Organic amendments increased Chinese milk vetch symbiotic nitrogen fixation by enriching Mesorhizobium in rhizosphere.

Symbiotic nitrogen fixation of Chinese milk vetch (Astragalus sinicus L.) can fix nitrogen from the atmosphere and serve as an organic nitrogen source in agricultural ecosystems. Exogenous organic material application is a common practice of affecting symbiotic nitrogen fixation; however, the results of the regulation activities remain under discussion. Studies on the impact of organic amendments on symbiotic nitrogen fixation have focused on dissolved organic carbon content changes, whereas the impact on dissolved organic carbon composition and the underlying mechanism remain unclear. In situ pot experiments were carried out using soils from a 40-year-old field experiment platform to investigate symbiotic nitrogen fixation rate trends, dissolved organic carbon concentration and component, and diazotroph community structure in roots and in rhizosphere soils following long-term application of different exogenous organic substrates, i.e., green manure, green manure and pig manure, and green manure and rice straw. Remarkable increases in rate were observed in and when compared with that in green manure treatment, with the greatest enhancement observed in the treatment. Moreover, organic amendments, particularly pig manure application, altered diazotroph community composition in rhizosphere soils, therefore increasing the abundance of the host-specific genus Mesorhizobium. Furthermore, organic amendments influence the diazotroph communities through two primary mechanisms. Firstly, the components of dissolved organic carbon promote an increase in available iron, facilitated by the presence of humus substrates. Secondly, the elevated content of dissolved organic carbon and available iron expands the niche breadth of Mesorhizobium within the rhizosphere. Consequently, these alterations result in a modified diazotroph community within the rhizosphere, which in turn influences Mesorhizobium nodulation in the root and symbiotic nitrogen fixation rate. The results of the present study enhance our understanding of the impact of organic amendments on symbiotic nitrogen fixation and the underlying mechanism, highlighting the key role of dissolved organic carbon composition on diazotroph community composition in the rhizosphere.

Body size mediates the functional potential of soil organisms by diversity and community assembly across soil aggregates.

Body size is an important life-history trait that affects organism niche occupancy and ecological interactions. However, it is still unclear to what extent the assembly process of organisms with different body sizes affects soil biogeochemical cycling processes at the aggregate level. Here, we examined the diversity and community assembly of soil microorganisms (bacteria, fungi, and protists) and microfauna (nematodes) with varying body sizes. The microbial functional potential associated with carbon, nitrogen, phosphorus, and sulfur metabolism within three soil aggregate sizes (large macroaggregates, > 2 mm; small macroaggregates, 0.25-2 mm; and microaggregates, < 0.25 mm) were determined by metagenomics. We found that the smallest microbes (bacteria) had higher α-diversity and lower ß-diversity and were mostly structured by stochastic processes, while all larger organisms (fungi, protists, and nematodes) had lower α-diversity and were relatively more influenced by deterministic processes. Structural equation modeling indicated that the microbial functional potential associated with carbon, nitrogen, phosphorus, and sulfur metabolism was mainly influenced by the bacterial and protist diversity in microaggregates. In contrast, the microbial functional potential was primarily mediated by the assembly processes of four organism groups, especially the nematode community in macroaggregates. This study reveals the important roles of soil organisms with different body sizes in the functional potential related to nutrient cycling, and provides new insights into the ecological processes structuring the diversity and community assembly of organisms of different body sizes at the soil aggregate level, with implications for soil nutrient cycling dynamics.

Community assembly of organisms regulates soil microbial functional potential through dual mechanisms.

