North American Sonoran Desert Research Articles

To betalains and back again: a tale of two pigments.

To betalains and back again: a tale of two pigments.

Evidence of aqueous secondary organic aerosol formation from biogenic emissions in the North American Sonoran Desert

This study examines the role of aqueous secondary organic aerosol formation in the North American Sonoran Desert as a result of intense solar radiation, enhanced moisture, and biogenic volatile organic compounds (BVOCs). The ratio of water-soluble organic carbon (WSOC) to organic carbon (OC) nearly doubles during the monsoon season relative to other seasons of the year. When normalized by mixing height, the WSOC enhancement during monsoon months relative to preceding dry months (May-June) exceeds that of sulfate by nearly a factor of 10. WSOC:OC and WSOC are most strongly correlated with moisture parameters, temperature, and concentrations of O3 and BVOCs. No positive relationship was identified between WSOC or WSOC:OC and anthropogenic tracers such as CO over a full year. This study points at the need for further work to understand the effect of BVOCs and moisture in altering aerosol properties in understudied desert regions.

Soil,Vegetation, and Seed Bank of a Sonoran Desert Ecosystem Along an Exotic Plant (Pennisetum ciliare) Treatment Gradient

Ecological conditions following removal of exotic plants are a key part of comprehensive environmental management strategies to combat exotic plant invasions. We examined ecological conditions following removal of the management-priority buffelgrass (Pennisetum ciliare) in Saguaro National Park of the North American Sonoran Desert. We assessed soil, vegetation, and soil seed banks on seven buffelgrass site types: five different frequencies of buffelgrass herbicide plus hand removal treatments (ranging from 5 years of annual treatment to a single year of treatment), untreated sites, and non-invaded sites, with three replicates for each of the seven site types. The 22 measured soil properties (e.g., pH) differed little among sites. Regarding vegetation, buffelgrass cover was low (≤1% median cover), or absent, across all treated sites but was high (10-70%) in untreated sites. Native vegetation cover, diversity, and composition were indistinguishable across site types. Species composition was dominated by native species (>93% relative cover) across all sites except untreated buffelgrass sites. Most (38 species, 93%) of the 41 species detected in soil seed banks were native, and native seed density did not differ significantly across sites. Results suggest that: (1) buffelgrass cover was minimal across treated sites; (2) aside from high buffelgrass cover in untreated sites, ecological conditions were largely indistinguishable across sites; (3) soil seed banks harbored ≥12 species that were frequent in the aboveground vegetation; and (4) native species dominated post-treatment vegetation composition, and removing buffelgrass did not result in replacement by other exotic species.

Annual and Warm Season Drought Intensity–Duration–Frequency Analysis for Sonora, Mexico

Abstract Located in northwestern Mexico, Sonora is a region affected by the North American monsoon (NAM). The region covers nearly 50% of the North American Sonoran Desert and is characterized by climatic conditions ranging from extremely arid to semiarid. The region has suffered from drought since 1995, and consequently, water supplies are threatened. The objectives of this work are to characterize the spatial and temporal variabilities of precipitation in Sonora and to conduct a meteorological drought intensity–duration–frequency analysis based on annual and warm season precipitation records. Monthly precipitation data are compiled from 76 meteorological stations located in Sonora, along with 19 stations in the neighboring American state of Arizona, for the period 1961–2004. For increased reliability, data are pooled within five plausible climatic regions. Among the results reported herein are summaries of precipitation variability, drought frequency estimates for annual and seasonal durations and return periods of 10–100 yr, and an estimate of the return period of the most recent multiyear drought.

