Search Results (3,220)

This study aims to uncover the structural and functional characteristics of rhizosphere soil bacterial communities of Kengyilia thoroldiana under five types of topographic habitats in the source region of the Yellow River, and to explore the interaction mechanisms between bacterial communities and plant-soil factors, thereby providing microbiological support for the ecological restoration of Kengyilia thoroldiana artificial grasslands in alpine desert grassland. In this study, high-throughput sequencing technology was employed to compare the species composition, diversity, interaction networks, and functional characteristics of rhizosphere bacterial communities of Kengyilia thoroldiana across five topographic habitats in the source region of the Yellow River. Additionally, Mantel tests and redundancy analysis (RDA)) were conducted to explore the key environmental factors driving the structure of bacterial communities. The results showed that habitat differences significantly influenced the community characteristics of Kengyilia thoroldiana and soil physicochemical properties. The plant height, coverage, biomass, and soil carbon, nitrogen, and phosphorus contents were highest in habitats H2 and H5, while they were lowest in habitats H1 and H3. In contrast, soil pH and electrical conductivity exhibited an opposite trend. At the bacterial community level, the number of operational taxonomic units (OTUs) in habitat H5 reached 1917, with α-diversity indices such as Shannon, Ace, and Chao1 being 6.13, 1820.85, and 1844.80, respectively, significantly higher than those in habitat H1. Cluster analysis revealed that habitat H3 formed a distinct group, while the bacterial community structures in the remaining four habitats were similar. Functional prediction indicated that chemoheterotrophy and aerobic chemoheterotrophy were the dominant functions across all habitats, with functional expression values exceeding 9300 in habitats H2, H4, and H5. Redundancy analysis confirmed that soil pH and SOC were the key factors driving the structure of rhizosphere bacterial communities of Kengyilia thoroldiana. In summary, topographic habitats influence the growth of Kengyilia thoroldiana plant communities by shaping soil environmental heterogeneity, thereby regulating the structure and function of rhizosphere bacteria associated with Kengyilia thoroldiana. Full article

The similar properties of the nitrogen atoms in azole ring complicate the regioselective N-functionalization of pyrazoles. This work demonstrates the role of the hydrazone substituent in the control of the alkylation selectivity of (trifluoromethyl)pyrazoles. Reaction conditions for the synthesis of 3- and 5-(trifluoromethyl)pyrazoles were developed, and all types of regioisomers formed under the alkylation of bis-pyrazolyl NH-ketazine were isolated. The structures of the synthesized compounds were confirmed by NMR spectroscopy and XRD data. Full article

The steel industry is responsible for 7–9% of global CO₂ emissions. Shifting from primary iron ore to recycled scrap in electric arc furnace (EAF) steelmaking offers significant decarbonization potential, reducing carbon intensity by 60–70%. However, increased scrap use in EAF operations leads to higher nitrogen absorption, which can degrade mechanical properties. Nitrogen dissolves into molten steel, where it forms Cottrell atmospheres at dislocations in the following processing steps, intensifying strain aging and reducing ductility. This study establishes a precipitation criterion based on the TiN solubility product to prevent harmful liquid TiN formation, enabling effective nitrogen fixation via fine TiN precipitates (5–20 nm). Multiscale characterization techniques, such as TEM and EBSD, show that Ti reduces the number of mobile N atoms by 60–70%, evidenced by a 50–65% decrease in Snoek/SKK peak intensities. Excessive titanium can refine ferrite grain size and prevents harmful TiN inclusions. Titanium microalloying presents a cost-effective, sustainable strategy to reduce strain aging in scrap-rich EAF steels, enabling more sustainable steel production without sacrificing material properties. Full article

Coastal reclamation reshapes both soils and vegetation, yet their coupled trajectories remain poorly understood. Here we investigated soil–vegetation co-evolution across a 15-year chronosequence on Hengsha Island in the Yangtze River estuary. The reclaimed soils were formed primarily from dredged estuarine silt and clay slurry deposited during hydraulic filling. Four representative sites were studied, spanning 3 (Y3), 7 (Y7), 10 (Y10), and 15 (Y15) years since reclamation. Soil physicochemical properties (pH, electrical conductivity, salinity, nitrogen, phosphorus, potassium) were measured, while vegetation cover was quantified using NDVI and fractional vegetation cover (FVC) derived from satellite data. Soil conditions improved markedly with reclamation age: pH, conductivity, and salinity declined, whereas nitrogen, phosphorus, and potassium accumulated significantly (p < 0.001). Vegetation shifted from salt-tolerant pioneers (e.g., Suaeda salsa, Phragmites australis) to mixed communities and cultivated rice fields (Oryza sativa), reflecting progressive improvements in soil quality. Vegetation cover increased in parallel, with NDVI rising from 0.12 ± 0.05 (Y3) to 0.35 ± 0.09 (Y15), reflecting a shift from salt-tolerant pioneers to structurally complex communities. Mantel tests revealed strong positive associations of NDVI with organic matter, nitrogen, and phosphorus, and negative associations with pH, conductivity, and salinity. Structural equation modeling identified organic matter and nitrogen enrichment, along with declining pH and dissolved salts, as dominant drivers of vegetation recovery. These results highlight a co-evolutionary process in which soil improvement and vegetation succession reinforce one another, offering insights for ecological restoration and sustainable management in coastal reclamation landscapes. Full article

