Extracellular Enzyme Activities Research Articles

Carbon and Nutrient Limitations of Microbial Metabolism in Xingkai Lake, China: Abiotic and Biotic Drivers.

Microbial communities are crucial for water quality and biogeochemical cycling in freshwaters. Microbes secrete extracellular enzymes to decompose organic matter for their needs of nutrients and scarce elements. Yet, there is a lack of knowledge on microbial metabolic limitations in freshwaters, especially in lake sediments. Here, we examined the carbon, nitrogen, and phosphorus-acquiring extracellular enzyme activities and the bacterial and fungal communities of 30 sediments across Xingkai Lake, the largest freshwater lake in Northeast Asia. We further analyzed the microbial metabolic limitations via extracellular enzyme stoichiometry and explored the direct and indirect effects of abiotic and biotic factors on the limitations. We found that microbial metabolisms were primarily limited by phosphorus in Xingkai Lake. For instance, microbial carbon and phosphorus limitations were closely correlated to abiotic factors like water depth, total dissolved solids, sediment total carbon, and conductivity. The metabolic limitations were also affected by biotic factors, such as showing positive relationships with the alpha and beta diversity of bacteria, and with the beta diversity of fungi. In addition, community compositions of bacteria and fungi were mainly correlated to abiotic factors such as total carbon and dissolved organic carbon, respectively. Collectively, microbial metabolic limitations were affected directly or indirectly by abiotic factors and microbial communities. Our findings indicate that microbial metabolic limitations are not only driven by bacteria and fungi but also by abiotic factors such as water depth and total nitrogen, and thus provide empirical evidence for effective management of freshwater lakes under climate warming and intensified human activities.

Long-term agricultural cultivation decreases microbial nutrient limitation in coastal saline soils

Soil enzyme activities are pivotal for diverse biochemical processes and are sensitive to land use changes. They can indicate soil microbial nutrient limitations. Nonetheless, the mechanism governing the response of soil microbial nutrient limitation to land use alterations in coastal regions remains elusive. We assessed soil nutrients, microbial biomass, and extracellular enzyme activities across various land use types—natural (wasteland and woodland) and agricultural (farmland and orchard)—in the Hangzhou Bay area, China. All four land use types experience co-limitation by carbon (C) and phosphorus (P). However, the extent of microbial resource limitations varies among them. Long-term agricultural practices diminish microbial C and P limitations in farmland and orchard soils compared to natural soils, as evidenced by lower ecoenzymatic C:N ratios and vector lengths, alongside higher microbial carbon use efficiency (CUE). Soil nutrient stoichiometric ratios and CUE are primary factors influencing microbial C and P limitations. Thus, fostering appropriate land use and management practices proves imperative to regulate soil nutrient cycles and foster the sustainable management of coastal areas.

Mycorrhizal association controls soil carbon-degrading enzyme activities and soil carbon dynamics under nitrogen addition: A systematic review

Recent evidence suggests that changes in carbon-degrading extracellular enzyme activities (C-EEAs) can help explain soil organic carbon (SOC) dynamics under nitrogen (N) addition. However, the factors controlling C-EEAs remain unclear, impeding the inclusion of microbial mechanisms in global C cycle models. Using meta-analysis, we show that the responses of C-EEAs to N addition were best explained by mycorrhizal association across a wide range of environmental and experimental factors. In ectomycorrhizal (ECM) dominated ecosystems, N addition suppressed C-EEAs targeting the decomposition of structurally complex macromolecules by 13.1 %, and increased SOC stocks by 5.2 %. In contrast, N addition did not affect C-EEAs and SOC stocks in arbuscular mycorrhizal (AM) dominated ecosystems. Our results indicate that earlier studies may have overestimated SOC changes under N addition in AM-dominated ecosystems and underestimated SOC changes in ECM-dominated ecosystems. Incorporating this mycorrhizal-dependent impact of EEAs on SOC dynamics into Earth system models could improve predictions of SOC dynamics under environmental changes.

Microbial remineralization processes during post-spring-bloom with excess phosphate available in the northern Baltic Sea.

