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2017, 9 (1) Online: 01 February 2017 Previous issue Next issue
  • Evolution and changes of permafrost on the Qinghai-Tibet Plateau during the Late Quaternary
  • XiaoLi Chang, HuiJun Jin, RuiXia He, LanZhi Lü, Stuart A. Harris
  • DOI: 10.3724/SP.J.1226.2017.00001
  • 2017, Vol.9 (1): 1–19 Abstract ( 29) HTML PDF (21882 KB) ( 5 )
  • Due to the uplift of Qinghai-Tibet Plateau (QTP), the cryosphere gradually developed on the higher mountain summits after the Neocene, becoming widespread during the Late Quaternary. During this time, permafrost on the QTP experienced repeated expansion and degradation. Based on the remains and cross-correlation with other proxy records such as those from glacial landforms, ice-core and paleogeography, the evolution and changes of permafrost and environmental changes on the QTP during the past 150,000 years were deduced and are presented in this paper. At least four obvious cycles of the extensive and intensive development, expansion and decay of permafrost occurred during the periods of 150-130, 80-50, 30-14 and after 10.8 ka B.P.. During the Holocene, fluctuating climatic environments affected the permafrost on the QTP, and the peripheral mountains experienced six periods of discernible permafrost changes:(1) Stable development of permafrost in the early Holocene (10.8 to 8.5-7.0 ka B.P.); (2) Intensive permafrost degradation during the Holocene Megathermal Period (HMP, from 8.5-7.0 to 4.0-3.0 ka B.P.); (3) Permafrost expansion during the early Neoglacial period (ca. 4,000-3,000 to 1,000 a B.P.); (4) Relative degradation during the Medieval Warm Period (MWP, from 1,000 to 500 a B.P.); (5) Expansion of permafrost during the Little Ice Age (LIA, from 500 to 100 a B.P.); (6) Observed and predicted degradation of permafrost during the 20th and 21st century. Each period differed greatly in paleoclimate, paleoenvironment, and permafrost distribution, thickness, areal extent, and ground temperatures, as well as in the development of periglacial phenomena. Statistically, closer dating of the onset permafrost formation, more identification of permafrost remains with richer proxy information about paleoenvironment, and more dating information enable higher resolution for paleo-permafrost reconstruction. Based on the scenarios of persistent climate warming of 2.2~2.6℃ in the next 50 years, and in combination of the monitored trends of climate and permafrost changes, and model predictions suggest an accelerated regional degradation of plateau permafrost. Therefore, during the first half of the 21st century, profound changes in the stability of alpine ecosystems and hydro(geo)logical environments in the source regions of the Yangtze and Yellow rivers may occur. The foundation stability of key engineering infrastructures and sustainable economic development in cold regions on the QTP may be affected.
  • Distribution of winter-spring snow over the Tibetan Plateau and its relationship with summer precipitation in Yangtze River
  • Zhuo Ga, Tao Chen, La Ba, PuBuCiRen, Ba Sang
  • DOI: 10.3724/SP.J.1226.2017.00020
  • 2017, Vol.9 (1): 20–28 Abstract ( 32) HTML PDF (11048 KB) ( 5 )
  • The distribution of winter-spring snow cover over the Tibetan Plateau (TP) and its relationship with summer precipitation in the middle and lower reaches of Yangtze River Valley (MLYRV) during 2003-2013 have been investigated with the moderate-resolution imaging spectrometer (MODIS) Terra data (MOD10A2) and precipitation observations. Results show that snow cover percentage (SCP) remains approximately 20% in winter and spring then tails off to below 5% with warmer temperature and snow melt in summer. The lower and highest percentages present a declining tendency while the middle SCP exhibits an opposite variation. The maximum value appears from the middle of October to March and the minimum emerges from July to August. The annual and winter-spring SCPs present a decreasing tendency. Snow cover is mainly situated in the periphery of the plateau and mountainous regions, and less snow in the interior of the plateau, basin and valley areas in view of snow cover frequency (SCF) over the TP. Whatever annual or winter-spring snow cover, they all have remarkable declining tendency during 2003-2013, and annual snow cover presents a decreasing trend in the interior of the TP and increasing trend in the periphery of the TP. The multi-year averaged eight-day SCP is negatively related to mean precipitation in the MLYRV. Spring SCP is negatively related to summer precipitation while winter SCP is positively related to summer precipitation in most parts of the MLYRV. Hence, the influence of winter snow cover on precipitation is much more significant than that in spring on the basis of correlation analysis. The oscillation of SCF from southeast to northwest over the TP corresponds well to the beginning, development and cessation of the rain belt in eastern China.
