Extracellular Enzyme Activities Research Articles

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.

Responses of soil microbial biomass C:N:P stoichiometry to increased precipitation and nitrogen deposition in temperate shrublands

Increased precipitation and nitrogen (N) deposition have considerable impacts on soil microbial communities in terrestrial ecosystems, ultimately influencing the carbon (C) cycling. However, the specific effects of the interactions between increased precipitation and N deposition on C:N:P stoichiometry in soil microbial biomass remain unclear. A long-term (9 yr) manipulated experiment was conducted to investigate the responses of soil microbial biomass C:N:P stoichiometry to increased precipitation and N deposition of the Desert shrubland in Gurbantunggut, northwest China. The results demonstrated that increased precipitation elevated C, N, and C:N ratios of microbial biomass by 26.9%, 18.7%, and 6.8% relative to ambient precipitation, respectively. In comparison to ambient N deposition, N addition resulted in a 37.5% increase in soil microbial biomass N and a 6.8% increase in the N:P ratio. Particularly, the interactive effects between increased precipitation and N deposition on microbial biomass P and N:P ratio were significant. Moreover, the influences of increased precipitation and N addition on microbial biomass C:N:P stoichiometry primarily occurred through changes in dissolved organic carbon content and extracellular enzyme activities. The findings underscore the crucial role of increased precipitation as a stronger driving force for variations in microbial biomass C:N:P stoichiometry in arid ecosystems, compared to N deposition.

The Effects of Dietary Chromium Supplementation along with Discontinuing a High-Fat Diet on the Microbial Enzymatic Activity and the Production of SCFAs in the Faeces of Rats.

The present study assessed the changes in faecal microbial activity in obese Wistar rats fed high-fat or low-fat diets supplemented with various forms of chromium (picolinate or nanoparticles). The 18-week study was divided into two phases: an introductory period (9 weeks; obesity status induction via a high-fat diet) and an experimental period (9 weeks; maintained on a high-fat diet or switched to a low-fat diet and Cr supplementation). During the experimental period (10-18 weeks of feeding), samples of fresh faeces were collected on chosen days. The bacterial enzymatic activity and short-chain fatty acids (SCFAs) concentration were assessed to characterise the dynamism of the changes in faecal microbial metabolic activity under the applied dietary treatments. The results indicated that faecal microbial metabolic activity displayed several adaptation mechanisms in response to modifications in dietary conditions, and a beneficial outcome resulted from a pro-healthy dietary habit change, that is, switching from a high-fat to a low-fat diet. Dietary supplementation with chromium nanoparticles further modulated the aforementioned microbial activity, i.e., diminished the extracellular and total enzymatic activities, while the effect of chromium picolinate addition was negligible. Both the high-fat diet and the addition of chromium nanoparticles reduced SCFA concentrations and increased the faecal pH values.

Enhanced organic degradation and microbial community cooperation by inoculating Bacillus licheniformis in low temperature composting

Microbial activity and interaction are the important driving factors in the start-up phase of food waste composting at low temperature. The aim of this study was to explore the effect of inoculating Bacillus licheniformis on the degradation of organic components and the potential microbe-driven mechanism from the aspects of organic matter degradation, enzyme activity, microbial community interaction, and microbial metabolic function. The results showed that after inoculating B. licheniformis, temperature increased to 47.8°C on day 2, and the degradation of readily degraded carbohydrates (RDC) increased by 31.2%, and the bioheat production increased by 16.5%. There was an obvious enhancement of extracellular enzymes activities after inoculation, especially amylase activity, which increased by 7.68 times on day 4. The inoculated B. licheniformis colonized in composting as key genus in the start-up phase. Modular network analysis and Mantel test indicated that inoculation drove the cooperation between microbial network modules who were responsible for various organic components (RDC, lipid, protein, and lignocellulose) degradation in the start-up phase. Metabolic function prediction suggested that carbohydrate metabolisms including starch and sucrose metabolism, glycolysis / gluconeogenesis, pyruvate metabolism, etc., were improved by increasing the abundance of related functional genes after inoculation. In conclusion, inoculating B. licheniformis accelerated organic degradation by driving the cooperation between microbial network modules and enhancing microbial metabolism in the start-up phase of composting.

