Panicum sonorum in Sonoran Desert agriculture

Evidence of prehistoric domestication of plants native to southwestern United States is rare. Presented here are archaeological, historic and contemporary ethnobotanical data suggesting that a native grain, Panicum sonorum,was harvested, sown and culturally selected in the Sonoran Desert Region. This indicator crop, other new clarifications of indigenous crops, and water management practices all point to the distinctiveness of the region’s agricultural complex. As redefined here, the Sonoran Desert Agricultural Region is diverse in both native crops and in cultivars of introduced crops originating elsewhere.     

Sesquiterpene lactones and species relationships among the shrubby Ambrosia taxa

The sesquiterpene lactone chemistry, chromosome numbers and morphology of selected Sonoran Desert Ambrosia taxa are reported. The sesquiterpene lactone distribution correlates with morphologically defined species groups.     

ECOTYPIC VARIATION IN LARREA DIVARICATA

Data on rate of germination, rate of growth, and temperature and moisture responses of croosotebush (Larrea divaricata Cav.) seedlings from the Sonoran Desert and Chihuahuan Desert suggest that the species as it occurs in North America is comprised of at least two major genetic population systems or ecotypes. Compared to the Chihuahuan Desert ecotype, that of the Sonoran Desert is characterized by a taller, more erect and more open growth form, more slender and less incurved leaflets, slower germination rate, slower initial growth rate of the seedling, less tolerance for low temperature, and greater tolerance for low moisture.     

Tracing Genetic Lineages of Captive Desert Tortoises in Arizona

Abstract: We genotyped 180 captive desert tortoises (Gopherus agassizii) from Kingman (n = 45), Phoenix (n = 113), and Tucson (n = 22), Arizona, USA, to determine if the genetic lineage of captives is associated with that of wild tortoises in the local area (Sonoran Desert). We tested all samples for 16 short tandem repeats and sequenced 1,109 base pairs of mitochondrial DNA (mtDNA). To determine genetic origin, we performed assignment tests against a reference database of 997 desert tortoise samples collected throughout the Mojave and Sonoran Deserts. We found that >40% of our Arizona captive samples were genetically of Mojave Desert or hybrid origin, with the percentage of individuals exhibiting the Mojave genotype increasing as the sample locations approached the California, USA, border. In Phoenix, 11.5% were Sonoran–Mojave crosses, and 8.8% were hybrids between desert tortoise and Texas tortoise (G. berlandieri). Our findings present many potential implications for wild tortoises in the Sonoran Desert of Arizona. Escaped or released captive tortoises with Mojave or hybrid genotypes have the potential to affect the genetic composition of Sonoran wild populations. Genotyping captive desert tortoises could be used to inform the adoption process, and thereby provide additional protection to native desert-tortoise populations in Arizona.     

Habitat Use by Sonoran Desert Tortoises

ABSTRACT The distribution of desert tortoises (Gopherus agassizii) spans a wide range of biotic and abiotic conditions in the southwestern United States and northwestern Mexico, with physical and behavioral differences distinguishing tortoises inhabiting the Mojave Desert from those inhabiting the Sonoran Desert. Relative to tortoise populations in the Mojave Desert, populations in the Sonoran Desert have not been well-studied. To assess how habitat use of desert tortoises in the Sonoran Desert was influenced by topography, vegetation, geomorphology, and soil, we surveyed 40 randomly located 3-ha sites for presence of adult tortoises within a site-occupancy framework. We modeled both occupancy and detection probability as a function of environmental features, and compared those results with a logistic regression model that assumed detection probability was equal to 1. Results from both approaches agreed, suggesting that habitat selection of tortoises in the Sonoran Desert was influenced primarily by topographic and geomorphologic features rather than by vegetation. Specifically, tortoises were more likely to occupy sites that were steep (we detected tortoises on 29% of sites with mean slope <5° and 92% of sites with mean slope >15°) and predominantly east-facing (53% of sites with <5% of site facing E and 92% of sites with >20% facing E), and less likely to occupy north-facing slopes (100% of sites with <10% of site facing N and 14% of sites with >60% facing N). Our results contrast with patterns of habitat use in the Mojave Desert where tortoises primarily occupy valley bottoms. Habitat use of tortoises in Sonoran and Mojave Desert populations differ considerably, contributing to the mounting body of evidence suggesting that these geographically distinct populations may represent separate species.     