Unraveling the influence of community assembly processes on soil ecosystem functioning presents a major challenge in the field of theoretical ecology, as it has received limited attention. Here, we used a series of long-term experiments spanning over 25 years to explore the assembly processes of bacterial, fungal, protist, and nematode communities using high-throughput sequencing. We characterized the soil microbial functional potential by the abundance of microbial genes associated with carbon, nitrogen, phosphorus, and sulfur cycling using GeoChip-based functional gene profiling, and determined how the assembly processes of organism groups regulate soil microbial functional potential through community diversity and network stability. Our results indicated that balanced fertilization (NPK) treatment improved the stochastic assembly of bacterial, fungal, and protist communities compared to phosphorus-deficient fertilization (NK) treatment. However, there was a nonsignificant increase in the normalized stochasticity ratio of the nematode community in response to fertilization across sites. Our findings emphasized that soil environmental factors influenced the assembly processes of the biotic community, which regulated soil microbial functional potential through dual mechanisms. One mechanism indicated that the high phosphorus levels and low soil nutrient stoichiometry may increase the stochasticity of bacterial, fungal, and protist communities and the determinism of the nematode community under NPK treatment, ultimately enhancing soil microbial functional potential by reinforcing the network stability of the biotic community. The other mechanism indicated that the low phosphorus levels and high soil nutrient stoichiometry may increase the stochastic process of the bacterial community and the determinism of the fungal, protist, and nematode communities under NK treatment, thereby enhancing soil microbial functional potential by improving the ß-diversity of the biotic community. Taken together, these results provide valuable insights into the mechanisms underlying the assembly processes of the biotic community that regulate ecosystem functioning.

[Effects of Organic Fertilization on Bacterial Community and Maize Productivity in Dryland Red Soil].

Since 2002, a long-term field experiment has been conducted to determine the effects of different organic fertilization treatments on the bacterial community characteristics and maize productivity in dryland red soil using high-throughput sequencing technology. The experiment consisted of four treatments:no manure, M0; low manure, M1; high manure, M2; and high manure with lime addition, M3. Our results showed that the different organic fertilization treatments(M1, M2, and M3) significantly promoted maize productivity with the highest values of pH, soil organic matter(SOM), total nitrogen(TN), and total phosphorus(TP) compared to that under the M0 treatment, and the high manure with lime addition(M3) treatment had the highest level of maize production. The different organic fertilization treatments significantly increased the Shannon index, Evenness index, Chao1 index, and ACE index and significantly shaped the composition of the bacterial community. TP and pH were the main variables determining soil bacterial diversity index based on random forest modeling analysis, whereas pH, SOM, TP, and TN were the main variables determining the structure of the soil bacterial community. Correlation analysis and structural equation modeling determined that TP and SOM indirectly affected maize productivity by varying the bacterial diversity and community structure. The results of this study provide the scientific basis for ensuring food security and sustainable agricultural development by improving the fertility and bacterial diversity in dryland red soil.

Fossil-fuel-dependent scenarios could lead to a significant decline of global plant-beneficial bacteria abundance in soils by 2100.

Exploiting the potential benefits of plant-associated microbes represents a sustainable approach to enhancing crop productivity. Plant-beneficial bacteria (PBB) provide multiple benefits to plants. However, the biogeography and community structure remain largely unknown. Here we constructed a PBB database to couple microbial taxonomy with their plant-beneficial traits and analysed the global atlas of potential PBB from 4,245 soil samples. We show that the diversity of PBB peaks in low-latitude regions, following a strong latitudinal diversity gradient. The distribution of potential PBB was primarily governed by environmental filtering, which was mainly determined by local climate. Our projections showed that fossil-fuel-dependent future scenarios would lead to a significant decline of potential PBB by 2100, especially biocontrol agents (-1.03%) and stress resistance bacteria (-0.61%), which may potentially threaten global food production and (agro)ecosystem services.

Comparison of Rare and Common Diseases in the Setting of Healthcare Priorities: Evidence of Social Preferences Based on a Systematic Review.

Background: In light of the limited availability of healthcare resources, providing universal access to healthcare is a challenging task. As a result, prioritizing healthcare services has emerged as a crucial issue. This study aims to explore the preferences of the public regarding healthcare prioritization for rare and common diseases. By examining public attitudes, this study seeks to inform government decisions concerning resource allocation and distribution within healthcare. Methods: "Social preference" and "rare disease" were searched as MeSH terms in the electronic databases of Ovid Medline, Web of Science, Embase, and Econlit for articles published since their establishment, and the information on the characteristics of the articles and the results of social preferences for rare diseases were analyzed and summarized. Results: The public held predominantly neutral views on the setting of healthcare priorities for rare and common diseases. The results of the included studies showed that with all else being equal, no social preference for rarity was found, but when the public considered the proportional advantage of rare diseases or when the respondents were young, a social preference for rarity existed. In addition, the public weighed attributes such as the health benefits of treatments, the effectiveness of treatment options, the safety of treatment, equity, unmet needs, and disease severity in the process of setting of treatment priorities for rare diseases. Furthermore, in consideration of equity, the public showed a willingness to pay for rare diseases in spite of the high medical costs. Conclusion: International studies on social preferences provide some evidence for the setting of healthcare priorities for rare diseases, and health policymakers should consider social preferences in an integrated manner in order to set healthcare priorities appropriately.

