Insights into the biodegradation of polyhydroxyalkanoates by the tropical marine isolate, Nocardiopsis dassonvillei NCIM 5124.

In the current study, the ability of an indigenous marine Actinomycete Nocardiopsis dassonvillei (NCIM 5124) to degrade poly(3-hydroxybutyrate)-PHB was examined. From the whole genome sequencing data of the organism, information regarding the PHB depolymerase gene and amino acid sequence (Accession number: MCK9871921.1) was retrieved. In silico studies indicated the presence of a signal peptide characteristic of extracellular enzymes. ProtParam tool predicted that the protein had a molecular mass of 42.46 kDa with an isoelectric point of 4.51. Aliphatic and instability index values suggested that the protein was stable and the observed GARVY value indicated its hydrophilic nature. 3D structure prediction and multiple sequence alignments revealed the presence of Type I catalytic domain [including the oxyanion histidine towards the N terminal, the catalytic triad with serine (as a part of GLSAG pentapeptide), aspartate and histidine], substrate binding and linker domain. The organism was able to grow on PHB in solid and liquid media and effectively degrade it. Maximum enzyme activity (1.8 U/mL/min) was observed after 5 d of incubation in Bushnell Hass Medium containing 0.1% PHB, 1.5% sodium chloride, at 30 °C, pH 7.5 with agitation at 130 rpm. Application of the organism in disintegrating films of PHB and its copolymers was successfully demonstrated on the basis of weight loss and scanning electron microscope analysis. To the best of our knowledge, this is the first report on production of PHB depolymerase with high efficiency by N. dassonvillei, an organism that holds promise in degrading PHB-derived waste material. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-024-04079-3.

[Characterizations of soil enzyme activities and stoichiometry in three subtropical forest stands]. / äºšçƒ­å¸¦ä¸‰ç§æž—åˆ†åœŸå£¤é ¶æ´»æ€§å’Œé ¶åŒ–å­¦è®¡é‡æ¯”ç‰¹å¾.

We conducted in a common garden experiment to explore the differences in soil enzyme activity, stoichiometry, and their influencing factors among a secondary Castanopsis carlesii forest, 10-year-old C. carlesii plantation, and Cunninghamia lanceolata plantation. The results showed that compared to the secondary forest, the soil organic carbon, total nitrogen, and dissolved organic carbon significantly decreased by 42.6%, 47.4%, and 60.9% in C. carlesii plantation, and by 42.9%, 36.7%, and 61.1% in C. lanceolata plantation. Soil microbial biomass C, microbial biomass N (MBN), and microbial biomass phosphorus decreased significantly by 40.6%, 35.5%, and 45.9% in C. carlesii plantation, and by 53.7%、56.4%, and 61.7% in C. lanceolata plantation. Compared to the secondary forest, soil enzymes activities in C. carlesii plantation did not change significantly, but in C. lanceolata plantation, the activities of ß-1,4-glucosidase and cellobiohydrolase significantly decreased by 51.2% and 59.8%, ß-N-acetyl glucosaminidase and acid phosphatase decreased significantly by 41.0% and 29.8%, and enzymatic C:N acquisition ratio and enzymatic C:P acquisition ratio significantly decreased by 11.3% and 7.7%, respectively. Results of redundancy analysis indicated that MBN and NO3--N were the primary factors influencing soil enzyme activity and enzymic stoichiometry. Collectively, there were significant differences in soil enzyme activity and microbial nutrient demands among different forest stands. Compared to secondary forests, the establishment of C. lanceolata plantations would intensify nutrient competition between plants and microbes, and exacerbate the N and P limitations for microbes.

Response of soil-microbe-extracellular enzyme stoichiometric characteristics to nitrogen deposition in a Pinus yunnanensis forest in central Yunnan Province, Southwest China.

