Seed mucilage improves seedling emergence of a sand desert shrub

The success of seedling establishment of desert plants is determined by seedling emergence response to an unpredictable precipitation regime. Sand burial is a crucial and frequent environmental stress that impacts seedling establishment on sand dunes. However, little is known about the ecological role of seed mucilage in seedling emergence in arid sandy environments. We hypothesized that seed mucilage enhances seedling emergence in a low precipitation regime and under conditions of sand burial. In a greenhouse experiment, two types of Artemisia sphaerocephala achenes (intact and demucilaged) were exposed to different combinations of burial depth (0, 5, 10, 20, 40 and 60 mm) and irrigation regimes (low, medium and high, which simulated the precipitation amount and frequency in May, June and July in the natural habitat, respectively). Seedling emergence increased with increasing irrigation. It was highest at 5 mm sand burial depth and ceased at burial depths greater than 20 mm in all irrigation regimes. Mucilage significantly enhanced seedling emergence at 0, 5 and 10 mm burial depths in low irrigation, at 0 and 5 mm burial depths in medium irrigation and at 0 and 10 mm burial depths in high irrigation. Seed mucilage also reduced seedling mortality at the shallow sand burial depths. Moreover, mucilage significantly affected seedling emergence time and quiescence and dormancy percentages. Our findings suggest that seed mucilage plays an ecologically important role in successful seedling establishment of A. sphaerocephala by improving seedling emergence and reducing seedling mortality in stressful habitats of the sandy desert environment.     

荒漠区固沙植物梭梭(Haloxylon ammodendron)耗水特征

利用SF-300热脉冲树干液流仪,连续观测了生长季节荒漠区固沙植物梭梭树干液流速率,研究了荒漠区固沙植物梭梭林木的耗水量及其与气象因子的关系。结果表明：在生长季节,梭梭树干液流速率昼夜变化小;不同的生长日,梭梭树干液流速率介于（5．9±0．7）～（14．5±3．6）gcm^-2h^-1;观测期间,梭梭平均日耗水量为（0．3±0．2）mm,生长季节单株木耗水量达49．4mm。树干液流速率对气象因子均有一定程度的响应,且在不同时间的影响程度不同。日耗水量与林冠投影面积、基径、基径的平方乘以树高的积、边材厚度和边材面积呈线性关系。     

Energy expenditure during level locomotion in large desert ungulates: the one-humped camel and the domestic donkey

This study sought to quantify the rate of energy expenditure (     ), the total cost of transport (COT_tot) and the net cost of transport (COT_net) in camels Camelus dromedaries and donkeys Equus asinus during level locomotion.     of camels and domestic donkeys were measured at exercise speeds between 0 and 4.17 m s⁻¹. Resting     for camels was significantly ( P <0.05) lower than predicted, while donkeys exhibited resting values similar to mammals of the same body mass. In both camels and donkeys     increased in a nearly linear fashion over the range of exercise speeds. The minimum COT_tot of camels in the walking and pacing gaits were not significantly different ( P =0.27). Similarly, donkeys exhibited no significant difference ( P =0.09) in the minimum COT_tot while walking and trotting. In both camels and donkeys, the minimum COT_tot was significantly ( P <0.05) lower than the predicted COT_tot for mammals of the same body mass. The COT_net in both camels and donkeys was determined to be gait dependent and significantly ( P <0.05) lower than the predicted minimum COT_net values for walking and running. The low COT seen in camels and donkeys results in energy and water savings.     

乌兰布和沙漠东缘固沙植被恢复重建与资源利用中的几个问题分析

乌兰布和沙漠是我国八大沙漠之一 ,处于我国北方半干旱与干旱区的转折位置上 ,进一步沙质荒漠化的潜在危险性。就乌兰布和沙漠东缘固沙植被恢复重建以及资源利用过程中发现的一些问题进行分析探讨 ,主要包括人工固沙植物种的选择与配置问题、绿洲外围天然植被破坏问题以及绿洲开发规模选择对未来固沙植被的潜在影响等问题。     

Geodermatophilus saharensis sp. nov., isolated from sand of the Saharan desert in Chad

