Search Results (319)

Increasing wildfire severity under climate change may alter the trajectory of belowground recovery in alpine forests, yet its long-term effects on soil microbial communities remain poorly understood. Here, we examined soil physicochemical properties and microbial communities eight years after fire across unburned, low-, moderate-, and high-severity fire sites in an alpine forest of western Sichuan, China. Fire severity was associated with persistent divergence at depths of 0–10 cm, with significant changes in soil organic carbon (SOC), soil water content (SWC), available nitrogen (AN), and microbial biomass. High-severity fire strongly reduced AN and available phosphorus (AP), whereas moderate-severity fire maintained the highest SOC and SWC. Bacterial alpha diversity remained relatively stable, whereas fungal richness declined markedly under high-severity fire, indicating greater fungal sensitivity to fire disturbance. Fire severity explained 57.35% and 87.32% of bacterial and fungal community variation, respectively, while structural equation modeling indicated that microbial responses were primarily mediated by changes in nutrient availability, soil moisture, and microbial biomass. Functionally, microbial communities shifted from resource-acquisition strategies under low-severity fire toward potential stress-tolerant and saprotrophic-dominated strategies under high-severity fire. Moderate-severity fire enhanced bacterial network complexity and increased the abundance of specific mycorrhizal taxa (e.g., Russula), whereas high-severity fire promoted saprotrophic and stress-resistant taxa such as Actinobacteriota and Penicillium, while suppressing mycorrhizal groups. Overall, fire severity acted as a persistent environmental filter that reorganized microbial community structure and functional strategies of the topsoil, suggesting that increasing fire severity may delay belowground recovery and weaken ecosystem resilience in alpine forests. Full article

Roegneria nutans, a premium grass on Western Sichuan Plateau, China, is vital for ecological stability and pastoral security. Studying its chromosomal architecture and environmental correlations lays a foundation for Roegneria genetic evolution research. This study used genomic in situ hybridization (GISH) and non-denaturing fluorescence in situ hybridization (ND-FISH) with two tandem repetitive sequence probes pAs1 and (AAG)₁₀) to analyze the species’ St and Y genomes of R. nutans from different altitudes. Our findings demonstrated that for both the number of probe signals and variant types, inter-population variation was higher than intra-population variation. Distinct altitudinal response patterns of (AAG)₁₀ and pAs1 FISH signals were detected between the St and Y genomes. Within the St genome, the abundance of (AAG)₁₀ loci exhibited a trend of initial decline followed by a marked rise with increasing altitude. The pAs1 probe displayed higher signal density than (AAG)₁₀, with its signal abundance peaking in medium-altitude populations, and polymorphic loci were most abundant in high-altitude populations. In contrast, medium-altitude samples harboured relatively fewer (AAG)₁₀ signals within the Y genome. Although pAs1 exhibited lower signal density than (AAG)₁₀ in the Y genome, its maximum signal number was observed in medium-altitude populations, where polymorphic loci predominated. Low-altitude populations maintained relatively conserved hybridization patterns, and chromosomal variation was mainly detected in the Y genome at medium altitudes and in the St genome at high altitudes. This study provides a valuable basis for exploring the genetic diversity of R. nutans across the Western Sichuan Plateau. Full article