To understand the effects of nitrogen deposition on element cycling and nutrient limitation status in forest ecosystems, we examined the effects of nitrogen deposition on the stoichiometric characteristics of forest soil-microbial-extracellular enzymes in Pinus yunnanensis forest. We conducted a field experiment with control (CK, 0 g N·m-2·a-1), low nitrogen (LN, 10 g N·m-2·a-1), medium nitrogen (MN, 20 g N·m-2·a-1) and high nitrogen (HN, 25 g N·m-2·a-1) since 2019. We collected soil samples (0-5 cm, 5-10 cm and 10-20 cm) at September 2022, and measured the contents of soil organic, total nitrogen, total phosphorus, microbial biomass carbon, nitrogen and phosphorus (MBC, MBN, MBP) and the activities of C, N, and P acquisition enzymes. The results showed that nitrogen deposition significantly reduced soil organic content, C:N and C:P by 6.9%-29.8%, 7.6%-45.2% and 6.5%-28.6%, and increased soil total N content and N:P by 10.0%-45.0% and 19.0%-46.0%, respectively. Nitrogen addition did not affect soil total P content. Except for soil C:N and C:P, soil nutrient content and stoichiometric ratio were highest in 0-5 cm soil layer. MN and HN treatments significantly decreased MBN by 11.0%-12.7%. MBC, MBP, and their stoichiometry did not change significantly under nitrogen deposition. Soil microbial nutrient content in 0-5 cm soil layer was significantly higher than that in other soil layers. Nitrogen deposition significantly decreased the activities of cellobiose hydrolase and leucine aminopeptidase (decreased by 14.5%-16.2% and 48.7%-66.3%). HN treatment promoted ß-1,4-glucosidase activity (increased by 68.0%), but inhibited soil enzyme stoichiometric carbon to nitrogen ratio and nitrogen to phosphorus ratio (decreased by 95.4% and 88.4%). LN and MN treatment promoted ß-1,4-N-acetylglucosaminidase activity (increased by 68.3%-116.6%), but inhibited enzyme stoichiometric carbon to phosphorus ratio (decreased by 14.9%-29.4%). Alkaline phosphatase activity had no significant change. Soil enzyme activities were significantly decreased with increasing soil depth. Soil total N and total P and microbial nutrients were negatively correlated with vector angle (representing microbial nitrogen or phosphorus limitation), while vector length (representing microbial carbon limitation) was consistently significantly positively correlated with vector angle, suggesting the synergistic promotion between microbial carbon limitation and phosphorus limitation. Nitrogen deposition gradually shifted to phosphorus limitation while alleviating microbial nitrogen limitation in P. yunnanensis forest. In addition, microbial activities in this region was limited by C availability, and the relationship between microbial C and P limitation was proportional.

Removal of dibutyl phthalate (DBP) by bacterial extracellular polymeric substances (EPS) via enzyme catalysis and electron transmission.

Phthalic acid esters (PAEs) showed high environmental risk due to the widely existence and toxicity. Microbial-excreted extracellular polymeric substances (EPS) showed potential of degrading organic compounds. In this study, the degradation ability and the mechanisms of EPS from two bacteria (PAEs degrader Gordonia sihwensis; electrochemically active strain Shewanella oneidensis MR-1) were investigated. Results showed that EPS of the two bacteria had different composition of C-type cytochromes, flavins, catalase, and α-glucosidase. The removal of dibutyl phthalate (DBP) by total EPS were 68% of G. sihwensis and 72% for S. oneidensis. For both bacteria, the degradation rates k of EPS were as TB-EPS > LB-EPS > S-EPS. The degradation mechanisms of EPS from the two bacteria showed difference with electrochemical active components mediated electron transmission for S. oneidensis MR-1 and enzymes catalysis for G. sihwensis. Results of this study illustrated the variation of the contribution of active components of EPS to degradation.

Initial Litter Chemistry and UV Radiation Drive Chemical Divergence in Litter during Decomposition.

