important controlling factors of SOC mineralization and microbial CUE, respectively. In conclusion, the application of straw alongside N to balance stoichiometric ratios can significantly increase SOC content, indicating the potential for carbon sequestration in agricultural subsoils.

Effect of drainage on microbial transformation processes of soil organic carbon in two typical wetlands of China

Wetlands store one third of global soil organic carbon (SOC) and are strongly affected by artificial drainage. The impact of drainage-induced water-table decline on carbon cycling in different wetlands, particularly microbial transformation processes, remains unclear. To address this knowledge gap, we collected soil samples from two typical wetlands of China (a nutrient-poor bog located in Dajiuhu and a nutrient-rich fen in Hongyuan) and conducted an incubation experiment with the addition of 13C-labeled glucose to analyze the effects of short- and long-term drainage on SOC decomposition, extracellular enzyme activity, microbial carbon use efficiency (CUE), and microbial carbon accumulation efficiency (CAE). The results showed that both short- and long-term drainage significantly increased SOC decomposition rates in both wetlands (from 1.47 μg C·g-1·h-1 in submerged soils to 2.47 μg C·g-1·h-1 in drained soils), microbial biomass carbon derived from glucose (from 0.21 mg C·g-1 to 1.00 mg C·g-1) and CAE (from 0.29 to 0.73), but did not alter CUE (ranging from 0.34 to 0.86). Long-term drainage increased α-glucosidase activity in the Dajiuhu wetland and decreased β-glucosidase and phenol oxidase activities in the Hongyuan wetland. In conclusion, drainage enhanced the 'microbial carbon pump' and its efficiency in wetlands mainly via increasing microbial intracellular metabolism (including respiration), but also acce-lerated SOC decomposition.

Soil microbial activity profiles associated with organic compost fertilizers in an urban garden

AbstractBiological soil health is recognized as an important component of sustainable agriculture due to microbial biomineralization of nutrients. However, soil health can be difficult to assess consistently across urban agricultural systems due to diverse land use histories, soil heterogeneity, and lack of mechanistic links to agricultural management practices (e.g., recycled compost addition) and crop outcomes. In this study, we characterized soil microbial activity profiles in an urban agriculture system in Minnesota, USA, including microbial abundance, soil respiration, extracellular enzyme activity, and crop yield. Garden plots were fertilized with recycled organic compost (either manure or municipal) at high or low rates (ranging from 2.6 to 39 tons ha−1) targeted to crop N and P demands. Control plots received inorganic fertilizer or no fertilizer. We found that a high application rate of manure compost supported 6–10x higher basal respiration than municipal compost or inorganic fertilizer. Enzyme activity data demonstrated that soil microbial communities exhibited unique profiles of biochemical function that varied among fertilizers of different compositions. Microbial biochemical function predicted 50% of the variability in bell pepper (Capsicum annuum) yield, while soil microbial community size alone was a poor predictor of yield. Yield was highest in plots fertilized with municipal compost, outperforming inorganic fertilizer by threefold. High‐yield plots exhibited higher ratios of N to P enzyme activity compared to those with lower yield. Our findings demonstrate that “more is better” may not necessarily be true regarding soil microorganisms in biological soil health, and that measures of soil microbial biochemical function may be more important.

Study on the Potential Probiotics Isolated from Marine Aquaculture System and Evaluation for Aquaculture Application

In recent years, more attention has been paid to the application of host‐associated microorganisms as an appropriate source of probiotics in aquaculture. These probiotics promoted effective colonization and application and provided better benefits than other sources. A total of 32 isolates were collected from the water, shrimp, and sediment of the cultured pond of Litopenaeus vannamei. Probiotic effects were comprehensively evaluated by extracellular enzyme activity, virulence genes detection, bacteriostatic activity, drug susceptibility test, tolerance to adverse environment, and challenge experiment. Six of these isolates exhibited bacteriostatic activity against pathogens, such as Vibrio cholerae, V. owensii, V. fluvialis, V. campbellii, V. rotiferianus, Photobacterium damselae, V. vulnificus, and V. parahaemolyticus. Using 16S rRNA gene sequencing analysis, isolates were identified as Bacillus subtilis (P8, P29, and P30), B. velezensis (P12), Prestia flexa (P21), and Cytobacillus firmus (P23). They were tolerant to high temperature, low acid (pH 2.0), bile salt (2%), and the simulated gastrointestinal environment, secreting phospholipase, amylase, protease, gelatinase, and lipase. They were sensitive to only two or fewer drugs among 27 antibacterial drugs and did not carry any of the tested virulence genes. Biosafety in vivo evaluations showed that they were safe for Ctenopharyngodon idella (P12 ＞ P23 ＝ P29 ＞ P8 ＞ P30 ＝ P21). The results suggest that P8, P12, P23, P21, P29, and P30 have high probiotic potential and can be used as good probiotics in aquaculture and the development of ecological preparations.