Insight into biomolecular interaction-based non-classical crystallization of bacterial biocement.

In an attempt to draw a correlation between calcium carbonate (CaCO3) precipitation and biomacromolecules such as extracellular polymeric substances and enzyme activity in biomineralizing microbe, this report aims to elucidate the ureolytic and ammonification route in Paenibacillus alkaliterrae to explore the possible role of organic biomolecule(s) present on cell surface in mediating nucleation and crystallization of biogenic CaCO3. After 168h of biomineralization in ureolysis and ammonification, 2.2g/l and 0.87g/l of CaCO3 precipitates were obtained, respectively. The highest carbonic anhydrase activity (31.8 µmoles/min/ml) was evidenced in ammonification as opposed to ureolysis (24.8 µmoles/min/ml). Highest urease activity reached up to 9.26 µmoles/min/ml in ureolytic pathway. Extracellular polymeric substances such as polysaccharides and proteins were found to have a vital role not only in the nucleation and crystal growth but also in addition direct polymorphic fate of CaCO3 nanoparticles. EPS production was higher during ammonification (3.1mg/ml) than in ureolysis (0.72mg/ml). CaCO3 nanoparticle-associated proteins were found to be 0.82mg/ml in ureolysis and 0.56mg/ml in ammonification. After 30days of biomineralization, all the polymorphic forms stabilized to calcite in ureolysis but in ammonification vaterite predominated. In our study, we showed that organic template-mediated prokaryotic biomineralization follows the non-classical nucleation and varying proportions of these organic components causes selective polymorphism of CaCO3 nanoparticles. Overall, the findings are expected to further the fundamental understanding of enzymes, EPS-driven non-classical nucleation of CaCO3, and we foresee the design of fit-for-purpose futuristic biominerals arising from such renewed understanding of biomineralization. KEY POINTS: • Organic-inorganic interface of cell surface promote crystallization of biominerals • Carbohydrate and proteins in the interface results selective polymorphism of CaCO3 • Calcite stabilized at 30days in ureolysis, vaterite-calcite mix in ammonification.

Crop diversification increases soil extracellular enzyme activities under no tillage: A global meta-analysis

Conservation agriculture with three management principles has been widely adopted to alleviate the current global agricultural soils facing threats such as soil erosion and nutrient loss. However, unclear understanding of rational crop rotation and the lack of global quantitative assessment limit our deeper insight into soil nutrient cycling under conservation agriculture. Considering the important role of soil extracellular enzyme activities (EEAs) on soil nutrient cycling, a meta-analysis with 3238 observations was conducted on the effects of no tillage (NT) and legumes incorporation into rotation system (LRS) on soil EEAs. NT significantly increased the activities of C-acquiring, N-acquiring, P-acquiring, and oxidative enzymes by 18.3%, 17.4%, 7.1%, and 14.0%, respectively, while LRS significantly increased only P-acquiring enzymes. The combination of NT and legume cultivation had no significant effect on EEAs. In contrast, crop diversity had a positive effect on the NT-induced increase in EEAs. In addition, the extent of NT-induced changes varied depending on other factors. Through further analysis, we clarified the important factors affecting NT-induced changes in EEAs, such as climatic conditions, soil properties, and agronomic practices at the experimental sites. Overall, our findings provide insights into the understanding of the mechanisms of conservation agriculture impacts on the soil nutrient cycling.

Recycled Waste Leaf Litter Pots Exhibit Excellent Biodegradability: An Experimental Analysis

The growth of the gardening kit market could result in the increased wasting of nursery pots, which are usually made of plastic. Replacing these pots with biodegradable pots made from green waste could have benefits for climate mitigation, the circular economy, and the greenness of gardening. To address this, we introduce a prototype recycled waste leaf litter (RWLL) nursery pot. Via an incubation experiment over 90 d, we examined their biodegradability and effects on microbial enzyme activity and inorganic nitrogen concentration, comparing them with commercially available biodegradable pots, namely peat–paper mixture pots (also known as Jiffypots®) and coco-coir pots. The effects of pot thickness were tested. Based on mass loss during incubation and on soil CO2 efflux, the RWLL pots exhibited excellent biodegradability, regardless of their thickness, with decomposition rates and soil CO2 efflux 1.5–6 times greater than other biodegradable pots. Biodegradability, extracellular enzyme activity, and soil inorganic nitrogen content were not affected by RWLL pot thickness or by the presence or absence of a plant in the soil. Unlike in natural ecosystems, leaf litter is treated as waste in urban green spaces, and its decomposition into soil organic matter is prevented. Creating plant pots from leaf litter enhances soil quality, reduces atmospheric carbon emissions, and satisfies the desire of gardeners for greenness.