Litter's chemical complexity influences carbon (C) cycling during its decomposition. However, the chemical and microbial mechanisms underlying the divergence or convergence of chemical complexity under UV radiation remain poorly understood. Here, we conducted a 397-day field experiment using 13C cross-polarization magic-angle spinning nuclear magnetic resonance (13C-CPMAS NMR) to investigate the interactions among the initial chemistry, microbial communities, and UV radiation during decomposition. Our study found that the initial concentrations of O-substituted aromatic C, di-O-alkyl C, and O-alkyl C in Deschampsia caespitosa were higher than those in Kobresia tibetica. Litter's chemical composition exhibited divergent patterns based on the initial chemistry, UV radiation, and decay time. Specifically, D. caespitosa consistently displayed higher concentrations of di-O-alkyl C and O-alkyl C compared to K. tibetica, regardless of the UV exposure and decay time. Additionally, litter's chemical complexity was positively correlated with changes in the extracellular enzyme activities, particularly those involved in lignin, cellulose, and hemicellulose degradation, which accounted for 9%, 20%, and 4% of the variation in litter's chemical complexity, respectively. These findings highlighted the role of distinct microbial communities in decomposing different C components through catabolism, leading to chemical divergence in litter. During the early decomposition stages, oligotrophic Planctomycetes and Acidobacteria metabolized O-alkyl C and di-O-alkyl C under UV-blocking conditions. In contrast, copiotrophic Actinobacteria and Chytridiomycota utilized these components under UV radiation exposure, reflecting their ability to thrive under UV stress conditions due to their rapid growth strategies in environments rich in labile C. Our study revealed that the inherent differences in the initial O-alkyl C and di-O-alkyl C contributed to the chemical divergence, while UV radiation further influenced this divergence by shifting the microbial community composition from oligotrophic to copiotrophic species. Thus, differences in the initial litter chemistry, microbial community, and UV radiation affected the quantity and quality of plant-derived C during decomposition.

Microbial remineralization processes during postspring-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 southwest Finnish archipelago, we examined nitrogen, phosphorus, and carbon acquiring extracellular enzyme activities in three size fractions (<0.2, 0.2-3, and >3 µm), 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 toward 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.

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.

Effects of exogenous copper on microbial metabolic function and carbon use efficiency of Panax notoginseng planting soil.

Soil copper (Cu) pollution is a serious environmental risk in the Panax notoginseng planting area. However, the effect of Cu on soil microbial metabolism and nutrient cycling in this area remains unknown. Therefore, Biolog ECO-plate and enzyme stoichiometry methods were utilized in this study to investigate the impact of exogenous Cu (control: 0 mg·kg-1; Cu100: 100 mg·kg-1; Cu400: 400 mg·kg-1; and Cu600: 600 mg·kg-1) on the metabolic function of soil microbial and nutrient limitation in the P. notoginseng soil. The results indicated that Cu100 significantly increased soil organic carbon (SOC), total phosphorus (TP), soil C:N, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) 9.89%, 15.65%, 17.91%, 61.87%, and 90.56% higher than the control, respectively. Moreover, the carbon source utilization ratio of carbohydrates, amino acids, and amphiphilic compounds of Cu100 also increased by 7.16%, 25.47%, and 84.68%, respectively, compared with the control. The activities of ß-1,4-glucosidase, cellobiohyrolase, leucine amino peptidase, ß-1,4-N-acetylglucosaminidase, and phosphatase significantly decreased with increasing Cu concentration. Soil enzyme stoichiometry showed that all treatments were limited by nitrogen (vector angle < 45°; 19.045-22.081). Cu600 led to the lowest carbon limitation (1.798) and highest carbon use efficiency (CUE:0.267). The PLS-SEM model also showed that MBC, MBN, MBP, and microbial diversity positively affected carbon and nitrogen limitation (0.654 and 0.424). Soil carbon, nitrogen, phosphorus, stoichiometric ratio, MBC, MBN, and MBP positively affected CUE (0.527 and 0.589). The microbial diversity index significantly negatively affected CUE (-1.490). Multiple linear stepwise regression analyses showed that CUE was mainly influenced by MBC, AP, C:P, and LAP. Thus, P. notoginseng soil can benefit soil microbial carbon and nitrogen limitations at low Cu concentrations. Clarifying the metabolic activity and nutritional status of microorganisms under Cu stress can provide some theoretical basis for realizing China's comprehensive and effective management and control policies for environmental risks from metals by 2035.

