Eastern Edge Of Tibetan Plateau Research Articles

Soil organic carbon accumulation and microbial carbon use efficiency in subalpine coniferous forest as influenced by forest floor vegetative communities

The importance of forest floor plants (herbs and mosses) and understory communities on soil C dynamics has been grossly understudied in forest ecosystems; however, there is currently very little knowledge on the impact of forest floor vegetation composition on soil organic C (SOC) accumulation and the microbial metabolic processes. To bridge this gap of knowledge, a forest floor vegetation-removal experiment involving nonvascular mosses (Pleurozium schreberi (PS); Rhizomnium tuomikoskii (RT); and Hylocomiastrum pyrenaicum (HP)) and vascular sedges (Carex sp., CS) was conducted in a subalpine coniferous forest on the eastern edge of Tibetan Plateau, to investigate the associations of different forest floor vegetation communities with mineral soil C accumulation and microbial physiology (C use efficiency (CUE) and microbial biomass turnover). Soils beneath the forest floor vegetative communities differed in soil C and nitrogen (N) concentrations and had distinctively different microbial community structure and physiology. Compared to bare soils, sedge soils had significantly greater SOC and dissolved organic C (DOC) accumulation, greater microbial DNA, biomass C and phospholipid fatty acids (PLFAs) concentrations, and higher microbial CUE and shorter microbial biomass turnover time. While effects of mosses differed among species, P. schreberi had similar effects as sedges, but the effects of H. pyrenaicum and R. tuomikoskii were minimal. Relative to bare soil, P. schreberi and Carex sp. soils were 61.5% and 51.6% higher in microbial CUE and had an obviously shorter microbial biomass turnover time. Variations in the level of DOC and PLFAs (rather than their portion relative to SOC) were the most important regulators of microbial CUE and biomass turnover rate in soils with different forest floor vegetation covers. These results highlight how differences in soil organic matter quality that are directly related to the forest floor vegetation community influence the microbial CUE and biomass turnover and the long-term soil C dynamics.

Upper Cretaceous–Paleocene Magnetostratigraphy of the Longmenshan Foreland Basin and Its Implications for the Tectonic Deformation of the Longmenshan Fault Zone

AbstractKnowledge of the history of the tectonic deformation of the eastern edge of Tibet is important for understanding the evolution of the entire Tibetan Plateau; however, the corresponding tectonic deformation process remains controversial. We conducted a detailed rock magnetic and magnetostratigraphic study of the Cretaceous Jiaguan and Guankou Formations (the Jinmenguan section) within the Longmenshan foreland basin on the eastern edge of Tibetan Plateau. The high‐temperature remanence components separated after thermal demagnetization passed the A‐class reversal test, Bootstrap Cartesian coordinate test, and fold test, at the 95% confidence level. The resulting magnetostratigraphy constrains the age range of the Jinmenguan section to 128.0–64.1 Ma, and that of the Jiaguan Formation to 128.0–83.6 Ma. The resulting chronology identifies two phases of rapid sedimentation (128.0–124.1, 68.8–64.1 Ma) that constrain two phases of tectonic uplift in the Longmenshan Fault Zone on the eastern margin of Tibet during the Cretaceous–early Cenozoic. Our findings suggest that the stress field generated by the subduction and closure of the Bangong‐Nujiang Ocean had already been transferred to the eastern edge of the Tibet in the Cretaceous (at ∼128 Ma).

The genetic admixture in Tibetan‐Yi Corridor

The Tibetan-Yi Corridor located on the eastern edge of Tibetan Plateau is suggested to be the key region for the origin and diversification of Tibeto-Burman speaking populations and the main route of the peopling of the Plateau. However, the genetic history of the populations in the Corridor is far from clear due to limited sampling in the northern part of the Corridor. We collected blood samples from 10 Tibetan and 10 Han Chinese individuals from Gansu province and genotyped about 600,000 genome-wide single nucleotide polymorphisms (SNPs). Our data revealed that the populations in the Corridor are all admixed on a genetic cline of deriving ancestry from Tibetans on the Plateau and surrounding lowland East Asians. The Tibetan and Han Chinese groups in the north of the Plateau show significant evidence of low-level West Eurasian admixture that could be probably traced back to 600∼900 years ago. We conclude that there have been huge population migrations from surrounding lowland onto the Tibetan Plateau via the Tibetan-Yi Corridor since the initial formation of Tibetans probably in Neolithic Time, which leads to the current genetic structure of Tibeto-Burman speaking populations.