Long-term rice cultivation increases contributions of plant and microbial-derived carbon to soil organic carbon in saline-sodic soils

Rice cultivation has been demonstrated to have the ability to improve saline-sodic soil. Whether this human activity can influence the accumulation of soil organic carbon (SOC) in saline-sodic soil remains unclear. In this study, the impact of rice cultivation across different planting durations (1, 5, 10, 27 years and abandoned land) on the carbon (C) levels, derived from plant residues and microbial necromass, were assessed. Compared to the control, plant residues and microbial necromass greatly contributed to the carbon accumulation. For the short-term of rice cultivation (1–10 years), the C content originated from both microbial and plant residues gradually accumulated. In the prolonged cultivation phase (27Y), plant residues and microbial necromasses contributed 40.82 % and 21.03 % of the total SOC, respectively. Additionally, rice cultivation significantly reduced the pH by 13.58–22.51 %, electrical conductivity (EC) by 60.06–90.30 %, and exchangeable sodium percentage (ESP) by 60.68–78.39 %. In contrast, total nitrogen (TN), total phosphorus (TP), SOC, particulate organic C, mineral-bound organic C, and microbial biomass all saw statistical increases. The activities of extracellular enzymes in paddy soils, such as peroxidase, phenol oxidase, and leucine aminopeptidase, were significantly reduced, and the decomposition of lignin, phenol, and amino sugars by soil microorganisms was consequently suppressed. The partial least squares path modeling results demonstrated that rice cultivation affected the accumulation of plant and microbial components via the corresponding chemical properties (pH, EC, and ESP), nutrient content (TN, TP, and SOC), enzyme activity (LAP, PER, and POX), microbial biomass, and plant biomass. These findings are crucial for understanding the organic carbon sequestration potential of sodic saline soils.

Rhizosphere interface microbiome reassembly by arbuscular mycorrhizal fungi weakens cadmium migration dynamics.

The prevalence of cadmium (Cd)-polluted agricultural soils is increasing globally, and arbuscular mycorrhizal fungi (AMF) can reduce the absorption of heavy metals by plants and improve mineral nutrition. However, the immobilization of the rhizosphere on cadmium is often overlooked. In this study, Glomus mosseae and Medicago sativa were established as symbiotes, and Cd migration and environmental properties in the rhizosphere were analyzed. AMF reduced Cd migration, and Cd2+ changed to an organic-bound state. AMF symbiosis treatment and Cd exposure resulted in microbial community variation, exhibiting a distinct deterministic process (|βNTI| > 2), which ultimately resulted in a core microbiome function of heavy metal resistance and nutrient cycling. AMF increased available N and P, extracellular enzyme activity(LaC, LiP, and CAT), organic matter content (TOC, EOC, and GRSP), and Eh of the rhizosphere soil, significantly correlating with decreased Cd migration (p < 0.05). Furthermore, AMF significantly affected root metabolism by upregulating 739 metabolites, with flavonoids being the main factor causing microbiome variation. The structural equation modeland variance partial analysisrevealed that the superposition of the root metabolites, microbial, and soil exhibited the maximum explanation rate for Cd migration reduction (42.4%), and the microbial model had the highest single explanation rate (15.5%). Thus, the AMF in the rhizosphere microenvironment can regulate metabolite-soil-microbial interactions, reducing Cd migration. In summary, the study provides a new scientific explanation for how AMF improves plant Cd tolerance and offers a sustainable solution that could benefit both the environment and human health.