Intermediate Disturbances Enhance Microbial Enzyme Activities in Soil Ecosystems.

The Intermediate Disturbance Hypothesis (IDH) posits that maximal plant biodiversity is attained in environments characterized by moderate ecological disturbances. Although the applicability of the IDH to microbial diversity has been explored in a limited number of studies, there is a notable absence of experimental reports on whether soil microbial 'activity' demonstrates a similar response to the frequency or intensity of environmental disturbances. In this investigation, we conducted five distinct experiments employing soils or wetland sediments exposed to varying intensities or frequencies of disturbances, with a specific emphasis on disturbances associated with human activity, such as chemical contamination, hydrologic changes, and forest thinning. Specifically, we examined the effects of bactericide and heavy metal contamination, long-term drainage, tidal flow, and thinning management on microbial enzyme activities in soils. Our findings revealed that microbial enzyme activities were highest at intermediate disturbance levels. Despite the diversity in experiment conditions, each trial consistently demonstrated analogous patterns, suggesting the robustness of the IDH in elucidating microbial activities alongside diversity in soils. These outcomes bear significant implications for ecological restoration and management, as intermediate disturbance may expedite organic matter decomposition and nutrient cycles, crucial for sustaining ecosystem services in soils.

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.

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 ß-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.

Patterns of prokaryotic activity along the marine planktonic matter continuum.

Prokaryotic abundance and activity are commonly assessed by dividing them into two size-fractions: free-living and attached to particles. Nevertheless, organic matter, essential for the growth of heterotrophic prokaryotes, is present in the environment in a continuum of sizes, from purely dissolved to large particles. Therefore, defining the activity of the prokaryotic community would be more accurate by considering all the distinct size fractions. To achieve this, we measured prokaryotic abundance (PA), heterotrophic prokaryotic activity (as leucine incorporation) and extracellular enzyme activities at a coastal site in the NW Mediterranean Sea. We conducted measurements in both bulk seawater and size fractionated samples sequentially passing through 5 different filter types: 0.2-0.8-3-5-10 µm pore size. Our results indicate that the fraction <0.8 µm contained the highest percentage of cells (91.6 ± 1.1 %) and leucine incorporation rates (72.2 ± 3.5 %). Most of the extracellular enzyme activity appeared in the dissolved fraction (<0.2 µm; 19.8-79.4 %), yet the specific activity of the enzymes (per cell activity) was 100-1000 times higher in the particulate (>0.8 µm) than in the free-living (0.2-0.8 µm) fraction. The size fraction with highest specific activities for leucine incorporation and most of the enzyme activities (ß-glucosidase, esterase, Leu-aminopeptidase and alkaline phosphatase) was the 5-10 µm fraction. In contrast, the higher specific chitobiase activity in the >10 µm fraction, suggests that the prokaryotic community colonizing large particles might be more specialized in the hydrolysis of organic matter of zooplanktonic origin than the community colonizing smaller particles.

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.

Vegetation restoration in an alpine meadow: Insights from soil microbial communities and resource limitation across soil depth.

Aboveground vegetation restoration shapes the soil microbial community structure and affects microbial resource acquisition. However, the changes in soil microbial resource limitation in subsoil during vegetation restoration are still unclear. In this study, the microbial community structure and resource limitation in an alpine meadow soil profile that had undergone natural restoration for short-term (4-year) and long-term (10-year) restoration in response to vegetation restoration were explored through high-throughput sequencing analysis and extracellular enzyme stoichiometry (EES). There was no significant difference in microbial composition and α diversity between short- and long-term restoration soils. Soil microorganisms in this alpine meadow were mainly limited by phosphorus. Carbon limitation of soil microorganisms was significantly decreased in each layer (0-15, 15-30, 30-45, 45-60, and 60-80 cm corresponding to L1, L2, L3, L4, and L5, respectively) of long-term restoration soils when compared to that of the short-term restoration soil layers, while phosphorus limitation of microorganisms in subsoil (60-80 cm) was significantly increased by 17.38%. Soil nutrients, pH, moisture content, and microbial composition are the main drivers of microbial resource limitation in restoration, and their effects on microbial resource limitation were different in short- and long-term restoration. Meanwhile, key microbial taxa have a significant impact on microbial resource limitation, especially in short-term restoration soils. This study suggested that vegetation restoration significantly affected soil microbial resource limitation, and could alleviate microbial resource limitations by adding nutrients, thus accelerating the process of vegetation restoration in alpine ecosystems.

