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Caragana is endemic to temperate Asia, with most species distributed on the Qinghai–Tibetan Plateau (QTP) and in Northwestern China. Consequently its biogeography should be hypothesized to have been affected by QTP uplift. To examine the biogeography of Caragana in relation to QTP uplift and consequent interior aridification, we conducted molecular dating analyses based on three genes (ITS, cpDNA trnS- trnG and rbcL). Results from relaxed Bayesian BEAST, relaxed Bayesian Multidivtime, and PL (penalized likelihood) indicate that QTP uplift, especially the onset of Himalayan motion at 21–17 Ma, triggered the origin of Caragana (with estimated ages 16–14 Ma). The subsequent QTP rapid uplift at 8 Ma is inferred to have driven the evolution and diversification of the three major clades of Caragana: section Caragana (northern China and the Junggar–Altai–Sayan region), section Frutescentes (Central Asia), and sections Bracteolatae and Jubatae, centered in the QTP. A rapid and active speciation process occurring in the QTP intense uplift at 3.4–1.8 Ma, is indicated by the chronogram. [ABSTRACT FROM AUTHOR]

The Songpan-Garze fold belt, located in the eastern part of the Tibetan Plateau, covers a huge triangular area bounded by the Yangtze (South China), the North China and the Tibetan Plateau blocks. In the northeastern part of the Songpan-Garze fold belt, the Yanggon and Maoergai granitoids provide insights into regional tectono-magmatic events, basement nature and tectonic evolution. U–Pb zircon SHRIMP dating shows that the Yanggon and Maoergai granitoids have magmatic crystallization ages of 221 ± 3.8 Ma and 216 ± 5.7 Ma, respectively. Both the granitoids display adakitic geochemical signatures, suggesting that their magma was derived from partial melting of thickened lower crust. Pb–Sr–Nd isotopic compositions for granitoids reveal that there is an unexposed Proterozoic basement in the Songpan-Garze belt, which has an affinity with the Yangtze block. During development of the Paleo-Tethys ocean, the basement of the Songpan-Garze belt would be a peninsula approaching the Paleo-Tethys ocean from the Yangtze block. [ABSTRACT FROM AUTHOR]

To study the viscosity coefficient and thickness of the viscous layer on the Tibetan Plateau, the relationship between the change in viscosity coefficient and thickness of a lower crustal flow and the change in elevation has been investigated based on the principle of a pipeline flow with different viscosity and thickness of terrain elevation. The viscosity and thickness of the lower crustal flow in different directions were determined based on the changes in the terrain along different directions on the Tibetan Plateau. The following results were obtained: (1) The greater the viscosity and the smaller the thickness of the lower crustal conduit flow, the steeper the ground elevation change formed; (2) The maximum viscosity coefficient in the region from India to the Kunlun Mountains in the southern Tibetan Plateau through the Himalayan boundary is approximately 1020Pas, and the thickness of the conduit flow is approximately 25 km. (3) The maximum value of the viscosity coefficient of the lower crustal flow in the region ranging from the Tibetan Plateau to the Qinghai- Gansu section is attained when the flow thickness in this region approaches 40 km (4) The maximum value of the viscosity coefficient of the lower crustal flow in the region ranging from the Tibetan Plateau to the Qinghai- Gansu section is attained when the flow thickness in this region approaches 40 km., which does not substantially differ from that of the region ranging from the Tibetan Plateau to the Qinghai-Gansu area. (5) The maximum viscosity coefficient of the lower crustal flow from the southeast of the Tibetan Plateau to Yunnan is approximately 1018Pas, and the thickness is approximately 32 km, which differs from the flow thickness in the Sichuan Basin and Qinghai-Gansu regions. The results show variations in the viscosity of the flow along different directions on the Tibetan Plateau, in addition to considerable variation in the thickness of the lower crustal channel flow from region to region, with the overall characteristics of thinness in the west and thickness in the east. The results of the four profiles reveal that the channel flow thickness is the steepest at the southwest border of the Tibetan Plateau with India. This paper presents a reasonable interpretation of the geomorphology of the Tibetan Plateau using different thickness and viscosity coefficients of the lower crustal channel flow model. In this paper, a possible mechanism for the formation of the Tibetan Plateau topography is explained using a horizontal pipe flow for four profiles of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Litter decomposition is a key pathway of metal cycling in terrestrial ecosystems, yet little is known about the dynamics of metals in decomposing roots. A two-year decomposition experiment was conducted to investigate the temporal dynamics of nine metals (Ca, K, Mg, Fe, Al, Mn, Cr, Cu, and Pb) in decomposing roots of three diameter classes (0–2 mm, 2–5 mm, and 5–10 mm) in two subalpine coniferous tree species (Picea asperata and Abies faxoniana) on the eastern Tibetan Plateau of China. Regardless of tree species and root diameters, macro metals (Ca, K, and Mg) and Cu often released over the experimental period and their remaining were 87.7%, 12.5%, 69.4%, and 47.98%, respectively. However, trace metals (Fe, Al, Mn, Cr, and Pb) generally accumulated during the decomposition process and their remaining were 159.6%, 121.5%, 196.4%, 119.6%, and 124.3%, respectively. The concentrations of Ca, K, Mg, Fe, and Al often decreased with increasing root diameters over the experimental period. For Picea asperata, the Ca, K, Fe, and Pb remaining were higher in the 5–10 mm than 0–5 mm roots, but contrasting trends were found for Mg, Mn, Cr, and Cu. For Abies faxoniana, the 5–10 mm roots had lower macronutrients (Ca, K, and Mg) but higher trace metals (Fe, Al, Mn, Cr, Cu, and Pb) remaining compared to 0–5 mm roots. Taken together, root diameter had pronounced influences on metal dynamics, depending on metallic properties, initial root quality, and/or decomposition period. Root initial chemistry (e.g., C, Mn and lignin) were significantly correlated with the metal remaining during the decomposition. Our findings address the importance of root diameter in understanding metal cycling via root decomposition pathways in forest ecosystems. [ABSTRACT FROM AUTHOR]