Effects of thinning on accumulation of soil microbial residue carbon of Picea asperata plantations in sub-alpine region of western Sichuan, China

Microbial residues are an important component of soil organic carbon (SOC). It is unclear how long-term thinning affects the accumulation characteristics of microbial residue carbon (C). We analyzed the differences in soil physicochemical properties, microbial communities, extracellular enzyme activities, and microbial residue C in topsoil (0-10 cm) and subsoil (20-30 cm) in Picea asperata plantation of non-thinned (control, 4950 trees·hm-2) and thinned for 14 years (1160 trees·hm-2) stands, aiming to reveal the regulatory mechanism of thinning on microbial residue C accumulation. The results showed that thinning significantly increased SOC content, total nitrogen content, available phosphorus content, the proportion of particulate organic C, soil water content, C-cycle hydrolase, and acid phosphatase activities, but significantly reduced the proportion of mineral-associated organic C. Thinning significantly affected the content of fungal and microbial residue C, and the contribution of microbial residue C to SOC, and these effects were independent of soil layer. The content of fungal and microbial residue C was 25.0% and 24.5% higher under thinning treatments. However, thinning significantly decreased the contribution of microbial residue C to SOC by 12.3%, indicating an increase in the proportion of plant-derived C in SOC. Stepwise regression analysis showed that total nitrogen and soil water content were key factors influencing fungal and micro-bial residue C accumulation. In summary, thinning promoted microbial residue C sequestration by altering soil pro-perties and changed the composition of SOC sources.

Biological evaluation of mangrove endophytic fungi Aspergillus terreus derived from Sonneratia alba

Mangroves represent highly diverse marine ecosystems, encompassing various vegetation such as shrubs, plants, trees, palms, and other plant forms that have adapted to thrive in both freshwater and saline environments. Within these mangrove ecosystems, secondary metabolites are present, contributing to various pharmacological functions and holding significant ecological importance. Endophytic fungi constitute a substantial and quantifiable portion of fungal biodiversity and are acknowledged for their impact on the composition and diversity of plant communities. This study aims to investigate the extracellular proteins and enzyme activity exhibited by endophytic fungi discovered in the leaves of Sonneratia alba mangroves collected in Buton, Southeast Sulawesi, Indonesia. The primary objective is to evaluate the compatibility of marine fungi with antibacterial and antioxidant activity. The research involves analyzing the biological activities of marine fungi containing cellulase enzyme through methods such as DNS for reducing sugar, protein concentration determination, antioxidant analysis, and total phenol content assessment. Sample A (shaker) has highest enzyme activity at Day 4 and Sample B has highest enzyme activity at Day 6 (static condition). The protein concentration in the purified cellulase from Aspergillus terreus surpassed that of crude enzyme extracts.

Land management of formerly subtropical Atlantic Forest reduces soil carbon stocks and alters microbial community structure and function

Soil carbon (C) sequestration has been proposed as one means to mitigate the effects of climate change and to guarantee food safety. However, forest conversion to managed land uses can deplete soil C stocks and affect soil microbial communities, potentially impacting a wide range of ecosystem services. Our objective was to investigate the effect of forest conversion to intensive land uses on soil C dynamics and soil microbial community structure and function in the subtropical portion of the Atlantic Forest biome. We evaluated four land uses - forest fragment, grassland, and agriculture with five or fifty years of cultivation. We analyzed soil C pools, edaphic variables, and soil bacterial/archaeal (16S) and fungal (ITS) communities. Forest conversion to managed land uses reduced soil C stocks and altered soil microbial community structure, with implications for soil C dynamics. Bacterial/archaeal and fungal community composition were strongly correlated with pH, base saturation, and calcium (Ca) and magnesium (Mg) content. However, soil C pools were not associated with potential extracellular enzyme activity or microbial diversity. Finally, the fungal species Mortierella minutissima ASV_1 and several bacterial groups were positively correlated with soil C stocks, potentially representing indicators of soil C storage. Our study indicates that land use change affects the interplay between soil microbial communities and soil C pools, with consequences to soil C storage. Our findings may support the development of soil C enhancement programs within the Atlantic Forest biome.