A novel Gram-positive, aerobic, actinobacterial strain, CF5/5, was isolated from soil in the Sahara desert, Chad. It grew best at 20–35 °C and at pH 6.0–8.0 and with 0–4 % (w/v) NaCl, forming black-colored colonies. Chemotaxonomic and molecular characteristics of the isolate matched those described for members of the genus Geodermatophilus. The DNA G + C content was 75.9 mol%. The peptidoglycan contained meso-diaminopimelic acid; galactose and xylose were detected as diagnostic sugars. The main phospholipids were diphosphatidylglycerol, phosphatidylcholine, and phosphatidylinositol; MK-9(H₄) was the dominant menaquinone. The major cellular fatty acids were: iso-C_16:0 and iso-C_15:0. The 16S rRNA gene showed 95.6–98.3 % sequence similarity with the other named members of the genus Geodermatophilus. Based on the polyphasic taxonomy data, the isolate is proposed to represent a novel species, Geodermatophilus saharensis with the type strain CF5/5^T = DSM 45423 = CCUG 62813 = MTCC 11416.     

Effects of an invasive plant on a desert sand dune landscape

Given the abundance of non-native species invading wildland habitats, managers need to employ informed triage to focus control efforts on weeds with the greatest potential for negative impacts. Our objective here was to determine the level of threat Sahara mustard, Brassica tournefortii, represents to meeting regional goals for protecting biodiversity. Sahara mustard has spread throughout much of the Mojave and lower Sonoran Deserts. It has occurred in southern California’s Coachella Valley for nearly 80 years, punctuated by years of extremely high abundance following high rainfall. In those years the mustard has clear negative impacts on the native flora. Using mustard removal experiments we identified reductions in native plant reproduction, shifting composition increasingly toward Sahara mustard while decreasing the fraction of native species. High between-year variance in precipitation may be a key to maintaining biodiversity as the mustard is less abundant in drier years. Sahara mustard impacts to the native fauna were much less evident. Of the animal species evaluated, only the Coachella Valley fringe-toed lizard, Uma inornata, demonstrated a negative response to mustard abundance; however the impacts were short-lived, lasting no more than a year after the mustard’s dominance waned. Without control measures the long-term impacts to desert biodiversity may rest on the changing climate. Wetter conditions or increased periodicity of high rainfall years will favor Sahara mustard and result in reduced biodiversity, especially of native annual plants. Drier conditions will keep the mustard from becoming dominant but may have other negative consequences on the native flora and fauna.     

Water detection in the desert sand scorpion,Paruroctonus mesaensis (Scorpionida,Vaejovidae)

Summary For the sand scorpion, Paruroctonus mesaensis, substrate moisture is a powerful and fast-acting stimulus of discrete behaviors related to localization and imbibitory uptake of water. These behaviors are readily observed in the field and quantified in the laboratory when free-roaming animals encounter sand substrates dampened by small amounts of water. Of 10 behaviors we monitored in laboratory tests, 5 (pedipalp-pull, rototiller-digging, prolonged stops, headstand, and backingup) occurred only after contact with a moistened substrate. These water-stimulated behaviors were selectively blocked when all 8 tarsal leg segments were coated with wax; coverings of the chemosensory pectine appendages had little to no effect. Electrophysiological recordings from chemoreceptor organs on the tarsi showed that neurons innervating the dorsal tarsal organ, were highly sensitive to humid air stimuli while the numerous, poretipped hairs on the ventral surface were responsive to aqueous solutions applied directly to their tips. Selective blocking of the 8 tarsal organs had no effect on water sensitive behavior indicating that the chemosensory hairs mediate detection of substrate moisture. Such localized, sensory triggering of a robust and directed behavior presents a useful model for further neuroethological studies.Abbreviations H headstand - PP pedipalp-pull - RD rototillerdigging - B backing-up - C wall-climbing - P pause - W walk-through - S stop - T turn - R rest - PST pacific standard time - SEM scanning electron microscopy     

Effect of age on pyridinoline and pentosidine matrix cross-links in the desert sand rat intervertebral disc

Spondylosis in the desert sand rat (Psammomys obesus) has been studied as a model for intervertebral disc degeneration. Reducing sugars, which react with protein amino groups to form a diverse group of moieties with fluorescence and cross-linking properties, have been implicated in the structural and functional alterations of proteins that occur during aging and long-term diabetes. This study was undertaken to determine the changes in two matrix cross-links of the intervertebral disc and to study their association with aging. Two types of cross-links were studied: the physiological cross-link, pyridinoline, which is initiated by lysyl oxidase; and the non-enzymatically initiated cross-link, pentosidine. A significant increase in pentosidine, but not pyridinoline, was observed in the intervertebral disc with aging. Radiological, histological and biochemical findings support a hypothesis that subchondral bone responses, marked by increased bone density, contribute to alterations in the intervertebral disc. Cross-link changes in the structural proteins of the disc may contribute to the progressive fibrocartilage degradation typical of intervertebral disc disease as an effect of age.     