Biochar shows potential for regulating nitrogen cycling in cold-region soils, but the roles of its different fractions during freeze-thaw cycles (FTCs) remain unclear. To elucidate the regulation of cold-region soil environments by biochar at the fraction scale, we examined the effects of biochar and its fractions (dissolved and undissolved) on soil nitrogen forms and microbial communities under simulated FTCs. The experiment included a constant-temperature control, a freeze–thaw control, and three biochar treatments with pristine biochar (PBC), dissolved biochar fraction (DBC), and undissolved biochar fraction (UBC), respectively, maintained in triplicate at five FTC frequencies (0, 1, 5, 10, and 20). Changes in soil physicochemical properties and nitrogen forms were measured at five FTC frequencies, and microbial community composition was analyzed by high-throughput sequencing after the 20th cycle. Both biochar fractions reduced inorganic nitrogen, with ammonium nitrogen decline resulting from joint action and nitrate nitrogen (NO₃⁻-N) reduction dominated by UBC. PBC alleviated microbial biomass nitrogen stress by relying primarily on its undissolved fraction to enhance soil water retention, organic carbon, and total nitrogen. Redundancy analysis indicated that total nitrogen and NO₃⁻-N were the key factors affecting microbial community composition. Partial least squares structural equation modeling results suggested that soil physicochemical properties influenced microbial community structure characteristics more strongly than nutrient properties. These findings provide a new perspective on the regulatory mechanism of biochar on the agricultural soil environment in cold regions. Full article

The influence of microplastics (MPs) on the availability of soil heavy metals (HMs) is a current research hotspot, but how MPs regulate HM availability via soil properties and the bacterial community remains unclear. This study investigated the effects of polyethylene (PE) MP concentrations on soil properties, bacterial communities, surface chemistry, and the speciation of cadmium (Cd) and lead (Pb) through soil incubation. Results indicated that as PE MP concentration increased, soil pH and cation exchange capacity declined, while organic carbon concentration increased. Available phosphorus and alkali–hydrolyzable nitrogen concentrations increased at 0.1% and 1% PE MPs, but decreased at 10% PE MPs. Bacterial community indices, including Simpson, ACE, and Chao1, increased at 0.1% and 1% PE MPs but decreased at 10% PE MPs. PE MPs (0.1% and 1%) reduced DTPA–Cd/Pb, promoting their transformation into stable forms and surface complexation with oxygen–containing groups. In contrast, 10% PE MPs disrupted the formation of PbO, PbCO₃, and Cd(OH)₂, producing the opposite effect. The random forest model revealed that soil organic carbon and available phosphorus were the primary factors influencing DTPA–Pb and DTPA–Cd, respectively. Partial least squares path modeling demonstrated that PE MPs altered the physicochemical characteristics of soil and structure of bacterial communities, ultimately impacting transformation of Cd and Pb speciation, with these changes being highly dependent on PE MP concentration. Full article