Modeling soil bacterial diversity: challenges and opportunities.

Understanding the mechanisms structuring soil bacterial diversity has critical implications to advance the parametrization of species distribution models. This forum article discusses recent advances in the use of the metabolic theory of ecology applicable to soil microbiology, and highlights challenges and opportunities to inform future empirical and theoretical studies.

Interaction between nematodes and bacteria enhances soil carbon sequestration under organic material amendments.

The process of carbon (C) sequestration plays an important role in soil fertility and productivity, yet most studies have focused on the individual role of the bacterial community. However, an in-depth mechanistic understanding of how soil nematodes interact with the bacterial community to regulate soil C accumulation is still lacking. We conducted a 10-year field experiment to explore the nematode and bacterial communities and determine the influence of nematode-bacteria interactions on C mineralization, microbial metabolic quotient (qCO2), and carbon use efficiency (CUE) under the organic material amendments, including chemical fertilizers with straw (NS), chemical fertilizers with straw and pig manure (NSM), and chemical fertilizer with straw biochar (NB). Here, our results showed the abundance of bacterial and nematode communities was significantly higher under NS, NSM, and NB treatments than under chemical fertilizers (N) treatment, with the highest abundance under the NSM treatment. The enrichment index and functional dispersion index were significantly higher under NSM treatment than under N, NS, and NB treatments, while the channel index followed the opposite pattern. Structural equation modeling indicated that the potential predation pressure induced by nematodes may improve bacterial abundance, with positive cascading effects on C sequestration. Collectively, our study highlights the functional importance of nematode-microorganism interactions in mediating C dynamics under organic material amendments.

Cadmium tolerance in Elodea canadensis Michx: Subcellular distribution and metabolomic analysis.

The aquatic plant Elodea canadensis is considered a good candidate for ecotoxicological investigations. Cadmium (Cd) is a widespread contaminant in aquatic systems. In this study, to better elucidate the underlying tolerance mechanism and molecular impact of environmentally relevant Cd concentration in aquatic plants, subcellular distribution, chemical forms, and gas chromatography-mass spectrometry-based non-targeted metabolomics profiles were comprehensively analyzed in E. canadensis subjected to 0 and 10 µM Cd treatment for 5 d. Subcellular fractionation analysis of Cd-containing leaves showed that 67% of Cd was compartmentalized in cell wall followed by the soluble fraction (24 %) and organelles (9 %). The majority of Cd (90 %) was found in the extraction using 1 M NaCl. Metabolomic analysis using unsupervised principal component analyses and a supervised partial least squares discriminant analysis revealed clear differences in metabolic profiles between the two groups, demonstrating the metabolic effects of Cd. The 155 identified compounds altered by Cd were mainly from primary metabolism, including sugars, amino acids, organic acids, and their derivatives. Secondary metabolites such as polyphenols and phenolamides were also detected. The massive up-regulation of metabolites, including trehalose, proline, sarcosine, nicotianamine, putrescine, α-ketoglutaric acid, citric acid, and phytol might represent a detoxification mechanism. These findings highlighted the mechanistic strategies that E. canadensis employs to defend against Cd toxicity.

The effect of ε-poly-l-lysine treatment on molecular, physiological and biochemical indicators related to resistance in longan fruit infected by Phomopsis longanae Chi.