Aichivirus D (AiV-D), a member of the genus Kobuvirus within the family Picornaviridae, is an emerging pathogen associated with diarrhea in multiple livestock species, including cattle, dairy cattle, Tibetan sheep, and yaks. In this study, a total of 280 fecal samples were collected from yaks with diarrhea in Sichuan, Gansu, and Qinghai Provinces, western China, between June 2025 and February 2026. The overall positive rate of AiV-D was 30.00% (84/280), and the farm-level positive rate was 87.5% (7/8). Four complete yak AiV-D genomes (GenBank: PZ424445–PZ424448) were obtained from the positive samples, with genome sizes ranging from 8369 to 8475 nt and GC contents ranging from 55.66 to 55.85%. Each genome contained a single open reading frame (ORF) of 7509–7518 bp, encoding a typical picornaviral polyprotein consisting of a leader protein (L), structural proteins P1 (VP0, VP3, and VP1), and nonstructural proteins P2 (2A, 2B, and 2C) and P3 (3A, 3B, 3C, and 3D). Pairwise comparisons of the ORF revealed nucleotide and amino acid identities of 82.07–99.63% and 81.96–99.56%, respectively, among the four strains. Phylogenetic analysis based on the complete genomes revealed that strain BKV/YAK/FX1/2025/CHN clustered with the bovine reference strain BKV5 (84.70% nt/88.35% aa identity), whereas the other three strains grouped with the yak reference strain BKV/Yak/SCDF77/2021/CHN (GenBank: OP776109.1) (89.80–93.07% nt 95.53–96.84% aa identity). Recombination analysis predicted a recombination event in strain BKV/YAK/SF1JK6/2025/CHN, with breakpoints located in the nonstructural protein coding region (2C–3D). Additionally, eight full-length VP0, VP3, and VP1 gene sequences were amplified from the AiV-D-positive samples, and a few co-mutational amino acid substitutions were identified in these structural proteins. Phylogenetic analysis based on the VP1 gene further divided the eight strains into two distinct clades: six strains formed an independent clade and were designated as a novel sub-genotype within AiV-D4, tentatively named AiV-D4-L1, closely related to but clearly distinguishable from the AiV-D4 reference strains reported in China, while the remaining two strains (BKV/YAK/FX1/2025/CHN and BKV/YAK/FX77/2025/CHN) clustered with the bovine reference strain and were designated as a novel genotype, AiV-D5. These results reveal genetic diversity among yak-derived AiV-D strains and suggest possible host adaptability or cross-host transmission, warranting further investigation in future studies. However, as all the samples were collected from diarrheic yaks without a healthy control group, the potential association between AiV-D and diarrhea requires further validation. Full article

Large deformation is one of the most critical hazards in tunnels excavated under complex geological conditions. It often causes significant economic losses and threatens construction safety. For layered soft rock tunnels subjected to high in situ stress, the deformation and failure mechanisms are largely governed by the bedding dip angle. To clarify these mechanisms and optimize the corresponding construction control measures, this study investigates a carbonaceous slate section of a railway tunnel in the Western Sichuan Plateau. Field monitoring and FLAC3D numerical modelling are coupled. The influence of the bedding dip angle on the plastic-zone evolution and the failure modes of the surrounding rock is analysed. The micro-bench, three-bench, and reserved core soil methods, together with the rock bolt length, are comparatively evaluated. On this basis, a differentiated reinforcement strategy is proposed for bedding-induced asymmetric loading. The results indicate that: (1) The bedding dip angle governs the failure mode of the surrounding rock. Under the micro-bench method, the plastic zone in subvertically bedded rock masses exhibits a quasi-symmetrical distribution along the normal direction of the bedding planes. The sidewalls predominantly undergo flexural failure. In contrast, under bedding-induced asymmetric loading, the plastic zone concentrates at the left springline and right shoulder. An asymmetric composite failure mode is formed, characterized by shallow flexural–tensile cracking and deep-seated interlayer shear. (2) Under the subvertical bedding condition (89°), the reserved core soil method mitigates the excavation-induced unloading disturbance most effectively. It achieves the lowest peak stress and the smallest tunnel convergence, which is 15.7% and 33.0% lower than those of the micro-bench and three-bench methods, respectively. Its plastic zone reaches full numerical convergence. The reserved core soil method is therefore identified as the optimal excavation Scenario under this condition. (3) The rock bolt length exhibits a threshold effect on deformation control. The most substantial improvement occurs when the bolt length is increased from 4 m to 6 m, beyond which the benefit tends to plateau. A bolt length of 6 m is therefore recommended as the best-performing Scenario among the tested values (4, 6, 8, and 10 m) for the investigated geological and support conditions. For surrounding rock subjected to bedding-induced asymmetric loading, a differentiated reinforcement strategy targeting the vulnerable zones reduces the maximum deformation by 18.8% and 28.3% compared with the uniform reinforcement Scenario and the baseline Scenario, respectively. These findings provide practical insights into excavation-method selection and support optimization for layered soft rock tunnels under similar conditions. Full article

