Potential Mortality Effects of Off-Highway Vehicles on the Flat-Tailed Horned Lizard (<Emphasis Type="Italic">Phrynosoma mcallii</Emphasis>): A Manipulative Experiment

Southern California desert public lands receive especially high levels of off-highway recreation due to large population centers nearby and popular riding environments such as sand dunes. Controversy has developed over the flat-tailed horned lizard (Phrynosoma mcallii), previously a candidate for listing under the Endangered Species Act. Some evidence suggests lower lizard abundance in areas of higher recreational use than in areas with low or no use. We designed a manipulative experiment to ensure maximum inference in evaluating the direct impact of recreational riding of off-highway vehicles on lizards. Thirty-six lizards, in situ, were treated with an off-highway vehicle treatment during hibernation season in three treatment groups: high impact, low impact, and control. Treatments consisted of timed riding by off-highway vehicles. In all treatment groups survival was 100%, despite hibernation of lizards at very shallow depths. Consequently, indirect effects of off-highway vehicles deserve increased attention. The relative importance of direct versus indirect (i.e., degradation of lizard habitat) impacts caused by off-highway vehicles remains unknown. These indirect effects may include the altering of vegetation, substrate, and prey. We recommend that a manipulative approach be adopted to investigate these possibilities.     

A System to Monitor Climate Change with Epilithic Lichens

The issue of biological monitoring of the local consequences of anticipated global climate change is considered for the Central Negev Highlands, Israel. Epilithic lichens are suggested as biological monitors. The proposed methodology of such monitoring consists of a sampling scheme, including lichen measurement along transects on flat calcareous rocks, and construction of a trend detection index (TDI). TDI is a sum of lichen species cover with coefficients chosen so as to ensure maximum ability to detect global climate trends. Coefficients have been estimated in a study of lichens along an altitudinal gradient from 500 to 1000 m a.s.l. The gradient study demonstrated that the TDI index is performed better than other integrated indices. Recommendations on this system to monitor climate change with epilthic lichens are given. Measuring, for instance, a hundred transects in fifty plots (two transet per plot scheme) allows one to detect a climate-driven change in the epilithic lichen community corresponding to a 0.8 °C shift in annual mean temperature. Such resolution appears sufficient in view of global warming of 2.5 °C considered by the Intergovernmental Panel on Climate Change as a realistic prediction for the end of the next century.     

Adaptation of Nitraria sphaerocarpa to wind-blown sand environments at the edge of a desert oasis

This study addresses the adaptation of Nitraria sphaervcarpa to blown sand at the edge of a desert oasis with regard to the aspects of soil seed banks, seedlings, and population. Horizontally, the total number of seeds per unit area decreased from the shrub canopy center to intershrub areas, and most seeds were found under shrub canopies. Vertically, the highest proportion of seeds was found at depths of 5-10 cm. The emergence percentage, seedling mass, and seedling height, which were significantly affected by both burial depth and seed size, were highest at the optimal burial depth of 2 cm, and decreased with increasing burial depth in each seed size-class. Although seedling mass was usually greatest for large seeds and least for small seeds at each burial depth, little difference was observed in seedling height at shallow burial depths of 0-3 cm. The population shows a patchy and discontinuous distribution pattern. Population height increases with increasing sand depth. Also the density increases with increasing depth of sand in the desert; however, there is a steady decrease when the depth of sand is more than 100 cm. This result indicates that the depth of sand that is most suitable for the growth of Nitraria sphaervcarpa is 100 cm. The size of the population is significantly correlated with the sand depth, which increases with increasing depth in the desert.     

Rheum palaestinum (desert rhubarb), a self-irrigating desert plant

The rare plant Rheum palaestinum (Polygonaceae) is a perennial hemicryptophyte that grows during the rainy winter in desert mountainous areas in Israel and Jordan that receive an average annual rainfall of ca. 75 mm. It produces between one and four large round leaves that are tightly attached to the ground and form large rosettes of up to 1 m². These leaves differ markedly from the typical small leaves of most desert plants. Moreover, they have a unique 3D morphology resembling a scaled-down mountainous area with well-developed steep drainage systems, raising the question which selective agents were involved in their evolution. We propose that the large leaves collect rainwater that then infiltrates the soil surrounding the root. We measured the seasonal course of leaf growth, examined the area of wet soil surrounding the root after actual and simulated rain, and modeled the water harvesting capacity using the plant leaf area and the weekly precipitation. We show that even in the slightest rains, water flows above the veins to the leaf’s base where it irrigates the vertical root. A typical plant harvests more than 4,100 cm³ of water per year, and enjoys a water regime of about 427 mm/year, equivalent to the water supply in a Mediterranean climate. This is the first example of self-irrigation by large leaves in a desert plant, creating a leaf-made mini oasis. All authors contributed equally to this paper.     