Postharvest longan fruits are subjected to Phomopsis longanae Chi (P. longanae) infection that lead to fruit quality deterioration. We hypothesized that ε-poly-l-lysine (ε-PL) could enhance fruit disease resistance in longans. Through physiological and transcriptomic analyses, the results showed that, compared to P. longanae-infected longan fruit, ε-PL + P. longanae treatment reduced the disease development of longan fruits. Additionally, ε-PL + P. longanae treatment increased the contents of disease-resistant substances (lignin and H2O2) and the activities of disease-resistance enzymes (CHI, PAL, PPO, C4H, CAD, GLU, 4CL, and POD). Furthermore, the expressions of genes relevant to the phenylpropanoid biosynthesis pathway and plant-pathogen interaction pathway (Rboh, FLS2, WRKY29, FRK1, and PR1) were up-regulated by ε-PL + P. longanae treatment. These findings demonstrated that ε-PL treatment inhibited the disease development of postharvest longan fruits were associated with the increased accumulation of disease-resistant related substances, as well as the raised activities and genes expressions of disease-resistance related enzymes.

Microbial keystone taxa drive succession of plant residue chemistry.

Managing above-ground plant carbon inputs can pave the way toward carbon neutrality and mitigating climate change. Chemical complexity of plant residues largely controls carbon sequestration. There exist conflicting opinions on whether residue chemistry diverges or converges after long-term decomposition. Moreover, whether and how microbial communities regulate residue chemistry remains unclear. This study investigated the decomposition processes and residue composition dynamics of maize straw and wheat straw and related microbiomes over a period of 9 years in three climate zones. Residue chemistry exhibited a divergent-convergent trajectory during decomposition, that is, the residue composition diverged during the 0.5-3 year period under the combined effect of straw type and climate and then converged to an array of common compounds during the 3-9 year period. Chemical divergence during the first 2-3 years was primarily driven by the changes in extracellular enzyme activity influenced by keystone taxa-guided bacterial networks, and the keystone taxa belonged to Alphaproteobacteria, particularly Rhizobiales. After 9 years, microbial assimilation became dominant, leading to chemical convergence, and fungi, particularly Chaetomium, were the main contributors to microbial assimilation. Overall, this study demonstrated that keystone taxa regulate the divergent-convergent trajectory in residue chemistry.

Effects of ultrasonic treatment on the surface bacteria of Lyophyllum decastes during storage.

This study explores the relationship between the storage quality and bacterial microflora in the mushroom Lyophyllum decastes. The surface bacteria of L. decastes were separated by combining the traditional culture plate separation and 16S rRNA sequencing method, to study the effects of ultrasonic (US) treatment on the surface bacteria of L. decastes during storage. The results demonstrated that Pantoea agglomerans and Pseudomonas fluorescens were among the 15 culturable bacteria isolated with traditional plate method during storage, belonging to 2 phyla and 7 genera. US treatment could inhibit the growth and significantly increase cell membrane permeability, and contents extravasation in P. agglomerans, though its inhibitory effect on P. fluorescens was less. The 16S rRNA sequencing revealed, bacteria from 9 phyla and 35 genera were isolated, and P. fluorescens was the dominant species throughout the storage time. These results indicated that the composition of mushroom surface microflora of Control (CK) and US groups are similar, and the bacterial microflora networks analysis also showed a positive correlation. The KEGG annotation for the functional classification of the bacteria showed that a total of 328 pathways were acquired at the KEGG l3 level, and the relative abundance of membrane transport, amino acid metabolism, carbohydrate metabolism, and energy metabolism pathway was high. Moreover, the relative abundance of the surface bacteria of L. decastes also decreased. Hence, the US treatment had a better bacteriostatic effect, maintained the whiteness index and firmness, and improved the sensory quality of L. decastes during storage.

Integrating pH into the metabolic theory of ecology to predict bacterial diversity in soil.

