Southern Sonoran Desert Research Articles

Functional metabolic diversity of the bacterial community in undisturbed resource island soils in the southern Sonoran Desert

AbstractResource islands (RIs), a natural revegetation phenomenon in arid lands, consist of a single nurse tree or few large shrubs and numerous understory nurslings. We analyzed 18 individual mesquite RIs for plant diversity and richness, area, trunk diameter (reflecting age), soil characteristics, physiological functionality of microbial populations, and interactions among these variables. Nursing Capacity reflected the availability of habitat and was positively correlated to plant richness, but not to plant diversity. No relationship between plant diversity and bacterial diversity was found. The structure of the bacterial communities of RIs differed from the bacterial communities of bare areas, which showed greater richness and diversity compared with those of RIs. The Nursing Capacity of the RIs was related to plant richness and accompanied by variations in soil properties. A high correlation was found by substrate utilization analysis between metabolic parameters of bacteria and diversity and richness of plants in the RIs. RI bacterial communities were more metabolically active and could degrade different carbon sources than bare area communities. RI bacterial communities contained species with greater capability to metabolize diverse carbon substrates in soil with more organic matter. Bacteria from low, medium, and high plant diversity areas were cultured and found to belong to four bacterial families. This study demonstrates that numerous parameters interact, but not every parameter significantly affected bacterial activity in the RI.

Floristic diversity and notes on the vegetation of Bahía Magdalena area, Baja California Sur, México

The Bahía Magdalena region of the Baja California Peninsula is floristically part of the southern Sonoran Desert. It has several particular geographical features, of particular importance the influence of the cold California Current. We present a floristic study of the higher plants on a land area covering 5,158 km2. The flora has 506 taxa: five ferns, two gymnosperms, 438 magnoliopsida (dicotyledons), and 60 liliopsida (monocotyledons), representing 85 families and 280 genera. The plant families with major species diversity are: Asteraceae, Poaceae, Euphorbiaceae, and Fabaceae. The flora was categorized into nine life forms: perennial herbs (127) and annuals (143) represent 54 % of all species. The flora occupies eight plant communities, which are described; the most extensive community is the fog sarcocaulescent scrubland. From a biological perspective, Margarita and Magdalena islands are important areas to preserve as core zones in a future management plan because they support 19 endemic species. Mangroves and sea grass marshes are important areas serving as nursery habitats for marine fauna. Mexican environmental authorities are considering establishing a reserve to protect biodiversity in the region.

Biogeography and conservation of aquatic fauna in spring-fed tropical canyons of the southern Sonoran Desert, Mexico

In arid regions, spring-fed habitats are frequently the only year-round source of surface water and are essential habitats for aquatic organisms and primary water sources for terrestrial animals and human settlements. While these habitats have been relatively well-studied in some regions, those of the southern Sonoran Desert have received little attention. In 2008 and 2009, we documented the biodiversity of aquatic animals at 19 sites across three arid mountain ranges in Sonora, Mexico, characterized macrohabitat types, examined seasonal variation in aquatic invertebrate communities, and explored the effects of an exotic fish (tilapia) on native communities. We documented >220 aquatic animal species, including several new species and range extensions for others. Macrohabitat type (oasis, tinaja, riffle, and seep) was more important than geographic location in structuring aquatic invertebrate communities at the scale of our study area (~9,000 km2). We found little evidence of predictable seasonal variation in invertebrate communities, despite dramatic hurricane-induced flooding. Aquatic vertebrates were not diverse across the study region (4 amphibian species and 2 species each of fishes and reptiles), but were often locally abundant. Presence of non-native tilapia at one site was associated with reduced abundances of native leopard frogs and reduced richness and density of native aquatic invertebrates. The most pressing aquatic habitat conservation concerns in the region, as in other deserts, are groundwater withdrawal, unmanaged recreational visitation, and the introduction of exotic species. Spring-fed habitats around the world have been called hotspots of freshwater biodiversity, and those of the Sonoran Desert are no exception.

