Field experiments and observations were used to define the functional roles and relationships of species in the rocky mid-intertidal community at Pelican Point in the northern Gulf of California. This approach provided resolution of the influences of grazing, predation, competition, and abiotic factors on community structure, and of the direct and indirect effects involved in species interactions. Competition for space, apparently via space pre-emption, between the barnacle Chthamalus anisopoma and encrusting algae of the genus Ralfsia was consistently evident. Grazing by the limpet Collisella strongiana was shown to limit algal abundance and bring about the replacement of Ralfsia by Chthamalus. Chthamalus also excluded Collisella from the rock surface. Predation on Chthamalus by the thaidid gastropod Acanthina angelica increased the abundances of both Ralfsia and Collisella. Some of the temporal variations in community structure observed during this study were clearly linked to variations in the abundances of Acanthina and Collisella and the above interactions. This relatively simple community, existing in what seems a rigorous physical environment, was characterized by strong, highly interdependent biological interactions. Indirect effects were consistently important in species interactions. An intriguing result of this study was the emergence of indirect mutualism between Acanthina and Collisella; this interaction appears to contribute to the persistence and continuing influences of both consumer species, and hence may be of major importance in the organization of this community. The zonation of the barnacles Chthamalus anisopoma and Tetraclita stalactifera at Pelican Point and elsewhere in the Gulf was examined in a test of recent ideas relating ecological and evolutionary patterns in barnacles to morphology and competition for space. Experiments and observations indicated the restriction of Tetraclita to the upper part of the shore by competition from Chthamalus, with Tetraclita able to survive above Chthamalus by virtue of greater tolerance to exposure. These results were in direct opposition to the presumed competitive dominance of large, rapidly-growing, tubiferous barnacles like Tetraclita. Comparisons with results from other shores suggested that numerical dominance goes hand-in-hand with competitive dominance in acorn barnacles. Morphological differences appear to be of minor importance.

Arid and semi-arid ecosystems of the southwestern U.S. are experiencing major changes that have profound impacts for community structure and ecosystem function. First, these ecosystems are experiencing dramatic shifts in vegetation composition as a result of the invasion of non-native species. Second these ecosystems are predicted to undergo substantial shifts in climate regime, which include increases in the variability and frequency of extreme temperature and precipitation events. It is not well understood how these current and predicted changes will affect the physiological performance of different plant types in arid and semi-arid ecosystems. To address the effect of these changes, this dissertation focused on the photosynthetic response of a native and non-native grass species, and dominant shrub species to precipitation across contrasting soil surfaces in southeastern Arizona. The native and non-native grasses were exposed to wet and dry seasonal precipitation and responses to precipitation events ('pulses') were measured over the course of a summer growing season. To gain a mechanistic understanding of these patterns, the biochemical and diffusion limitations to photosynthetic function were measured over the course of a pulse period. Building on this foundation, natural stands of the non-native grass species were exposed to sequences of different sized pulse events. The physiological performance of a dominant shrub species, Larrea tridentata, was measured in order to determine the biochemical and diffusional constraints to photosynthetic function across seasons and contrasting soil surfaces. The results showed that leaf area development of these grass species affects water availability and time lags in photosynthetic response. Initial soil moisture conditions across contrasting soil surfaces influence the magnitude of photosynthetic response in grasses. Large photosynthetic responses of the non-native grass require large and consecutive precipitation pulses. Co-limitation of photosynthesis of Larrea tridentata by diffusion and biochemistry does not illustrate typical trends across seasons and soil surfaces. Overall results demonstrate the importance of determining the mechanisms responsible for observed leaf-level photosynthetic patterns across individual pulse events, seasons, and contrasting soil surfaces. This is especially important for predicting the magnitude of the response of plant communities in arid and semi-arid ecosystems to species invasions and changes in climate.

Awarded second place in Biological Sciences for GPSC Student Showcase

See also: Jojoba: An Annotated Bibliographic Update (1978), in the Additional Links field

From the 1840s to 1950s, interpretations of nature played a central role in the defining and enculturating the Sonoran Desert into the American nation. Written works and physical nature like plants became an archive for cultural interpretations of the region. Scientific descriptions of nature became stories of place as they were consumed. Proxy landscapes like national monuments became the spaces for demonstrating these stories. Throughout the period of this study, a constant give and take between regional nature and global arid lands shaped the national interpretations used to describe regional nature within the American nation-state. This work follows the production and consumption of meaning and the definition of a desert region.

No description available.

Nitrogen (N) cycling involves the gains, losses, and transformations of N from sources such as soil organic matter, crop residues, and fertilizers. These sources are the primary N supplies potentially available to non-leguminous crops. Through the use of a stable N isotope tracer (¹⁵N), transformations among various soil N pools can be studied. We conducted three separate studies using ¹⁵N. Two studies dealt with methodologies of ¹⁵N use and analysis, while the third study investigated mineralization of ¹⁵N labeled crop residues under field conditions. The first study evaluated a new apparatus for applying ¹⁵N by fertigation to subplots under buried drip irrigation. We determined that this method was an effective means of uniformly applying tracers using buried drip irrigation. The second study evaluated a new method for fine-grinding soils based on particle size distribution and variability of organic N and ¹⁵N analyses. Soils of varying texture were rapidly ground to achieve acceptable analytical precision for N and ¹⁵N analysis. The objectives of the third experiment were to: (i) evaluate mineralization of inorganic N from ¹⁵N -labeled crop residues with different C/N ratios and at different loading rates and (ii) evaluate the influence of residue loading rate and type on the percent net mineralization from ¹⁵N-labeled crop residues in a basin irrigated wheat cropping system in Southern Arizona. Mineralization of crop residues in this hyperthermic soil was rapid and was often followed by periods of re-immobilization. Net end-of-season mineralization of residue N was 30-50% for lettuce, and 30-40% for wheat.