EGGS SUFFER IN HEAT

Art Woods is fascinated by tobacco hornworms. And he's luckier than most,he's seen them in their natural environment, the North American Sonoran desert, where they are far more intriguing than the dull insects reared in laboratories. Wondering how the insects extract all of the essential elements they require from their harsh environment, Woods has turned his attention to their eggs. He was puzzled by the problems insect eggs face supplying the developing embryo with adequate oxygen, while remaining sufficiently watertight to protect the egg from dehydration. Woods wondered whether the environmental temperature might affect oxygen diffusion into the egg and limit the developing embryo's access to oxygen at temperatures experienced by the embryos on a typical Sonoran day(p. 2267).But first, Woods needed to discover whether the developing embryos were sensitive to oxygen availability, as adults seem unaffected by varying oxygen levels. Maybe the embryos' development would be unaffected. Working with the team in the local chemistry workshop, Woods designed a Plexiglas block where he could control the partial pressure of oxygen in various egg-filled chambers while filming their development. Monitoring the eggs' development at oxygen concentrations ranging from 21% down to 9%, and temperatures from 22 up to 32°C, the results were dramatic. Woods watched the hatching events move through his Plexiglas box like a wave, with the warmest and most highly oxygenated eggs hatching first, while eggs incubated at lower oxygen concentrations and temperatures hatched later. But when he looked closely to see if there was an interaction between temperature and oxygen that affected the insects' development, he failed to find any. Would he see a strong interaction by looking at other metabolic indicators over a shorter period?Woods decided to measure the eggs' carbon dioxide production rates to see if temperature and oxygen supply might affect their metabolic rate. But it took another trip to the chemistry workshop to crack the problem of measuring the tiny amounts of carbon dioxide produced by clutches of 40 eggs. Woods was now ready measure the eggs' carbon dioxide production rates over oxygen concentrations ranging from 5–50%.This time he found a strong interaction between temperature and oxygen levels; the eggs' carbon dioxide production rates were far more sensitive to oxygen availability at higher temperatures. And when Woods raised the oxygen level to 50%, the egg's metabolic rate rose still further. It seemed that the oxygen supply within the egg was limited even at naturally occurring temperatures, and as the temperature rose, the limitation became worse.But would this be reflected in the amount of oxygen inside the egg's tissues? Woods measured the oxygen gradient within the eggs by gently inserting an oxygen electrode, and found that the oxygen concentrations dropped dramatically, plummeting to 7% of air saturated levels at the egg's core. `This is really neat, that such a small piece of tissue could have problems with oxygen supply' says Woods.Having found that tobacco hornworm's eggs appear to be oxygen limited,Woods is keen to investigate how the eggs respond to the natural temperature fluctuations they experience while incubating on leaves in the desert, and the challenges they face supplying sufficient oxygen to the embryo within.

Candida orba sp. nov., a new cactus-specific yeast species from Queensland, Australia.

A new species of yeast from decaying cladodes of Opuntia cactus, Candida orba, is described. This species is a member of a four-species clade of cactophilic yeasts. The new species has only been found in one region of Queensland, Australia, where it was presumably introduced during attempts to eradicate prickly pear cactus. DNA-DNA relatedness, phylogenetic analysis, physiological differences, killer-sensitivity profiles and mating reactions establish the distinctness of the taxon as a new species. C. orba is most closely related to Phaffomyces thermotolerans, a species found associated with columnar cacti in the North American Sonoran Desert. The type strain of C. orba, isolated from rotting cladodes of Opuntia stricta in the State of Queensland, Australia, is strain UCD-FST 84-833.1T (= CBS 8782T = NRRL Y-27336T = ATCC MYA-341). Only the h- mating type of the species has been recovered. The lack of the opposite mating type could be the result of a bottleneck during its introduction to Australia. The original geographic/host distribution of this species in the Americas is unknown.

Effect of arbuscular mycorrhizal (AM) fungal communities on growth of ‘Volkamer’ lemon in continually moist or periodically dry soil

Citrus volkameriana Tan. and Pasq. (‘Volkamer’ lemon) seedlings were inoculated with five different communities of arbuscular mycorrhizal (AM) fungi collected from citrus orchards in Mesa and Yuma, AZ, USA, and undisturbed North American Sonoran Desert and Chihuahuan Desert soils. Plants were then grown in a glasshouse for four months under continually moist or periodically dry conditions achieved by altering watering frequency so that before watering events container soil water tensions were approximately −0.01 MPa (continually moist) or −0.06 MPa (periodically dry) one half way down the container profile. Plants grown in continually moist soil had greater shoot growth than plants grown in periodically dry soil. Plant P status did not limit growth, and there was no interaction between watering frequency and AM fungal inoculum treatments. Plants inoculated with AM fungi from the Yuma orchard soil had significantly less root dry weight and total root length, and lower photosynthetic fluxes than plants treated with inoculum from the other soils. Specific soil respiration and an estimated carbon cost to benefit ratio were also higher for plants inoculated with AM fungi from the Yuma orchard soil than for plants treated with inoculum from the other soils. The Yuma orchard inoculum was distinctive in that > 80% of the total number of AM fungal spores were from a single species, Glomus occultum. These data showed that root growth suppression of plants treated with the Yuma inoculum, compared with plants treated with inoculum from all other sites, was substantial and greater in magnitude than the effect of periodic soil drying. Suppression of root growth might have resulted from increased AM fungal activity resulting in higher carbon costs to the plant.