Microorganisms play essential roles in soil ecosystem functioning and maintenance, but methods are currently lacking for quantitative assessments of the mechanisms underlying microbial diversity patterns observed across disparate systems and scales. Here we established a quantitative model to incorporate pH into metabolic theory to capture and explain some of the unexplained variation in the relationship between temperature and soil bacterial diversity. We then tested and validated our newly developed models across multiple scales of ecological organization. At the species level, we modeled the diversification rate of the model bacterium Pseudomonas fluorescens evolving under laboratory media gradients varying in temperature and pH. At the community level, we modeled patterns of bacterial communities in paddy soils across a continental scale, which included natural gradients of pH and temperature. Last, we further extended our model at a global scale by integrating a meta-analysis comprising 870 soils collected worldwide from a wide range of ecosystems. Our results were robust in consistently predicting the distributional patterns of bacterial diversity across soil temperature and pH gradients-with model variation explaining from 7 to 66% of the variation in bacterial diversity, depending on the scale and system complexity. Together, our study represents a nexus point for the integration of soil bacterial diversity and quantitative models with the potential to be used at distinct spatiotemporal scales. By mechanistically representing pH into metabolic theory, our study enhances our capacity to explain and predict the patterns of bacterial diversity and functioning under current or future climate change scenarios.

Toxicity sharing model of earthworm intestinal microbiome reveals shared functional genes are more powerful than species in resisting pesticide stress.

Earthworm intestinal bacteria and indigenous soil bacteria work closely during various biochemical processes and play a crucial role in maintaining the internal stability of the soil environment. However, the response mechanism of these bacterial communities to external pesticide disturbance is unknown. In this study, soil and earthworm gut contents were metagenomically sequenced after exposure to various concentrations of nitrochlorobenzene (0-1026.7 mg kg-1). A high degree of similarity was found between the microbial community composition and abundance in the worm gut and soil, both of which decreased significantly (P < 0.05) under elevated pesticide stress. The toxicity sharing model (TSM) showed that the toxicity sharing capacity was 97.4-125.7 % and 100.4-130.2 % for Egenes (genes in the worm gut) and Emet(degradation genes in the worm gut) in the earthworm intestinal microbiome, respectively. This indicated that the earthworm intestinal microbiome assisted in relieving the pesticide toxicity of the indigenous soil microbiome. This study showed that the TSM could quantitatively describe the toxic effect of pesticides on the earthworm intestinal microbiome. It provides a new analytical model for investigating the ecological alliance between earthworm intestinal microbiome and indigenous soil microbiome under pesticide stress while contributing a more profound understanding of the potential to use earthworms to mitigate pesticide pollution in soils and develop earthworm-based soil remediation techniques.

Biogeographical patterns of abundant and rare bacterial biospheres in paddy soils across East Asia.

Soil bacterial communities play fundamental roles in ecosystem functioning and often display a skewed distribution of abundant and rare taxa. So far, relatively little is known about the biogeographical patterns and mechanisms structuring the assembly of abundant and rare biospheres of soil bacterial communities. Here, we studied the geographical distribution of different bacterial sub-communities by examining the relative influence of environmental selection and dispersal limitation on taxa distributions in paddy soils across East Asia. Our results indicated that the geographical patterns of four different bacterial sub-communities consistently displayed significant distance-decay relationships (DDRs). In addition, we found niche breadth and dispersal rates to significantly explain differences in community assembly of abundant and rare taxa, directly affecting the strength of DDRs. While conditionally rare and abundant taxa displayed the strongest DDR due to higher environmental filtering and dispersal limitation, moderate taxa sub-communities had the weakest DDR due to greater environmental tolerance and dispersal rate. Random forest models indicated that soil pH (9.13%-49.78%) and average annual air temperature (16.59%-46.49%) were the most important predictors of the variation in the bacterial community. This study advances our understanding of the intrinsic links between fundamental ecological processes and microbial biogeographical patterns in paddy soils.

Flammutoxin, a Degradation Product of Transepithelial Electrical Resistance-Decreasing Protein, Induces Reactive Oxygen Species and Apoptosis in HepG2 Cells.

