microorganisms detected there. The other characteristic bacterial phyla in hyperarid AT-12 include Acetothermia, Armatimonadetes, Hydrothermae, and Thermotogae, bacteria within which generally adapt to nutrient-depleted and high temperature conditions (Hao et al. 2018; Jungbluth et al. 2017; Lee et al. 2014). Actinobacteria survived in the pre-rainfall hyperarid core of the AtacamaDesert in 2012 were only belong to 9 species – uncultured Ilumatobacteraceae, Corynebacterium sp., Micrococcus sp., Lawsonella sp., uncultured Geodermatophilus sp., uncultured Rothia sp., uncultured MB-A2-108, uncultured RBG-16-55-12, and unclassified Acidimicrobiia. All species in classes Nitriliruptoria, Rubrobacteria, and Thermoleophilia, and most of species in classes Actinobacteria and Acidimicrobiia have disappeared after decades or centuries of the extreme hyperaridity, similar to the microbiota structure of the salt flat ecosystems in the AtacamaDesert (Farias et al. 2014; Farias et al. 2013; Ley et al. 2006; Mobberley et al. 2012; Rasuk et al. 2016; Rasuk et al. 2014; Sahl et al. 2008). Besides the long-term hyperaridity, the deficiency of extractable Actinobacteria in hyperarid AT-12 may be also caused by incomplete extraction or sequencing because of the limit of technology and the novelty of extremophilic actinobacterial species (Goodfellow et al. 2018; Idris et al. 2017). Additionally, some Actinobacteria such as its classes Actinobacteria, Acidimicrobiia, and Rubrobacteria can form spores that are difficult to break down during DNA extraction to counterattack ultraviolet radiation and dehydration (Barka et al. 2016). Analogously, the decreasing proportions of Firmicutes (majorly Bacilli, and minorly Clostridia, Erysipelotrichia, and Limnochordia) in the hyperarid core may be a result of their sporulation (Rose et al. 2011).
To date some Ramalina species have been recorded for the coastal AtacamaDesert that show a considerable morphological variation (Rundel, 1978; Santiago, Gonçalves, Gómez‐Silva, Galetovic, & Rosa, 2018) but this is the first record of R. thrausta for the southern hemi‐ sphere. Typical are the filamentous thin branches that are slightly and irregularly swollen, the small hooked shaped terminal soralia, the spot‐ like to elongate pseudocyphellae and the presence of usnic acid only (Bowler, 1977). Apothecia are very rare in the Northern hemisphere and no information on the spore length is given. However, the speci‐ men investigated here frequently does have apothecia and the spores are 9–16 × 2–4 µm. Interestingly there is a macaronesian species, F I G U R E 4 Phylogenetic tree of the lichenicolous fungi rooted to Xanthoria parietina KJ027708.1 and micrographs. (a) ITS maximum‐ likelihood tree of the photobionts. Numbers at nodes represent the ML bootstrap support (values ≥ 50%) and second the posterior probabilities from the Bayesian analysis (values ≥ 50%). The scale indicates the numbers of substitutions per site and generated sequences are connected by color code to the corresponding micrographs (orange = terricolous lichens; blue = epiphytic lichens). Micrographs show the gall of Tremella sp. attached to R. thrausta (white triangle, b) and as thin section of the same gall (c). Neonectria sp. is shown on top of the thallus of Placidium sp. (d) and within the epinecral layer of the lichen (e). The infected thalli of Acarospora conafii are shown in (f) and Polysporina sp. within the pycnidia of the lichen in (g)
Our research hypothesis was confirmed, i.e., reproductive tissue (flower buds and open flowers) of Eulychnia brevi- flora, an endemic, arbuscular cactus of the hyperarid AtacamaDesert, was present nearly always on the equator- ial (north) side of the plants and on the equatorial side of the individual stems on which they were located. Such orientation of the reproductive tissue, places it adjacent to areas of the stems that receive maximum exposure to PAR, thus minimizing the energetic cost of translocating photo- synthates. In addition to nectar, pollinating insects in this cool desert may also be attracted to the flowers of this species due to the potential thermal reward from flowers that receive abundant solar radiation.