The Dilaqiu pegmatite-type rare-metal deposit lies in the southeastern part of the Ke’eryin orefield, within the Central Songpan–Ganzi orogenic belt. It is a large, recently discovered lithium-dominated deposit with associated tin, niobium, and tantalum resources. Detailed petrographic observations were combined with electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) trace element analysis and U−Pb dating of cassiterite from albite–spodumene pegmatite. The mineralogical, EPMA major element, and LA-ICP-MS trace element data indicate that cassiterite is genetically linked to the rare-metal pegmatite rather than to a later hydrothermal event. Cassiterite U−Pb dating yielded an age of 194.8 ± 1.2 Ma (n = 28, MSWD = 0.94), which is interpreted to indicate Early Jurassic mineralization associated with early Yanshanian magmatism. Comparison with rare-metal deposits elsewhere in the Songpan–Ganzi orogenic belt further indicates broadly similar metallogenic ages and mineralization types and a shared post-orogenic extensional setting. Full article

The expansion and spatial concentration of livestock and poultry farming have intensified the mismatch between manure nutrient pressures and regional environmental carrying capacity, creating persistent obstacles to the sector’s green transformation. Using a balanced panel dataset covering 21 prefecture-level cities and autonomous prefectures in Sichuan Province from 2015 to 2024, we evaluate theoretical environmental carrying capacity (ECC), production comparative advantage (PCA), environmental comparative advantage (ECA), and comprehensive comparative advantage (CCA) under nitrogen and phosphorus constraints. The framework considers cropland as well as the potential nutrient assimilation capacity of grassland and forestland under suitable manure application conditions. We measure ECA by comparing residual carrying capacity per unit of actual livestock population with the provincial benchmark. We construct CCA using a signed geometric mean that preserves the direction of environmental constraints when ECA is negative. Prefecture-level spatial patterns are mapped using polygon-based choropleths. The Northwest Sichuan Ecological Economic Zone and the Panxi Economic Zone show the strongest PCA, while Zigong and Dazhou also retain production advantages outside these core areas. Under the nitrogen constraint, Ya’an and Panzhihua record negative ECA values. Under the phosphorus constraint, high ECA values are concentrated in Ganzi, Aba, and Liangshan. CCA is concentrated in western Sichuan and displays a clear spatial gradient, with the Northwest Sichuan Ecological Economic Zone ranking first under both nutrient constraints. These patterns indicate that the spatial layout of livestock and poultry farming should be better aligned with the existing production base, land-based nutrient assimilation capacity, and ecological protection constraints. Differentiated regional regulation, species-specific specialization, and coordinated manure recycling across land types can improve the fit between livestock production and environmental carrying conditions. The framework provides a quantitative basis for spatially differentiated livestock planning in Sichuan and can be adapted to other mountainous agro-pastoral transition regions through locally calibrated technical parameters and land-use assumptions. Full article

Severe drill string vibration can accelerate tool fatigue and failure, but direct measurement near the drill bit is difficult. Using a 6376 m vertical shale-gas well in western Sichuan as a case study, this study established and validated a coupled drill string dynamic model. Lateral acceleration signals under three operating conditions were generated, filtered, and normalized. XGBoost models were then trained using vibration signals measured at shallow and intermediate locations to estimate deep-level lateral acceleration. The results showed that vibration originated near the drill bit and propagated upward with a measurable delay, while its amplitude was generally higher in the middle section of the drill string. For single-point monitoring, the coefficient of determination (R²) ranged from 0.013 at 500 m to 0.64 at 10 m from the bit. Combining multiple monitoring locations increased R² to 0.7071. XGBoost achieved the best balance between accuracy and computational efficiency among the tested models. The 10–300 m interval from the bit is recommended for monitoring, whereas 300–500 m is considered an uncertain zone. Full article

The Grain for Green Program is one of China’s major long-term ecological restoration policies, but its land-use response should not be interpreted as a one-off shock or a simple increase in ecological land. Using Sichuan, an early-pilot and internally heterogeneous western province, and prefecture-level land-use panel data from 1985 to 2024, this study examines stage-lagged, spatially embedded, and regionally heterogeneous land-use ecological transition under the program. The analysis defines 1985–1998 as the pre-policy reference period and compares three post-policy stages: early implementation (1999–2006), achievement consolidation (2007–2013), and new-round key-area governance (2014–2024). Baseline cropland share in 1985 is used as a proxy for potential policy exposure because it reflects pre-policy pressure for cropland conversion, rather than official project implementation intensity. Ecological land share is measured as the proportion of forest, shrubland, grassland, water bodies, and wetlands in total land area. Improvements did not fully emerge immediately after policy initiation but became most pronounced in 2014–2024. Ecological land change also formed spatial clustering and was embedded in shared terrain, watershed linkages, sloping cropland distribution, and governance tasks. Most prefecture-level units experienced increases, whereas areas with high initial ecological endowments had limited proportional growth. The findings suggest that long-term ecological restoration should be evaluated through policy stages, spatial relations, and regional conditions rather than a single ecological outcome. Full article