Geographical analysis of scorpion populations on habitat islands

We examined the population structure of sand scorpions (Paruroctonus mesaensis) by performing genetic and morphological analyses. Sand scorpions were expected to show large genetic distances among populations because they are limited to sandy habitats. However, allozyme analysis showed only moderate genetic differentiation among populations. The morphological analysis showed a geographical association among regional sites. A positive association was found among genetic, morphological and geographical distance matrices. However, the morphological distance matrix showed a higher correlation value with geographical distance than with genetic distance. This result suggests that local environmental conditions may affect scorpion morphology more than they affect genetic structure among populations. The sand scorpion population structure can be described as one with gene flow among populations in the middle of the range and increased isolation along the range boundaries. The major mechanism of genetic exchange is probably sand corridors that periodically connect different sand dune systems. As the age of the North American Sonoran Desert may be less than 10 000 years, it is also possible that isolation has not existed long enough to differentiate the populations to a greater extent.

Candida caseinolytica sp. nov., a new species of yeast occurring in necrotic tissue of Opuntia and Stenocereus species in the southwestern United States and Baja California, Mexico.

We describe Candida caseinolytica, a new yeast species which occurs in rotting tissues of opuntias and other cacti in the North American Sonoran Desert and a few other localities. This small-celled, slowly growing yeast does not ferment any sugar and assimilates a limited number of carbon compounds, including 2- and 5-ketogluconic acids. It exhibits strong extracellular proteolytic activity on casein at pH 6.5, but gelatin is not hydrolyzed or is only weakly hydrolyzed by a few strains. The type strain of C. caseinolytica is strain UCD-FST 83-438.3 (= ATCC 90546 = CBS 7781).

Seasonal changes of the adrenocortical response to stress in birds of the Sonoran Desert.

Many avian species of the North American Sonoran desert, e.g., the black-throated sparrow, Amphispiza bilineata, cactus wren, Campylorhynchus brunneicapillus, and curve-billed thrasher, Toxostoma curvirostre, can potentially breed from March/April to August. It is possible that, at least in summer, intense heat and aridity may have inhibitory effects on breeding by precipitating a stress response. Stress typically results in a rise in secretion of adrenocorticosteroid hormones that then inhibit reproduction by suppressing release of gonadal hormones. However, we found that plasma levels of corticosterone were not higher during summer, compared with winter, even in 1989 when summer temperatures were higher than normal. In June 1990, temperatures were also above normal and soared to the highest level recorded in Arizona (50 degrees C). Plasma levels of corticosterone during June were high in black-throated sparrows, but less so in two other species (Abert's towhee, Pipilo aberti, and Inca dove, Scardafella inca) found in more shady riparian and suburban habitat with constant access to water. The adrenocortical response to stress (as measured by the rate of corticosterone increase following capture) was reduced in the hottest summer months in black-throated sparrows, cactus wrens, and curve-billed thrashers, but less so in Abert's towhee an Inca dove. These data suggest that at least some birds breeding in the open desert with restricted access to water are able to suppress the classical adrenocortical response to stress. The response is then reactivated in winter after breeding has ceased. It is possible that this stress modulation may allow breeding to continue despite severe heat. Analysis of plasma from these species indicated that the apparent modulation of the adrenocortical response to stress was not an artifact of reduced affinity or capacity of corticosterone binding proteins.

Pichia pseudocactophila, a new species of yeast occurring in necrotic tissue of columnar cacti in the North American Sonoran Desert

A description is given of Pichia pseudocactophila, a new species of yeast which is closely related to Pichia cactophila. Pichia pseudocactophila is heterothallic and produces four-spored asci, whereas P. cactophila is homothallic and its asci contain a maximum of two spores. Their morphological and physiological properties and G + C contents of their nuclear deoxyribonucleic acids (DNAs) are similar, but the DNA of P. pseudocactophila shows only 35% homology with the DNA of P. cactophila. In addition, strains of P. pseudocactophila have electrophoretic enzyme patterns for glucose-6-phosphate dehydrogenase, hexokinase-1, hexokinase-2, and phosphoglucomutase that allow them to be distinguished from P. cactophila strains. Lastly, P. pseudocactophila has been found only in rotting tissue of columnar cacti (Pachycereus pringlei and close relatives) in Mexico and southern Arizona, whereas P. cactophila is a host-plant generalist and is distributed worldwide in all cactus species so far investigated.

