Chinese Deserts Research Articles

Characteristics of seed germination in five non-halophytic Chinese desert shrub species

The effects of temperature, NaCl, and polyethylene glycol (PEG)-6000 on the seed germination of five non-halophytic Chinese desert shrub species were investigated. The minimum temperature of germination was 10°C for all species, and the maximum temperature varied among species from 25 to 35°C. Isotonic solutions of NaCl and PEG caused different effects on seed germination in all five species. When seeds were moistened with −5·0 MPa NaCl solution for 5 days, the seeds of three species completely lost their germinability, while the seed germinability of the other two species was much less affected. These results are discussed with regard to the rehabilitation of desertified lands in China by seed dispersal.

Effects of sodium chloride on seed germination and growth of two Chinese desert shrubs, Haloxylon ammodendron and H. persicum (Chenopodiaceae)

The effects of sodium chloride (NaCl), polyethylene glycol-6000, temperature and light on germination and the effects of NaCl on growth were investigated in two Chinese desert shrubs, Haloxylon ammodendron (C.A.Mey.) Bunge and H. persicum Bunge ex Boiss. et Buhse. Both species occur in non-saline sand dunes; H. ammodendron also occurs in saline land, although it is not dominant there. Percentage germination of H. ammodendron and H. persicum in –3.0 MPa (667 mmol kg –1 ) NaCl was 91 and 64%, respectively. Hydroponic culture of each species for c. 3 months with NaCl solutions of 0, 200, 400 and 600 mmol kg –1 showed that the survival of H. ammodendron was highest (82.3%) at 400 mmol kg –1 NaCl, while that of H. persicum decreased with increasing NaCl concentration and was low (11.1%) at 400 mmol kg –1 NaCl. Sodium concentration in shoot tissues of 99-day-old seedlings grown at 400 mmol kg–1 NaCl exceeded 1000 mmol kg –1 in both species, while Na concentration in non-transpiring young seedlings grown in 400 mmol kg –1 NaCl was 240 and 350 mmol kg –1 for H. ammodendron andH. persicum, respectively. The results indicate that both species have relatively low adaptability to salinity at the older seedling stage compared with that at the germination and young seedling stage, and that H. ammodendron shows higher adaptability to salinity at the older seedling stage than H. persicum. It was concluded that salinity adaptability in the later developmental stage of these species determines their distribution with respect to salinity.

Concentration, size-distribution and deposition of mineral aerosol over Chinese desert regions

Concentration, size-distribution and deposition of mineral aerosol over Chinese desert regions

Concentration, size-distribution and deposition of mineral aerosol over Chinese desert regions

The mass-particle size distributions (MSDs) of 9 elements in ground-based aerosol samples from dust storm (DS) and non-dust storm (N-DS) periods were determined for 12 sites in 9 major desert regions in northern China. The masses of the 9 elements (Al, Fe, K, Mg, Mn, Sc, Si, Sr and Ti) in the atmosphere were dominated by local mineral dust that averaged 270 mg m−3, and the MSDs for the elements were approximately log-normal. On the basis of Al data, the < 10 mm particles account for ˜84% of the total dust mass over the deserts. Model-calculated (‘‘100-step’’ method) dry deposition velocities (Vd) for the 9 dust-derived elements during N-DS periods ranged from 4.4 to 6.8 cm s−1, with a median value of 5.6 cm s−1. On the basis of a statistical relationship between D99% (the dust particle diameter corresponding to the uppermost 1% of the cumulative mass distribution) and Vd, one can also predict dry velocities, especially when D99% ranges from 30 to 70 mm. This provides a simple way to reconstruct Vd for dust deposits ( like aeolian loess sediments in the Loess Plateau). The estimated daily dry deposition fluxes were higher during DS vs. N-DS periods, but in most cases, the monthly averaged fluxes were mainly attributable to N-DS dust. Two regions with high dust loading and fluxes are identified: the ‘‘Western High-Dust Desert’’ and the ‘‘Northern High-Dust Desert,’’ with Taklimakan Desert and Badain Juran Desert as their respective centers. These are energetic regions in which desert-air is actively exchanged, and these apparently are the major source areas for Asian dust.

