安西荒漠鼠类群落结构与环境因子的无偏对应分析

本文通过对安西荒漠鼠类群落结构与环境因子的无偏对应分析,得出决定鼠类群落结构的环境主导因子因季节不同而所有同;春季是地下水位、海拔高度、平均奖降水量和平均气温;夏季是植被覆盖度、植物平均高度、土壤含水率和土壤坚实度;秋季是土壤含水率。综合主导因子。其中水是决定荒漠地区鼠类群结构的最重要因子。     

Composition and diversity of endolichenic microfungal communities from saxicolous lichens at Nahal Boker,the central Negev Desert,Israel

We studied the endolichenic fungal communities from saxicolous lichens occupying the cobbles at Nahal Boker, the central Negev Desert, Israel. Overall, 101 species belonging to 64 genera were isolated from 12 lichen species collected in three seasons from the south-facing slope (SFS) and north-facing slope (NFS) of the wadi. The endolichenic communities possessed a set of traits, which helped them to cope with harsh internal and external conditions. It included a prevalence of melanin-containing fungi with thick-walled and multicellular spores and a comparatively high contribution of thermotolerant species and species with meiospore-producing life cycle stage at the more microclimatically severe SFS. Species richness and isolate density of endolichenic communities was the highest in fruticose lichens with thick and wrinkled thalli, and the lowest in endolithic species possessing thin and smooth thalli. The communities from lichens formed a more diverse group than those from surrounding cobbles probably due to the influence of various species of lichens belonging to different growth forms.     

Seasonal light characteristics for a newly formed reservoir in Southwestern USA

Seasonal transparency and extinction coefficients are presented for two major habitats in the Lake Powell system, a large newly formed reservoir in the arid southwestern USA. These habitats include a shallow side canyon station subjected to periodic influx of dissolved and suspended materials and an open bay system. Maximum Secchi disk levels in the open bay station were at 7.7 meters with the Secchi disk estimated to disappear at a level of penetration approximating 10% of the solar radiation entering the lake surface. Mean compensation depth was calculated at 11.7 meters. Seasonal extinction coefficient for unfiltered light in the deeper bay station was 0.321 while extinction coefficients for blue, green and red filtered light were 0.323, 0.309 and 0.474 respectively. The effect of periodic influx of dissolved and suspended substances on the underwater light climate and phytoplankton populations are discussed for desert lakes.This study was supported in part by funds provided by the Navajo and Kaiparowits participants.This study was supported in part by funds provided by the Navajo and Kaiparowits participants.     

Nutrient variation induced by rodent disturbance in Haloxylon ammodendron as a target transfer strategy

Nutrients form a link between herbivores and plant. This study explored the physiological and ecological response mechanism of Haloxylon ammodendron population to rodent disturbance in Gurbantunggut Desert from the perspective of nutrient cycle. Through field investigation, we quantified rodent disturbance intensity (DI) to H. ammodendron and analyzed the ecological response mechanism of H. ammodendron population to rodent disturbance from the perspective of plant and soil nutrient cycling and changes. The results indicated that moderate rodent DI (number of effective burrows = 3–6) was the maximum limit that can be tolerated by H. ammodendron; the threshold for optimal H. ammodendron response to rodent disturbance was mild (number of burrows = 1–3). Meanwhile, the rodent disturbance caused significant nutrient enrichment (e.g., organic carbon, available phosphorus, and available potassium) in the deeper soil (at 20–40 and 40–60 cm depth) and significantly reduced the soil total salt content (p < .05). Furthermore, as the DI increased, the branches of H. ammodendron showed significantly increased soluble total sugar, crude fiber, and total nitrogen contents (p < .05) but significantly decreased crude fat and crude protein contents (p < .05); these results are related to the nutritional target transfer strategy evolved by H. ammodendron for long‐term resistance to rodent disturbance. The current study clarified the optimal disturbance model for mutually beneficial H. ammodendron–great gerbil relationship, on the basis of which the ecological response mechanism of H. ammodendron population to rodent disturbance in deserts was illustrated. The current study provides a scientific basis for the protection mechanisms of desert plants to rodent disturbance.     