Landscape Character Assessment (LCA) has struggled with scale mismatches and inadequate treatment of cultural expression when applied to high-density cultural landscapes in Asia. On the Chengdu Plain, Western Sichuan, China, remote sensing shows convergent settlement patterns across case sites, but fieldwork reveals substantial divergences in landscape character. We examined five cases representing different rural development models in the Chengdu metropolitan area. By integrating 10 m Sentinel-2 imagery and with systematic fieldwork (3200 photographs and 42 semi-structured interviews, July–August 2023), we constructed a framework that combines macro-scale spatial analysis with micro-scale field investigation. For macro-level quantification, six landscape pattern indices were adopted: number of patches (NP), patch density (PD), contagion index (CONTAG), aggregation index (AI), Shannon’s diversity index (SHDI), and Shannon’s evenness index (SHEI). The micro-level investigation followed a three-tier scheme (natural environment, settlement space, architectural details) to record vertical ecological communities, spatial expressions of cultural embeddedness, and visual landscape character. Indicator screening employed the KJ method and two rounds of Delphi consultation with ten experts; weights were then determined through the Analytic Hierarchy Process (AHP). Macro-level results display a clustered, low-fragmentation pattern (woodland AI = 97.48, water body AI = 99.40), anchored by a stable mosaic of Linpan, farmland, water bodies, and homesteads. Micro-level features include multi-strata vertical communities of trees, shrubs, grasses, and water, along with cultural embeddedness expressed through irrigation systems, farming patterns, and courtyard layouts. The VLEAS (Vernacular Landscape Elements Assessment System) framework encompasses three dimensions (natural, cultural, and visual) and comprises 12 indicators. The cultural dimension receives the highest weight (0.42), followed by natural (0.32) and visual (0.26) dimensions. Comparative analysis shows that the framework differentiates cases with similar macro-scale patterns but divergent micro-features, capturing differences that a purely macro-index benchmark misses, and it also reveals trade-offs among ecological integrity, cultural heritage, and visual quality. Sensitivity analysis displays that case rankings remain stable across four extreme weighting scenarios (cultural, ecological, visual, equal), with only one swap (Xingfu Pastoral Park and Nongke Village) under ecological priority and no rank change greater than one position, confirming that the results are not driven by any specific weight assignment. This approach extends the utility of LCA in high-density rural cultural landscapes and offers a practical tool for differentiated conservation and management, especially in tourism-influenced rural settings on the Chengdu Plain. Transferability to other regions would require recalibration of locally relevant indicators. Full article

Climate change may substantially alter the habitat suitability and spatial stability of highland edible and medicinal plant resources. Argentina anserina (L.) Rydb. is an important wild resource plant in western China, but its potential distribution and future climate-change response in the three ethnic prefectures of Sichuan Province remain insufficiently understood. In this study, we used an ensemble species distribution modeling framework based on 31 spatially filtered occurrence records and 12 environmental predictors to evaluate the current and future habitat suitability of A. anserina under SSP126, SSP370, and SSP585 scenarios for the 2050s and 2090s. The ensemble model showed acceptable overall discrimination ability and was used to identify broad-scale suitability patterns. Mean diurnal range, precipitation of the driest quarter, isothermality, and topsoil pH were the main environmental predictors, indicating that thermal variability, dry-season moisture availability, and edaphic conditions jointly shaped habitat suitability. Under current conditions, the total suitable habitat area was predicted to be 15.57 × 10⁴ km², accounting for 57.2% of the study region, with high-suitability habitats mainly concentrated in the northern, northwestern, and central areas. Future projections suggested an overall decline in suitable habitats, especially in high-suitability areas, although the magnitude varied among scenarios and periods. Spatial change and centroid migration analyses indicated that future suitable habitats may undergo contraction and westward or northwestward redistribution rather than uniform expansion. Niche overlap analysis further showed moderate to relatively high overlap between current and future environmental spaces, suggesting partial niche stability with scenario-dependent shifts. Given the limited field-based occurrence records, these findings should be interpreted as broad-scale spatial guidance rather than precise local predictions. Full article