  • Study on the freezing-thawing deformation of consolidated soils under high pressure
  • DaYan Wang, Wei Ma, LeLe Lei
  • DOI: 10.3724/SP.J.1226.2017.00029
  • 2017, Vol.9 (1): 29–37 Abstract ( 42) HTML PDF (10367 KB) ( 8 )
  • The freezing-thawing deformation behaviors of consolidated soils under high pressure have been investigated in a high-pressure-low-temperature (HPLT) K0 consolidation apparatus with a small strain sensor. The tests cover a variety of frozen soil temperatures ranging from -2℃ to -10℃, and a series of applied pressures ranging from 1 MPa to 5 MPa. The test results show that, for the consolidated soils under high pressure, their freezing-thawing deformation was caused by the realignment and the deformation of soil particles, the phase change of water, and the water redistribution in the soil. As for the deformation produced by thermal expansion and contraction, it is about 0.04~0.05 mm, accounting for only about 7%~9% of the total deformation. Taking the freezing-thawing deformation produced by temperature disturbance as a creep deformation, the creep models of the developing soil deformation will be determined by the soil's final temperature, i.e., the desired temperature. For the soils under a desired temperature between -2℃ and -5℃, the freezing-thawing deformation develops according to a non-attenuation creep model; but for the soils with a desired temperature lower than -5℃, a full attenuation creep model is followed. The applied pressure and soil type also have a significant influence on the maximum freezing deformation. Generally, the greater the desired pressure applied, the less the maximum deformation is; and the loess freezing deformation is larger than that of sand.
  • δ18O,δD and d-excess signatures of ground ice in permafrost in the Beiluhe Basin on the Qinghai-Tibet Plateau,China
  • YuZhong Yang, QingBai Wu, HuiJun Jin, Peng Zhang
  • DOI: 10.3724/SP.J.1226.2017.00038
  • 2017, Vol.9 (1): 38–45 Abstract ( 32) HTML PDF (7983 KB) ( 4 )
  • In this paper, stable isotope (δ18O, δD) investigations were completed in ground ice from a deep borehole in the Beiluhe Basin on northern Qinghai-Tibet Plateau to unravel the isotopic variations of ground ice and their possible source water. The δ18O and δD of ground ice show distinctive characteristics compared with precipitation and surface water. The near-surface ground ice is highly enriched in heavier isotopes (δ18O and δD), which were gradually depleted from top to bottom along the profile. It is suggestive of different origin and ice formation process. According to isotopic variations, the ice profile was divided into three sections:the near-surface ground ice at 2.5 m is frozen by the active-layer water which suffered evaporation. It is possible that ground ice between 3 and 4.2 m is recharged by the infiltration of snowmelt. From 5 to 6 m, the ground ice show complex origin and formation processes. Isotopic variations from 6 to 11.1 m and 20.55 m indicate different replenishment water. The calculated slope of freezing line (S=6.4) is larger than the experimental value (5.76), and is suggestive of complex origin and formation process of ground ice.
  • CO2 seasonal variation and global change: Test global warming from another point of view
  • XiuMing Liu, JiaSheng Chen
  • DOI: 10.3724/SP.J.1226.2017.00046
  • 2017, Vol.9 (1): 46–53 Abstract ( 51) HTML PDF (8626 KB) ( 9 )
  • CO2 and temperature records at Mauna Loa, Hawaii, and other observation stations show that the correlation between CO2 and temperature is not significant. These stations are located away from big cities, and in various latitudes and hemispheres. But the correlation is significant in global mean data. Over the last five decades, CO2 has grown at an accelerating rate with no corresponding rise in temperature in the stations. This discrepancy indicates that CO2 probably is not the driving force of temperature change globally but only locally (mainly in big cities). We suggest that the Earth's atmospheric concentration of CO2 is too low to drive global temperature change. Our empirical perception of the global warming record is due to the urban heat island effect:temperature rises in areas with rising population density and rising industrial activity. This effect mainly occurs in the areas with high population and intense human activities, and is not representative of global warming. Regions far from cities, such as the Mauna Loa highland, show no evident warming trend. The global monthly mean temperature calculated by record data, widely used by academic researchers, shows R2=0.765, a high degree of correlation with CO2. However, the R2 shows much less significance (mean R2=0.024) if calculated by each record for 188 selected stations over the world. This test suggests that the inflated high correlation between CO2 and temperature (mean R2=0.765-0.024=0.741) used in reports from the Intergovernmental Panel on Climate Change (IPCC) was very likely produced during data correction and processing. This untrue global monthly mean temperature has created a picture:human emission drives global warming.
  • Microcoring and dendrometer-detected intra-annual wood formation of Populus euphratica in the Ejina Oasis,northwestern China
  • XiaoMei Peng, ShengChun Xiao, GuoDong Cheng, QuanYan Tian, HongLang Xiao
  • DOI: 10.3724/SP.J.1226.2017.00054
  • 2017, Vol.9 (1): 54–66 Abstract ( 31) HTML PDF (15616 KB) ( 8 )
  • Seasonal stem radial growth and wood formation of trees have become research hotspots because of their significance for dendroclimatological and dendroecological studies. However, until recently, these studies concentrated on coniferous tree species in high-altitude and high-latitude regions, while detailed information on arid-zone riparian forests is scarce. The main focus of this study is to monitor the intra-annual dynamics of radial growth and tree ring formation in a deciduous species, Populus euphratica. In 2013, we combined the dendrometer and microcoring methods to study this species in the riparian forest of the Ejina Oasis, in arid northwestern China. Vessel enlargement began in early May, and the maximum rate of cell production occurred in early June. The cell division then ceased from early to mid-July. The dendrometer method failed to reliably detect the date of growth initiation and cessation, but succeeded to detect the time of maximum growth rate just like the microcoring method did. We found that weekly stem radial increment data described xylem growth more accurately than daily datasets. Based on correlation analysis among climatic and hydrologic variables, and weekly stem radial increment, weekly ring width increase dataset, the depth to groundwater was the main factor that limited tree ring growth. From a practical perspective, such studies of intra-annual wood formation can provide empirical guidance for seasonal water allocations within a river basin.