Seed Menus: An integrated decision‐support framework for native plant restoration in the Mojave Desert

The combination of ecosystem stressors, rapid climate change, and increasing landscape‐scale development has necessitated active restoration across large tracts of disturbed habitats in the arid southwestern United States. In this context, programmatic directives such as the National Seed Strategy for Rehabilitation and Restoration have increasingly emphasized improved restoration practices that promote resilient, diverse plant communities, and enhance native seed reserves. While decision‐support tools have been implemented to support genetic diversity by guiding seed transfer decisions based on patterns in local adaptation, less emphasis has been placed on identifying priority seed mixes composed of native species assemblages. Well‐designed seed mixes can provide foundational ecosystem services including resilience to disturbance, resistance to invasive species, plant canopy structure to facilitate natural seedling recruitment, and habitat to support wildlife and pollinator communities. Drawing from a newly developed dataset of species distribution models for priority native plant taxa in the Mojave Desert, we created a novel decision support tool by pairing spatial predictions of species habitat with a database of key species traits including life history, flowering characteristics, pollinator relationships, and propagation methods. This publicly available web application, Mojave Seed Menus, helps restoration practitioners generate customized seed mixes for native plant restoration in the Mojave Desert based on project locations. Our application forms part of an integrated Mojave Desert restoration program designed to help practitioners identify species to include in local seed mixes and nursery stock development while accounting for local adaptation by identifying appropriate seed source locations from key restoration species.     

Differing climate and landscape effects on regional dryland vegetation responses during wet periods allude to future patterns

Dryland vegetation is influenced by biotic and abiotic land surface template (LST) conditions and precipitation (PPT), such that enhanced vegetation responses to periods of high PPT may be shaped by multiple factors. High PPT stochasticity in the Chihuahuan Desert suggests that enhanced responses across broad geographic areas are improbable. Yet, multiyear wet periods may homogenize PPT patterns, interact with favorable LST conditions, and in this way produce enhanced responses. In contrast, periods containing multiple extreme high PPT pulse events could overwhelm LST influences, suggesting a divergence in how climate change could influence vegetation by altering PPT periods. Using a suite of stacked remote sensing and LST datasets from the 1980s to the present, we evaluated PPT‐LST‐Vegetation relationships across this region and tested the hypothesis that enhanced vegetation responses would be initiated by high PPT, but that LST favorability would underlie response magnitude, producing geographic differences between wet periods. We focused on two multiyear wet periods; one of above average, regionally distributed PPT (1990–1993) and a second with locally distributed PPT that contained two extreme wet pulses (2006–2008). 1990–1993 had regional vegetation responses that were correlated with soil properties. 2006–2008 had higher vegetation responses over a smaller area that were correlated primarily with PPT and secondarily to soil properties. Within the overlapping PPT area of both periods, enhanced vegetation responses occurred in similar locations. Thus, LST favorability underlied the geographic pattern of vegetation responses, whereas PPT initiated the response and controlled response area and maximum response magnitude. Multiyear periods provide foresight on the differing impacts that directional changes in mean climate and changes in extreme PPT pulses could have in drylands. Our study shows that future vegetation responses during wet periods will be tied to LST favorability, yet will be shaped by the pattern and magnitude of multiyear PPT events.     

A diversity of bacteriophage forms and genomes can be isolated from the surface sands of the Sahara Desert

The surface sands of the Sahara Desert are exposed to extremes of ultraviolet light irradiation, desiccation and temperature variation. Nonetheless, the presence of bacteria has recently been demonstrated in this environment by cultivation methods and by 16S rDNA analyses from total DNA isolated from surface sands. To discern the presence of bacteriophages in this harsh environment, we searched for extracellular phages and intracellularly located phages present as prophages or within pseudolysogens. Mild sonication of the sand, in different liquid culture media, incubated with and without Mitomycin-C, was followed by differential centrifugation to enrich for dsDNA phages. The resulting preparations, examined by electron microscopy, revealed the presence of virus-like particles with a diversity of morphotypes representative of all three major double-stranded DNA bacteriophage families (Myoviridae, Siphoviridae and Podoviridae). Moreover, pulsed-field gel electrophoresis of DNA, extracted from the enriched bacteriophage preparations, revealed the presence of distinct bands suggesting the presence of putative dsDNA phage genomes ranging in size from 45 kb to 270 kb. Characterization of the bacteriophages present in the surface sands of the Sahara Desert extends the range of environments from which bacteriophages can be isolated, and provides an important point of departure for the study of phages in extreme terrestrial environments.Magali Prigent and Magali Leroy contributed equally to this work     