Proteins from Flammulina filiformis were prepared by sodium chloride extraction and fractionated by ammonium sulfate precipitation with increasing saturation degrees to obtain the protein fractions Ffsp-30, Ffsp-50, Ffsp-70, Ffsp-90, and Ffp-90. Among these protein fractions, Ffsp-50 possessed the most significant cytotoxic effect against three human gastrointestinal cancer cell lines, viz. HT-29, SGC-7901, and HepG2. SDS-PAGE and MALDI-TOF/TOF MS/MS analyses revealed that flammutoxin (FTX) was present as a dominating protein in Ffsp-50, which was further evidenced by HPLC-MS/MS determination. Furthermore, native FTX was purified from Ffsp-50 with a molecular weight of 26.78 kDa, exhibiting notable cytotoxicity against gastrointestinal cancer cell lines. Both Ffsp-50 and FTX exposure could enhance intercellular reactive oxygen species (ROS) generation and induce significant apoptosis in HepG2 cells. FTX was identified to be relatively conserved in basidiomycetes according to phylogenetic analysis, and its expression was highly upregulated in the primordium as well as the pileus of the fruiting body from the elongation and maturation stages, as compared with that in mycelium. Taken together, FTX could remarkably inhibit cell growth and induce ROS and apoptosis in HepG2 cells, potentially participating in the growth and development of the fruiting body. These findings from our investigation provided insight into the antigastrointestinal cancer activity of FTX, which could serve as a biological source of health-promoting and biomedical applications.

Fertilization treatments affect soil CO2 emission through regulating soil bacterial community composition in the semiarid Loess Plateau.

A growing body of literature have emphasized the effects of fertilization regimes on soil respiration and microbial community in the semiarid region, however, fertilization treatment effects on the soil CO2 emission, soil bacterial community, and their relationships from long-term experiments is lacking. In the present study, we investigated the effects of long-term fertilization regimes on soil bacterial community and thereafter on soil CO2 emission. A 9-year field experiment was conducted with five treatments, including no fertilizer (NA) and four fertilization treatments (inorganic fertilizer (CF), inorganic plus organic fertilizer (SC), organic fertilizer (SM), and maize straw (MS)) with equal N input as N 200 kg hm-2. The results indicated that CO2 emission was significantly increased under fertilization treatments compared to NA treatment. The bacterial abundance was higher under MS treatment than under NA treatment, while the Chao1 richness showed opposite trend. MS treatment significantly change soil bacterial community composition compared to NA treatment, the phyla (Alphaproteobacteria and Gammaproteobacteria) and potential keystone taxa (Nitrosomonadaceae and Beijerinckiaceae) were higher, while the Acidobacteriota was lower under MS treatment than under NA treatment. CO2 emission was positively correlated with the abundance of Alphaproteobacteria, Gammaproteobacteria, and keystone taxa, negatively correlated with these of Acidobacteriota. Random forest modeling and structural equation modeling determined soil organic carbon, total nitrogen, and the composition and network module III of the bacterial community are the main factors contribute to CO2 emission. In conclusion, our results suggest that the increased CO2 emission was affected by the varied of soil bacterial community composition derived from fertilization treatments, which was related to Alphaproteobacteria, Gammaproteobacteria, Acidobacteriota, and potential keystone taxa (Nitrosomonadaceae and Beijerinckiaceae), and highlight that the ecological importance of the bacterial community in mediating carbon cycling in the semiarid Loess Plateau.

[Effects of ultrasound on the physiological characteristics and competitive growth between Microcystis aeruginosa and Chlorella pyrenoidosa]. / è¶ å£°æ³¢å¯¹é“œç»¿å¾®å›Šè—»ä¸Žè›‹ç™½æ ¸å°çƒè—»ç”Ÿç†ç‰¹å¾åŠç«žäº‰ç”Ÿé•¿çš„å½±å“.