The phosphorus (P) concentration is increasing in parts of the Baltic Sea following the spring bloom. The fate of this excess P-pool is an open question and here we investigate the role of microbial degradation processes in the excess P assimilation phase. During a 17-day-long mesocosm experiment in the south-west Finnish archipelago, we examined nitrogen, phosphorus and carbon acquiring extracellular enzyme activities in three size fractions (<0.2µm, 0.2-3µm, and >3µm), bacterial abundance, production, community composition and its predicted metabolic functions. The mesocosms received carbon (C) and nitrogen (N) amendments individually and in combination (NC) to distinguish between heterotrophic and autotrophic processes. Alkaline phosphatase activity occurred mainly in the dissolved form and likely contributed to the excess phosphate conditions together with grazing. At the beginning of the experiment, peptidolytic and glycolytic enzymes were mostly produced by free-living bacteria. However, by the end of the experiment, the NC-treatment induced a shift in peptidolytic and glycolytic activities and degradation of phosphomonoesters towards the particle-associated fraction, likely as a consequence of higher substrate availability. This would potentially promote retention of nutrients in the surface as opposed to sedimentation, but direct sedimentation measurements are needed to verify this hypothesis.

Migrating ripples create streambed heterogeneity altering microbial diversity and metabolic activity

AbstractSandy sediments of lowland streams are typically transported at low flow in the form of migrating ripples. In these bedforms, microbial communities spanning all trophic guilds (heterotrophic bacteria, fungi, photoautotrophic and phagotrophic protists) are exposed to highly frequent moving–resting cycles of sediment grains. Up to date, it is unknown to what extent ripple migration impacts community metabolism and composition as well as the vertical zonation of sediment‐associated multitrophic microbial communities compared to stationary sediments. We hypothesize that, as a result of mechanical abrasion and limited light supply, migrating ripple sediments have lower microbial abundance, diversity, metabolism and resource acquisition and no vertical zonation compared to stationary sediments. We collected samples from five lowland streams in north‐eastern Germany between May and June 2020. The coarser and better sorted sediments of migrating ripples had a higher oxygen concentration and less organic matter than stationary sediments. Photosynthetic pigments, potential extracellular enzyme activities, bacterial cell counts, and fungal gene copies were lower in migrating ripples than in stationary sediments. In contrast, cell‐specific bacterial production was higher in migrating ripples. Metabarcoding revealed that bedform migration was important in shaping the community structure of bacteria, fungi, and phagotrophic protists. Dry mass‐related net community production, respiration, and bacterial production were higher in superficial compared to underlying layers irrespective of sediment transport. By modulating the abundance, diversity, and structure of different trophic guilds of microbial communities and their resource acquisition, migrating bedforms create streambed heterogeneity, shaping regional biodiversity and the flow of matter through the benthic food web.

The effects of postfire regeneration patterns on soil microbial metabolic limitation based on eco-enzyme stoichiometry in the boreal forest of China

Postfire regeneration is essential for maintaining the stability and functionality of forest ecosystems following wildfires. However, it is unclear whether regeneration patterns affect carbon (C), nitrogen (N), or phosphorus (P) limitations on microbial metabolism in the soil. In this study, we investigated the soil extracellular enzyme activities (EEAs) in different forest types regenerated by five patterns (Dahurian larch monocultures, Dahurian larch and birch mixed plantations, Mongolian pine monocultures, Mongolian pine and birch mixed plantations, and naturally regenerated forests). Based on the principles of ecoenzymatic stoichiometry, we elucidated the spatiotemporal variation in energy (C) and nutrient (N or P) limitations on soil microbial metabolism by collecting a total of 135 composite soil samples across three seasons in the five regeneration patterns. The regeneration pattern had a significant effect on the activities of C-, N- and P-acquiring soil extracellular enzymes (P<0.05). The P-acquiring enzyme activity was 2.71 times greater than the C-acquiring enzyme activity and 3.44 times greater than the N-acquiring enzyme activity across all forest types and seasons. The activities of microbial metabolic C-, N-, and P-acquiring enzymes showed similar seasonal dynamic patterns, with the exception of L-leucine aminopeptidase. In all forest types, the activities of enzymes responsible for acquiring C, N, and P were linearly correlated with one another according to the findings from standard major axis regression analysis (P<0.001). The values of the enzymatic vectors were greater than 45°, indicating that P rather than N was the dominant constraint on soil microbial metabolism. Forests with mixed regeneration patterns had greater P limitations than did the corresponding monoculture forests. Soil temperature was the common soil variable affecting the activities of EEAs across seasons, while the contents of soil organic carbon, dissolved carbon, ammonium nitrogen, and nitrate nitrogen were the significant driving factors of EEAs in a single season. However, forest productivity, including tree density, stand basal area, and forest stand volume had a predominant influence on microbial metabolic P limitation. This study suggests a pronounced role of P in soil microbial metabolism within boreal forests regenerated after wildfires.