Dust emission from Chinese desert sources linked to variations in atmospheric circulation

Estimates of atmospheric dust deposition to five Asian/Pacific regions indicate that ∼800 Tg of Chinese desert dust is injected into the atmosphere annually; about 30% of this is redeposited onto the deserts, 20% is transported over regional scales, primarily within continental China. The remaining 50% of the dust is subject to long‐range transport to the Pacific Ocean and beyond. Elemental tracers based on several dustderived elements (Al, Fe, Mg, and Sc) reveal high‐frequency variability in the contributions of the western desert sources versus northern high‐dust and low‐dust desert sources to eolian deposits from the center of the Loess Plateau. Comparisons of the patterns uncovered with climate signals from the remote North Atlantic region for the last glaciation show that shifts in source areas of Asian dust were synchronous with large‐scale variations in atmospheric circulation.

Seed Germination of Chinese Desert Plants

To investigate the effects of global warming on the germination behavior of Chinese desert plants, responses of seed germination to temperature, light illumination and water and salt stresses were examined on Artemisia ordosica and Lespedeza davurica. The optimal temperature for germination was 20°C for both species. In the dark condition, the final germination rates were higher than 50% under temperature regimes in the range of 15-30°C for A. ordosica and 10-30°C for L. davurica. This result shows that seed germination of both tested species are relatively insensitive to changes in temperature. Both water and salt stresses resulted in decreases in final germination rates and retardation of germination in both species. Seed germination of L. davurica was less affected by both stresses than that of A. ordosica. Although some A. ordosica seeds germinated when they were wetted with NaCl solutions having water potentials of -0.3--0.6MPa, most of the radicles subsequently died in these media. This result suggests that salinization of the soil is critical for the survival of this species. It was concluded that although a temperature rise by itself does not much affect the germination behavior of these species, changes in seasonal distribution of rainfall events and salinization of the soil caused by climate change can have crucial effects on their distribution.

Variability of Monsoon Climate in East Asia at the End of the Last Glaciation

High-resolution paleomonsoon proxy records from peat and eolian sand–paleosol sequences at the desert–loess transition zone in China denote a rapid oscillation from cold–dry conditions (11,200–10,60014C yr B.P.) to cool–humid conditions (10,600–10,20014C yr B.P.), followed by a return to cold–dry climate (10,200–10,00014C yr B.P.). Variations in precipitation proxies suggest that significant climatic variability occurred in monsoonal eastern Asia during the Younger Dryas interval. Late-glacial climate in the Chinese desert–loess belt that lies downwind from Europe was strongly influenced by cold air from high latitudes and from the North Atlantic via the westerlies. The inferred precipitation variations were likely caused by variations in the strength of the Siberian high, which influenced the pressure gradient between land and ocean and therefore influenced the position of the East Asian monsoon front.

Remote mineral aerosols in Westerlies and their contributions to the Chinese loess

The concentrations of 28 trace and rare earth elements in the aerosol particle samples were determined for a site at 4800m above the sea level on the Qinghai-Xizang Plateau. The mass of the particulate materials in the mid-troposphere atmosphere over this site is dominated by local dust particles (70%) and remote ones in Westerlies (25%). On the basis of the main dust-derived elements (Al, Fe, Mg and Sc) and corresponding data from the Chinese deserts, an elemental tracer system has been established to proportion the dust input to the loess deposited on the center of the Loess Plateau during the last glacial cyde, which suggests that the contribution of the remote dust in Westerlies is much smaller than that of the Chinese deserts.

