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[Objective] This study aimed to explore the influence mechanism of rock strata dip on soil erodibility and provide references for preventing and controlling water and soil erosion in karst trough valley area. [Methods] The study focused on the dip/anti-dip slope of Qingmuguan karst trough valley area in Chongqing city. Through flume erosion experiments, we analyzed the differences in soil erodibility between different land use types on the dip/anti-dip slopes and investigated the impact of soil physicochemical properties on soil erodibility. [Results] (1) Both dip/anti-dip slopes showed a significant negative correlation with organic matter content, >0.25 mm water-stable aggregates content, and total nitrogen content (p0.25 mm water-stable aggregate content, and total nitrogen compared to the dip slope. (2) Soil erodibility was higher on the dip slope than on the anti-dip slope for all four land use types studied. Additionally, grassland had lower comprehensive scores of soil erodibility than pepper fields, cornfields, and bare land on both the dip/anti-dip slopes. (3) Based on stepwise multiple regression analysis results, prediction models for soil erodibility on the dip/anti-dip slopes were established using organic matter content and >0.25 mm water-stable aggregate content as predictors with determination coefficients R2 of 0.77 and 0.85 respectively. [Conclusion] In summary, grassland had the lowest soil erodibility among all land use types studied regardless of the dip/anti-dip slopes in karst trough valley. Therefore, in order to prevent soil erosion and promote ecological restoration in karst trough valley, it is necessary to cultivate the land reasonably and increase grassland coverage appropriately, thus enhancing the soil's resistance against erosion.

[Objective] In order to accurately evaluate the soil quality characteristics of the dip/anti-dip erosion slope in the karst trough valley screen out suitable soil quality evaluation methods and explore the obstacle factors limiting soil quality in this area. [Methods] Five typical land use types (forest land, grassland, bare land, corn land, pepper land) were selected as the research objects in Qingmuguan Karst trough Valley of Chongqing, and the minimum data set (MDS) was established by principal component analysis combined with Norm value. The nonlinear soil quality evaluation method and membership function were used to evaluate the soil quality of the diplanti-dip erosion Slope and down-slope in the karst trough valley. [Results] (1) MDS of soil quality evaluation indexes in karst troughs valleys included capillary water capacity, capillary porosity and total phosphorus. (2) According to the nonlinear soil quality evaluation method, the soil quality of anti-dip erosion slope (0.519) was better than that of dip erosion slope (0.451). The soil quality of anti-dip erosion slope forest land was the best (0.653), and that of pepper field was the worst (0.426). (3) The coefficient of determination (R2) of the nonlinear evaluation method was higher than the membership function in the dip erosion slope and the anti-dip erosion slope, so the non-linear scoring model was more suitable for the karst trough valley. (4) There were significant differences in soil quality barrier factors, and only total nitrogen was the common barrier factor. [Conclusion] Appropriately increasing grassland and forest cover can improve soil quality in karst trough and valley area. The results of this study can provide basis for soil quality control and rational fertilization of slope erosion along/against slope in karst trough valley according to local conditions.

Grain refinement is of very important significance for improving the microstructure and mechanical properties of Mg alloys. This work investigated how the addition of various amounts of Y element affected the microstructure and mechanical properties of Mg-9Al-1Zn alloy. It was found that the grain size of Mg-9Al-1Zn alloy decreases as Y element content increases. When 1.2 wt.% Y element content was added, the grain size of Mg-9Al-1Zn alloy could be reduced from 334.2 μm to 134.6 μm, and grain refinement efficiency of 60% was achieved. HRTEM analysis demonstrated a good orientation relationship between the Al2Y phase and the Mg interface, and therefore, it was determined that the Al2Y phase can be used as a heterogeneous nucleation site for α-Mg grains, which promotes the grain refinement of α-Mg grain. Furthermore, the addition of Y element can also significantly refine the eutectic Mg17Al12 phase of the Mg-9Al-1Zn alloy. In this way, the mechanical properties of the Mg-9Al-1Zn alloy are significantly enhanced. It was found that the YS and UTS of the Mg-9Al-1Zn alloy reached 87 MPa and 154 MPa with the addition of 0.9 wt.% of Y element—24% and 43% higher than the Mg-9Al-1Zn alloy. [ABSTRACT FROM AUTHOR]