Influence of tree residue retention in Mediterranean forest on soil microbial communities responses to frequent warming and drying events

In the coming decades, Mediterranean forests are likely to experience higher heat-wave frequency that may severely affect soil microbial functioning. Here, we studied the effects of warming intensification on soil microbial communities and tested whether certain types of Mediterranean plant residues favor soil biological resistance to frequent drying and warming events (FDW). To this aim, we set-up mesocosms in which soils originating from six Mediterranean forest stands (i.e, Quercus ilex and Q. pubescens and Pinus halepensis and P. sylvestris monospecific and mixed stands) were amended with corresponding coarse (crushed branches) and fine (crushed twigs with leaves/needles) woody debris. A quantity of residues corresponding to five-fold the equivalent of the quantity left on the floor after tree harvesting/logging (equivalent to 35 gC.kg−1 soil DW) was added to each pot, and mesocosms were laid out into a split-plot design and subjected to FDW. After nineteen months, soil physico-chemical properties and changes in microbial communities' diversity and structure, biomass and extracellular enzymatic activities were measured. We showed that FDW reduced the richness of the soil fungal community by ca. 11% and functional diversity by ca. 4% and increased bacterial richness by ca. 40%. We observed a drastic down-regulation of extracellular enzyme activities related with N and C cycles (respectively -44% for protease, -54% for cellulase and -31% for tyrosinase activities). We also found that residues inputs types (fine vs. coarse) only slightly mitigate those effects, while species origin did. Our study showed that residues retention could alleviate the consequences of hydric and thermic stresses on microbial communities by modulating communities’ resistance in specific stands. These results suggest that tree residues retention, in specific stands, could contribute to sustain soil biological properties in the context of Mediterranean climate intensification.

Long-term agro-management strategies shape soil bacterial community structure in dryland wheat systems

Soil microbes play a crucial role in soil organic matter decomposition and nutrient cycling and are influenced by management practices. Therefore, quantifying the impacts of various agricultural management practices on soil microbiomes and their activity is crucial for making informed management decisions. This study aimed to assess the impact of various management systems on soil bacterial abundance and diversity, soil enzyme activities and carbon mineralization potential in wheat-based systems. To accomplish this, soil samples from 0 to 15 cm depth were collected from ongoing long-term field trials in eastern Oregon region under wheat (Triticum aestivum L.)-fallow (WF), WF with different tillage (WT), wheat-pea (Pisum sativum L.) (WP), WF under different crop residue management (CR) and natural undisturbed/unmanaged grassland pasture (GP). These trials consisted of an array of treatments like tillage intensities, nitrogen rates, organic amendments, and seasonal residue burning. This study was a part of the Soil Health Institute’s North American Project to Evaluate Soil Health measurements (NAPESHM). Bacterial community structure was determined using amplicon sequencing of the V4 region of 16SrRNA genes and followed the protocols of the Earth Microbiome Project. In addition, extracellular enzyme activities, and carbon mineralization potential (1d-CO2) were measured. Among different trials, 1d-CO2 in WT, WP, and CR studies averaged 53%, 51% and 87% lower than GP systems, respectively. Enzyme activities were significantly greater in GP compared to the other managements and followed similar trend as respiration. We observed higher evenness in GP and higher richness in spring residue burning treatment of CR study. Our results indicated that species evenness is perhaps a better indicator of soil health in comparison to other indices in dryland wheat systems.

Sequence composition and location of CRE motifs affect the binding ability of CcpA protein

Bacillus catabolite control protein (CcpA) mediates carbon catabolite repression (CCR) by binding with catabolite response elements (CREs) of genes or operons. Although numerous CREs had been predicted and identified, the influence of the changes in sequence and structure of CREs on recognition and binding for CcpA has yet to be unclear. This study aimed at revealing how CcpA could bind such diverse sites and focused on the analysis of multiple mutants of the CRE motif derived from the α-amylase promoter. Molecular docking and free energy calculation insights into the binding ability between the CRE sequences composition and CcpA protein. Disruption of conserved nucleotides in the CRE motifs, as well as altering the symmetric structure of the CRE sequences and the relative position of the displaced CRE motifs near the transcription start site contribute to some extent to weakening the strength of CcpA - dependent regulation. These main factors contribute to the understanding of the subtle changes in CRE motifs leading to differential regulatory effects of CcpA. Finally, an engineered promoter with a high level of transcription was obtained, and elevated extracellular enzyme activity was achieved in the expression system of Bacillus amyloliquefaciens, including alkaline protease, keratinase, aminopeptidase and acid-stable alpha amylase. The study also provides a reference for the application of other promoters with CRE motifts.