PHOTOPERIODIC ADAPTATION IN DESERT POPULATIONS OF XANTHIUM STRUMARIUM

Reproductive adaptation to photoperiod is diverse among desert populations of Xanthium. Chihuahuan Desert populations require dark periods of 9.5–10.5 hr for reproduction, and Sonoran Desert populations require 9–10.5 hr. Many Chihuahuan populations from western Texas two weeks from sowing need only 10 cycles of 11-hr nights to produce 100% flowering, but Sonoran populations from western Mexico four weeks from sowing need 18 cycles or more. Some Sonoran plants produce buds only at a cooler temperature program, 24–15 C, but Chihuahuan plants produce them more readily under the warmer program, 30–24 C. Chihuahuan plants that were germinated under 11-hr nights and four different temperature programs were induced to flower in each condition. Differences in photoperiod and ripeness-to-flower (maturity) responses were also demonstrated under natural day lengths in central Texas. Although desert populations occurring at approximately the same latitude in either the Chihuahuan or Sonoran Desert are exposed to similar day lengths, each population may be adapted to different photoperiod cues that maximize its utilization of the local growing conditions.     

Ecophysiological studies of Sonoran Desert plants

Summary The gas exchange of two Sonoran Desert plants was measured near optimum soil water conditions occurring in the summer and winter. Photosynthesis and stomatal conductance rates of a drought-deciduous shrub, Ambrosia deltoidea, and an evergreen non-riparian tree, Olneya tesota, are mainly affected by plant water potential. During such periods the diurnal gas exchange patterns are characterized by maximum rates of photosynthesis and stomatal conductance occurring early in the day, which decrease progressively thereafter. The effect of plant water potential on gas exchange is both direct and indirect. Decreasing plant water potential indirectly affects ¹⁴CO₂ assimilation by closure of stomata, and the effect is similar in both species. However, the direct effects of decreasing plant water potential are dissimilar in the two species. Plants of the shrub species have a higher potential maximum photosynthesis, but are more sensitive to plant water stress than are plants of the tree species. Both species respond to favorable growth conditions in the summer and winter, and have the potential for rapid carbon input into the Sonoran Desert ecosystem.This research was supported by National Science Foundation Grant BMS 74-02671-A04, through the U.S./I.B.P. Desert Biome     

A phytogeographical characterization of the vine flora of the Sonoran and Chihuahuan deserts

Aim This study presents a phytogeographical characterization of the vine flora of two lower North American desert regions as a biogeographical framework for further ecological inquiry into desert vines. Location The phytogeography of the vine flora of the Sonoran and Chihuahuan Deserts was c haracterized based on 263 known species. Methods Checklists of the vines of each desert were developed. Represented genera were then grouped into 10 phytogeographical elements based on worldwide distribution patterns. To compare the floristic composition of the desert floras, an index of species similarity was calculated. Results About a third more species of vines occur in the Sonoran Desert than in the Chihuahuan Desert. Based on the analysis, cosmopolitan genera are the only group more numerous in absolute terms in the Chihuahuan Desert than in the Sonoran Desert. Tropical elements are represented in about the same proportion in each desert as the number of species, however, nearly twice as many pantropical and neotropical genera are represented in the Sonoran Desert as in the Chihuahuan Desert. Proportionately, more genera of temperate elements occur in the Chihuahuan Desert than in the Sonoran desert, although the absolute number of genera is slightly higher in the latter. Main conclusions As these deserts are relatively recent ecological formations and as vines evolved in forest ecosystems, the composition of the desert vine floras is the result of the interaction between historical vegetation types, their constituent taxa and climatic and geological history. The main differences in the vining floras of the present‐day Sonoran and Chihuahuan Deserts appear to be the result of greater historical influence in the Sonoran Desert of (1) tropical vegetation types and (2) the emergence of the Gulf of California. The Chihuahuan Desert vine flora seems to be the result of (1) a more pronounced historical temperate vegetation, (2) the lack of an important isolating event, such as the creation of the Baja California peninsula, and (3) a cooler climate with shorter growing seasons.     

