中国沙漠植物区系相似性的数值分析

应用Jaccard相似系数对中国沙漠植物区系进行了聚类分析。结果表明,可以将20个沙漠植物区系划归入蒙古沙漠植物区、西北沙漠植物区和华北沙漠植物区。根据科、属和种相似性系数的系统聚类结果,柴达木盆地、河西走廊、祁连山山前及腾格里沙漠边缘和吐-哈盆地相对较为孤立。区系相似性数值分析结果基本符合各地区植物区系存在的特点,与传统的典型植被划分结论相一致。     

准噶尔盆地的气候变化与荒漠环境研究

通过对北疆及准噶尔盆地的气候变化与荒漠环境效应研究认为,该区一是受气候变化的影响,其次是受地形和人类活动的影响。在气候变化和环境效应研究中,该地区有着不可替代的区域特征和学科意义。尤其是该区域受西风环流控制和受太平洋季风的影响较少,因此具有季风气候和地中海气候的双重性。因此,该研究区荒漠环境的正逆发展过程不仅受降水和温度的重大影响,而且季节性积雪和高山雪冰融水为荒漠植物的萌发与生长提供了有效的水资源。但是,该地区的生态环境十分脆弱,人类的过度开发和扰动对其的影响也非常严重。所以,加强气候变化与环境效应的相互影响研究,保护干旱生态的平衡发展,再造秀美山川,是该地区今后研究的重要任务和发展方向。     

阿拉善荒漠草地恢复初期植被与土壤环境的变化

对阿拉善荒漠草地恢复初期(1998-2001)植被特征和土壤养分的变化进行了研究。结果表明:草地恢复过程中,植被的盖度和生物量比封育前分别增加272%~536%和44.39%~305.3%。植被的恢复使土壤理化性质发生了变化,与封育前相比土壤中有机质、全N、速效K以及细砂、特别细砂和粘粒含量显著增加;速效N、速效P降低。土壤有机质、全N和全P的含量与土壤中<0.05 mm颗粒和速效K含量呈极显著正相关,并且前三者之间也呈极显著正相关(P<0.01)。     

沙漠人工植被区土壤蒸发测定

在2003年生长季,应用自制的微型蒸渗仪(Micro Lysimeter)、大型称重式蒸渗仪(Lysimeter)和TDR对比测定沙漠油蒿(Artemisia ordosica)和柠条(Caragana korshinskii)人工植被区与裸沙土壤蒸发,结果表明:在沙漠人工植被区由于植被比较稀疏,土壤蒸发不受植株的遮阴的影响,但不同样地的蒸发量是有差异的,而样地和位置间的互作不显著。为提高蒸发测定精度,建议微型蒸渗仪勤于换土,尤其是在大降水发生之后;将横插式 TDR探头改为竖插式能探测到小降水后的蒸发量。在沙漠区有很大比例的蒸发发生在紧接降水之后。以微型蒸渗仪的测定结果为主,结合大型称重式蒸渗仪的测定结果推算出整个试验期间的裸沙、油蒿和柠条样地的蒸发量为 111.6mm、93.8 mm和99.3 mm,油蒿和柠条样地的蒸发量分别占同期蒸散量的45.1%和43.6%;油蒿和柠条样地均以8月份日蒸发量0.93 mm·d^-1和1.10 mm·d^-1最高,5月份日蒸发量0.30 mm·d^-1和0.28 mm·d^-1最低。     

Rainfall–runoff relationship over encrusted dune surfaces,Nizzana, Western Negev,Israel

A thin microbial crust covers the lower part of longitudinal dunes in the western Negev, where average annual rainfall is 95 mm. In order to study the effect of the microbial crust on rainfall–runoff relationships under natural rainfall conditions, runoff plots equipped with pressure gauges were established on opposite north- and south-facing slopes that differ in their vegetal cover and crust properties. The study covered four years (1990–94). The first two years were wet and the following two years relatively dry. One to five flow events were recorded per year. No correlation was found between runoff yield, rain amount and rain intensity. Unlike many microbial crusts reported in the literature, the microbial crust in the western Negev is not hydrophobic. Infiltration rate is high under dry surface conditions and of the order of 9–12 mm h⁻¹ when the crust is saturated. The high final infiltration rate is explained by the occurrence of large pores that do not seal when the crust is saturated. Typical hydrographs have very steep rising and falling limbs, pointing at a limited contributing area. Most flows last less than 10 min and runoff volumes collected are, on the whole, very small. Owing to differences in crust properties, runoff is higher on north- than on south-facing slopes. © 1997 John Wiley & Sons, Ltd.     