Secretory expression and fermentation optimization for extracellular production of pullulanase in Vibrio natriegens

Pullulanase is a starch debranching enzyme, which is difficult in secretory expression due to its large molecular weight. Vibrio natriegens is a novel expression host with excellent efficiency in protein synthesis. In this study, we achieved secretory expression of the full-length pullulanase PulA and its truncated mutant PulN2 using V. natriegens VnDX strain. Subsequently, we investigated the effects of signal peptide, fermentation temperature, inducer concentration, glycine concentration and fermentation time on the secretory expression. Moreover, the extracellular enzyme activities of the two pullulanases produced in V. natriegens VnDX and E. coli BL21(DE3) were compared. The highest extracellular enzyme activity of PulA and PulN2 in V. natriegens VnDX were 61.6 U/mL and 64.3 U/mL, which were 110% and 62% that of those in E. coli BL21(DE3), respectively. The results indicated that V. natriegens VnDX can be used for secretory expression of the full-length PulA with large molecular weight, which may provide a reference for the secretory expression of other large molecular weight proteins in V. natriegens VnDX.

Key decomposers of straw depending on tillage and fertilization

Crop straw is often incorporated into soil, but how agricultural practices affect straw decomposition and the involved biological mechanisms are not fully understood. We conducted a half-year straw decomposition assay in a 16-year experiment with tillage (conventional tillage or no-tillage) and fertilization (single or combined nitrogen, phosphorus and/or cow manure addition) regimes in a dryland agroecosystem. Straw decomposition and extracellular enzyme activities as well as bacterial, fungal, protistan and metazoan communities in the straw residues were analyzed. Straw mass loss was accelerated by tillage, whereas it was slowered by all but not single nitrogen fertilization treatments and correlated negatively with soil fertility. Enzyme activities were sensitive to tillage and fertilization but not correlated with straw decomposition. Straw mass loss was positively correlated with the relative abundances of a dominant saprotrophic fungus (related to Apodus deciduus) and an ecological cluster of the inter-kingdom co-occurrence network, whose abundances were increased by tillage and decreased with increasing soil fertility. This study shows strong effects of agricultural practices on straw decomposition, and highlights the importance of key decomposers and inter-kingdom interactions in regulating straw decomposition. We propose that straw incorporation should be applied with appropriate tillage and reduced fertilizers in dryland agroecosystems.

Soil extracellular enzyme stoichiometry reveals the increased P limitation of microbial metabolism after the mixed cultivation of Korean pine and Manchurian walnut in Northeast China

Korean pine (Pinus koraiensis) and Manchurian walnut (Juglans mandshurica) are the main tree species used for plantation regeneration in Northeast China, and their mixed cultivation is typically used to address a decline in stand productivity in long-term monocultures. However, little is known about the changes in the C, N and P requirements of soil microbial metabolism between monocultures and mixed plantations. In this study, we examined the effect of plantation type on the soil microbial metabolic limitations by investigating the soil extracellular enzyme activities across three plantation types (P. koraiensis monocultures, J. mandshurica monocultures, P. koraiensis and J. mandshurica mixed plantations) of the same age (32 years old). We used ecoenzymatic stoichiometry methods to reveal the patterns of microbial metabolic C, N and P limitations along a soil depth gradient of 0–10, 10–20, and 20–40 cm by collecting a total of 81 composite soil samples including three plantation types. With the increased soil depth, the activities of C-, N- and P-acquiring enzymes in mixed plantations decreased from 93.60 nmol g−1 soil h−1 to 20.52 nmol g−1 soil h−1, 33.46 nmol g−1 soil h−1 to 22.09 nmol g−1 soil h−1, and 11.80 nmol g−1 soil h−1 to 7.30 nmol g−1 soil h−1, respectively. Enzymatic vector analysis (vector angle >45°) revealed P limitation rather than N limitation of microbial metabolism across all plantation types. Of the plantations, the mixed stands had the greatest vector length (1.15 ± 0.02) and vector angle (56.91 ± 1.47). The interactions of plantation type and soil depth had significant effects on microbial metabolic C and P requirements. Changes in soil available nutrient contents and stoichiometry ratios of C, N and P across different plantation types were the two most important soil variables affecting microbial metabolic C and P requirements.