Restoration of eroded soil in the Sonoran Desert with native leguminous trees using plant growth-promoting microorganisms and limited amounts of compost and water

Restoration of highly eroded desert land was attempted in the southern Sonoran Desert that had lost its natural capacity for self-revegetation. In six field experiments, the fields were planted with three native leguminous trees: mesquite amargo Prosopis articulata, and yellow and blue palo verde Parkinsonia microphylla and Parkinsonia florida. Restoration included inoculation with two of plant growth-promoting bacteria (PGPB; Azospirillum brasilense and Bacillus pumilus), native arbuscular mycorrhizal (AM) fungi, and small quantities of compost. Irrigation was applied, when necessary, to reach a rainy year (300mm) of the area. The plots were maintained for 61 months. Survival of the trees was marginally affected by all supplements after 30 months, in the range of 60-90%. This variation depended on the plant species, where all young trees were established after 3 months. Plant density was a crucial variable and, in general, low plant density enhanced survival. High planting density was detrimental. Survival significantly declined in trees 61 months after planting. No general response of the trees to plant growth-promoting microorganisms and compost was found. Mesquite amargo and yellow palo verde responded well (height, number of branches, and diameter of the main stem) to inoculation with PGPB, AM fungi, and compost supplementation after three months of application. Fewer positive effects were recorded after 30 months. Blue palo verde did not respond to most treatments and had the lowest survival. Specific plant growth parameters were affected to varying degrees to inoculations or amendments, primarily depending on the tree species. Some combinations of tree/inoculant/amendment resulted in small negative effects or no response when measured after extended periods of time. Using native leguminous trees, this study demonstrated that restoration of severely eroded desert lands was possible.

Reproductive behavior of Homalonychus selenopoides (Araneae: Homalonychidae)

Abstract Homalonychus selenopoides Marx 1891 is endemic to the coastal plains of the Sonoran Desert in the state of Sonora, Mexico and the southwestern United States. Although the species was described more than a century ago, nothing is known about its behavior. We collected spiders in the southern Sonoran Desert to study their reproductive behavior, which we recorded with an infrared camera, mainly at night. Sperm induction was of an indirect type; males wove a triangular sperm web about 2 cm2 near the ground. Females and males prepared threads of silk and sand. Courtship behavior was intermediate between levels I and II, and the copulation position was a modification of type III, where the male tied the female's legs with silk before mating. Sexual cannibalism may occur during mating. Females began to spin their egg sac at ∼11 days after mating and completed it in ∼15 h, including ovipositioning. The outer layer of the egg sac contained sand, and the sac was surrounded by a garniture of cords of silk a...

Endophytic bacteria of Mammillaria fraileana, an endemic rock-colonizing cactus of the southern Sonoran Desert

The small cactus Mammillaria fraileana is a pioneer rock-colonizing plant harboring endophytic bacteria with the potential for nitrogen fixation and rock weathering (phosphate solubilization and rock degradation). In seeds, only a combination of culture-independent methods, such as fluorescence in situ hybridization, scanning electron microscopy, and fluorescence vital staining, detected significant amounts of non-culturable, but living, endophytic bacteria distributed underneath the membrane covering the embryo, in the undifferentiated tissue of the embryo, and in the vascular tissue. Large populations of culturable endophytic bacteria were detected in stems and roots of wild plants colonizing rocks in the southern Sonoran Desert, but not in seeds. Among 14 endophytic bacterial isolates found in roots, four isolates were identified by full sequencing of their 16S rRNA gene. In vitro tests indicated that Azotobacter vinelandii M2Per is a potent nitrogen fixer. Solubilization of inorganic phosphate was exhibited by Pseudomonas putida M5TSA, Enterobacter sakazakii M2PFe, and Bacillus megaterium M1PCa, while A. vinelandii M2Per, P. putida M5TSA, and B. megaterium M1PCa weathered rock by reducing the size of rock particles, probably by changing the pH of the liquid media. Cultivated seedlings of M. fraileana, derived from disinfected seeds and inoculated with endophytic bacteria, showed re-colonization 105 days after inoculation. Their densities decreased from the root toward the stem and apical zones. Functional traits in planta of culturable and non-culturable endophytic bacteria in seeds remain unknown.