In alpine ecosystems, plant growth is often constrained by multiple environmental factors, especially the infertile soils with lower temperature that decelerate the rate of nutrient turnover, thus leading to a diminished availability of nutrients in the soil, notably nitrogen (N), and its different forms, which is a pivotal factor for limiting plant growth and species coexistence in these alpine areas. Androsace tapete (A. tapete) is an endemic species and the most widely distributed cushion plant on the Qinghai–Tibet Plateau (QTP). Its positive interactions can facilitate other associated plants to deal with severe environmental conditions in the alpine grassland ecosystem. The change in soil nutrient availability is one of the main positive interactions, but little is known about how A. tapete changes soil nutrient availability and affects the N uptake pattern of associated plants. This study investigated the N utilization patterns of three associated plant species —Carex atrofusca (C. atrofusca), Cyananthus incanus (C. incanus), and Potentilla saundersiana (P. saundersiana)— growing inside the cushion area A. tapete (CA) and the ambient grassland without cushion plants (CK), using a ¹⁵N labeling method to clarify the effect of A. tapete on the N uptake strategies with NH₄⁺, NO₃⁻, and organic N of its associated species. The results showed the following: (1) compared to CK, the soil total C, total N, and available NH₄⁺ contents under the A. tapete showed a significant 47.82%, 40.96%, and 47.33% increase, respectively; (2) A. tapete showed a stronger preference for NH₄⁺ (>80%), whereas the associated species in CK exhibited a more balanced uptake, deriving 39.29–55.59% of N from NO₃⁻, 25.72–44.00% from NH₄⁺, and 16.15–18.69% from glycine. (3) The three associated plants possessing A. tapete significantly reduced their uptake of glycine by 9.76%, 12.55%, and 7.15%, respectively, while the absorption of NH₄⁺ by C. atrofusca and C. incanus increased by 18.46% and 36.11%; meanwhile, NO₃⁻ uptake decreased by 8.70% in C. atrofusca and 23.55% in C. incanus. These findings indicated that the A. tapete can change the N uptake pattern of the associated plants growing inside the cushion body, such as enhancing the absorption of inorganic N and decreasing the organic N. This adaptive strategy of the associated plants with cushion plant enables them to counteract the N-limited conditions prevalent in alpine environments, and, as a consequence, facilitates their growth and promotes local plant community diversity in the alpine environment. Full article

Plant litter decay is an essential process for recycling C and nutrients in natural ecosystems. However, the impacts of N addition on litter decay are not well understood in global forest ecosystems. Therefore, a meta-analysis was used to examine how N addition affects the litter decay rate through three kinds of litter decay traits (i.e., common litter trait (litter collected from control plot is decomposed in N addition plots); common site trait (litter collected from N addition plots is decomposed in control plot); and in situ trait (litter collected from control and N addition plots is decomposed in situ)), based on 1145 field observations from 166 published studies on global forests. Nitrogen addition significantly reduced the litter decay rate by 3.92% across the three kinds of decay traits. However, there were different responses of the litter decay rate to N addition among the decay traits. The N addition notably inhibited litter decay by 5.99% for the common litter trait but consistently promoted it by 8.37% and 7.48% for common soil and situ traits, respectively. The magnitude and direction of such effects varied with the N addition amount, form and duration. The effect size of the litter decay rate due to N addition was negatively related to the initial N concentration and C:N ratio for the common litter trait. The N concentration in litter was raised by N addition, resulting in an increase in the litter decay rate for the common situ trait. For the situ trait, N addition increased N concentration and reduced C:N and lignin/N in litter, resulting in an increase in the decay rate, and the responses of the litter decay rate to N addition were also influenced by the humidity index. Overall, our results showed that the responses of the litter decay rate to N addition were different among the three kinds of decay traits and were controlled by environmental and experimental factors. These findings help us to better understand the effects of N addition on biogeochemical cycling in global forest ecosystems. Full article

Effect-based toxicity assessments are crucial for evaluating the risks of disinfection byproducts (DBPs), particularly unknown species, generated during drinking water chlorination. However, the accuracy of this approach is highly dependent on unbiased sample extraction. Conventional methods often employ single, low-pH extraction, which may fail to recover pH-sensitive amphoteric DBPs derived from amphoteric precursors (e.g., nitrogenous compounds). This study investigated how extraction pH affects the measured biotoxicity of DBPs formed from three model precursors: biopterin (Bip), cytosine (Cyt), and tryptophan (Trp). Under excess chlorine conditions, all three precursors degraded rapidly. The formation of aliphatic DBPs followed the order Trp > Cyt > Bip, and the maximum toxicity of the non-volatile extracts, assessed via a Vibrio fischeri bioassay, followed the reverse order: Bip > Trp > Cyt. This toxicity profile was significantly influenced by extraction pH, with maximum toxicity observed for Bip at around pH 4.0, under weakly acidic conditions for Trp, and under neutral to alkaline conditions for Cyt. For all precursors, the total organic carbon concentration remained constant throughout chlorination, indicating negligible mineralization and the predominant formation of non-aliphatic, likely heteroaromatic, products. These findings demonstrate that conventional extractions at a single low pH can lead to the incomplete recovery of toxic DBPs from amphoteric precursors. Therefore, pH-optimized extraction protocols are necessary for a more accurate risk assessment of chlorinated drinking water. Full article