Activin A Is a Master Regulator of Phenotypic Switch in Adipose Stromal Cells Initiated by Activated Immune Cell-Secreted Interleukin-1β.

Prolonged tissue ischemia and inflammation lead to organ deterioration and are often accompanied by microvasculature rarefaction, fibrosis, and elevated systemic Activin A (ActA), the level of which frequently correlates with disease severity. Mesenchymal stromal cells are prevalent in the perivascular niche and are likely involved in tissue homeostasis and pathology. This study investigated the effects of inflammatory cells on modulation of phenotype of adipose mesenchymal stromal cells (ASC) and the role of ActA in this process. Peripheral blood mononuclear cells were activated with lipopolysaccharide (activated peripheral blood mononuclear cells [aPBMC]) and presented to ASC. Expression of smooth muscle/myofibroblast markers, ActA, transforming growth factors beta 1-3 (TGFβ1-3), and connective tissue growth factor (CTGF) was assessed in ASC. Silencing approaches were used to dissect the signaling cascade of aPBMC-induced acquisition of myofibroblast phenotype by ASC. ASC cocultured with aPBMC or exposed to the secretome of aPBMC upregulated smooth muscle cell markers alpha smooth muscle actin (αSMA), SM22α, and Calponin I; increased contractility; and initiated expression of ActA. Interleukin (IL)-1β was sufficient to replicate this response, whereas blocking IL-1β eliminated aPBMC effects. ASC-derived ActA stimulated CTGF and αSMA expression in ASC; the latter independent of CTGF. Induction of αSMA in ASC by IL-1β or ActA-enriched media relied on extracellular enzymatic activity. ActA upregulated mRNA levels of several extracellular matrix proteins in ASC, albeit to a lesser degree than TGFβ1, and marginally increased cell contractility. In conclusion, the study suggests that aPBMC induce myofibroblast phenotype with weak fibrotic activity in perivascular progenitors, such as ASC, through the IL-1β-ActA signaling axis, which also promotes CTGF secretion, and these effects require ActA extracellular enzymatic processing.

Different regulatory mechanisms on carbon-degrading enzyme activities under short-term litter input manipulations in subalpine coniferous and broad-leaved forest soils

Soil carbon (C)-degrading extracellular enzyme activities (EEAs) are important regulators in targeting litter and soil organic carbon (SOC) decomposition in territorial ecosystems. However, the responses of enzymes involved in C-cycling to short-term litter input manipulations in different forest ecosystems remain unclear. Here, we examined oxidative C-degrading EEAs (Ox-EEAs), hydrolytic C-degrading EEAs (Hy-EEAs) and their ratios (Ox-to-Hy C EEA ratios) at topsoil (0–10 cm) and subsoil (10–30 cm) after two years of litter manipulations (i.e., Detritus Input and Removal Treatments-DIRT: control, CK; double litter, DL; no roots and double litter, NRDL; no litter, NL; no roots, NR; no roots and no litter, NRNL) in a coniferous forest (Pinus yunnanensis) and a broad-leaved forest (Quercus pannosa) in subalpine area of Southwest China. The litter addition did not significantly affect Ox-EEAs, Hy-EEAs, and their ratios in two forest soils. In contrast, the litter removal significantly decreased Hy-EEAs and slightly affected Ox-EEAs in coniferous forest soil, whereas they increased Ox-EEAs and slightly affected Hy-EEAs in broad-leaved forest soil. Consequently, the Ox-to-Hy C EEA ratios were significantly enhanced by litter removal in both two forest soils. This different variation in Ox-EEAs and Hy-EEAs under litter removal in two forest soils could be attributed to initial soil properties, where soil properties (e.g., pH, total nitrogen [TN], NO3−-N, SOC) with lower C: N ratios in coniferous forest were more likely to promote Hy-EEAs. Whereas microbial parameters (e.g., microbial biomass C) and soil properties (e.g., dissolved organic C) mainly regulated Ox-to-Hy C EEA ratios at topsoil and subsoil in broad-leaved forest, respectively. Overall, our findings revealed different mechanisms and associated drivers on enzymes involved in C-cycling under short-term litter input manipulation of the subalpine coniferous forest and broad-leaved forest soils, which further strengthened our understanding of C-cycling in forest soils.

