Understanding the influence of vegetation types on soil particle-size distribution (PSD) is essential to evaluate the effects of sediment control by vegetation restoration. In this work, we studied the effects of different vegetation types, including bare land, meadow, shrub and forest on soil PSD in Jiangjiagou gully, Yunnan province, China. A total of 60 soil samples were collected and analyzed for soil particle size distribution using the laser diffraction method. Fractal theory was used to calculate multifractal parameters. The volume fraction of silt particles in shrub and forest is significantly higher than that in bare land, meadow, whereas the total volume fraction of sand particles in bare land and meadow exceed that in shrub and forest. The soil particle size distribution along soil layers has no significant difference in each vegetation type. The volumetric fractal dimension is significantly higher in forest and shrub than in bare land and grassland, but there is no significant difference between forest and shrub. In addition, soil erosion resistance exhibits significant differences of forest > shrub > grassland > bare land. Multifractal parameters are highest in bare land except for multifractal spectrum values ( f (α max ) and f (α min )) and the maximum value of singularity index (α min ). All generalized dimensions spectra curves of the PSD are sigmoidal, whereas the singular spectrum function shows an asymmetric upward convex curve. Furthermore, soil erosion resistance has significant relationships with multifractal parameters. Our results suggest that multifractal parameters of the soil PSD can predict its anti-ability to erosion. This study also provides an important insight for the evaluation of soil structure improvement and the effects of erosion control by vegetation restoration in dry-hot valley areas.
Major earthquakes cause serious damage to ecosystem structure and function through their huge destructive force and subsequent geohazards. Understanding the characteristics of post-earthquake land use change is of great interest to assess the effects of ecological restoration in earthquake-affected areas. However, little is known about the consequences of land use change on a small scale due to incomplete, non-comprehensive, and sparse research data. Here, we used remote-sensing images to study the land use change characteristics of the Longxi River before and after the Wenchuan earthquake by calculating the land use dynamics degree, transition matrix, and gravity center of the Longxi River Basin from 2005 to 2015. The Wenchuan earthquake disaster did not affect the main dominance of forests. Grassland, the second dominant land type, was replaced by geohazard-induced unutilized land after the earthquake. Compared with pre-earthquake in 2005, the areas of cultivated land, forest, grassland, and water area decreased, while those of construction land and unutilized land increased in 2015. The single land use dynamic degree and spatial dynamic change degree show the highest transition intensity of other land use types to unutilized land between 2005 and 2009. However, the degrees of all land use types decreased between 2009 and 2015. Both banks of the lower reach of the Longxi River had high and developing comprehensive indexes of land use degrees during the study period. The gravity centers of grassland, construction land, water, and cultivated land changed from north to south, while forest and unutilized land had the opposite pattern. Our results provide useful information for ecological restoration, ecological security, and soil-erosion control in earthquake-affected areas.
Deregulation of Roundabout homolog 1 (Robo1) has been demonstrated to be associated with several types of human cancer, including gastric cancer. However, the detailed role of Robo1 and its regulatory mechanism in gastric cancer remain largely unclear. In the current study, it was demonstrated that the expression of microRNA (miR)‑29a was frequently reduced in gastric cancer tissues, compared with their matched normal adjacent tissues. Similar results were additionally observed in AGS and SGC‑7901 human gastric cancer cells. Overexpression of miR‑29a led to reduced migration and invasion of AGS cells. To explore the targets of miR‑29a in gastric cancer, bioinformatics analysis was conducted and Robo1 was identified as a putative target of miR‑29a. Further western blotting and luciferase activity assay data confirmed that miR‑29a was able to negatively regulate the protein expression of Robo1, through directly binding to the 3'‑untranslated region of Robo1 mRNA in gastric cancer cells. In addition, it was demonstrated that Robo1 was frequently upregulated in gastric cancer tissues compared with their matched adjacent normal tissues, and a significant inverse correlation was identified between miR‑29a and Robo1 expression. In addition, knockdown of Robo1 by small interfering RNA markedly inhibited the migratory and invasive capabilities of AGS cells, which the results obtained with overexpression of miR‑29a. In conclusion, to the best of our knowledge the current study suggested for the first time, that miR‑29a inhibits migration and invasion in part via direct inhibition of Robo1 in gastric cancer cells. Therefore, Robo1 and miR‑29a may serve as diagnostic or therapeutic targets for gastric cancer.