Rock-colonizing plants: abundance of the endemic cactus Mammillaria fraileana related to rock type in the southern Sonoran Desert

Establishment, colonization, and permanence of plants affect biogenic and physical processes leading to development of soil. Rockiness, temperature, and humidity are accepted explanations to the influence and the presence of rock-dwelling plants, but the relationship between mineral and chemical composition of rocks with plant abundance is unknown in some regions. This study documents plant species growing on rocks, their capacity as rock colonizers measured by the Importance Index, and the relationships between the chemical composition of rocks and the abundance of the dominant plant. The community is composed of eight species and is dominated by the small cactus Mammillaria fraileana. Sites with low abundance of this species contain volcanic breccias, high amounts Ca, Fe, Mg, Ti, Al, and Mn as part of moderately weatherable minerals, such as plagioclase and pyroxene. Sites with higher abundance contain rhyodacite, rhyolite, and andesite rocks rich in more weatherable minerals, such as volcanic glass and minerals containing Si, K, and Na. K and Na were present in equal proportions only at the site with more plants. Since Na is toxic for most plants, an experiment was carried out to assess its effect on the survival of M. fraileana seedlings. Decreased survival occurred as the concentration of Na increased. Even in the treatment without Na, survival decreased slightly. In summary, presence and abundance of plants is related to the type of bedrock, their weathering characteristics, and proportion of elements. The interactions among elements, rather than the isolated effect of specific elements, could be the most reliable explanation for local variations in the abundance and dominance of Mammillaria fraileana in rocky habitat in the southern Sonoran Desert.

Leaf litter decomposition in a southern Sonoran Desert ecosystem, northwestern Mexico: Effects of habitat and litter quality

Leaf litter decomposition of dominant woody perennial species in the three most common habitats of the southern Sonoran Desert was studied using the litter-bag method. Our objective was to assess the influence of litter quality on decomposition rates in three contrasting desert environments. The hypotheses were: (1) decomposition rates within the same litter type are faster in more mesic habitats, (2) decomposition rates are lower in higher lignin content or lower nutrient quality substrates, and (3) species-rich substrates enhance decomposition rates. For all litter types and habitats, a rapid loss of mass occurred during the summer rains at the start of the experiment, but total loss within the same litter type differed significantly among habitats. Decay rates were not higher in the more mesic habitat, but in the dry plains where solar irradiance and termite activity were highest. While termite activity was less important in the arroyos and absent in the hillsides habitats, proliferation of fungal mycelium in these sites was much higher than in the plains, suggesting that biotic and abiotic factors act both independently of litter richness. Lignin content seems to be an important factor controlling the loss of litter, because decay rates were inversely related to litter initial lignin content in all three habitats. Leaf litter diversity did not enhance rates of decomposition. The leaf litter mixture had k-values similar to the most recalcitrant monospecific litter in all three habitats, indicating a neutral or even antagonistic role of species-specific compounds in decomposition rates.

Diurnal and seasonal patterns of gas exchange and carbon gain contribution of leaves and stems of Justicia californica in the Sonoran Desert

Several studies have explored the contribution of stem photosynthesis to the total carbon gain of desert plants, but they have been limited to narrow desert systems in extra tropical regions. To have a better understanding of the role of photosynthetic stems in carbon fixation for tropical deserts, it is important to extend our studies into areas with different ecological conditions. This study compared the photosynthetic capacity, and seasonal variation of gas exchange of leaves and stems of Justicia californica, in the southern Sonoran Desert. It also compared their relative contribution to carbon gain, and their photosynthetic response to seasonal changes in xylem tension and vapor pressure deficit (VPD). Leaves and stems showed the same photosynthetic capacity and similar diurnal patterns of A and g s during the rainy season. VPD and water potential influenced the diurnal and seasonal patterns of A and g s, and their influence was different for leaves and stems. Stems were less sensitive to water stress than leaves. The relative contribution of stems and leaves to whole canopy carbon gain, depended mainly on the variation of their photosynthetic areas. On a year-round basis, leaves contributed 77% and stems 23% of the carbon gain. However, stems were the only source of carbon gain for about 7 months.