Coplanar tridentate nitrogen-donor ligands have been extensively employed to stabilize transition metal complexes by chelation. Some complexes exhibit interesting structures and photoluminescent properties. In this work, 2,6-bis(5-isopropyl-1H-pyrazole-3-yl)pyridine (denoted as L), its iron(II) and manganese(II) dichlorido complexes, and its bis-chelate iron(II) complexes, viz. [FeCl₂(L)]·2(MeOH) and [MnCl₂(L)]·2(MeOH), and [Fe(L)₂](PF₆) ·5(thf), respectively, were synthesized and characterized by single-crystal X-ray structural analysis. These solid-state structures contained N–H donors that formed hydrogen bonds with the coordinated halogenide ions and lattice solvent molecules, methanol or tetrahydrofuran. The iron(II) and manganese(II) dichlorido complexes [FeCl₂(L)]·2(MeOH) and [MnCl₂(L)]·2(MeOH) displayed distorted trigonal pyramidal structures in the solid state. However, [FeCl₂(L)]·2(MeOH) was not stable in methanol and formed the bis-chelate iron(II) complex [Fe(L)₂](FeCl₄). Therefore, the bis-chelate iron(II) complex [Fe(L)₂](PF₆)·5(thf) was also synthesized and structurally and spectroscopically authenticated. Full article

Winter wheat covers approximately 2.21 × 10⁸ ha globally, making it the most widely cultivated cereal crop in the world. In recent years, integrated water and fertilizer management has significantly improved winter wheat yield and nitrogen use efficiency; however, quantitative assessments of nitrogen cycling under different fertilizer forms in such high-yield systems remain limited. From 2022 to 2024, a two-year field experiment was conducted in drip-irrigated winter wheat fields in northern China. Four nitrogen fertilizer forms were applied: nitrate nitrogen fertilizer (NON), ammonium nitrogen fertilizer (NHN), amide nitrogen fertilizer (CON), and urea ammonium nitrate fertilizer (UAN), along with an unfertilized control (CK). Compared with NON, NHN, and CON, UAN reduced cumulative N₂O emissions by 10.40–15.64% and NH₃ volatilization by 2.04–9.33% (p < 0.05). It also increased the leaf area index and biomass accumulation at maturity, as well as grain yield (3.70–10.28%), nitrogen harvest index (4.58–12.88%), and nitrogen use efficiency (12.14–39.25%) (p < 0.05). Furthermore, UAN significantly decreased the net nitrogen surplus (24.18–45.70%) and nitrogen balance values (25.64–55.82%) (p < 0.05). Correlation analysis indicated that the reduction in nitrogen balance was primarily attributed to lower N₂O emissions and improved nitrogen use efficiency (p < 0.05). In conclusion, the application of urea ammonium nitrate under integrated water–fertilizer management achieved higher yield, greater efficiency, and environmentally sustainable production in drip-irrigated winter wheat systems in northern China. Full article

Drought poses a severe challenge to ornamental tree growth under climate change. This study employed a 2 × 4 factorial design—with two soil moisture levels (80–85% vs. 50–55% field capacity) and four nitrogen treatments (NN: no nitrogen; NO: nitrate nitrogen; NH: ammonium nitrogen; MN: mixed nitrate-ammonium nitrogen)—to examine the efficacy of nitrogen addition in enhancing drought resistance in Machilus yunnanensis seedlings. Results revealed that (1) drought stress leads to the acidification of rhizosphere soil, resulting in a decrease of 7.67%, 29.51%, 14.07%, and 44.09% in the content of soil organic matter (SOM), available phosphorus (AP), available potassium (AK), and dissolved organic nitrogen (DON), respectively. This adverse change directly impacts plant growth; it is manifested by a significant reduction of 45% in total chlorophyll (T Chl), a 67.18% decrease in photosynthetic rate (Pn), as well as reductions of 10.61%, 27.59%, 14.81%, and 12.35% in plant height, leaf, stem, and total biomass, respectively. (2) The application of all three forms of nitrogen helps alleviate drought stress, as evidenced by the recovery of photosynthetic levels and the reduction in malondialdehyde (MDA) content, with ammonium-N exhibiting superior efficacy over nitrate-N across most metrics. (3) Strikingly, the mixed nitrogen form outperformed singular applications by demonstrating multifaceted advantages: It maintains soil pH levels and rhizosphere nutrient availability under drought conditions, particularly with a 10.99% and 33.44% increase in dissolved organic nitrogen and available phosphorus content, respectively. More importantly, under drought stress, it increased leaf water content by 20.31%, nitrogen use efficiency by 15.67%, and photosynthetic nitrogen use efficiency by 439.44%, promoted the accumulation of osmolytes, while upregulating antioxidant enzyme activity to counteract osmotic imbalance and alleviate oxidative damage. These findings highlight that nitrogen supplementation, particularly mixed nitrogen application, enhances drought resistance in M. yunnanensis, offering a viable management strategy to sustain urban tree landscapes in water-limited environments. Full article