Geodermatophilus siccatus sp. nov., isolated from arid sand of the Saharan desert in Chad

A novel Gram-positive, aerobic, actinobacterial strain, CF6/1^T, was isolated in 2007 during environmental screening of arid desert soil in the Sahara near to Ourba, Chad. The isolate was found to grow best in a temperature range of 20–37 °C and at pH 6.0–8.5 and showed no NaCl tolerance, forming black-coloured and nearly circular colonies on GYM agar. Chemotaxonomic and molecular characteristics determined for the isolate match those previously described for members of the genus Geodermatophilus. The DNA G + C content of the novel strain was determined to be 74.9 mol %. The peptidoglycan was found to contain meso-diaminopimelic acid as the diagnostic diamino acid. The main phospholipids were determined to be phosphatidylethanolamine, phosphatidylinositol, phosphatidylcholine, diphosphatidylglycerol and traces of phosphatidylglycerol; MK-9(H₄) was identified as the dominant menaquinone and galactose as the diagnostic sugar. The major cellular fatty acids were found to be the branched-chain saturated acids iso-C_16:0 and iso-C_15:0, as well as C_17:1ω8c. The 16S rRNA gene sequence shows 97.5–97.9 % sequence identity with the four validly named or at least effectively published members of the genus: Geodermatophilus obscurus (97.5 %), Geodermatophilus arenarius (97.7 %), Geodermatophilus ruber (97.9 %) and Geodermatophilus nigrescens (97.9 %). Based on the results from this polyphasic taxonomic analysis and DNA–DNA hybridizations with all type strains of the genus, we propose that strain CF6/1^T represents a novel species, Geodermatophilus siccatus, with the type strain CF6/1^T = DSM 45419^T = CCUG 62765^T = MTCC 11414^T.     

荒漠绿洲边缘不同粒径砂砾凝结水量

根据临泽荒漠绿洲边缘的凝结水观测数据,分析了砂砾粒径与凝结水形成量的关系。结果表明：粒径＜0.02 mm的粉砂凝结量最大,7—10月日平均凝结量为(0.097±0.032) mm,其次是砂壤土,日平均凝结量(0.072±0.026) mm;而粒径为5.0～2.0 mm、2.0～0.2 mm和0.2～0.02 mm的砂砾凝结量较小,日平均凝结量分别为(0.052±0.021) mm、(0.057±0.018) mm和(0.059±0.016) mm。总之,凝结量随砂砾粒径的减小而增大,同时本文还分析了旱季农田砂土覆盖对土壤水分蒸发的抑制作用。     

荒漠区固沙植物梭梭(Haloxylon ammodendron)耗水特征

利用SF-300热脉冲树干液流仪,连续观测了生长季节荒漠区固沙植物梭梭树干液流速率,研究了荒漠区固沙植物梭梭林木的耗水量及其与气象因子的关系。结果表明：在生长季节,梭梭树干液流速率昼夜变化小;不同的生长日,梭梭树干液流速率介于(5.9±0.7)～(14.5±3.6)g cm^-2h^-1;观测期间,梭梭平均日耗水量为(0.3±0.2)mm,生长季节单株木耗水量达494mm。树干液流速率对气象因子均有一定程度的响应,且在不同时间的影响程度不同。日耗水量与林冠投影面积、基径、基径的平方乘以树高的积、边材厚度和边材面积呈线性关系。     

Leaf temperature of desert sand dune plants: perspectives on the adaptability of leaf morphology

The leaf temperature of six annual and six perennial plant species was monitored during spring and summer on a sand dune ecosystem in the delta Mediterranean coast of Egypt. During winter, leaves of all tested perennial species attained temperatures higher than the air temperature at night and shortly after sunrise, with maximum leaf–air temperature differences reaching up to 8°C. The lowest differences were less than 1°C. Around noon, the leaves of several species attained temperatures lower than that of the air whereas others showed higher temperatures. The opposite was true during summer, when leaf temperatures were lower than air temperature. The maximum leaf–air temperature differences occurred after midnight towards sunrise and reached up to 10°C. The lowest differences were found around noon and were of less than 5°C. The annual plant species have more pronounced variations than perennials in their leaf temperatures during the night and for most of the day. The leaves were heated or cooled a few degrees above or below the air temperature. The results are discussed in relation to the morphological characters of the leaves. The variation in leaf temperature at different times of the day was significantly related to leaf morphology, specific leaf area, thickness, volume, leaf area index and the surrounding environment.     