Phyllostachys praecox is a valuable tree species in karst ecosystems, but improper mulching practices can worsen soil degradation. Understanding soil nutrient limitations is crucial for successful restoration and sustainable development. However, it remains unclear whether and how mulching management of Phyllostachys praecox affects soil enzyme stoichiometry and nutrient limitation in karst areas. Here, we conducted a field experiment in Chongqing karst bamboo forest ecosystems with four mulching treatments: 1-year (T1), 2-years (T2), 1-year and recovery and 1-year (T3), and no mulching (CK). We investigated the activities of the C-acquiring enzyme β-1,4-glucosidase (BG), N-acquiring enzymes L-leucine aminopeptidase (LAP) and β-1,4-N-acetylglucosaminidase (BNA), as well as P-acquiring enzyme phosphatase activity (AP), to assess the limitations of C, N or P and identify the main factors influencing soil microbial nutrient limitation. Compared with the CK treatment, both the T2 and T3 management treatments significantly increased the SOC, TN, MBC, and MBN. Furthermore, the soil enzyme stoichiometric ratio in the karst bamboo forests deviated from the global ecosystem ratio of 1:1:1. T1 > T3 > CK > T2 presented higher values of C/(C + N) and C/(C + P), with T1 having values that were 1.10 and 1.12 greater than those of T2, respectively. Additionally, there was a significant negative correlation between microbial C and N limitations and total nutrients, but a positive correlation with microbial biomass ratios. In conclusion, changes in mulching management of Phyllostachys praecox affect soil enzyme stoichiometry activities and their ratios by influencing total nutrients and microbial biomass ratios. This study suggests an alternate year cover pattern (mulching in one year and resting in the next) as a scientific management approach for bamboo forests, contributing to a better understanding of nutrient limitation mechanisms in karst bamboo forest ecosystems. [ABSTRACT FROM AUTHOR]

The topographies of soil erosion and deposition are critical factors that significantly influence soil quality, subsequently impacting the erodibility of soils in karst regions. However, the investigation into the effects of erosion and deposition topographies on soil erodibility across different stages of vegetation succession in karst trough valleys is still at a preliminary stage. Therefore, three distinct topographic features (dip slopes, anti-dip slopes, and valley depressions) were selected at erosion (dip/anti-dip slope) and deposition sites (valley) to investigate the spatial heterogeneity of soil physicochemical properties, infiltration capacity, aggregate stability, and erodibility in karst trough valleys. Additionally, five different stages of vegetation succession in karst forests were considered: Abandoned land stage (ALS), Herb stage (HS), Herb-Shrub stage (HES), Shrub stage (SHS), and Forest stage (FS). Additionally, the relationships among these factors were analyzed to identify the key driving factors influencing soil erodibility. The results revealed that soil physicochemical properties and soil aggregate stability at the deposition site were significantly superior to those at the erosion site. The FS resulted in the best soil physicochemical properties, whereas the HS resulted in the highest soil aggregate stability within the deposition site. However, the soil infiltration capacity at the erosion site was significantly greater than that at the deposition sites. The ALS had the strongest soil infiltration capacity at both the erosion and deposition sites. The soil erodibility at erosion sites (0.064) was significantly greater than that at deposition sites (0.051), with the highest soil erodibility observed on anti-dip slopes during the HES at erosion sites (0.142). The structural equation model reveals that erosion and deposition topographies, vegetation succession, soil physicochemical properties, soil aggregates, and soil infiltration characteristics collectively account for 88% of the variation in soil erodibility under different conditions. Specifically, both direct and indirect influences on soil erodibility are most significantly exerted by soil aggregate stability and vegetation succession. This study provides scientific evidence to support the management of soil erosion and ecological restoration in karst trough valleys while offering technical assistance for regional ecological improvement and poverty alleviation. [ABSTRACT FROM AUTHOR]

Magnesium alloys with a high volume fraction of secondary phases exhibit inferior formability. Therefore, investigating their thermal deformation characteristics is critical for optimizing thermal processing techniques. In this work, isothermal compression experiments were performed on a Mg-15Gd-8Y-6Al-0.3Mn alloy with an elastic modulus of 51.3 GPa with a substantial volume of aluminum-rare earth (Al2RE) phases. The rheological behavior and microstructural evolution of the material were systematically investigated at varying temperatures (350–500 °C) and strain rates (0.001–1.000 s−1). The calculated thermal processing diagram indicates that the unstable region gradually enlarges with increased strain, and all unstable regions appear within the high-strain-rate, low-temperature domain. The ideal thermal processing range of the alloy is 350–500 °C at strain rates ranging from 0.001 to 0.016 s−1. Particle-stimulated nucleation and discontinuous dynamic recrystallization are both verified to be responsible for the recrystallized microstructure of the alloy. The recrystallized grains exhibit a relatively random crystallographic orientation. As recrystallization proceeds, the texture gradually transitions from a typical [0001] texture in the compression direction to a random texture accompanied by decreased texture intensity. This work sheds new light on the thermo-mechanical processing of high-modulus Mg alloys, which could help design suitable processing techniques for related materials. [ABSTRACT FROM AUTHOR]