Food-grade expression and characterization of cyclomaltodextrinase from B. sphaericus E−244 in Bacillussubtilis

As the utilization of maltodextrins in food, pharmaceuticals, and agriculture continues to expand, substantial research has been conducted to enhance their functionality. Among the methods presented, the one-pot approach for the synthesis of nonreducing maltoheptaose offers a novel solution to the challenge of maltodextrins with varying degrees of polymerization and reducing ends. Nevertheless, the key enzyme in this method was currently only expressed in Escherichia coli, which restricts the applicability of this method in the food and pharmaceutical industries. In this study, the food-grade expression of cyclomaltodextrinase (CDase, EC 3.2.1.54), one of the key enzymes, was achieved using Bacillus subtilis as a host. The enzymatic properties of the recombinant CDase were then investigated, and the extracellular secretion of the CDase was enhanced in order to make it more widely available for use in the food industry. The enzyme exhibited optimal activity at a pH of 8.0 and a temperature range of 35–45 °C. After incubation at 25–35 °C for 10 h, 90% of the enzyme activity was retained. Additionally, the enzyme retained 80% of its initial activity after 24 h at pH 5.5–9.5. Finally, Cu2+ completely inhibited the enzyme activity. The extracellular secretion efficiency of recombinant CDase was significantly increased by the addition of Mn2+ to the fermentation medium. The percentage of extracellular enzyme activity increased to 63.75% when the final concentration of Mn2+ in the fermentation medium was 5 mM, which was 5.3-fold higher than that of the unadded one.

Changes in soil microbial metabolic limitations after half-century forest restoration in degraded tropical lands

Due to increasing anthropogenic pressure, over half of the world’s tropical forests are reforested or afforested secondary forests or plantations. The recovery pace and potential of these forests depend largely on soil microbially-mediated biogeochemical cycling. Here we measured soil extracellular enzyme activities and quantified microbial metabolic limitations using a vector analysis in a bare land (BL, representing the original state before restoration), two afforested sites [i.e. a restored secondary forest (MF) and a managed Eucalyptus exserta plantation (EP)] and a nearby undisturbed forest (UF) in south China. Results showed that soil microbial metabolisms were co-limited by carbon (C) and phosphorus (P) across the four forests. Both microbial C and P limitations were higher in BL than UF. Microbial C limitation significantly reduced after restoration only in MF when compared to BL, but it was still higher than that in UF. Interestingly, microbial P limitation significantly enhanced after restoration in both EP and MF when compared to BL, and it did not differ between the two restored forests. Structural equation modeling (SEM) showed that microbial C limitation was primarily attributed to microbial C use efficiency, while microbial P limitation was co-driven by plant biomass, microbial C use efficiency and soil P availability. These findings suggest microbial C limitation could be gradually recovered after forest restoration in southern China, which would facilitate soil organic carbon accumulation. However, the enhanced microbial P limitation after forest restoration underlines the necessity to develop optimal P management in these restored forests.

Determination of soil phenanthrene degradation through a fungal-bacterial consortium.

Fungal-bacterial consortia enhance organic pollutant removal, but the underlying mechanisms are unclear. We used stable isotope probing (SIP) to explore the mechanism of bioaugmentation involved in polycyclic aromatic hydrocarbon (PAH) biodegradation in petroleum-contaminated soil by introducing the indigenous fungal strain Aspergillus sp. LJD-29 and the bacterial strain Pseudomonas XH-1. While each strain alone increased phenanthrene (PHE) degradation, the simultaneous addition of both strains showed no significant enhancement compared to treatment with XH-1 alone. Nonetheless, the assimilation effect of microorganisms on PHE was significantly enhanced. SIP revealed a role of XH-1 in PHE degradation, while the absence of LJD-29 in 13C-DNA indicated a supporting role. The correlations between fungal abundance, degradation efficiency, and soil extracellular enzyme activity indicated that LJD-29, while not directly involved in PHE assimilation, played a crucial role in the breakdown of PHE through extracellular enzymes, facilitating the assimilation of metabolites by bacteria. This observation was substantiated by the results of metabolite analysis. Furthermore, the combination of fungus and bacterium significantly influenced the diversity of PHE degraders. Taken together, this study highlighted the synergistic effects of fungi and bacteria in PAH degradation, revealed a new fungal-bacterial bioaugmentation mechanism and diversity of PAH-degrading microorganisms, and provided insights for in situ bioremediation of PAH-contaminated soil.IMPORTANCEThis study was performed to explore the mechanism of bioaugmentation by a fungal-bacterial consortium for phenanthrene (PHE) degradation in petroleum-contaminated soil. Using the indigenous fungal strain Aspergillus sp. LJD-29 and bacterial strain Pseudomonas XH-1, we performed stable isotope probing (SIP) to trace active PHE-degrading microorganisms. While inoculation of either organism alone significantly enhanced PHE degradation, the simultaneous addition of both strains revealed complex interactions. The efficiency plateaued, highlighting the nuanced microbial interactions. SIP identified XH-1 as the primary contributor to in situ PHE degradation, in contrast to the limited role of LJD-29. Correlations between fungal abundance, degradation efficiency, and extracellular enzyme activity underscored the pivotal role of LJD-29 in enzymatically facilitating PHE breakdown and enriching bacterial assimilation. Metabolite analysis validated this synergy, unveiling distinct biodegradation mechanisms. Furthermore, this fungal-bacterial alliance significantly impacted PHE-degrading microorganism diversity. These findings advance our understanding of fungal-bacterial bioaugmentation and microorganism diversity in polycyclic aromatic hydrocarbon (PAH) degradation as well as providing insights for theoretical guidance in the in situ bioremediation of PAH-contaminated soil.