To address the severe challenge of soil salinization, effective soil amelioration methods are urgently needed; however, current research on the microbial mechanisms of the combined application of multiple amendments is insufficient. Therefore, this study aims to investigate the impacts of biochar combined with humic acid (HA) on the physicochemical properties and microbial community structure of saline–alkali soils by a field experiment. The results showed that the co-application treatments significantly improved soil physicochemical properties and increased bacterial community richness; specific effects depended on the biochar feedstock. Notably, the H-MBC treatment was the most effective in reducing soil electrical conductivity (EC) by 44.1%, while the H-SBC treatment most significantly increased soil water content by 80.3%. Stochastic processes influenced the assembly of microbial communities, particularly the co-application group, forming a more complex and stable microbial network. Furthermore, Spearman correlation and random forest analyses revealed EC, nitrate nitrogen, and available phosphorus as the primary variables affecting microbial communities. These findings support the potential of the combined application of biochar and HA for saline–alkali soil amelioration, as this strategy mitigates salt stress and increases nutrient availability, thereby reshaping microbial communities toward states conducive to ecological restoration. Full article

Red-bed desertification represents a critical form of land degradation in subtropical regions, yet the coupled soil–vegetation processes remain poorly understood. This study integrates Sentinel-2 vegetation indices with soil fertility gradients to assess vegetation–soil interactions in the Nanxiong Basin of South China. By combining Normalized Difference Vegetation Index (NDVI)-based vegetation classification with comprehensive soil property analyses, we aim to uncover the spatial patterns and driving mechanisms of degradation. The results revealed a clear gradient from intact forests to exposed red-bed bare land (RBBL). NDVI classification achieved an overall accuracy of 77.8% (κ = 0.723), with mixed forests being identified most reliably (97.1%), while Red-Bed Bare Land (RBBL) exhibited the highest omission rate. Along this gradient, soil organic matter, available nitrogen, and phosphorus declined sharply, while pH shifted from near-neutral in forests to strongly acidic in bare lands. Principal component analysis (PCA) identified a dominant fertility axis (PC1, explaining 56.7% of the variance), which clustered forested sites in nutrient-rich zones and isolated RBBL as the most degraded state. The observed vegetation–soil pattern aligns with a “weathering–transport–exposure” sequence, whereby physical disintegration and selective erosion during monsoonal rainfall drive organic matter depletion, soil thinning, and acidification, with human disturbance further accelerating these processes. To our knowledge, this study is the first to directly couple PCA-derived soil fertility gradients with vegetation patterns in red-bed regions. By integrating vegetation indices with soil fertility gradients, this study establishes a process-based framework for interpreting red-bed desertification. These findings underscore the utility of remote sensing, especially NDVI classification, as a powerful tool for identifying degradation stages and linking vegetation patterns with soil processes, providing a scientific foundation for monitoring and managing land degradation in monsoonal and semi-arid regions. Full article

The bloom-forming dinoflagellates and euglenophyceae were observed in the coastal waters of Hammam-Lif (Southern Mediterranean), during a green tide event on 3 June 2023. The bloom was dominated by Lepidodinium chlorophorum, identified through ribotyping with densities reaching 2.3 × 10⁷ cells·L⁻¹. Euglena spp. and Eutrepsiella spp. contributed to the discoloration, with abundances up to 2.9 × 10⁷ cells·L⁻¹. Environmental data revealed significant depletion of nitrite and nitrate, coinciding with a rapid increase in sunlight duration, likely promoting the proliferation of L. chlorophorum and euglenophyceae. By 5 June, two days after the bloom, nutrient stocks were exhausted. Diatoms appeared limited by low silicate concentrations (<0.05 µmol·L⁻¹), while dissolved inorganic phosphate and Nitrogen-ammonia were elevated during the bloom (0.88 and 4.8 µmol·L⁻¹, respectively), then decreased significantly afterward (0.23 and 1.06 µmol·L⁻¹, respectively). Low salinity (34.0) indicated substantial freshwater input from the Meliane River, likely contributing to nutrient enrichment and bloom initiation. After the event, phytoplankton abundance and chlorophyll levels declined, with a shift from dinoflagellates to diatoms. The accumulation of pigments (chlorophyll b and carotenoids) and the presence of Mycosporine-like amino acids (MAAs) during and after the bloom suggest that UV radiation and Nitrogen-ammonia were key drivers of this green tide. Full article