Compound hot–humid events are placing increasing pressure on urban health and land-use governance as climate warming and urban expansion continue. This study examined urban built-up areas in 21 prefecture-level cities and prefectures of Sichuan Province for 2000, 2005, 2010, 2015, 2020, and 2024. Using the IPCC hazard–exposure–vulnerability framework, ERA5-Land, MODIS land-cover, GHSL population, and socioeconomic data were combined to construct the Humid Heat Hazard Index (HI), Population-Density Exposure Index (EI), Socioeconomic Vulnerability Index (VI), and Comprehensive Urban Heat–Humidity Risk Index (HHRI). Contribution decomposition, LISA, and standard deviation ellipse analysis were then used to examine risk changes and spatial patterns. The mean HHRI decreased from 0.42 to 0.24, but rebounds appeared in 2010 and 2024. HI varied strongly among years and drove short-term risk changes, EI declined continuously, and VI dropped from 0.87 to 0.30, making it the main factor behind long-term risk reduction. Higher-risk areas were mainly located in southern Sichuan, southeastern Sichuan, and the central-eastern Sichuan Basin. LISA results showed high-risk clusters in basin cities and low-risk clusters on the western Sichuan Plateau. The standard deviation ellipse remained mostly within the basin and followed the basin urban belt. Future adaptation should combine public-service improvement with heat warnings, cooling services, and emergency preparedness. Full article

The traditional market towns of the Western Sichuan Plain, known as Changzhen, represent a distinctive form of vernacular settlement shaped by the interplay of geographical conditions, migration history, and socio-economic dynamics. In the context of rural revitalisation and integrated urban–rural development, the conservation and renewal of these towns require a deeper understanding of their underlying spatial logic. This study employs a mixed-methods approach combining typo-morphological analysis with spatial measurement and statistical testing to investigate the core morphological indicator that determines plot-type differentiation in linear market towns, using Luodai and Yuantong as two representative cases in the Chengdu Plain. A total of 1113 plots are digitised and measured across four morphological indicators, supplemented by XGBoost classification and SHAP analysis for cross-validation. The findings reveal that plot depth is the core morphological indicator distinguishing the linear type from the enclosed courtyard type, with an effect size substantially larger than that of frontage-to-depth ratio and distance from the street, indicating that plot depth matters more than plot location in determining plot type. The two towns present contrasting patterns of plot-type composition, with frontage enclosed courtyard plots significantly larger than their non-frontage counterparts and no meaningful correlation between plot area and courtyard ratio. This study provides a quantifiable morphological framework for understanding plot-level differentiation in linear market towns and offers practical parameters for conservation and renewal. The findings highlight a specific threshold, with depths below approximately 12 m associated with the linear type and depths above approximately 18 m associated with the enclosed courtyard type, providing a tangible reference for planning decisions in historic districts. Full article

To address the challenges of ambiguous regional feature identification, high digital modeling costs, and limited regional adaptability of general-purpose AIGC tools in the micro-renewal of Western Sichuan Linpan, this study proposes a typology-constrained small-sample learning framework. A structured dataset of 80 high-quality, semantically annotated images was constructed to extract typological features, including spatial layouts, architectural forms, and environmental relationships. Based on Stable Diffusion, the framework integrates LoRA fine-tuning for style adaptation and ControlNet for structural control. To constrain the number of trainable parameters under the limited-data setting, LoRA rank control, dropout regularization, and early stopping were incorporated into the training procedure. Under the fixed 80-image dataset and experimental configuration, the complete framework achieved lower FID values and higher CLIP and expert-evaluation scores than the prompt-only baseline. Compared with Scheme A, the FID decreased by 22.7% (from 284.52 to 220.00), while the CLIP Score increased by 18.3% (from 0.224 to 0.265). Under the evaluated configuration, the complete framework showed closer correspondence with the specified Linpan architectural characteristics and spatial conditions than the prompt-only baseline. The results support the feasibility of translating architectural typological knowledge into semantic and geometric conditioning signals under the evaluated limited-data setting. However, the influence of training-set size on model stability and generation performance was not examined and requires further investigation. Full article