After eight months, the seedlings were carefully removed from their pots (Additional file 3A), and the total number of rhizomes and the number of rhizomes per plant formed was counted (Additional file 3B). To evaluate viability, the rhizomes were separated using a scalpel; each rhizome remained attached to its storage organ (Additional file 3C). Each rhizome was then buried in a pot with fresh sand:nu- tritive soil (3:1) at 3 cm belowground for two years in the greenhouse. During these two years, the pots were exposed to temperatures, humidity and light conditions occurring naturally in La Serena throughout the year (Additional file 4). Watering of pots was completely suspended during this resting period, again mimicking natural climatic conditions for geophytes in the AtacamaDesert. After two years, the viability of the rhizomes was evaluated by watering the pots daily with ~ 50 mL of tap water every three days for one month (Additional file 3D). The chemical composition of the tap water used in this stage is shown in Additional file 5. The number of emerged vs non-emerged seedlings were evaluated by counting the emergence of new shoots during the entire reactivation time period and presented as the percentage of re-sprouting. When a shoot reached 5 mm, we considered that rhizome viable.
species of the Coastal AtacamaDesert (R.P. López, personal observation), thus suggesting that these species are more dependent on rain for seedling establishment. Finally, the positive effects of shade under dry condi- tions as well as with increased irrigation were even more evident when considering the trajectory of the survival curve with the Cox's proportional hazards model, which showed a positive effect in all four species. Our results are in agreement with those of other studies that show that a facilitative effect of shade under dry conditions is a key driver for seedling establishment not only in Mediterranean (Maestre et al. 2003b, Sánchez- Gómez et al. 2006) and desert ecosystems (Martínez- Tillería et al. 2012) but also in a wet tropical environment (Holmgren et al. 2012).
Prosopis tamarugo Phil. is a legume tree native to the AtacamaDesert, Chile. Tamarugo has physiological characteristics that are highly adapted to extreme life conditions in the Pampa del Tamarugal. Null precipitation makes tamarugo completely dependent on groundwater, developing in areas where the groundwater depth is closest to the surface. Groundwater extraction for domestic consumption, mining, and agriculture affects the desert ecosystem by lowering the water table. Measuring and describing the impacts on vegetation through the monitoring of physiological variables along with groundwater depletion in salt flats where extraction wells are located has contributed to a better understanding of tamarugo response to this stress factor. Integrated variables such as green canopy fraction, normalized difference vegetation index (NDVI), 18 O isotope enrichment in foliar tissue, and twig growth proved to be far more reactive toward groundwater depth increase and presented lower error values. These variables respond to mechanisms that tamarugo has to maintain a stable water condition when water offer (water table depth (WTD)) decreases regarding water demand (transpiration). Defoliation along with twig growth diminishment would combine toward a canopy reduction strategy in order to reduce water demand. Green biomass loss, beyond a certain WTD, would lead to complete drying of the tamarugo. Up to 10 m of groundwater table depth, Tamarugo grows, has photosynthetic activity, and has the ability to perform pulvinary movements. Beyond 20 m of water table depth, tamarugo survival is compromised and hydraulic failure is inferred to occur. The current scenario is of groundwater over-exploitation; if economic efforts will be made to conserve and/or restore tamarugo, habitat groundwater extraction is a key element in effective management. Reaching of the thresholds depends on the adequate authority management of groundwater. The objectives of this review are (a) to review information collected from scientific studies regarding tamarugo condition and its response, over time, to WTD increase, (b) to identify WTD thresholds that affect tamarugo ’ s functioning, and (c) to propose a sequence of physiological events triggered by groundwater (GW) depletion.
Myrcianthes coquimbensis (Barnéoud) Landrum et Grifo is an endangered, evergreen shrub, endemic to the Elqui Province in the southern edge of the AtacamaDesert in Chile (Marticorena et al. 2001; García-Guzmán et al. 2012). It has large, subglobose fleshy drupes (2.5 × 3.5 cm) that typically contain only one seed (Saldías and Velozo 2014), which is large (diameter: 0.8 to 2.5 cm; weight: 2.6 to 11 g) and recalcitrant. When ripe or green fruits fall to the ground, they are removed by rodents, which cache them and later consume both their pulp and seeds. Each year, approximately 35% of the seed crop is presumably lost to post-dispersal seed predation. Rodents, however, do not always eat seeds in their totality; often, seed dam- age by rodents is only partial (Loayza et al. 2014). Conse- quently, post-dispersal seed predation results in seed mass loss but not inevitably in seed death.