Water purification using sand

Slow sand filters are used to purify drinking water. Each filter consists of a large tank containing a bed of sand through which water passes at typical rates of 0.1–0.3 m h^–1. Water is cleaned by physico–chemical and biological processes occurring at the air–water interface, within the bulk water, over the surface of the sand, and within the bed of sand. The processes found in sand filters replicate many of those found in natural sand banks and sandy beaches.     

Energetics of actively powered locomotion using the simplest walking model

We modified an irreducibly simple model of passive dynamic walking to walk on level ground, and used it to study the energetics of walking and the preferred relationship between speed and step length in humans. Powered walking was explored using an impulse applied at toe-off immediately before heel strike, and a torque applied on the stance leg. Although both methods can supply energy through mechanical work on the center of mass, the toe-off impulse is four times less costly because it decreases the collision loss at heel strike. We also studied the use of a hip torque on the swing leg that tunes its frequency but adds no propulsive energy to gait. This spring-like actuation can further reduce the collision loss at heel strike, improving walking energetics. An idealized model yields a set of simple power laws relating the toe-off impulses and effective spring constant to the speed and step length of the corresponding gait. Simulations incorporating nonlinear equations of motion and more realistic inertial parameters show that these power laws apply to more complex models as well.     

大小蠹来源地的COⅠ基因标记

【背景】大小蠹属昆虫是重要的林木害虫,我国口岸有多次截获记录,确定大小蠹的来源地可以有针对性地加强对大小蠹的检验检疫工作。【方法】测定了5种高风险大小蠹(红脂大小蠹、红翅大小蠹、中欧山松大小蠹、落叶松大小蠹和间大小蠹)共12个样本的线粒体DNA细胞色素氧化酶C亚基Ⅰ基因(COⅠ)的部分序列。【结果】利用巢式PCR技术,在不同种类的大小蠹样本中均获得了530bp的靶标片段,比对分析显示,不同种大小蠹之间的COⅠ序列差异显著,同种大小蠹不同个体之间的COⅠ序列存在一定的差异,但差异不显著。系统进化树分析结果显示,大小蠹可以明显分为2支,其中,间大小蠹单独为一分支,另一分支由红脂大小蠹、红翅大小蠹、中欧山松大小蠹和落叶松大小蠹组成;同时,同种大小蠹不同个体的来源情况在进化树中有一定体现。【结论与意义】COⅠ基因可以较好地反映样本的来源地,对今后制定大小蠹的具体检验检疫措施有实际指导意义。     

内蒙古荒漠草原防风固沙服务变化及其驱动力

荒漠化是内蒙古荒漠草原面临的最严重的生态环境问题之一,而风蚀则是造成土地退化的主要因素。采用修正风蚀方程（Revised wind erosion equation,RWEQ）定量评估了内蒙古荒漠草原2000和2017年的固沙量,并结合土地利用、降水、风速、植被覆盖度数据分析了该区域防风固沙服务的影响因素。结果表明：内蒙古荒漠草原的防风固沙服务表现出明显的空间异质性,不同土地利用类型提供的防风固沙服务有所差异,其中高覆盖度草地的固沙量相对较高。总体来说,2000年固沙量与降水、风速、植被覆盖度均为正相关,2017年固沙量与降水为负相关,与风速和植被覆盖度为正相关。2000-2017年内蒙古荒漠草原固沙物质总量增幅为53.95%,其中9.65%来源于土地利用变化区域,土地利用方式发生变化的面积占研究区总面积的5.6%。2000-2017年土地利用变化以林地的恢复、建设用地的扩张以及不同覆盖度间草地的转换为主。2000-2017年,风力因子的分布模式对防风固沙服务的空间分布变化的影响较大。总的来说,土地利用变化对内蒙古荒漠草原的防风固沙服务有一定的增强作用,防风固沙服务的空间分布在时间上的变化主要受气候因子的影响。     