Microchemistry of small desert varnish samples,western New South Wales,Australia

The chemistry of varnish scrapings from within and adjacent to rock engravings on sandstone outcrops in semiarid Australia was analysed using an electron microprobe (WDS mode). Small-area analyses were used to reduce potential contamination from identifiable within-varnish detrital grains and from substrate material. Ratios of (Ca + K):Ti were compared for rock engravings on older and younger rock surfaces, and between different engraving styles. Although ratios from varnish on the older surface were lower than for the younger surface, differences were not statistically significant. Sorting of analyses for potentially anomalous amounts of minor elements had little effect on the ranking of individual ratio values. Rankings of within-engraving ratio values were generally in accord with relative age expectations but differences between samples were not significant, with the chemical variability of varnish being high even without the contribution of discernible detrital inclusions. © 1998 John Wiley & Sons, Ltd.     

Nebkha dune morphology in the gobi deserts of northern China and potential implications for dust emission

Nebkhas (coppice dunes) have formed throughout the gobi desert regions of China in response to the decreased near-surface wind speed caused by vegetation, combined with deposition of aeolian sediment in and around the vegetation. Although nebkhas have been extensively studied on several land surfaces, they have not yet been fully described where they form in areas of gobi desert. Based on field investigations of nebkha morphology and adjacent land surface sediment content on and inside the surface of these dunes, the following were found: (i) the nebkhas that develop in gobi deserts consist of two types – dunes with or without a depositional tail (a shadow dune); (ii) the nebkhas in the area of gobi desert were smaller than those found in sandy deserts, oases, or other areas with a rich sediment source, with a mean height of 0.28 m, mean width 1.63 m and mean length 1.34 m; and (iii) the dune height, length and width were significantly positively linearly related to the vegetation height, length and width. These patterns were similar at all four of the study sites, but the relationships with dune width differed among the sites. The average particle-size distributions on and inside the vegetation did not differ between the four sites. However, significant spatial differences in the sediments on and inside the dunes indicate that nebkhas can capture both local and distant sediments driven by the wind. These findings suggest a potential role of nebkhas in dust emission, although this role must be confirmed in future research.     

渤海涟虫类和软体动物幼虫食性的观察

根据消化道内食物分析结果得出：涟虫类、三叶针尾涟虫和驼背涟虫、瓣锶类后期幼虫和腹足类后期幼虫都营浮游植物食性,以硅藻类为主要食物。细长涟虫以星脐圆筛藻、未查明的圆筛藻和辐射圆筛藻为主要摄食对象;三叶针尾涟虫以舟形藻和新月菱形藻为主要摄食对象;驼背涟虫以辐射圆筛为主要摄食对象。鳃类后期幼虫以辐射圆筛藻和未查明的圆筛藻为主要摄食对象;腹足类后期幼虫以未查明的圆筛藻、辐射圆筛藻和中心圆筛藻为主要摄食对象     

FIELD EXPERIMENTS ON PHYSICAL WEATHERING AND WIND EROSION IN AN ANTARCTIC COLD DESERT

Field experiments were carried out over a five year period with the aim of understanding contemporary weathering and erosional environments in the Sør Rondane Mountains, an Antarctic cold desert region. These include observations of (1) scaling from rockwalls, (2) disintegration of tuff blocks with or without saline solutions, and (3) abrasion of artificial walls by wind. Monitoring was also made of rock surface temperature and wind speed. Despite frequent temperature oscillations across 0°C, rock scaling due to frost action was generally very slow because of low moisture content in the rockwalls. Exposure to the cold, dry climate led to the rapid disintegration of porous tuff blocks including soluble salts like halite and thenardite. This indicates that rates of weathering are increased greatly with the accumulation of such salts in the bedrock. Although gypsum did not cause any visible damage over four years, its widespread occurrence in heavily damaged rocks demonstrates that increasing gypsum contents may also intensify rock breakdown. The snow-laden katabatic wind resulted in rapid wearing of the windward face of an asbestos board with the peak erosion at 30–40 cm above the ground. Nonetheless, the landforms expected from the unidirectional wind characteristics are by no means common features because of lack of abrasive materials, such as snow and sand particles. These experiments suggest that frost weathering and wind erosion are only locally effective where plenty of moisture or an abrasive material is available, whilst salt weathering and removal of the waste by wind play a major role in constructing erosional landforms over the mountains.     

Food web structure of the coastal area adjacent to the Tagus estuary revealed by stable isotope analysis

The identification of energy sources, pathways and trophic linkages among organisms is crucial for the understanding of food web dynamics. Stable isotopes were used to identify the trophic level of food web components and track the incorporation of organic matter of different origins in the coastal ecosystem adjacent to the Tagus estuary. It was shown that the river Tagus is a major source of organic carbon to this system. Also, the wide difference in δ¹³C among the primary consumers allowed the identification of the pelagic and the benthic energy pathways. The maximum trophic level observed was 2.4 for Sepia officinalis. This value is indicative of a short food web. It was concluded that the diet of the upper trophic level species relies directly on the lower food web levels to a considerable extent, instead of relying mostly on intermediate trophic level species. Moreover, the δ¹⁵N values of primary consumers were very close to that of particulate organic matter, probably due to poorly known processes occurring at the basis of the food web. This lowers the trophic length of the whole food web. Reliance on benthic affinity prey was high for all upper trophic level secondary consumers.