Blooms of the woloszynskioid dinoflagellate Tovellia diexiensis sp. nov. (Dinophyceae) in Baishihai Lake at the eastern edge of Tibetan Plateau

Freshwater red tides due to dinoflagellates have caused spectacular and regular summer reddening in recent years in Baishihai Lake, a temperate, meromictic, meso- or oligotrophic, high-altitude, landslide-dammed, deep lake located at the eastern edge of Tibetan Plateau in China. Based on morphological and molecular analyses, the causative organism has been identified as a new woloszynskioid dinoflagellate, Tovellia diexiensis Q. Zhang et G.X. Liu sp. nov. The vegetative cells are 20-32 mu m long and 16-24 mu m wide. They have a hemispherical episome and a broadly rounded hyposome with a short characteristic antapical spine. Usually cells are bright red due to the presence of numerous red-pigmented bodies, which often masked the yellowish green discoid chloroplasts. The amphiesma of motile cells comprise mainly quadrilateral, pentagonal or hexagonal thin plates, arranged in 4-5 latitudinal series on the episome, 1 in the cingulum and 4 on, the hyposome. Molecular phylogenies based on small subunit ribosomal DNA and large subunit ribosomal DNA (LSU) indicate T diexiensis from Baishihai Lake to belong to the family Tovelliaceae, which was monophyletic in our LSU phylogenies. During the bloom-forming period in 2005, cell density of T diexiensis reached 9.15 x 10(5) cells L-1. Astaxanthin and its diester were found to be the major pigments in T diexiensis, resulting in a characteristic blood-red color of the water in Baishihai Lake.

Discriminating types of precipitation in Qilian Mountains, Tibetan Plateau

Abstract Study region Hulugou River Basin (HRB) of Qilian Mountains, eastern edge of Tibetan Plateau. Study focus Traditional manual observations only record point-scale precipitation rather than regional-scale precipitation. Automatic weather stations just record precipitation amount without discriminating by type of precipitation. This study observed precipitation types all over the HRB and analyzed air temperature and humidity conditions at daily and half-hour resolution. New hydrological insights for the region Combined observations of air temperature and precipitation type indicate that, at daily resolution the threshold air temperature between rain and snow is 0 °C and the air temperature at rain/snow boundary is from 0 °C to 7.6 °C, which means the rain and mixed precipitation threshold air temperature can shift more than 7.0 °C in the HRB. At half-hour resolution, air temperature is above 0 °C during rainfall, under 0 °C for snowfall, and above 0 °C at the rain/snow precipitation boundary, and could either be above 0 °C or fluctuate around 0 °C for mixed precipitation. Corresponding relative humidity observations indicate that rainfall and mixed precipitation events correspond with high humidity conditions in warm season of the HRB. Snowfall events correspond with low humidity conditions in the HRB.

Study of modern pollen and stomata from surficial lacustrine sediments from the eastern edge of Tibetan Plateau, China

To examine the relationships between pollen, conifer stomata and vegetation in high mountainous areas, the pollen and conifer stomata contents of surface sediments from 26 lakes in the eastern edge of the Tibetan Plateau were analyzed. Pollen analyses show that pine forests have distinct pollen assemblages that are characterized by high abundance of Pinus pollen and subtropical taxa such as Castanopsis, Eurya pollen. Detrended correspondence analysis (DCA) also indicates that pine forests can be distinguished from cold coniferous forests and the Alpine shrub and meadow based on pollen analysis. However, cold coniferous forests and the alpine shrub and meadow cannot be differentiated by pollen analyses. This is best illustrated by the DCA analysis, which shows that both plant communities are characterized by a higher abundance of pollen such as Picea, Tsuga, and Quercus. Analyses of stomata reveal that Pinus stomata only occur in samples collected from the regions with pine forests, and cold conifer stomata were not found in the Alpine lakes except for one lake, which was likely influenced by human activities. Therefore, conifer stomata appear to be an important tool that complements pollen analysis in reconstructing vegetation history of high mountainous areas, especially for tree line migration.