五种荒漠植物幼苗出土及生长对沙埋深度的响应

研究了红砂、泡泡刺、花棒、白刺和沙拐枣5种荒漠优势植物的幼苗出土和生长对沙埋的响应,判断了幼苗的生长特征能否预测植物的定植能力。进行了0、1、2、3、5cm和8cm等6个沙埋深度处理,每个处理5个重复。结果表明：每种植物的出苗率都随着沙埋深度的增加而降低,而且遵循着指数方程关系。红砂种子的最佳沙埋深度应为0-1cm,3cm已是出苗和存活的最大沙埋深度;泡泡刺、花棒和白刺种子的最佳深埋深度为0—3cm;沙拐枣在0—8cm各个深度都有出苗现象,且出苗率没有显著差异,但8cm深度的出苗率只有4％,最佳沙埋深度约为5cm。幼苗的生长高度受沙埋深度的影响显著,在同一时间,幼苗的最大生长高度并不在0cm表层,但红砂幼苗除外。泡泡刺、花棒和白刺在0—3cm的沙埋深度的幼苗生长高度大于5-8cm沙埋深度的生长高度,但沙拐枣幼苗在5cm深度的生长高度最大。5种荒漠植物幼苗的生物量受沙埋深度的影响不显著。在同一沙埋深度下,红砂的绝对高度生长率明显低于其余4种植物,沙拐枣的绝对高度生长率高于其余4种植物幼苗;5种植物的相对高度生长率对沙埋深度的响应并不敏感。绝对高度生长率与相对高度生长率并不能预示幼苗存活成功率。     

Seed germination and seedling emergence of three annuals growing on desert sand dunes in China

BACKGROUND AND AIMS: Information on the initial growth characteristics of annuals found in Chinese deserts is very limited. The aim of this study was to investigate seed germination and interactive effects of irrigation and seed burial depth in sand on seedling emergence and seedling survival in three annuals (Agriophyllum squarrosum, Bassia dasyphylla and Aristida adscensionis) commonly growing on sand dunes in these regions. METHODS: Effects of temperature, light and polyethylene glycol-6000 on seed germination were examined by irrigating seeds sown on filter paper in Petri dishes. Seedling emergence was examined for seeds sown on the surface of, or at different depths (5, 10, 20, 30, 40 and 50 mm) in, sand-filled pots, which were irrigated under different regimes. For seeds buried at a depth of 50 mm, seed viability was examined after irrigation of the pots. KEY RESULTS: Seeds of three species germinated at most temperatures recorded between spring and autumn in their native habitats. No seed dormancy was found in any species. For all three species, seedling emergence was most favoured when seeds were buried at a depth of 10 mm. When seeds sown on the sand surface were irrigated, seed germination was considerably suppressed due to water deficiency, but many seeds remained viable. For A. squarrosum and B. dasyphylla, many seeds that were deeply buried and irrigated remained ungerminated but viable, while for A. adscensionis deeply buried seeds germinated, but the seedlings did not emerge due to unfavourable seedling growth in deep sand. CONCLUSIONS: Precipitation is the most crucial factor in determining the seasonal emergence of seedlings of the three tested species in the field. The vertical distribution of seeds in sand determines the proportion of seeds that germinate after precipitation and acts to maintain seed banks over multiple years.     

Prey and feeding phenology of the desert sand scorpion Pamroctonus mesaensis (Scorpionidae: Vaejovidae)

The diet and feeding of the vaejovid scorpion Pamroctonus mesaensis Stahnke was investigated during a five-year study. Foraging and feeding behaviour are described. This scorpion is a "sit and wait" predator that eats a wide variety of cursorial, fossorial and aerial prey. Ninety-five prey species were recorded. Three year classes of scorpions exist. Each class captures a different proportion of major prey species and a significantly different average size of prey.
The proportion of each major taxon of prey in the diet is as follows: tenebrionid beetles (42%), Orthoptera (17%), other scorpions (16%) and Hymenoptera (12%). When analysed in relation to biomass, larger prey species assume more importance while smaller species are relatively less important. Although P. mesaensis ranks as the fourth most numerous prey species, they represent the most important diet item in terms of ingested biomass.
When observed, 3·75% of all scorpions were feeding. This percentage varied seasonally from a high in spring (7.0%) to a low in November and December (0.5 %). The proportions of major prey taxa in the diet also varied seasonally. Prey species were classified into three phenological categories: pulsed, seasonal and annual. Examples of each are given.