Effects of Short-Term Tillage on Rhizosphere Soil Nitrogen Mineralization and Microbial Community Composition in the Double-Cropping Rice Field.

Soil extracellular enzyme plays a vital role in changing soil nitrogen (N) mineralization of rice field. However, the effects of soil extracellular enzyme activities (EEA) and microbial community composition response to N mineralization of rice field under short-term tillage treatment needed to be further explored. In this study, we investigated the impact of short-term (8-year) tillage practices on rhizosphere soil N transformation rate, soil enzyme activities, soil microorganism community structure and their N mineralization function genes in double-cropping rice field in southern China. The experiment consisted of four tillage treatments: rotary tillage with crop straw input (RT), conventional tillage with crop straw input (CT), no-tillage with crop straw retention (NT), and rotary tillage with all crop straws removed as a control (RTO). The results indicated that rhizosphere soil N transformation rate in paddy field in NT and RTO treatments were significantly lower than that in RT and CT treatments. Compared with NT and RTO treatments, soil protease, urease, β-glucosaminidase and arginase activities with CT treatment were significantly improved, as were abundances of soil sub, npr and chiA with CT and RT treatments. Moreover, diversity of overall soil bacterial communities in NT and RTO treatments were significantly lower than that in RT and CT treatments. Soil chitinolytic and bacterial ureolytic communities were also obviously changed combined with tillage and crop straw input practices.

Response of a simulated aquatic fungal community to nanoplastics exposure and functional consequence on leaf decomposition

Nanoplastics pose a potential threat to a wide variety of aquatic organisms. Despite the awareness of this existing hazard, the impact of nanoplastics on natural fungal communities remains a research gap. In this study, five dominant fungi species, isolated from a stream ecosystem, were used to explore the effects of different nano-polystyrene (nano-PS) particles concentrations on a simulated fungal community. Specifically, the evaluation was conducted regarding the fungal growth, reproductivity, structural composition, and ecological function in leaf litter decomposition. A 15-day exposure experiment showed that 100 μg/L nano-PS significantly reduced the microcosm pH. The extracellular enzyme activities of β-glucosidase, leucine-aminopeptidase, and peroxidase were significantly promoted by nano-PS exposure for 5 days or 15 days. Total sporulation rate significantly decreased after the 15-day exposure to 1 and 100 μg/L nano-PS and significantly increased under 10 μg/L nano-PS. In contrast, nano-PS concentrations had no effects on fungal biomass. In addition, the reduced relative abundance of Geotrichum candidum lowered its contribution to leaf decomposition, resulting in a decreased litter decomposition rate of a 24.5–27.9 % after exposure. This suggests that 1–100 μg/L nano-PS inhibited leaf decomposition by inhibiting fungal reproduction and reducing the contribution of specific fungal species. In addition, the findings highlight the importance of exploring the potential mechanisms of the interaction between nanoplastics and fungal species.