The Hyperion image analysis provided mixed results. Gypsum has strong features and was identifiable in the images and extractable by the SISAL algorithm. The resulting Ca-sulfate abundance estimates produced using an endmember set drawn from a mixture of SISAL extracted spectra and scaled USGS spectra were in agreement with the sample Q-XRD values from this area. Despite the extensive pre-processing outlined in this study only one of the eight final images had clean enough data to produce interpretable results with SMA. Hyperion returns the highest SNR data in the visible portion of its images but the diagnostic absorptions for those salts that have any in the VNIR are primarily above 1.5 µm where the instrument SNR is poor. Together with the weak absorptions expected for many common chlorides and perchlorates, the high inherent noise and presence of strongly absorbing minerals meant that the only salt identifiable and quantifiable in the images was sulfate, in particular gypsum. Even in an area such as the AtacamaDesert where there is a stable and predominantly cloud free atmosphere and the ground is well exposed, Hyperion struggles to provide data of sufficient quality for quantitative analysis. However, for exploration of planetary surfaces beyond Earth, such as Mars, it is likely that the techniques explored in this work would be potentially successful using hyperspectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on board the Mars Reconnaissance Orbiter. In particular, the successful identification and estimated quantification of sulfate minerals is highly applicable to Mars exploration, where sulfate minerals are abundant and record a significant part of Mars’ surface history.
Analysis of the fish otoliths from Camarones Punta Norte and Caleta Vitor archaeological sites provides further and finer evidence documenting the reliance of the people of the AtacamaDesert on marine resources. Without this bountiful and apparently inexhaustible resource provider, the deep history of humanity in this remote part of the planet would be different. The long-term chronological otolith analysis shows that there were important differential fluctuations in the species production along the coastal ecosystem throughout the Holocene (ca 9500–300 years ago), and that people likely managed these fluctuations by relocating their settlements either within the estuaries, or by moving out from them.
The extreme aridity of the AtacamaDesert, together with broad daily temperature fluctuations and intense ultraviolet radiation, contribute to make the core of this desert an extreme habitat approaching ‘the dry limit of life on Earth’ . Nevertheless, micro-organisms inhabit this extreme environment. Studies have reported low numbers of culturable bacteria in soil samples of the arid core, ranging from not detectable to 10 6 CFU/g of soil, and reflecting a great spatial heterogeneity [8,9,11-15]. With the use of molecular methods, the subsurface layers of the hyper-arid core were shown to harbor a very limited microbial community dominated by Gemmatimonadetes and Plantomycetes bacteria and also including Actinobac- teria , Thermomicrobia , and one member of the Proteobac- teria [9,11,12]. These micro-organisms were identified in soil samples where no vascular plant has grown for mil- lions of years and rain occurs only once every 20 to 50 years [8,9,11,12]. In less arid parts of the desert, soil bac- terial communities were characterized by a high abun- dance of novel Actinobacteria and Chloroflexi taxa, and low levels of Acidobacteria and Proteobacteria [11,16]. Fungi cultured from samples collected in several locations of the Atacama were all spore-forming saprophytes, sug- gesting that they might not be indigenous to the desert but rather dispersed by wind .