Restoration of giant cardon cacti in barren desert soil amended with common compost and inoculated with Azospirillum brasilense

Barren desert soil that otherwise could not support perennial plant growth was amended with six levels of common agricultural compost. Seedlings of the giant cardon cactus, one of the primary plant species responsible for soil stabilization in the southern Sonoran Desert, were inoculated with the plant-growth-promoting bacterium Azospirillum brasilense Cd, planted, and grown for 18 months under nursery conditions typical for slow- growth cacti. Control plants were grown without compost amendment, without inoculation (negative control), or in fertile, rare "resource island" soil preferred by cardon seedlings (positive control). During the prolonged growth period, the decisive factor in seedling growth in barren soil was the addition of small amounts of common compost; 6 to 25% of the growth substrate volume gave the best growth response and, to a lesser extent, so did inoculation with A. brasilense Cd. Although the bacteria significantly affects plant growth when amended with "resource island" soil and added to barren soil, its effect on plant growth was far smaller than when compost alone was added. Compost added to barren soil significantly increased the dry weight parameters of the plant to almost similar levels obtained by the "resource island" soil; however, the compost amend- ment supports a more voluminous and greener plant with elevated pigment levels. This study shows that barren soil supplemented with compost can replace the rare "resource island" soil for cardon nurseries destined to abate soil erosion in the desert.

Carbon mineralization in the southern Sonoran Desert

Abstract We measured carbon mineralization in four different desert habitats (Arroyos, Hillsides, Canopies-Plains and Open-Plains) and the separate effect of litter addition from annual and perennial plants on soil microbial respiration using two laboratory soil incubation experiments. The differences in total aboveground phytomass among habitats correlates with soil nutrient content, soil particulate organic matter (POM) and consequently, C mineralization. The Arroyos habitat with the highest perennial plant phytomass and litter production, had the highest soil nutrient content, soil POM and C mineralization. Litter from annual plants had twice the P concentration than litter from the perennials, but only half the N concentration. Soil microbial respiration was higher with annual plant litter than with perennial plant litter in the Hillsides and Canopies-Plains, suggesting that microbial activity in both habitats was improved by litter with a higher C quality. In contrast, in the poorest habitat, the Open-Plains, the better response to the addition of perennial plant litter suggests that microbial activity may have been constrained by N input.

Epicuticular hydrocarbon composition of gallito ( Pedilanthus macrocarpus) from Baja California and Sonora, Mexico

Gallito is a dominant euphorbiaceous desert shrub native to the southern Sonoran Desert and along the coastal plains into northern Sinaloa as well as in the plains of southern Baja California. It has a waxy layer coating its succulent leafless stems. Objective of our study was to elucidate the variation in the hydrocarbon composition of gallito for its possible use as an agricultural non-food industrial product. Air-dried gallito ( Pedilanthus macrocarpus Bent.) stems harvested in Baja California and Sonora (Mexico) were analysed using GC-MS techniques for their saturated and unsaturated hydrocarbons (alkanes and alkenes). Hydrocarbon composition ranged from C21 to C35.The largest components were tritriacontane C33 with 36.9–51.6% for the peninsular and 59.8–65.4% for the mainland, as well as hentriacontane C31 with 41.1–56.2% for the peninsular and 7.5–9.6% for the mainland Sonoran populations. Peaks C31, C33, C29 and C34 were most obvious between the peninsular and mainland populations. Plant to plant variations within a given population were observed, as were stem to stem variations within a single plant.

The ants of the southern Sonoran desert: community structure and the role of trees

In contrast to other North American deserts, the southern Sonoran desert is dominated by trees that provide shaded microhabitats necessary for the establishment and survival of several plant species. Near the southern limit of the Sonoran desert in Sonora, Mexico, we evaluated the role that tree microhabitats may play in structuring ant communities. We recorded 39 species and 21 genera of ants from a 9.7-ha area. Total species richness was estimated to be between 47 and 49 species, a much greater species richness than that reported for other North American arid-zone habitats. Although species richness did not differ between open ground and tree-shaded microhabitats, species composition did. Opportunistic species, Camponotus species, Pheidole sciophila and P. titanis were more common near trees, whereas Pheidole sp. A and granivorous species were more active in open areas. The imperilment of trees in the Sonoran desert due to commercial cutting and the spread of buffelgrass Pennisetum ciliare may alter the existing composition of ant communities.