In this study, we examined plant C:N:P stoichiometry of herbaceous plants in different sections (stable area, unstable area and deposition area) of the unstable slope on both shade and sunny aspects of dry-hot valley with different soil properties. The results showed that C concentration (320.59 g·kg-1), N concentration (12.15 g·kg-1), and N:P ratio (25.37) of shoot on the unstable slope were significantly higher than those of root, with 254.01 g·kg-1, 6.12 g·kg-1 and 13.43, respectively. The average value of the C:N ratio was significantly higher in root (43.09) than shoot (31.90). The C content and N:P ratio of shoot and root in stable and unstable areas were significantly higher than in deposition area, whereas the N content in unstable area was significantly higher than that in deposition area on the sunny slope. In addition, the N and P contents of shoot and the root P content in deposition area were significantly higher than in stable and unstable areas, whereas the C content of root in stable and unstable areas were significantly higher than in deposition area on the shade slope. Moreover, the shoot growth of plants was mainly limited by P, whereas root growth was mainly limited by N and the limitation gradually increased as the section goes down. Soil water content (SWC) was an important factor controlling the C, N, and P contents change of shoot with the relative influence ratios of 28.8%, 20.8%, and 19.9%, respectively. Soil organic carbon (SOC) had a significant impact on the C and P contents of root with the relative influence ratios of 49.5% and 22.1%. The change of root N content was mainly affected by soil pH (24.3%). Our results revealed that nutrient allocation of plant was significantly affected by slope aspects, sections and soil factors, which were mainly constituted by SWC, SOC, and soil pH.以干热河谷阴坡和阳坡典型失稳性坡面不同区段(稳定区、失稳区和堆积区)的草本植物为研究对象,分析植物地上和地下碳(C)、氮(N)、磷(P)含量及其化学计量特征对土壤性质的响应机制。结果表明:失稳性坡面植物地上C含量(320.59 g·kg-1)、N含量(12.15 g·kg-1)和C/P(25.37)均显著高于地下(分别为254.01 g·kg-1、6.12 g·kg-1、13.43),C/N则表现为地下(43.09)显著高于地上(31.90)。阳坡植物地上和地下C含量、N/P均表现为稳定区和失稳区显著高于堆积区,N含量则表现为失稳区显著高于堆积区;阴坡植物地上N、P含量及地下P含量均表现为堆积区显著高于稳定区和失稳区,地下C含量则反之。植物地上生长主要受P限制,根系生长主要受N限制并随区段向下呈逐渐增加趋势;阴坡植物生长受P的限制程度高于阳坡,N限制弱于阳坡。土壤含水量(SWC)是影响植物地上C、N、P含量变化的重要因子,影响值分别为28.8%、20.8%、19.9%,土壤有机碳(SOC)则显著影响植物地下C、N含量,影响值分别为49.5%、22.1%,植物地下N含量的变化主要受土壤pH值的影响(24.3%)。坡向、区段及土壤因子均显著影响植物养分的分配,SWC和SOC是主要影响因子,同时还受土壤pH值的影响。.
The 2008 8.0 Ms Wenchuan earthquake caused serious ecological degradation in the northwest of China’s Sichuan Province. Elucidating landscape fragmentation and spatial pattern of post-earthquake landscape is of great interest in order to improve ecological restoration and predict the spatial distribution of damaged ecosystems in earthquake-affected areas. We used four real-time remote sensing images to analyze the landscape pattern characteristics and spatial autocorrelation of the Longxi River Basin before and after the Wenchuan earthquake during the period from 2005 to 2015. In the study period, the degree of landscape fragmentation increased 1 year after the earthquake in 2009 but decreased in 2011 and 2015. The spatial distribution of forest, farmland, and shrub-grassland had significantly positive spatial correlation and the characteristics of spatial aggregation from 2005 to 2015. Construction land had no significant spatial correlation before the earthquake in 2005, but significantly positive spatial correlation after the earthquake, while traffic land had no significant spatial correlation across the study period. Unlike the other landscape types, geological disasters changed from a significantly negative spatial correlation before the earthquake to a significantly positive spatial correlation after the earthquake. However, the positive autocorrelation of all landscape types decreased with the increase of space distance, but in different distance-decay rates. The High-high spatial aggregation areas of geological disasters and construction land clustered gradually upstream of the basin and distributed in Longchi town, respectively; those of farmland distributed in the southeast of the basin increased in 2009 but then decreased, while those of forests had the opposite pattern as the dominant landscape type after the earthquake. Our results elucidated the spatial structure and distribution features of the Longxi River Basin to give a theoretical foundation for assessing the effects of ecological restoration and reconstruction management in earthquake-affected areas.
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