COMPONENTS OF FLOWERING TIME VARIATION IN A DESERT ANNUAL

How much of the variation seen in life histories is consistent with adaptive hypotheses, and how much requires other kinds of explanation? Differences in flowering time between Sonoran (earlier flowering) and Chihuahuan Desert (later flowering) populations of the desert annual Eriogonum abertianum Torr. (Polygonaceae) are significant, repeatable between greenhouse experiments, and persist into a second greenhouse generation. These apparent genetic differences are consistent with a hypothesis of local adaptation: field demographic studies (Fox, 1989b) show that many fewer Sonoran than Chihuahuan Desert plants survive to the summer rainy season, suggesting selection for earlier flowering in the Sonoran Desert. Within natural populations there is considerable phenological complexity: time of first flowering varies by up to six months, and individuals may have zero, one, or several reproductive episodes. Greenhouse sib analyses revealed only marginal among-family genetic variation for flowering size. The resemblance between parents and offspring for size and time of flowering varied with growth conditions, suggesting that this marginal variation among families may be at least partly due to factors other than additive genetic variance. On the other hand, moisture limitation significantly delayed the onset of flowering in two independent experiments. Variation in moisture availability in both time and space is characteristic of desert environments. The phenological complexity in natural populations may thus be generated by random variation in moisture availability, possibly in conjunction with variation in germination date and plant size. The results call into question the claim that drought generally induces flowering in desert annuals.     

Is the Sonoran Desert losing its cool?

Freezing temperatures strongly influence vegetation in the hottest desert of North America, in part determining both its overall boundary and distributions of plant species within. To evaluate recent variability of freezing temperatures in this context, minimum temperature data from weather stations in the Sonoran Desert are examined. Data show widespread warming trends in winter and spring, decreased frequency of freezing temperatures, lengthening of the freeze‐free season, and increased minimum temperatures per winter year. Local land use and multidecadal modes of the global climate system such as the Pacific decadal oscillation and the Atlantic multidecadal oscillation do not appear to be principal drivers of this warming. Minimum temperature variability in the Sonoran Desert does, however, correspond to global temperature variability attributed to human‐dominated global warming. With warming expected to continue at faster rates throughout the 21st century, potential ecological responses may include contraction of the overall boundary of the Sonoran Desert in the south‐east and expansion northward, eastward, and upward in elevation, as well as changes to distributions of plant species within and other characteristics of Sonoran Desert ecosystems. Potential trajectories of vegetation change in the Sonoran Desert region may be affected or made more difficult to predict by uncertain changes in warm season precipitation variability and fire. Opportunities now exist to investigate ecosystem response to regional climate disturbance, as well as to anticipate and plan for continued warming in the Sonoran Desert region.     