  • Field determination for roughness length above the different non-erodible surfaces
  • HeQiang Du, Tao Wang, Xian Xue
  • DOI: 10.3724/SP.J.1226.2017.00067
  • 2017, Vol.9 (1): 67–77 Abstract ( 27) HTML PDF (12226 KB) ( 4 )
  • Non-erodible elements, for its disturbance to the near-surface airflow, have been widely used in arid and semi-arid regions to protect the surface from wind erosion. Roughness length was usually used to evaluate the protection effect of non-erodible elements from wind erosion. In this study, the wind profiles above five types of non-erodible surfaces including gravel, wheat straw checkerboard barriers, cotton stem checkerboard barriers, shrubs, and herbs were measured and analyzed. The wind velocities above these surfaces increased with height approximately in logarithmic functions. The roughness length of different non-erodible surfaces was calculated by the functions of wind profiles. The results reveal that:(1) Roughness length increased with wind velocity in given wind velocity ranges. (2) On vegetative surfaces, wind did not effectively bend the stems. The threshold wind velocity for bending the stems of Achnatherum splendens was 4 m/s, 10 m/s for Agropyron cristatum, and for Artemisia ordosica, no obvious bending of stems even for wind velocity reaching 12 m/s. (3) Correlation analysis results show that the vegetation's coverage and frontal area affect the roughness length more significantly than the other parameters. (4) The protective results of these non-erodible elements were evaluated. The checkerboard sand barriers made of cotton stem could provide more effective protection than that made of wheat straw. In the same coverage conditions, vegetation could provide more effective protection from wind erosion than gravel, and the blending of different non-erodible elements especially the combination of blending of vegeation and checkerboard sand barriers could provide more effective protection to the surface.
  • Adaptive evolution of rbcL in Reaumuria soongarica (Tamaricaceae)
  • ChaoJu Qian, MengHe Gu, HengXia Yin, Yong Shi, ChengLiang Yin, Xia Yan, XiaoFei Ma
  • DOI: 10.3724/SP.J.1226.2017.00078
  • 2017, Vol.9 (1): 78–88 Abstract ( 30) HTML PDF (12947 KB) ( 7 )
  • In the field of phylogenetic analyses, the rbcL gene encoded large subunit Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco, EC4.1.1.39), which plays a crucial role in the process of photosynthesis for most terrestrial plants, has been considered to be conserved; however, recent controversy regarding rbcL conservation has appeared since it was proposed to be under natural selection within all principal lineages of land plants. In this study, by examining the variation of DNA and protein sequences among 17 species in the family Tamaricaceae, three nonsynonymous mutations were identified to be under positive selection. The favored sites were located in the alph-helix domains of Rubisco, with decreased hydrophobicity and increased entropy, which could facilitate CO2 penetration into the active site of Rubisco. We also found that the expression level of rbcL in different genotypes of Reaumuria soongarica shifted in response to various stresses such as drought, temperature, salt, and light. This study not only sheds light on the functional/structural features of Rubisco in the evolution scenarios from C3-like into C4 in Tamaricaceae but also provides useful information on directing genetic performance to enhance photosynthesis efficiency of desert plants for sustaining fragile desert ecosystems; furthermore, it promotes the ability to cope with desert aridification and global warming.
  • Identification of Kalidium species (Chenopodiaceae) by DNA barcoding
  • XiaoHui Liang, YuXia Wu
  • DOI: 10.3724/SP.J.1226.2017.00089
  • 2017, Vol.9 (1): 89–96 Abstract ( 23) HTML PDF (7305 KB) ( 4 )
  • DNA barcoding is an increasingly prevalent molecular biological technology which uses a short and conserved DNA fragment to facilitate rapid and accurate species identification. Kalidium species are distributed in saline soil habitat throughout Southeast Europe and Northwest Asia, and used mainly as forage grass in China. The discrimination of Kalidium species was based only on morphology-based identification systems and limited to recognized species. Here, we tested four DNA candidate loci, one nuclear locus (ITS, internal transcribed spacer) and three plastid loci (rbcL, matK and ycf1b), to select potential DNA barcodes for identifying different Kalidium species. Results showed that the best DNA barcode was ITS locus, which displayed the highest species discrimination rate (100%), followed by matK (33.3%), ycf1b (16.7%), and rbcL (16.7%). Meanwhile, four loci clearly identified the variant species, Kalidium cuspidatum (Ung.-Sternb.) Grub.var. sinicum A. J. Li, as a single species in Kalidium.