The New Western Land–Sea Corridor (NWLSC), a key logistics initiative of China, serves as a strategic passage connecting Eurasia. This study establishes an indicator system to evaluate its logistics resilience, and explores the structural evolution and corresponding driving mechanisms of the logistics resilience spatial correlation network. With the panel data of 13 provincial-level regions along the corridor, this study adopts the standard deviational ellipse and centroid migration model to examine the spatial distribution of logistics resilience and the migration trajectory of its gravity center, respectively. It also employs the modified gravity model and social network analysis (SNA) to investigate the structural configuration of the logistics resilience spatial correlation network, and applies the QAP (Quadratic Assignment Procedure) model to reveal the relevant driving mechanisms. The findings are concluded as follows. (1) The overall logistics resilience level of the NWLSC has been continuously improving, with a prominent regional imbalance; its spatial gravity center has long been located within Sichuan Province and has begun to shift toward the northeast. Meanwhile, the logistics resilience spatial correlation network has gradually evolved from a relatively dispersed and loose pattern to a mature, hierarchical, and integrated network system with a clear core–periphery structure, presenting the evolutionary trends of agglomerative morphology, stable connection direction, and orderly centroid migration. (2) The logistics resilience spatial correlation network features high accessibility with no isolated nodes, but the overall scale and density of network connections remain relatively fragmented. It has displayed a tendency of phased contraction under external shocks, followed by restoration and further enhancement. (3) Each block has a clear functional division, forming a pattern of “net beneficiary absorption, broker connection, net spillover supply, and bidirectional spillover linkage”. The network has formed a mature tributary system with distinct functional division of blocks: the core cluster plays the role of a sink for resilience resources, the peripheral blocks serve as resource supply sources, and some provinces have evolved into pivotal broker nodes, with inter-block spillovers becoming the core of the correlation network. (4) The QAP analysis confirms that the structural evolution of the logistics resilience spatial correlation network is significantly and positively driven by the economic development, educational advancement, and geographical proximity, which together form a hierarchical and synergistic driving mechanism, while the effects of inclusive finance and informatization are not significant due to the relevant conditional constraints. Robustness tests confirm the reliability of the aforementioned findings. Therefore, this study provides an important academic basis and practical enlightenment for optimizing the spatial network structure and enhancing the development quality of logistics resilience in the NWLSC. Full article

Beam bridges in mountainous and high-altitude transport corridors are frequently exposed to large diurnal temperature differences, intense solar radiation, low humidity, freeze–thaw action and repeated wetting–drying cycles. These coupled actions can accelerate concrete surface cracking and reduce the durability of prestressed concrete T-girder bridges, but field evidence linking crack morphology, crack depth, concrete cover and short-term environmental response remains limited. This study investigates a representative 40 m in-service prestressed concrete T-girder bridge on the Western Sichuan Plateau through field survey and four-month continuous monitoring. Crack location, length, width, depth and concrete cover thickness were measured, and representative crack-width responses to ambient temperature were analyzed. The results show that web cracks are dominated by reticular and irregular microcracks, bottom cracks are mainly longitudinal intermittent short cracks, and diaphragm cracks are concentrated near reticular zones and local corner discontinuities. The sunny side of the edge girder contained approximately 598 cracks, about 4.8 times the 123 cracks observed on the shaded side. Web and diaphragm crack widths were mainly 0–0.04 mm, while bottom-crack widths of 0–0.10 mm accounted for about 92.7%; most crack lengths were 2–20 cm. During monitoring, newly developed cracks accounted for about 6.0% of all recorded cracks, and only 3 of 721 existing cracks increased by 4–6 cm. Representative crack widths fluctuated by about 0.02 mm under −1 to 24 °C without sustained growth. Cracks wider than 0.20 mm generally exceeded the approximately 40 mm concrete cover. Such penetrating cracks should be prioritized in durability maintenance and long-term monitoring. Full article