Altertoxins with potent anti-HIV activity from Alternaria tenuissima QUE1Se,a fungal endophyte of Quercus emoryi

Screening of a small library of natural product extracts derived from endophytic fungi of the Sonoran desert plants in a cell-based anti-HIV assay involving T-cells infected with the HIV-1 virus identified the EtOAc extract of a fermentation broth of Alternaria tenuissima QUE1Se inhabiting the stem tissue of Quercus emoryi as a promising candidate for further investigation. Bioactivity-guided fractionation of this extract led to the isolation and identification of two new metabolites, altertoxins V (1) and VI (2) together with the known compounds, altertoxins I (3), II (4), and III (5). The structures of 1 and 2 were determined by detailed spectroscopic analysis and those of 3–5 were established by comparison with reported data. When tested in our cell-based assay at concentrations insignificantly toxic to T-cells, altertoxins V (1), I (3), II (4), and III (5) completely inhibited replication of the HIV-1 virus at concentrations of 0.50, 2.20, 0.30, and 1.50 μM, respectively. Our findings suggest that the epoxyperylene structural scaffold in altertoxins may be manipulated to produce potent anti-HIV therapeutics.     

What Drives the Conversion of Native Rangeland to Buffelgrass (<Emphasis Type="Italic">Pennisetum ciliare</Emphasis>) Pasture in Mexico’s Sonoran Desert?: The Social Dimensions of a Biological Invasion

The introduction of invasive exotic plants has many social dimensions. Although a diverse literature identifies some of the social drivers of exotic plant introduction and subsequent invasion, relatively little attention has been given to the motives of individuals involved. This research focuses on the extensive conversion of native rangeland to exotic buffelgrass (Pennisetum ciliare) pasture by ranchers in Mexico’s Sonoran Desert using data gathered through systematic interviews and ordinary least squares regression modeling to demonstrate how a few social variables determine the extent of buffelgrass introductions. Results show that land allocation to pasture is determined chiefly by ranch size, with significant roles also played by rotational grazing, buffelgrass seed harvest, and exposure to government research. Results are contextualized and explored in depth, illustrating how the extent of rangeland-to-pasture conversion in this part of the Sonoran Desert is determined by direct and indirect social factors. The study also highlights implications for buffelgrass invasion.     

Truffles in the sky: The impact of stochastic and deterministic drivers on Rhizopogon communities of the Madrean sky island archipelago

Temperate forests across the globe are migrating as a result of global warming, but little is known about how changes in climate and host geographic distributions will affect the obligate symbionts of these forests. Analysis of past events can provide insight into how these symbionts have responded to previous climatic changes and inform predictions for contemporary and future climate change events. The Madrean Sky Islands Archipelago (MSIA) comprises mountain “islands” whose Pine-Oak forests appear in stark contrast to the surrounding “sea” of Sonoran Desert vegetation. The archipelago formed due to a post-Pleistocene warming climate that resulted in the expansion of the Sonoran Desert and migration of forests to fragmented, higher elevation areas. Rhizopogon (Boletales) consists of obligate ectomycorrhizal (EcM) symbionts that form truffle sporocarps and associate exclusively with Pinaceae. As such, the MSIA-Rhizopogon system represents a natural experiment of how fungal symbionts responded to climatic change and host migration. Rhizopogon was sampled from nine islands at two sites (one Pinus site and one Pseudotsuga site) per island, and diversity was characterized using the ITS rRNA gene determined from both sporocarps and bioassay-based EcM root tips derived from soil samples collected at each site. We described the biodiversity of Rhizopogon within and among sky islands of the MSIA, and tested whether symbiont species richness and community structure were determined by host association, island identity, geographic distance, or some interaction among these factors. Twenty-five OTUs at 99% similarity in the genus Rhizopogon were identified across nine sky islands with a range of 5–15 OTUs per island. While differential host association with Pinus and Pseudotsuga was a significant driver of community composition, our results supported an even stronger island effect. Furthermore, Rhizopogon communities associated with Pinus forest sites were characterized by random phylogenetic structures across sky islands and are not structured by geographic distance. Our results supported a strong isolation effect that involved historical habitat fragmentation of sky islands in response to past climate changes, and that both host association and stochastic processes, e.g., ecological drift, played a role in shaping Rhizopogon communities of the MSIA.     