Soil properties and microbial functional attributes drive the response of soil multifunctionality to long-term fertilization management

Fertilization is a vital management practice to improve soil fertility and promote agricultural production. However, there is limited knowledge about the interactive effects between soil abiotic and biotic factors and soil multifunctionality after long-term fertilization. There has been little research on determining whether the application of organic fertilizers can improve the functional potential of microorganisms to maintain multifunctional stability. In this study, we integrated soil physicochemical properties, extracellular enzyme activities, bacterial community characteristics, and the abundance of functional genes related to carbon (C) and nitrogen (N) cycling to evaluate the mechanism of soil functional potential response to 13 years of fertilization management. Four treatments were compared, including no fertilizer (CK), conventional fertilization (CF), formulated fertilization by soil testing (SF), SF with organic fertilizer (SFO). The addition of organic fertilizer enhanced the soil electrical conductivity, N-cycling enzyme activities, contents of macroaggregate and associated C, and soil nutrients, while decreasing the content of microaggregates compared with other treatments. The co-application of chemical and organic fertilizer led to significant increases in soil multifunctionality and the bacterial Shannon index compared with the CK and CF treatments. Soil abiotic factors are the key predictors for shaping soil multifunctionality. The addition of organic fertilizer could increase the abundance of functional genes related to C- and N-cycling mediated by the contents of nutrients and the aggregates associated with nutrients. Additionally, treatment with organic fertilizer can mitigate the decrease in genes for C-cycling function caused by the long-term application of chemical fertilizer (SF). In addition, the structural equation models revealed that the fertilization positively affected soil multifunctionality indirectly by changing the bacterial diversity and community composition, as well as the functional potential related to N-cycling. Overall, soil properties and microbial functional attributes jointly drive the response of soil multifunctionality to long-term fertilization management. These results suggest that the combination of organic and chemical fertilizer is worth popularizing to improve multifunctionality and its stability to maintain agricultural sustainability.

Effects of thinning and understorey removal on soil extracellular enzyme activity vary over time during forest recovery after treatment

Effects of thinning and understorey removal on soil extracellular enzyme activity vary over time during forest recovery after treatment

Adaptability of agricultural soil microbial nutrient utilization regulates community assembly under mulching measures on the Loess Plateau

Soil microbial nutrients and resource availability improve with mulching in agroecosystems, resulting in changes of soil microbial nutrient utilization strategies. However, the responses of soil microorganisms to nutrient utilization processes to regulate community assembly and thus maintain resource availability have not been clarified. Here, we performed a long-term field experiment with mulching measures, including no-mulching (NM), straw mulching (SM), plastic mulching (PM), and ridge mulching (RM), conducted on the Loess Plateau of China, to explore the community assembly process in response to microbial nutrient utilization. Microbial nutrient utilization strategies were analysed by measuring soil nutrients, microbial biomass, and extracellular enzyme activities. The results showed that PM and RM acquired C and N nutrients by secreting C- and N-extracellular enzymes in response to C:N- and C:P imbalances in soil chemistry, thereby reducing the nutrient limitation on microbial metabolism and improving microbial C utilization efficiency (CUE). Soil extracellular enzymatic stoichiometry increased and N utilization efficiency (NUE) decreased under mulching and drove an increase in beta-diversity and dominant species abundance in fungal communities. Mulching measures promoted the modular distribution of sensitive microorganisms and aggregation of fungal networks under PM and RM by reducing the stoichiometric imbalance and extracellular enzymatic N:P. At the same time, the microbial community assembly gradually changed from a stochastic to a deterministic process in response to the alleviation of soil C:P imbalance and changes in microbial nutrient utilization, in which the fungal community was dominant. In conclusion, soil microorganisms adaptively responded to changes in soil microbial nutrient utilization through the enhancement of aggregation of fungal co-occurrence networks and deterministic assembly processes. This study provides a better understanding of the impact of mulching on microbial nutrient utilization strategies from a community assembly perspective.