Abstract. Paleoclimate reconstructions reveal that Earth sys- tem has experienced sub-millennial scale climate changes over the past two millennia in response to internal/external forcing. Although sub-millennial hydroclimate fluctuations have been detected in the central Andes during this inter- val, the timing, magnitude, extent and direction of change of these events remain poorly defined. Here, we present a reconstruction of hydroclimate variations on the Pacific slope of the central Andes based on exceptionally well- preserved plant macrofossils and associated archaeological remains from a hyperarid drainage (Quebrada Man´ı, ∼ 21 ◦ S, 1000 m a.s.l.) in the AtacamaDesert. During the late Holocene, riparian ecosystems and farming social groups flourished in the hyperarid Atacama core as surface water availability increased throughout this presently sterile land- scape. Twenty-six radiocarbon dates indicate that these events occurred between 1050–680, 1615–1350 and 2500– 2040 cal yr BP. Regional comparisons with rodent middens and other records suggest that these events were synchronous with pluvial stages detected at higher-elevations in the cen- tral Andes over the last 2500 yr. These hydroclimate changes also coincide with periods of pronounced SST gradients in the Tropical Pacific (La Ni˜na-like mode), conditions that are conducive to significantly increased rainfall in the central Andean highlands and flood events in the low-elevation wa- tersheds at inter-annual timescales. Our findings indicate that the positive anomalies in the hyperarid Atacama over the past
Desert is a normative concept because it tells us what benefits ought to be received for a particular performance, or what ought to be done in order to receive benefits. But aside from the characteristics of desert (agent-relative, minimum control, expression and appraisal of value, conferral of status, past- orientation, proportionality), the concept per se does not provide the resources to determine the substantive normative content of desert in each case. This is because each desert-claim is partly internally defined and partly externally defined.18 The characteristics will limit what can count as deserving, but will not tell us what is actually valued by others and the degree of voluntariness that is necessary in each case. Rather, the more precise content of desert is given by the purposes present in the particular situation in which desert is being applied. That is to say, the mode of deserving treatment (i.e. grades, wages, prizes, honours, office, punishments etc.). Hence, the specification of control and value depends on the general objectives of each mode. (For example, the employer will allocate wages to existing staff based on contribution to revenue. But in choosing a new member of staff the employer will be more concerned with the control the candidate has shown over their productive outputs in the past, so as to predict the likelihood of continued productivity in the future.) Even greater specificity is provided by the objectives stated in each case (e.g. grades may be allocated based on effort shown by the student or the student’s grasp of the subject).
This study was conducted in 1988-1993 and in 1998-2003 respectively. We collected rodent data from 68 sites located in the desert and semi desert areas of Inner Mongolia, covering an area of 380,000 km 2 (Figure 1). We selected 3 - 5 sampling plots in each of the 68 sites to capture rodents. The number of sampling plots was deter- mined in consideration of changes of landforms, topography and vegetation in the area. The sampling plots in- cluded all kinds of vegetation and landforms. Finally, we set 317 sampling plots. Five transect lines were set in each sampling plot, and transect lines were 50 m apart. Along a transect line, 100 snap-traps, baited with peanuts, were spaced at an interval of 5 m. The traps were set after sunset and checked two times in 24 hours after they have been laid. The rodents captured were measured and weighted; the reproductive status and contents in the stomach were also checked. Since the sampling investigation could not be completed in the whole investigated area in a year, it can only be unanimous in months (or seasons); therefore, the investigated time was from May to August.
Sand migration in the vast Taklamakan desert within the Tarim Basin (Xinjiang Uyghur Autonomous region, PR China) is governed by two competing transport agents: wind and water, which work in diametrically opposed directions. Net aeolian transport is from northeast to south, while ﬂuvial transport occurs from the south to the north and then west to east at the northern rim, due to a gradual northward slope of the underlying topography. We here present the ﬁrst comprehensive provenance study of Taklamakan desert sand with the aim to characterise the interplay of these two transport mechanisms and their roles in the formation of the sand sea, and to consider the potential of the Tarim Basin as a contributing source to the Chinese Loess Plateau (CLP). Our dataset comprises 39 aeolian and ﬂuvial samples, which were characterised by detrital-zircon U–Pb geochronology, heavy-mineral, and bulk-petrography analyses. Although the inter-sample differences of all three datasets are subtle, a multivariate statistical analysis using multidimensional scaling (MDS) clearly shows that Tarim desert sand is most similar in composition to rivers draining the Kunlun Shan (south) and the Pamirs (west), and is distinctly different from sediment sources in the Tian Shan (north). A small set of samples from the Junggar Basin (north of the Tian Shan) yields different detrital compositions and age spectra than anywhere in the Tarim Basin, indicating that aeolian sediment exchange between the two basins is minimal. Although river transport dominates delivery of sand into the Tarim Basin, wind remobilises and reworks the sediment in the central sand sea. Characteristic signatures of main rivers can be traced from entrance into the basin to the terminus of the Tarim River, and those crossing the desert from the south to north can seasonally bypass sediment through the sand sea. Smaller ephemeral rivers from the Kunlun Shan end in the desert and discharge their sediment there. Both river run-off and wind intensity are strongly seasonal, their respective transport strength and opposing directions maintain the Taklamakan in its position and topography.