Temperature and precipitation variations at two meteorological stations on eastern slope of Gongga Mountain, SW China in the past two decades

Gongga Mountain, locates on the eastern edge of Tibetan Plateau of China, is the highest mountain in China except summits in Tibet. Only limited meteorological data on Gongga Mountain have been published so far. Here we present the meteorological records from two stations, Moxi Station (at 1,621.7 m above sea level (a.s.l.), 1992–2010) and Hailuogou Station (at 2,947.8 m a.s.l., 1988–2010), on the eastern slope of Gongga Mountain. In the past two decades, the annual precipitation decreased while the annual mean temperature increased at Hailuogou Station. Both precipitation and temperature increased at Moxi Station. The precipitation variation on the eastern slope of Gongga Mountain is influenced by both East Asian Monsoon and Indian Monsoon, so that the precipitation concentrated between May and October. The temperature variation on the eastern slope of Gongga Mountain in the past two decades showed similar trends as that of the northern hemispheric and global. In the past two decades, the temperature increased 0.35°C and 0.3°C/decade at Hailuogou Station and Moxi Station respectively, which was higher than the increase extents of northern hemispheric and global temperature. The most intense warming occurred at the first decade of 21st century. The winter temperature increased more at Hailuogou Station than at Moxi Station. A remarkable increase of temperature in March was observed with only a little precipitation at both high and low altitude stations.

Climate constraints on growth and recruitment patterns of Abies faxoniana over altitudinal gradients in the Wanglang Natural Reserve, eastern Tibetan Plateau

The radial growth and recruitment patterns of trees in subalpine areas are subject to the influence of changing environmental conditions associated with changes in elevation. To investigate responses of fir radial growth and recruitment to climate factors at different elevations, tree-ring width chronologies and age structures of Abies faxoniana were developed from five sampling sites at ~2800–3300 m elevation on the north-western and south-eastern aspects in the Wanglang Natural Reserve on the eastern edge of Tibetan Plateau. Statistical characteristics of the chronologies indicated that expressed population signal and signal-to-noise ratio increased with increasing elevation in the north-western aspect; the reverse was observed on the south-eastern aspect. Correlation analysis between chronologies and climate variables showed that fir radial growth was negatively correlated with previous growing season mean temperatures and was positively correlated with January precipitation in all plots. The amount of precipitation in the growing season (June and July) greatly influenced radial growth in the two lower sites of both the aspects. The three plots on the north-western aspect were characterised by significant rates of tree recruitment in the past five decades. There were multi-decadal periods of heightened recruitment over the past three centuries in the two south-eastern plots. Widespread disturbances after 1920s were not observed in any plots and the infrequent small-scale disturbances that occurred were not the main factors influencing recent recruitment in any plots. Correlation analysis between recruitment residuals and climate variables showed that fir seedling recruitment in the north-western aspect plots was mainly controlled by spring–summer temperatures. But recruitment was greatly restricted by competition with dense bamboos and other tree species in the south-eastern aspect. Overall, previous August mean temperature and January precipitation were the dominant factors determining fir radial growth in all plots, and recruitment was sensitive to spring–summer temperatures in the plots with sparse bamboo cover.

Surface Energy-Balance Closure in a Gully Region of the Loess Plateau at SACOL on Eastern Edge of Tibetan Plateau

Surface Energy-Balance Closure in a Gully Region of the Loess Plateau at SACOL on Eastern Edge of Tibetan Plateau

Late Cenozoic denudation by large-magnitude landslides in the eastern edge of Tibetan Plateau

Abstract Eastern edge of the Tibetan Plateau is marked by the Longmen Shan, which experienced pronounced denudation in late Cenozoic and was previously attributed to river erosion. Our recent work, however, demonstrated that the landsliding must have played an important integral role in the surface processes. Various-scale landslides are present in the peripheral zone of the southern Longmen Shan, which were interpreted as overthrust-related klippen in previous works. We revisited these exotic blocks, and demonstrated that they were actually gravity-driven landslides in origin. The landslides are composed mostly of thick-bedded marine limestone and sandstone of Paleozoic–Early Triassic ages, and were detached along some weak zones like Lower Silurian phyllite and unconformities. Three types of landslides can be categorized, distributed, stacked, and coherent, and their differential occurrence is considered to bear upon both uplift rates of the Longmen Shan and foreland topography. Outward flow of lower-crustal materials from the Tibetan Plateau interior provides a feasible mechanism for initiating the uplift of its eastern flank in Cenozoic. Positive feedbacks are believed to have existed between extrusion of lower-crustal channel flow and surface denudation processes. Rapid denudation by large-magnitude landslides in conjunction with coeval river erosion in the southern Longmen Shan might have led to predominant sub-vertical extrusion of lower-crustal flow channel, as evidenced by nearly symmetric exhumation of the Pengguan massif. The northern Longmen Shan was comparatively less denuded, with few basement rocks cropping out, and landslides are absent in its front as well. Differential denudation between the southern and northern Longmen Shan might have in large part resulted from the lower-crustal flow that presumably moved to the southeast and had less impact on the northern Longmen Shan.