Enhanced denitrification by graphene oxide–modified cathode for the secondary effluent of wastewater treatment plants in three-dimensional biofilm electrode reactors

ABSTRACT In this study, a novel three-dimensional biofilm electrode reactor (3D-BER) with a graphene oxide (GO)–modified cathode was developed to enhance the denitrification performance of secondary effluent from wastewater treatment plants (SEWTPs). The effects of different hydraulic retention times (HRTs) and currents on the 3D-BER were explored. The results indicated that at the optimal HRT of 4 h and current of 350 mA/m2, the 3D-BER with GO-modified cathode had a higher denitrification rate (2.40 ± 0.1 mg TN/L/h) and less accumulation of intermediate products, especially with 3.34% total nitrogen (TN) molar conversion to N2O. The GO-modified cathode offered a large biocompatible specific surface area and enhanced the conductivity, which favored microbial growth and increased electron transfer efficiency and extracellular enzyme activities. Moreover, the activity of nitrite reductase increased more than that of nitrate reductase to accelerate nitrite reduction, thus facilitating the denitrification process. The proposed 3D-BER provided an effective solution to elevate tertiary denitrification in the SEWTP.

Morphological variation and expressed sequence tags-simple sequence repeats-based genetic diversity of Aspergillus cristatus in Chinese dark tea.

Aspergillus cristatus is a homothallic fungus that is used in the natural fermentation process of Chinese Fuzhuan tea and has been linked to the production of bioactive components. However, not much is known about the variations present in the fungus. To understand the variation of the dominant microorganism, A. cristatus, within dark tea, the present study investigated the genetic and morphological diversity of 70 A. cristatus collected across six provinces of China. Expressed sequence tags-simple sequence repeats (EST-SSR) loci for A. cristatus were identified and corresponding primers were developed. Subsequently, 15 specimens were selected for PCR amplification. The phylogenetic tree obtained revealed four distinct clusters with a genetic similarity coefficient of 0.983, corresponding to previously identified morphological groups. Five strains (A1, A11, B1, D1, and JH1805) with considerable differences in EST-SSR results were selected for further physiological variation investigation. Microstructural examinations revealed no apparent differentiation among the representative strains. However, colony morphology under a range of culture media varied substantially between strains, as did the extracellular enzymatic activity (cellulase, pectinase, protease, and polyphenol oxidase); the data indicate that there are differences in physiological metabolic capacity among A. cristatus strains. Notably, JH1805, B1, and A11 exhibited higher enzymatic activity, indicating their potential application in the production of genetically improved strains. The findings provide valuable insights into species identification, genetic diversity determination, and marker-assisted breeding strategies for A. cristatus.

Extracellular Enzyme Activity and Stoichiometry Across Vegetated and Non-Vegetated Coastal Ecosystems

The conversion of organic matter by extracellular enzymes can reveal important insights into carbon and nutrient cycling. The activity and stoichiometry of hydrolytic extracellular enzymes were investigated to assess the effects of vegetation cover and sediment characteristics on microbial-enzyme-mediated decomposition in coastal ecosystems. Extracellular enzyme activity (EEA) was quantified across transects extending from mangrove to tidal flat habitats in two New Zealand coastal ecosystems that differ in mud content (sandy: Hobson Bay, muddy: Snells Beach). We determined the activity of five key hydrolyzing enzymes: β-glucosidase (hydrolyzes cellulose to glucose); β-N-acetylglucosaminidase (catalyzes the terminal reaction in chitin degradation); alkaline phosphatase (releases soluble inorganic phosphate groups from organophosphates); β-D-cellobiohydrolase (hydrolyzes cellulose to generate cellobiose); and β-xylosidase (catalyzes hemicellulose). All enzymes involved in C acquisition and in N and P cycling had higher activity at the muddy site. No habitat differences in EEA were observed at the sandy site, whereas EEA was lower in the non-vegetated habitats for some enzymes at the muddy site. Models of microbial metabolic limitations highlighted that most habitats at both muddy and sandy sites were predominately C and P limited. The EEA in these coastal wetlands was generally lower than has been reported for other terrestrial, freshwater, and estuarine ecosystems, with values often one to two orders of magnitude lower than other wetland studies. These results can be used to advance our understanding of the biogeochemical processes underpinning the response of coastal ecosystems to land-derived nutrient and sediment inputs.