Microcystis aeruginosa is a common bloom-forming cyanobacterium, which generally coexists and competes with Chlorella pyrenoidosa in lakes. Sonication can be used for emergency management of algal blooms. Ultrasound influences algal growth and physiological parameters, as well as interspecific competition in algal community. To explore the effects of ultrasonic stress (35 kHz, 0.035 W·cm-3) on physiological characteristics and interspecific competition of algae, M. aeruginosa and C. pyrenoidosa were sonicated in mono- and co-cultures (1:1 mixture, according to cell concentration). Results showed that M. aeruginosa was more sensitive to ultrasonic stress. After the sonication for 600 s, both photosynthetic activity (Fv/Fm) and esterase activity of M. aeruginosa showed significant changes, with Fv/Fm values in mono- and co-cultures being decreased by 51.8% and 64.7%, respectively. In comparison, Fv/Fm values of C. pyrenoidosa changed slightly. M. aeruginosa released more chromophoric dissolved organic matter (CDOM, including tryptophan-, tyrosine-, and fulvic-like substances) than C. pyrenoidosa. The cell concentration of C. pyrenoidosa showed little changes regardless of sonication time, while the cell concentration of M. aeruginosa decreased at different degrees. The cell concentration of M. aeruginosa in co-cultures decreased by 42.6% after sonication for 600 s, which might be responsible for the dominance of C. pyrenoidosa during 8 days after sonication. M. aeruginosa inhibited C. pyrenoidosa in other treatments, but mutual inhibition appeared in the 600 s sonication treatment. After ultrasonic treatment, the activity of M. aeruginosa could recover gradually. The treatment should be conducted again within a week to improve the persistence of algal control.

Positive feedback between peanut and arbuscular mycorrhizal fungi with the application of hairy vetch in Ultisol.

Multiple agricultural practices are being applied to increase crop yield in order to overcome the food shortage. Green manure has emerged as an appropriate practice to improve soil fertility and crop yield. However, the potential functions of arbuscular mycorrhizal fungi (AMF) in the below-ground ecosystems following the application of green manure in Ultisols remain largely unexplored. In this study, qPCR and high-throughput sequencing were used to investigate the response of AMF abundance and communities in different treatment groups, i.e., control (without fertilization), mineral fertilization (NPK), mineral fertilization with returning peanut straw (NPKS), and with green manure (hairy vetch; NPKG). The NPKG treatment significantly increased soil fertility compared to other treatment groups. Compared with control, the NPK, NPKS, and NPKG treatments increased peanut yield by 12.3, 13.1, and 25.4%, respectively. NPKS and NPKG treatments significantly altered the AMF community composition decreased the AMF diversity and increased AMF abundance compared to the control. The AMF network of the NPKG treatment group showed the highest complexity and stability compared to other treatment groups. The structural equation modeling revealed that the application of hairy vetch improved soil nutrients and peanut yield by increasing the soil AMF abundance and network stability. Overall, the results suggested that the application of hairy vetch might trigger positive feedback between the peanut and AMF community, contributing to fertility and yield improvement in the dryland of Ultisol.

Impact of soil amendments on nitrous oxide emissions and the associated denitrifying communities in a semi-arid environment.

Denitrifying bacteria produce and utilize nitrous oxide (N2O), a potent greenhouse gas. However, there is little information on how organic fertilization treatments affect the denitrifying communities and N2O emissions in the semi-arid Loess Plateau. Here, we evaluated how the denitrifying communities are responsible for potential denitrification activity (PDA) and N2O emissions. A field experiment was conducted with five fertilization treatments, including no fertilization (CK), mineral fertilizer (MF), mineral fertilizer plus commercial organic fertilizer (MOF), commercial organic fertilizer (OFP), and maize straw (MSP). Our result showed that soil pH, soil organic carbon (SOC), and dissolved organic nitrogen (DON) were significantly increased under MSP treatment compared to MF treatment, while nitrate nitrogen (NO3 --N) followed the opposite trend. Organic fertilization treatments (MOF, OFP, and MSP treatments) significantly increased the abundance and diversity of nirS- and nosZ-harboring denitrifiers, and modified the community structure compared to CK treatment. The identified potential keystone taxa within the denitrifying bacterial networks belonged to the distinct genera. Denitrification potentials were significantly positively correlated with the abundance of nirS-harboring denitrifiers, rather than that of nirK- and nosZ-harboring denitrifiers. Random forest modeling and structural equation modeling consistently determined that the abundance, community composition, and network module I of nirS-harboring denitrifiers may contribute significantly to PDA and N2O emissions. Collectively, our findings highlight the ecological importance of the denitrifying communities in mediating denitrification potentials and the stimulatory impact of organic fertilization treatments on nitrogen dynamics in the semi-arid Loess Plateau.