Modern surface pollen from three transects across the Southern Sonoran desert margin, Northwestern Mexico

Surface pollen samples collected along three transects that cross the southern margin of the Sonoran Desert east of the Gulf of California reflect regional vegetation gradients but also show strong local variability, notably within the southern desert. Chenopodiaceae‐Amaranthaceae (Cheno‐Am) and Gramineae pollen dominate in tropical deciduous forest; Pinus and Quercus in temperate‐climate vegetation at high elevations; and Gramineae and High‐Spine Compositae in the central Sonoran Desert (>29° N). The ERA group (composed largely of Euphorbiaceae, Rutaceae, Anacardiaceae), Gramineae, Cheno‐Am, and High‐Spine Compositae pollen inter‐vary but dominate as a group in the southern desert; Cheno‐Am here may signal irrigated agriculture. Coastal sites differ from the above, with Cheno‐Am pollen strongly dominant in saline conditions.

High‐Temperature Responses of North American Cacti

High—temperature tolerances of 14 species of North American cacti were investigated. A reduction in the proportion of chlorenchyma cells taking up a vital stain (neutral red) and reduced nocturnal acid accumulation were used as indicators of high—temperature damage. All species tolerated relatively high tissue temperatures, the mean maximum tolerance being 64°C, with an absolute maximum of 69° for two species of Ferocactus. Such tissue tolerances to high temperature may be unsurpassed in vascular plants. Morphological features can affect tissue temperatures. Specifically, thin—stemmed species such as the cylindropuntias attain lower maximum temperatures under identical microclimatic conditions than do more massive species; they also tend to be less tolerant of high—temperature stress. Stem diameter changes of three species of columnar ceroid cacti along a Sonoran Desert latitudinal transect were previously attributed to adaptation to progressively colder temperatures northward. Such changes can also be interpreted as a morphological adaptation to high temperatures, particularly in the southern Sonoran Desert. Interspecific differences in high—temperature tolerance may account for distributional differences among other species, e.g., the coastal—sage—inhabiting Ferocactus viridescens was less tolerant of high temperature than were the three Ferocactus species that inhabit desert regions. Acclimation of high—temperature tolerances in response to increasing day/night air temperatures was observed in all 14 species, especially at higher growth temperatures. From 40° day/30° night to 50°/40°, the tolerable tissue temperatures increased an average of 6°. Half—times for the acclimation shifts were 1—3 d. Although cacti attain extremely high tissue temperatures in desert habitats, tolerance of high temperatures and pronounced acclimation potential allow them to occur in some of the hottest habitats in North America.

Populations of Two Sonoran Desert Plants, and Deductions as to Factors Limiting Their Northward Extension

Recently discovered populations of ocotillo Fouquieria splendens, and smoke tree, Dalea spinosa in extreme southern Nevada were studied. Sparse distribution, reduced vigor and size all indicate that these populations have reached their northern geographic and ecologic limits. It is suggested that nothern dispersal and establishment of smoke tree is checked in extreme southern Nevada by lowered and more prolonged winter temperatures. Populations of ocotillo are disjunct and may be relict. Populations of ocotillo, Fouquieria splendens, Engelm and smoke tree, Dalea spinosa Gray have recently been located along the Colo- rado River in extreme southern Nevada. Neither species has been defi- nitely reported prior to this study as occurring in Nevada although Tidestrom (1925) and Muller (1940) suggest the possibility of oco- tillos being present in the most southern part of the state. Both species are found in the southern part of the Mohave Desert and are wide- spread in the more southern Sonoran Desert. The most northern ex- tension of the Sonoran Desert in California is in the vicinity of Needles, California where both species are found in suitable habitats. The population in Nevada represent a northern extension of the known range of both species into the northern Mohave Desert. No- menclature used in this paper follows Munz (1959). DESCRIPTION OF THE STUDY AREA. The area studied was the flood plain of the Colorado River on the Nevada side extending from south of Davis Dam to the California-Nevada boundary. The flood plain along this portion of the river is several miles wide, usually about three miles in width on the Nevada side, and varies from about 700 to 500 feet in elevation. The soil is primarily alluvial sand but small areas elevated above the main flood plain may be sandy loam. Several vegetation types are represented, the most common and widespread being creosote bush (Larrea divaricata) and burro-weed (Franseria dumosa). Thick stands of quail bush (Atriplex lenti- formis) are located near the river. Riparian populations of such species