Community assembly of ectomycorrhizal fungal communities in pure and mixed Pinus massoniana forests

Ectomycorrhizal (EcM) fungi play an important role in nutrient cycling and community ecological dynamics and are widely acknowledged as important components of forest ecosystems. However, little information is available regarding EcM fungal community structure or the possible relationship between EcM fungi, soil properties, and forestry activities in Pinus massoniana forests. In this study, we evaluated soil properties, extracellular enzyme activities, and fungal diversity and community composition in root and soil samples from pure Pinus massoniana natural forests, pure P. massoniana plantations, and P. massoniana and Liquidambar gracilipes mixed forests. The mixed forest showed the highest EcM fungal diversity in both root and bulk soil samples. Community composition and co-occurrence network structures differed significantly between forest types. Variation in the EcM fungal community was significantly correlated with the activities of β-glucuronidase and β−1,4-N-acetylglucosaminidase, whereas non-EcM fungal community characteristics were significantly correlated with β-1,4-glucosidase and β-glucuronidase activities. Furthermore, stochastic processes predominantly drove the assembly of both EcM and non-EcM fungal communities, while deterministic processes exerted greater influence on soil fungal communities in mixed forests compared to pure forests. Our findings may inform a deeper understanding of how the assembly processes and environmental roles of subterranean fungal communities differ between mixed and pure plantations and may provide insights for how to promote forest sustainability in subtropical areas.

Long-term soil warming decreases soil microbial necromass carbon by adversely affecting its production and decomposition.

Microbial necromass carbon (MNC) accounts for a large fraction of soil organic carbon (SOC) in terrestrial ecosystems. Yet our understanding of the fate of this large carbon pool under long-term warming is uncertain. Here, we show that 14 years of soil warming (+4°C) in a temperate forest resulted in a reduction in MNC by 11% (0-10 cm) and 33% (10-20 cm). Warming caused a decrease in the content of MNC due to a decline in microbial biomass carbon and reduced microbial carbon use efficiency. This reduction was primarily caused by warming-induced limitations in available soil phosphorus, which, in turn, constrained the production of microbial biomass. Conversely, warming increased the activity of soil extracellular enzymes, specifically N-acetylglucosaminidase and leucine aminopeptidase, which accelerated the decomposition of MNC. These findings collectively demonstrate that decoupling of MNC formation and decomposition underlie the observed MNC loss under climate warming, which could affect SOC content in temperate forest ecosystems more widespread.

Study on the Effects of Different Light Supply Modes on the Development and Extracellular Enzyme Activity of Ganoderma lucidum

Study on the Effects of Different Light Supply Modes on the Development and Extracellular Enzyme Activity of Ganoderma lucidum

Soil erosion‐induced decline in aggregate stability and soil organic carbon reduces aggregate‐associated microbial diversity and multifunctionality of agricultural slope in the Mollisol region

AbstractSoil erosion has become a serious ecological problem hindering the agricultural and economic development in Northeast China. Soil aggregates are basic units that regulate soil fertility and microbial activity. However, there have been few reports on the role of soil erosion in regulating the microbial diversity, multiple ecosystem services, and functions (multifunctionality) of soil aggregates. In this study, we investigated the effects of soil erosion on microbial diversity and the activities of various extracellular enzymes associated with soil aggregates by using Mollisol soil in Northeastern China at different positions of a slope, and how soil erosion affects soil multifunctionality indexes obtained by normalized calculation of soil enzyme activities. The results showed that soil erosion could reduce the physicochemical properties, soil enzyme activity, and microbial diversity of the aggregates, resulting in accumulation of aggregate nutrients and increase in microbial diversity and enzyme activity in the sedimentation area. Compared with smaller soil aggregates, larger soil aggregates had higher nutrient content, enzyme activity, and microbial diversity. However, with the intensification of soil erosion, the differences in microbial diversity and soil enzyme activities among different sizes of aggregates were reduced. Soil erosion also significantly reduced soil multifunctionality (p &lt; 0.001). The multifunctionality of 2000–250 μm, 250–53 μm, and &lt;53 μm aggregates respectively declined from 0.52, 0.20, and 0.08 (no erosion sites) to −0.17, −0.66, and −0.77 (heavy erosion sites). Additionally, microbial diversity was found to have a linear positive correlation with soil multifunctionality (R2 = 0.23, p &lt; 0.01). Structural equation modeling and random forest analysis revealed that soil organic carbon and aggregate water stability are main predictors of soil multifunctionality. Furthermore, soil physicochemical properties had a greater influence on soil multifunctionality than microbial diversity. Collectively, our results demonstrate that soil erosion negatively affects the structure, resource effectiveness, and microbial activity of soil aggregates, thereby reducing to differential soil multifunctionality.