Pichia mexicana, a New Heterothallic Yeast from Cereoid Cacti in the North American Sonoran Desert

A description is given of a novel member of the yeast genus Pichia that was recovered 13 times in the Sonoran Desert from necrotic tissue of cereoid cacti. Most of the isolates came from organ-pipe cacti. The new yeast occurs in the cactus “rot pockets“ in the haploid condition and is heterothallic. Upon mixing of appropriate mating types, zygotes developed with hat-shaped ascospores. Physiologically, the haploid strains resemble Candida tenuis, but this species has a different habitat and shares only 9.2% of its nuclear deoxyribonucleic acid base sequences with P. mexicana. The sexual state is physiologically similar to P. stipitis and an as yet undescribed cactus-specific species of the genus Clavispora, but their deoxyribonucleic acid sequence complementarity is less than 1% compared with P. mexicana. The base composition of the nuclear deoxyribonucleic acid of P. mexicana ranged from 42.2 to 43.0 mol% guanine plus cytosine (five strains). The type strain of P. mexicana is UCD-FST 76-308A (= ATCC 42175 = CBS 7066) and the complementary mating type is UCD-FST 76-391B ( = ATCC 42176 = CBS 7067).

Pichia opuntiae, a New Heterothallic Species of Yeast Found in Decaying Cladodes of Opuntia inermis and in Necrotic Tissue of Cereoid Cacti

A new heterothallic species of Pichia has been recovered 25 times from widely separated cactus substrates. The organism has been named Pichia opuntiae because the sexually most compatible strains were isolated from Opuntia inermis in Australia. Two varieties are designated based on differences in physiology, habitat, and geographic distribution. P. opuntiae var. opuntiae has a maximum temperature for growth of 30 to 33°C and assimilates citric acid strongly, but assimilation of cellobiose is latent, weak, or negative. P. opuntiae var. thermotolerans grows well at 37°C, but not at 39°C; it assimilates cellobiose strongly but does not assimilate citric acid. Ecologically, P. opuntiae var. opuntiae is associated with Opuntia inermis (tribe Opuntiaeae, subtribe Opuntiinae) in Australia; P. opuntiae var. thermotolerans is associated with species of the cactus tribe Pachycereeae, subtribe Pachycereinae, from various locations in the North American Sonoran Desert. A discussion of the physiological and host-plant shifts for these two varieties and three similar cactophilic yeasts is presented. The base composition of the nuclear deoxyribonucleic acid of P. opuntiae var. opuntiae (average of four strains) is 33.64 ± 0.25 mol% guanine plus cytosine and that of P. opuntiae var. thermotolerans (average of 3 strains) is 33.13 ±0.23 mol% guanine plus cytosine. The type strain of P. opuntiae and of the type variety, P. opuntiae var. opuntiae, is UCD-FS&T 77-40 (= ATCC 36836 = CBS 7010). The type strain of P. opuntiae var. thermotolerans is UCD-FS&T 76-211 (= ATCC 36834 = CBS 7012).

Pichia heedii, a New Species of Yeast Indigenous to Necrotic Cacti in the North American Sonoran Desert

A novel member of the yeast genus Pichia was recovered 67 times during the period 1971 to 1976. We have named this new species Pichia heedii in honor of William B. Heed. Most strains were isolated from the soft-rot of Lophocereus schottii and from Drosophila pachea, which utilizes L. schottii as a host plant. All strains were found in the Sonoran Desert. The species has four-spored asci and is heterothallic. P. heedii has metabolic capabilities similar to those of P. membranaefaciens, but the base composition of its nuclear deoxyribonucleic acid is 10 to 12 mol% lower than that of P. membranaefaciens. P. heedii may be differentiated from other cactus-specific Pichia species by its ability to assimilate D-xylose and from P. membranaefaciens by its cactus habitat, small cell size, and relatively high maximum temperature of growth. The type strain of P. heedii is UCD-FST 76-356 (= ATCC 34936 = CBS 6930).

Origins and Affinities of Vertebrates of the North American Sonoran Desert and the Monte Desert of Northwestern Argentina

Origins and Affinities of Vertebrates of the North American Sonoran Desert and the Monte Desert of Northwestern Argentina