Changes in nutrient availability substantially alter bacteria and extracellular enzymatic activities in Antarctic soils.

In polar regions, global warming has accelerated the melting of glacial and buried ice, resulting in meltwater run-off and the mobilization of surface nutrients. Yet, the short-term effects of altered nutrient regimes on the diversity and function of soil microbiota in polyextreme environments such as Antarctica, remains poorly understood. We studied these effects by constructing soil microcosms simulating augmented carbon, nitrogen, and moisture. Addition of nitrogen significantly decreased the diversity of Antarctic soil microbial assemblages, compared with other treatments. Other treatments led to a shift in the relative abundances of these microbial assemblages although the distributional patterns were random. Only nitrogen treatment appeared to lead to distinct community structural patterns, with increases in abundance of Proteobacteria (Gammaproteobateria) and a decrease in Verrucomicrobiota (Chlamydiae and Verrucomicrobiae).The effects of extracellular enzyme activities and soil parameters on changes in microbial taxa were also significant following nitrogen addition. Structural equation modeling revealed that nutrient source and extracellular enzyme activities were positive predictors of microbial diversity. Our study highlights the effect of nitrogen addition on Antarctic soil microorganisms, supporting evidence of microbial resilience to nutrient increases. In contrast with studies suggesting that these communities may be resistant to change, Antarctic soil microbiota responded rapidly to augmented nutrient regimes.

Rare microbial taxa as the major drivers of nutrient acquisition under moss biocrusts in karst area.

Karst rocky desertification refers to the process of land degradation caused by various factors such as climate change and human activities including deforestation and agriculture on a fragile karst substrate. Nutrient limitation is common in karst areas. Moss crust grows widely in karst areas. The microorganisms associated with bryophytes are vital to maintaining ecological functions, including climate regulation and nutrient circulation. The synergistic effect of moss crusts and microorganisms may hold great potential for restoring degraded karst ecosystems. However, our understanding of the responses of microbial communities, especially abundant and rare taxa, to nutrient limitations and acquisition in the presence of moss crusts is limited. Different moss habitats exhibit varying patterns of nutrient availability, which also affect microbial diversity and composition. Therefore, in this study, we investigated three habitats of mosses: autochthonal bryophytes under forest, lithophytic bryophytes under forest and on cliff rock. We measured soil physicochemical properties and enzymatic activities. We conducted high-throughput sequencing and analysis of soil microorganisms. Our finding revealed that autochthonal moss crusts under forest had higher nutrient availability and a higher proportion of copiotrophic microbial communities compared to lithophytic moss crusts under forest or on cliff rock. However, enzyme activities were lower in autochthonal moss crusts under forest. Additionally, rare taxa exhibited distinct structures in all three habitats. Analysis of co-occurrence network showed that rare taxa had a relatively high proportion in the main modules. Furthermore, we found that both abundant and rare taxa were primarily assembled by stochastic processes. Soil properties significantly affected the community assembly of the rare taxa, indirectly affecting microbial diversity and complexity and finally nutrient acquisition. These findings highlight the importance of rare taxa under moss crusts for nutrient acquisition. Addressing this knowledge gap is essential for guiding ongoing ecological restoration projects in karst rocky desertification regions.

Effects of seasonal precipitation regimes on microbial biomass and extracellular enzyme activity during shrub foliar litter decomposition in a subtropical forest.