The importance of Olneya tesota as a nurse plant in the Sonoran Desert

Abstract. The function of Olneya tesota (ironwood) as a nurse plant and habitat modifier species in the Sonoran Desert was evaluated at five study sites (using 75 250-m² sample plots) from Bahia Kino, Sonora to Organ Pipe Cactus National Monument, Arizona. Beneath the canopy of O. tesota trees 75 perennial plant species were found. A principal component ordination of the plots created three groups: southern, perturbed and protected sites. A strong triple association of columnar cacti, big shrubs with berry type fruits and O. tesota was detected. The relationships of Lophocereus schottii and Peniocereus striatus with O. tesota were studied in more detail. Significant differences in soil surface temperatures and stem temperatures of P. striatus were detected beneath the shade of O. tesota trees compared with soils and plants in open spaces. Olneya tesota must be considered as a habitat modifier species with ecological and conservational importance to the plant communities in the Sonoran Desert.     

The natural history of Jojoba (Simmondsia chinensis) and its cultural aspects

Simmondsia chinensis is unique in many ways. Endemic to the Sonoran Desert of Mexico and the United States, its broad, persistent, heavy leaves are unlike any of its associates. Its large edible seeds contain about 50% oil, which is directly used as a cooking oil and as a hair oil. The oil has excellent qualities for many industrial and medicinal uses. Chemically it is a liquid wax and by hydrogenation is easily converted to a hard white wax. Jojoba’s singular characteristics as a desert shrub, however, present many problems facing its development as a cultivated plant.     

Seedling Responses to Water Pulses in Shrubs with Contrasting Histories of Grassland Encroachment

Woody plant encroachment into grasslands has occurred worldwide, but it is unclear why some tree and shrub species have been markedly more successful than others. For example, Prosopis velutina has proliferated in many grasslands of the Sonoran Desert in North America over the past century, while other shrub species with similar growth form and life history, such as Acacia greggii, have not. We conducted a glasshouse experiment to assess whether differences in early seedling development could help explain why one species and not the other came to dominate many Sonoran Desert grasslands. We established eight watering treatments mimicking a range of natural precipitation patterns and harvested seedlings 16 or 17 days after germination. A. greggii had nearly 7 times more seed mass than P. velutina, but P. velutina emerged earlier (by 3.0±0.3 d) and grew faster (by 8.7±0.5 mg d⁻¹). Shoot mass at harvest was higher in A. greggii (99±6 mg seedling⁻¹) than in P. velutina (74±2 mg seedling⁻¹), but there was no significant difference in root mass (54±3 and 49±2 mg seedling⁻¹, respectively). Taproot elongation was differentially sensitive to water supply: under the highest initial watering pulse, taproots were 52±19 mm longer in P. velutina than in A. greggii. Enhanced taproot elongation under favorable rainfall conditions could give nascent P. velutina seedlings growth and survivorship advantages by helping reduce competition with grasses and maintain contact with soil water during drought. Conversely, A. greggii''s greater investment in mass per seed appeared to provide little return in early seedling growth. We suggest that such differences in recruitment traits and their sensitivities to environmental conditions may help explain ecological differences between species that are highly similar as adults and help identify pivotal drivers of shrub encroachment into grasslands.     

Cell Cycle Duration in the Root Meristem of Sonoran Desert Cactaceae as Estimated by Cell-flow and Rate-of-cell-production Methods

