Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Znaleziono wyników: 3

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: Tibetan plateau

Sortuj według:

Ogranicz wyniki do:

Crustal electrical structure across the Tangra-Yumco tectonic belt revealed by magnetotelluric data: new insights on the east-west extension mechanism of the Tibetan plateau

Chen Ning, Wang Xuben, Shao Changsheng, Zou Jun, Xu Zhengwei, Li Dewei, Wang Xiangpeng

Acta Geophysica

2023

Vol. 71, no. 2

783--794

Geologic evolution of the Tibetan plateau is characterized by crustal extension and horizontal movement in the post-collision stage, during which, approximate north–south (N–S) trending tectonic belts typically represented by Tangra-Yumco rift are developed. The Tangra-Yumco tectonic belt is an ideal object to investigate the deep structure and mechanism of the crustal extension. The magnetotelluric (MT) method is effective in probing crustal structures, especially for high-conductivity bodies. A MT profile of east–west direction with dense stations has been carried out across the Tangra-Yumco tectonic belt. Resistivity models independently derived from two-dimensional and three-dimensional inversions provided more detailed geophysical constraints on the mechanism of crustal extension and deformation. A significant conductor with estimated melt fraction as 3.0–7.5% in mid-lower crust was revealed under the N–S tectonic belt, where the asthenospheric upwelling through the slab-tearing window might have induced partial melting of the lithospheric mantle and lower crust. Combined with previous studies, the upward migration of hot mantle materials and the expansion of the lower crust should be the primary mechanism driving east–west (E–W) extension of the brittle upper crust with high resistivity above the depth of 30 km. According to lateral electrical discontinuity in the upper crust, we inferred that there might exist three normal faults with the reference of topography and the trend of extension of the existing faults. The expansion and deformation of the conductor might have pulled the brittle upper crust and cause significant E–W extension, leading to the formation of the approximate N–S trending rift and normal faults.

Effects of altitude and leaf age on leaf shape in an alpine shrub: the relevance for the leaf area estimation model

Li Qing, He Xiao, Huang Xueju, Zhang Lin

Polish Journal of Ecology

2022

Vol. 70, nr 1

33--43

Nondestructive methods to estimate leaf area (LA) by leaf length (L) and/or width (W) are useful in plant physiology and ecology studies. However, both environmental and ontogenic factors may influence leaf size and/or shape, which may alter the coefficient of LA models. We carried an investigation along an altitudinal gradient in the Sergyemla Mountains, southeast Tibet. In August 2009, we selected nine sites at about every 50 m in altitude from 4,250 m to 4,640 m a.s.l. A total of 4,245 different leaf-aged Rhododendron aganniphum var. schizopeplum (a dominant overstory species) leaves were measured. Compared with the single dimensional models, the two-dimensional model encompassing both L and W (model 5) reflected higher R2 (0.98–0.99) and lower MSE (1.19–3.21) across different leaf age groups for each site, implying that such model could provide the best fit for LA estimation. Analysis of covariance further illustrated that two leaf dimensions model was irrespective of leaf age effects in eight out of the nine sites. Leaf shape (L:W ratio) varied between sites and tended to decrease at higher altitudes (4500–4640 m a.s.l.), leading to significant differences in coefficients of the two-dimension model between every two adjacent sites. For overstory species in alpine habitats, altitude rather than leaf age may affect leaf shape which alters the coefficients of LA estimation models. Since leaf shape of different species (overstory species versus understory ones) may show different responses to a certain environmental gradient, researchers must pay attention to the variation of leaf shape when estimating species-specific LA by measuring L and W, especially when leaves of the top overstory species were collected at different sites.

Actinobacterial Communities of Chosen Extreme Habitats in China

Jia Pengli, Li Miao, Feng Haiyan, Ma Mutian, Gai Jingping, Yang Zhongfang

Polish Journal of Ecology

2020

Vol. 68, nr 3

181--194

Actinobacteria living in frozen soils which potentially could be producers of valuable and biologically active metabolites, remain still largely unexplored. Therefore, the diversity of culturable actinobacteria in the six frozen soil samples collected from the high-latitude and the high-altitude regions in China was investigated by using the culture-dependent method and 16S rRNA gene analysis. A total of 184 culturable actinobacterial isolates (morphotypes) were obtained. The abundance of culturable actinobacteria was 6.20 × 103–3.49 × 105 colony forming units (CFU) per gram of soil (dry weight). The actinobacteria isolated from the high-latitude region in China belong to five genera: Streptacidiphilus, Kitasatospora, Streptomyces, Arthrobacter, and Rhodococcus. The strains belonging to Arthrobacter were dominant, the 19 strains were closely related to Arthrobacter globiformis in terms of evolutionary distance. The actinobacterial isolates from the high-altitude region, from 2,813 m to 4,775 m in elevation, in China could be grouped into six genera (Arthrobacter, Microbacterium, Streptomyces, Rhodococcus, Nocardia, and Nocardiopsis), with dominant Streptomyces and Arthrobacter strains. The 4 strains were closely related to Rhodococcus fascians and one strain was closely with Microbacterium hydrocarbonoxydans in terms of evolutionary distance. Three genera of Arthrobacter, Streptomyces, and Rhodococcus were found in both areas. Our research provides new insight into the characteristics of the distribution of actinobacteria associated with frozen soils, which help us gain a better understanding of the potential of the cryogenic environments – the potential source of actinobacterial antibiotics.