The Anninghe-Zemuhe-Xiaojiang fault zone (AZXFZ) is an important boundary fault zone on the southeastern margin of the Tibetan Plateau, with frequent strong earthquakes. Previous studies have imaged widespread low-velocity zones in this area. However, there are still many disputes on the connectivity and genesis of the low-velocity zones. In this study, we obtain the Rayleigh wave phase velocity dispersion curves at 4–25-s periods using observations from 378 broadband stations located near the AZXFZ. The new 3D S-wave velocity model has a lateral resolution of about 30 km in 0–35-km depth and is obtained by direct inversion of surface wave dispersion data. The new results clearly image two low-velocity zones and a high-velocity zone in the middle crust of the study region. The low-velocity zone on the western side of the Lijiang-Xiaojinhe fault is related to the eastward flow of crustal material and the movement of the left lateral strike-slip faults in the Tibetan Plateau, while the low-velocity anomaly distributed along the Daliangshan fault and Xiaojiang fault is the superimposition effect of shear heating of the faults and upwelling of mantle material. The uplift of Gongga Shan is a combination of the continuous accumulation of crustal material in the middle and lower crust of the southeastern margin of the Tibetan Plateau as well as the bending and compression of the Sichuan-Yunnan Block and the Xianshuihe-Anninghe fault zone. [ABSTRACT FROM AUTHOR]

Fencing is an important method for restoring and reconstructing degraded grasslands on the Tibetan Plateau. Understanding the characteristics of soil water percolation and soil dissolved organic carbon (DOC) leaching and their response to long-term fencing (10 years) could provide a scientific basis for the management of soil water resources and carbon sinks in alpine grasslands. In this study, grazing plots and plots fenced for 10 years were selected in an alpine meadow, and soil bulk density, soil organic carbon (SOC) density, vegetative carbon (VC) density, soil water percolation and DOC leaching were monitored regularly in the two treatments. The results were as follows: (1) Long-term fencing reduced the soil bulk density and improved carbon sequestration in the alpine meadow. The soil bulk density at a depth of 0-20 cm in the fenced plots was significantly lower than that of the grazing plots ( p < 0.05), and SOC density and VC density at a depth of 0-40 cm were higher than those of the grazing plots to a different degree. (2) During the non-frozen period (from May to September), total soil water leakage at a depth of 40 cm in the grazing plots was 9.6 mm, which accounted for 2.2% of the total rainfall in this period. After fencing for 10 years, soil water leakage was increased by 53.1%. (3) From May to September, total DOC leaching from the grazing plots was 34.6 gC m, and total DOC leaching from the fenced plots was increased by 55.5% compared to the grazing plots. Our results demonstrated obvious soil water percolation and DOC leaching in the alpine meadow. The DOC entered into the groundwater system with the percolation water and finally flowed into lakes and rivers, which represents an important soil carbon loss pathway in alpine meadows. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau, a unique cold and dry region recognized as the Earth's third pole, is primarily composed of alpine grasslands (>60 %). While a warming climate in the plateau is being recorded, phenology of alpine grasslands and its climatic dependencies are less investigated. This study tests the feasibility of the frequently observed Moderate Resolution Imaging Spectroradiometer (MODIS) time series (500 m, 8 days) in examining alpine phenology in the plateau. A set of phenological metrics are extracted from the MODIS Normalized Difference Vegetation Index (NDVI) series in each year, 2000-2010. A nonparametric Mann-Kendall trend analysis is performed to find the trends of these phenological metrics, which are then linked to monthly climatic records in the growing season. Opposite trends of phenological change are observed between the east and west of the plateau, with delayed start of season, peak date, and end of season in the west and advanced phenophases in the east. The correlation analysis indicates that precipitation, with a decreasing trend in the west and increasing trend in the east, may serve as the primary driver of the onset and peak dates of greenness. Temperature increases all over the plateau. While the delay of the end of season in the west could be related to higher late-season temperature, its advance in the east needs further investigation in this unique cold region. This study demonstrates that frequent satellite observations are able to extract phenological features of alpine grasslands and to provide spatiotemporally detailed base information for long-term monitoring on the plateau under rapid climate change. [ABSTRACT FROM AUTHOR]