不同放牧制度下短花针茅荒漠草原植物种群作用和种间关系分析

以短花针茅荒漠草原植物种群为研究对象,采用2×2列联表法和灰色关联分析方法,探讨植物种群地位和作用及种间关系在不同放牧制度下的变化。结果表明,放牧会使建群种短花针茅（Stipa breviflora Griseb.）重要值增大,使碱韭(Allium polyrhizum Turcz. ex Regel)的重要值减小;轮牧有利于无芒隐子草(Cleistogenes songorica (Roshev.) Ohwi)在群落中的地位和作用增加,自由放牧则相反。植物群落种间关系正联结强度表现为禁牧区(CK)>划区轮牧区(RG)>自由放牧区(CG),负联结种对数的多少表现为CK相似文献   

青藏高寒草地植被生产力与生物多样性的经度格局

沿昌都到噶尔县的经度梯度,对西藏典型高寒草地植被生产力与植物多样性开展了1 700 km的野外样带调查。实验结果表明：高寒草地的群落结构特征（地上生物量、地下生物量、盖度和密度）与生物多样性（物种丰富度、物种多样性和物种均匀度）均具有明显的经度分布格局。整体而言,这些特征参数均表现出自西向东沿荒漠草原—典型草原—草甸草原呈逐渐递增的趋势;其经度格局主要受降雨量和平均气温所趋动,但降雨量和平均温度的影响在不同指标间存在较大差异;地上生物量由二者共同决定,而物种丰富度受降雨量的影响更大。西藏高寒草地的物种丰富度与地上生物量间存在显著的幂指数关系（y=0.219 7 x 0.754 9, R²= 0.61, P< 0.01）。上述规律的发现,不仅有利于我们更好地理解高寒草地对未来气候变化的响应机制与适应途径,也将帮助我们合理制定放牧策略以实现该地区高寒草地的可持续发展。     

植物群落蒸散耗水量研究进展

本文主要介绍了植物群落蒸散量的研究方法及影响因素，并根据作者所处地区的特点，对内蒙古典型草原的蒸散研究进展进行了综述。     

两种典型大气环境下7A85铝合金的腐蚀行为研究

目的研究湿热海洋、干热沙漠两种典型大气环境对7A85铝合金腐蚀行为的影响。方法在万宁、敦煌两种典型环境中开展7A85铝合金大气暴露试验,利用金相显微镜分析7A85铝合金在我国两种典型大气环境中的腐蚀特征,定期测试该材料的拉伸强度和腐蚀深度。结果暴露3 a,7A85铝合金湿热海洋、干热沙漠两种典型大气环境中的最大腐蚀深度分别为254、90μm,抗拉强度分别下降了18%和5%,断后伸长率分别下降了72%和22%。结论 7A85铝合金暴露于相对湿度较低的干热沙漠环境,表面形成的腐蚀产物膜会阻止腐蚀的进一步发生;暴露于湿热海洋大气环境,随暴露时间的延长,7A85铝合金腐蚀逐渐加深。     

阿拉善沙漠高原降水化学特征与离子来源判别

为查明我国北方沙漠地区降水化学组成及来源,在阿拉善沙漠高原阿右旗气象站采集了2013—2015年的降水样品,测定了降水pH、EC（电导率）及主要离子当量浓度.结果表明:阿拉善沙漠阿右旗气象站降水pH和EC的范围分别为6.66~8.05和35~1 237 μS/cm;Ca2+、SO₄2-、Na+和Cl-为降水中的主要离子,其总和占总离子的85%以上.降水pH、EC和主要离子当量浓度是反映空气质量的基本参数,较高的降水pH反映出当地降水具有明显的碱性特征.与其他地区相比,该地区降水的EC和可溶性离子日均湿沉降通量也较高,且随月份有较大的变化,表明干旱沙漠粉尘对当地降水水化学的贡献较大.根据离子来源相对贡献的计算结果发现,降水中92.8%的SO₄2-和98%的NO₃-来自人为源,98.8%的Ca2+和88.7%的K+为陆地来源,55%的Mg2+为海洋源,24.8%的Na+来自矿物风化,极少部分Cl-为人为源.研究显示:除降水中的NH₄+外,其他主要离子之间的相关性表明各种成因物质在风力作用下同时进入了大气;基于[NH₄+]（NH₄+的当量浓度）与[K+]（K+的当量浓度）相关性分析,降水中的NH₄+来自生物质燃烧、肥料使用、动物粪便等.      

内蒙古典型草原羊粪和牛粪的分解特征

为了解畜粪的分解特征及对半干旱典型草原养分循环的影响,于2008年6月~2009年10月采用人为控制的野外实验,研究了羊粪和牛粪对内蒙古典型草原草地的输入量,分解过程中的重量损失、有机物和氮(N)、磷(P)浓度变化.结果表明,羊粪和牛粪的年输入量分别约为(17.8±13.8)kg hm-2和(365.6±495.9)kg hm-2.分解450 d后,残留粪样中有机物浓度较鲜粪减少约14.46%(羊粪)和48.78%(牛粪),即羊粪的分解速率较牛粪显著缓慢,2种粪的残留粪块在草地中堆置时间至少可达2个生长季以上.两种粪中,N素以有机态为主,矿化和释放速度均较慢;P素以无机态为主,释放速度较快;春季冻融变化可以显著促进两种粪中N和P的矿化速率;实验结束时,残留粪样中的全N浓度较鲜粪分别降低了25.89%(羊粪)和16.07%(牛粪),全P分别降低了30.73%和27.21%.埋入地下处理,可以消除风蚀对羊粪块失重的影响,使残留粪样保持较高湿度,促进有机质分解,并改变淋溶作用对粪块中养分含量的影响;但对牛粪分解无明显影响.从研究结果可以看出,家畜粪在半干旱草地环境中分解较慢,堆积过程中对草地的养分循环有重要影响.