Large 3D seismic surveys completed in Chinese desert

Large 3D seismic surveys completed in Chinese desert

Sand Sea History of the Taklimakan for the Past 30,000 Years

A series of absolute dates for surface sediments in the Taklimakan Desert, reveals the evolution of aeolian processes over the past 30,000 years. Sandy materials from flood plains and palaeo-lacustrine plains through wind erosion are the main sources of the desert. Cold air intrusions from the northeast of the Tarim Basin are the main form of aeolian motivation. During the past 30,000 years, an arid climate has dominated the desert. However, sand sources and wind conditions affected by ice, snow cover, glacial meltwater and lower evaporation as well as more stable air conditions during very cold periods may have led to temporary decreases in aeolian actions. In contrast with other Chinese deserts, the evolution of the Taklimakan Desert has seen alternating periods of hot, arid, strong aeolian action and cold, relatively humid, weak aeolian action in response to global climate changes. It is predicted that desertification will continue due to the effects of global warming.

Optimal apportionment of reliability and redundancy in series systems under multiple objectives : Anoop K. Dhingra. IEEE Transactions on Reliability, 41(4), 576 (1992)

Lead isotopic compositions were determined in leachates that were generated using sequential extractions of dry deposition samples of Asian dust (AD) and non-Asian dust (NAD) and Chinese desert soils, and used to apportion Pb sources. Results showed significant differences in 206Pb/207Pb and 206Pb/204Pb isotopic compositions in non-residual fractions between the dry deposition samples and the Chinese desert soils while 206Pb/207Pb and 206Pb/204Pb isotopic compositions in residual fraction of the dry deposition of AD and NAD were similar to the mean 206Pb/207Pb and 206Pb/204Pb in residual fraction of the Alashan Plateau soil. These results indicate that the geogenic materials of the dry deposition of AD and NAD were largely influenced by the Alashan Plateau soil, while the secondary sources of the dry deposition were different from those of the Chinese desert soils. In particular, the lead isotopic compositions in non-residual fractions of the dry deposition were homogenous, which implies that the non-residual four fractions (F1 to F4) shared the primary anthropogenic origin. 206Pb/207Pb values and the predominant wind directions in the study area suggested that airborne particulates of heavily industrialized Chinese cities were one of the main Pb sources. Source apportionment calculations showed that the average proportion of anthropogenic Pb in the dry deposition of AD and NAD was 87% and 95% respectively in total Pb extraction, 92% and 97% in non-residual fractions, 15% and 49% in residual fraction. Approximately 81% and 80% of the anthropogenic Pb was contributed by coal combustion in China in the dry deposition of AD and NAD respectively while the remainder was derived from industrial Pb contamination. The research result proposes that sequential extractions with Pb isotope analysis are a useful tool for the discrimination of anthropogenic and geogenic origins in highly contaminated AD and NAD.

Characteristics of the Tengger dunefield, north-central China, and comparison with the central Australian dunefields

The Chinese desert dunefields are little-known outside China, since almost all the relevant literature is in Chinese. This note summarises soil and vegetation characteristics for a site in the Tengger dunefield of north central China, and provides a brief comparison with the central Australian dunefields. The Tengger dunes are transverse, mobile and up to 30 m high. The sands are unimodal and oligotrophic, with no catenary variation. Mean total phosphate and nitrogen contents are 290 and 16 p.p.m. respectively. Their vegetation is very sparse, consisting of isolated plants of Caragana korshinskii and Calligonum caput-medusae on the lower flanks, and small patches of Artemisia sphaerocephala in the interdune depressions. Most of the dunes are bare. The Tengger dunefields are at higher latitude and elevation than those of central Australia, and receive significantly higher rainfall, yet the Tengger dunes are bare whilst those in central Australia are densely vegetated, except on the crests. The difference is probably due to the lower soil nitrogen content of the Tengger dunes, and perhaps also to their greater mobility. Both these factors are themselves influenced by plant cover, however, in a positive feedback sense. Further comparative studies of dunefield ecosystem dynamics would be valuable in both theoretical and applied contexts.