Slow rates of cactus growth in the Sonoran Desert and high productivityof some Cactaceae under cultivation suggest that relativelylow growth rates are not the consequence of a long cell divisioncycle but of short optimal periods for growth and adverse environmentalfactors. To verify this hypothesis, the duration of the celldivision cycle (T)in the root apical meristem of seedlings ofthree sympatric species from the Sonoran Desert [Ferocactuspeninsulae(F. A. C. Weber) Britton & Rose ‘Townsendianus’(Britton & Rose) N. P. Taylor, stat. nov.,Stenocereus gummosus(Engelm.)Gibson & Horak andPachycereus pringlei(S. Watson) Britton& Rose] was estimated with the rate-of-cell-production (RCP)and the cell-flow (colchicine) methods. Both methods were appliedduring the steady-state growth phase, which was relatively shortin the first two species because of the determinate patternof root growth. The RCP method permitted estimation ofTin eachroot individually. Durations of the cell division cycle wereinversely proportional to the rate of root growth (r²rangedfrom 0.42 to 0.88,P<0.05).T,determined by the cell-flow method,ranged from 14.4 to 19.3 h in these species and was within thesame range asTdetermined by the RCP method. The averageTdeterminedby the RCP method was 67 to 75% of that determined by the cell-flowmethod. Results obtained with both methods are compared andanalysed. The proposed hypothesis appears to be correct, indicatingthat these species can be more productive under cultivationthan in the wild due to the relatively short duration of thecell division cycle. Adaptive features of these findings arealso considered.Copyright 1998 Annals of Botany Company Cactaceae, cell division cycle, root growth, root meristem, Sonoran Desert     

A Revision of the genus Wislizenia (Capparidaceae) based on population studies

Morphological and cytological studies of mass collections from the southwestern United States and Baja California, and morphological studies on herbarium specimens from these areas and northern Mexico have been used to solve a taxonomic problem within the genusWislizenia. Canonical analysis of morphological data from mass collections separates three geographic groups from: California, Baja California, and states east of California. A similar analysis of herbarium specimens collected throughout the range ofWislizenia refracta confirms the reality of these groups, for which the status of subspecies is proposed: 1) subsp.californica from the California central valley, 2) subsp.palmeri from Baja California and the Sonoran coast, and 3 ) subsp.refracta from states east of California. This taxonomic treatment differs from any of the varied previous ones. Chromosome numbers for six of the mass collections were found to ben = 20, in agreement with other reports.     

Rhizobial Ecology of the Woody Legume Mesquite (Prosopis glandulosa) in the Sonoran Desert

Soil samples were collected from the surface (0 to 0.6 m) and phreatic (3.9 to 4.5 m) root systems of a Prosopis glandulosa woodland in the Sonoran Desert of southern California. P. glandulosa seedlings were inoculated with these soils, and rhizobia were isolated from nodules. The phreatic soil, characterized by constant moisture and temperature but low nutrient availability, favored slow-growing (SG) isolates as nodule occupants (85%). SG isolates from the surface and phreatic soil were distinct based on differences in colony morphology. Isolates from the surface soil, characterized by high nutrient availability and widely fluctuating water content and temperature, were equally represented by fast-growing and SG rhizobia. Most SG isolates (83%) had nodule relative efficiencies of <0.80, whereas 54% of the fast-growing isolates had relative efficiency values of >0.80.     

Accumulation of Amino Acids in Rhizobium sp. Strain WR1001 in Response to Sodium Chloride Salinity

Rhizobium sp. strain WR1001, isolated from the Sonoran Desert by Eskew and Ting, was found to be able to grow in defined medium containing NaCl up to 500 mM, a concentration approaching that of sea water. Therefore, it is a valuable strain for studying the biochemical basis of salt tolerance. Intracellular free glutamate was found to increase rapidly in response to osmotic stress by NaCl. It accounted for 88% of the amino acid pool when the bacterium was grown in 500 mM NaCl. The role of glutamate dehydrogenase in glutamate biosynthesis was examined in several Rhizobium strains. Both NADH- and NADPH-dependent glutamate dehydrogenase activities in various Rhizobium strains were observed. The range of activity differed considerably depending on the particular strain. KCl (500 mM) did not stimulate glutamate dehydrogenase activity, as reported in a number of bacterial strains by Measures. The low activity of glutamate dehydrogenase in Rhizobium sp. strain WR1001 apparently cannot fulfill a biosynthetic function of glutamate formation in response to medium NaCl concentrations.