Elucidating the mechanisms underlying microbial biomass and extracellular enzyme activity responses to the seasonal precipitation regime during foliar litter decomposition is highly important for understanding the material cycle of forest ecosystems in the context of global climate change; however, the specific underlying mechanisms remain unclear. Hence, a precipitation manipulation experiment involving a control (CK) and treatments with decreased precipitation in the dry season and extremely increased precipitation in the wet season (IE) and decreased precipitation in the dry season and proportionally increased precipitation in the wet season (IP) was conducted in a subtropical evergreen broad-leaved forest in China from October 2020 to October 2021. The moisture, microbial biomass, and extracellular enzyme activities of foliar litter from two dominant shrub species, Phyllostachys violascens and Alangium chinense, were measured at six stages during the dry and wet seasons. The results showed that (1) both IE and IP significantly decreased the microbial biomass carbon and microbial biomass nitrogen content and the activities of ß-1,4-glucosidase, ß-1,4-N-acetylglucosaminidase, acid phosphatase and cellulase in the dry season, while the opposite effects were observed in the wet season. (2) Compared with those of IE, the effects of IP on foliar litter microbial biomass and extracellular enzyme activity were more significant. (3) The results from the partial least squares model indicated that extracellular enzyme activity during foliar litter decomposition was strongly controlled by the foliar litter water content, microbial biomass nitrogen, the ratio of total carbon to total phosphorus, foliar litter total carbon, and foliar litter total nitrogen. These results provide an important theoretical basis for elucidating the microbial mechanisms driving litter decomposition in a subtropical forest under global climate change scenarios.

Long-term cultivation reduces soil carbon storage by altering microbial network complexity and metabolism activity in macroaggregates.

Cultivation alters soil aggregation, microbial compositions and the potential for carbon sequestration in cropland soils. However, the specific effects of long-term cultivation and the underlying mechanisms on soil organic carbon (SOC) storage at different aggregate sizes remain poorly understood. We characterized the dynamics of SOC storage in macroaggregates (>0.25 mm) and microaggregates (<0.25 mm) across four paddy soils successively cultivated for 60, 100, 125, and 150 years. Microbial community compositions, network patterns, enzyme activities and carbon use efficiency (CUE) were examined to elucidate the underlying microbial pathways governing SOC storage. The results showed that prolonged cultivation led to an average reduction of 45 % in SOC storage, particularly in macroaggregates. Partial least squares path modeling revealed that shifts in microorganisms in macroaggregates explained almost 80 % of the variation in SOC storage. Specifically, variations in fungal composition and decreased complexity of microbial interaction networks were strongly correlated with SOC storage. Fungal community and microbial interactions also indirectly affected SOC storage by positively correlating with extracellular enzyme activity. Moreover, bacterial composition indirectly regulated SOC storage by positively correlating with carbon use efficiency. Our findings indicated that the macroaggregate-associated microbial interactions and the metabolism activities had significant implications for SOC sequestration in paddy fields. We suggest that implementation of management practices targeted at improvement of these microbial attributes could enhance agroecosystems sustainability.

Effects of TrPLDs on the pathogenicity of Trichothecium roseum infected apple fruit.

Phospholipase D plays a critical regulatory role in the pathogenicity of filamentous fungi. However, the molecular mechanism of PLD regulating the pathogenicity of filamentous fungi has not been reported. In this research, the previously constructed TrPLD1 and TrPLD2 (TrPLDs) mutants were used as test strains. Firstly, the function of TrPLDs in Trichothecium roseum was studied. Then, the effects of TrPLDs on the pathogenicity of T. roseum and the quality of the inoculated apples were verified. The results suggested that the deletion of TrPLD1 delayed the spore germination of ΔTrPLD1 and inhibited germ tube elongation by down-regulating the expressions of TrbrlA, TrabaA and TrwetA. By down-regulating the extracellular enzyme-coding gene expressions, ΔTrPLD1 inhibited the degradation of apple fruit cell wall and the change of fatty acid content during infection, reduced the cell membrane permeability and malondialdehyde (MDA) content of apple fruit, thereby maintaining the integrity of fruit cell membrane, and reduced the pathogenicity of ΔTrPLD1 to apple and kept the quality of apple. However, ΔTrPLD2 did not have a significant effect on the infection process of apple fruit by the pathogen.

Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including ß-1,4-glucosidase, ß-D-cellobiosidase, ß-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.