Two defatted jojoba seed meals were prepared; one using whole seeds (JM), and the other from which seed coats were removed prior to extraction of the oil (DJM). The protein content of both meals was about 24%. The proteins from JM and DJM were extracted according to their solubility in water, dilute saline, alcohol, and alkali solutions. These extractions produced the albumin, globulin, prolamine and glutelin protein concentrates. The major concentration of proteins in jojoba were the albumin (65%) and globulin (21%) fractions. The amino acid compositions of both JM and DJM were found to be very similar. Methionine was the limiting amino acid in jojoba seed proteins. The protein composition was determined, and the molecular weight was estimated through chromatographic analysis using gel filtration on Sephadex G-100 and ion-exchange chromatography on DEAE-Sephadex and CM-Sephadex. At least 5 separate protein fractions in each of the albumin and globulin concentrates and 8 separate protein fractions in each of the prolamine and glutelin concentrates were found. The molecular weights of jojoba protein concentrates varied from 19,000 to 150,000 for albumins, from 18,000 to 128,800 for globulins, from 11,700 to 141,200 for prolamines, and from 29,500 to 150,000 for glutelins. All protein concentrates showed very good fat absorption and solubility at values of pH below 3.0 and above 4.0. Albumins and globulins showed very good foamability and emulsion properties. The prolamine and glutelin concentrates showed very poor foamability and emulsion properties. The buffering capacity of jojoba protein concentrates was very low.

Land managers have struggled to develop successful control strategies to address buffelgrass invasion in the Sonoran Desert. Two important variables for control strategies are dispersal type and patch expansion rate (i.e. satellite or invasion front). We investigated these variables along a highway invaded within the last 10 years located south of Gila Bend, Arizona, USA. Dispersal type was calculated by documenting the location of each buffelgrass individual along a 16 km stretch of highway and using an average nearest neighbor analysis in ArcMap 10.2.2. Thirty-six patches were monitored for four years along a 56 km stretch of highway 85 by documenting the outlines of each patch. Dispersal type registered as satellite dispersal (i.e. clustered on the Nearest Neighbor test), z-score = -47.2, p < 0.01. Patch expansion exhibited a median doubling time of 0.81 years. The results of the dispersal type analysis represent an opportunity to enhance control strategies, by targeting buffelgrass satellites and theoretically reducing patch expansion exponentially. The patch expansion rates for buffelgrass were faster than found in past research, giving land managers a clearer understanding buffelgrass patch expansion behavior.

Survey of crops of common bean (Phaseolus vulgaris L.) in Sonora, Mexico revealed the presence of two isometric viruses and one flexuous rod virus on the basis of host reaction, particle morphology, serology and physico-chemical properties. The isometric viruses were identified as Bean Southern Mosaic Virus (BSMV) and Cowpea Chlorotic Mottle Virus (CCMV); the flexuous rod virus was identified as Bean Common Mosaic Virus (BCMV). Using bean cultivar differentials, two strains of the potyvirus BCMV were identified, NY-15 and a previously undescribed strain designated YV-1. Host range, serological tests, and RNA electrophoresis indicated that the Sonoran BSMV cultures are similar to BSMV-strain A. Serology and RNA-electrophoresis indicated that the Sonoran CCMV isolates are identical to CCMV-strain A. BSMV and CCMV were always isolated as a mixture from seed lots and from field collected bean tissue. BCMV occurred alone or in mixed infections with BSMV and CCMV. BCMV was seed transmitted with an average efficiency of 58 percent. The BSMV-CCMV mixture was transmitted with an efficiency of 6 percent. BSMV and CCMV were seed transmitted together, but separate transmission of BSMV or CCMV was not detected. Commercial seed lots from two major bean growing regions of Sonora (Hermosillo Coast, Sonora River) were contaminated with the BSMV-CCMV mixture but not with BCMV. The average contamination level was 13 percent. Two common weeds present in Sonoran agricultural areas were found to be potential alternate hosts of CCMV. Both Sisymbrium irio L. and Melilotus indica L. were infected systemically, although the infection in M. indica was latent. Potential losses due to Sonoran bean viruses were measured in greenhouse experiments with the cultivar Pinto 111. BCMV strains caused a 29.4 to 60.1% reduction, whereas BSMV-CCMV mixtures induced a 22.5 to 74.6% yield reduction. A synergism occurred between the BSMV-CCMV mixture and BCMV resulting in more severe symptoms and a yield reduction of 92.7%. Synergistic effects were also observed between BSMV and CCMV. Actual yield reduction resulted from impaired flower production and, consequently, reduced pod production. Significant effects on plant tissue production, flower fertilization and seed quality were not observed. Cowpea chlorotic mottle virus infected mung bean (Vigna radiata (L.) Wilczek) a previously unreported host. Infection of mung bean by BSMV was only possible when CCMV was present in the inoculum. Both BSMV and CCMV could be isolated from symptomatic plants infected with the BSMV-CCMV mixture, however, symptoms on mung bean were unchanged from infection by CCMV alone.