Diversity, spatial arrangement, and endemism of Cactaceae in the Huizache area, a hot-spot in the Chihuahuan Desert

We studied several aspects of the cactus diversity in the Huizache, an area located in the southern extreme of the Chihuahuan Desert Region, in San Luis Potosí, Mexico. Fieldwork was conducted in a square-shaped polygon (22°30–23°00 N, 100°00–100°30 W), where a total of 80 systematically-chosen localities were sampled for cactus species. Results showed that the Huizache is an important focal point for the conservation of the Cactaceae, due to the remarkably high diversity of members of this plant family in the area. With 75 species recorded, this area has the highest concentration of cactus species in the American Continent, in comparison with other comparably-sized regions. The outstanding diversity of cactus species in the Huizache area may be explained by the relatively favorable climate of this desert area, its environmental heterogeneity, and its location in a transitional position between three regions with distinct cactus floras: Chihuahuan Desert Region, Queretaroan-Hidalgoan Arid Zone, and Tula-Jaumave Valleys. Species richness is not distributed evenly in the area; the zones of highest species concentration are primarily located in the lowland valleys, in the northwestern portion of the grid square, where typical Chihuahuan Desert conditions prevail. Of the 75 cactus species found in the area, 63% are endemic to the Chihuahuan Desert. Among these, ten species are outstanding for being endemic or nearly endemic to the Huizache area. The Huizache grid square is part of a recently declared natural reserve, The Real de Guadalcázar Natural Reserve.     

Slow‐motion population dynamics in Mojave Desert perennial plants

Abstract. To investigate survivorship and regeneration in desert perennial plants, individual shrubs were mapped, measured and tagged on a nearly level 360 m² plot of diverse Mojave Desert vegetation in 1981, they were re‐mapped and measured 15 years later, in 1996. A large majority of the shrubs persisted between censuses. Modest birth (establishment) and death rates indicate that plants are replaced approximately every century, while the median longevity of several species is much longer. A 15‐yr intercensus interval, appropriate for most species (i.e. birth and death rates were measurable), is too short for several larger shrubs (including Larrea divaricata, Ephedra nevadensis, Yucca schidigera and the larger Opuntia spp.) in which virtually no births or deaths occurred and in which longevity must be extremely high. While individuals of most species grew over the 15‐yr interval, others did not, and some individuals shrank in size. In a number of species, individual growth rates were significantly reduced according to the number of neighbouring plants rooted 0.5–2.0 m distant. Even Larrea tridentata, one of the largest species, showed significant effects of growth rate reduction where crowded by allospecific plants, despite the generally much smaller sizes of these neighbours.     

Responding to a three-pronged attack: desert lilies subject to herbivory by dorcas gazelles

We examined the effects of herbivory by the dorcas gazelle, Gazella dorcas, on different phenological stages of the lily Pancratium sickenbergeri from 1990–1996 in the Negev desert, Israel. We placed particular emphasis on the role of gazelle herbivory on selecting for plant defences and the effectiveness of these defences against subsequent herbivory. In the summer months, the gazelles dig in the sand to remove all or part of the bulb of the lily. Plants with partially-consumed bulbs were less likely to produce leaves the following winter and probably have lower lifetime flower production. Herbivory has resulted in greater downward growth of the bulb in populations with herbivory than those without herbivory, which reduces the probability that the entire plant will be consumed. Gazelles eat the leaves in the winter; this herbivory has a negative impact on leaf growth rates. However, the production of calcium oxalate limits gazelle consumption to the tips, and consequently reduces the effects of leaf herbivory. In the fall, the gazelles consumed virtually all flowers, yet we found no defence or growth strategy that might ameliorate this impact, with the possible exception of forgoing the output of a second flower stalk after the first has been consumed. The results of this study suggest that lilies employ different strategies to resist gazelle herbivory, and that these strategies are dependent on the phenological stage that is eaten. Avoidance by defence is the strategy in the leaves, avoidance by escape is utilized in bulbs. Forgoing the output of a second flower stalk after the first has been consumed can be considered as a form of escape based on a bet-hedging strategy or a shift in energy allocation.