Meet the Fellows
Current Fellows
Anna Boeck
Factors that Influence the Growth of Heliotropium tenellum in Central Texas Cedar Glades
Cedar glades within Juniperus woodlands are well documented in eastern North America but they are also present in other regions of North America and throughout central Texas, particularly in the Edwards Plateau Region. These cedar glades are dominated by herbaceous vegetation and have low plant cover, relative to the surrounding Juniperus woodlands. We examined the gas exchange rates and xylem water potential of a summer annual, Heliotropium tenellum (white heliotrope), found within these glades. There were significant differences in photosynthetic rates at different light levels (One-way ANOVA; Tukey-Kramer HSD; P < 0.0001). There was no significant difference between stomatal conductance and the light levels tested (One-way ANOVA; P = 0.1796). There were significant differences in transpiration rates at different light levels (One-way ANOVA; Tukey-Kramer HSD; P = 0.0011). There were significant differences in xylem water potential at different times of the day (One-way ANOVA; Tukey-Kramer HSD; P < 0.001). Most gas exchange rate factors measured were high and suggest that H. tenellum is a sun plant. These measurements might explain why this plant occurs in the full sun, open cedar glades of central Texas and not below or within the surrounding Juniperus woodlands. The relatively low xylem water potential measured at mid-day suggests that H. tenellum is not under considerable water stress. This might help explain why H. tenellum is able to survive and thrive during the hottest, driest portion of the season.
Joshua Conner
Volatilization of Camphor from Juniperus ashei
Volatile organic compounds (VOC’s) emitted from the leaves of Ashe juniper (Juniperus ashei) were collected using a dynamic headspace system in order to establish an adequate sampling time, to further investigate the potential role of the VOC’s as allelopathic compounds. Sampling times of 0, 5, 10, 20, 30, and 40 minutes were conducted using 20-30 mg of HayeSep® Q80/100 adsorbent. The samples were eluded with 150 µl of hexane and analyzed using gas chromatography/ mass spectrometry. Retention times were established using commercially purchased standards. The peak intensities of the VOC’s for both replicates generally increased as the sampling time increased, with the exception of the 20 min. sample in replicate 1. It was determined that 30 minutes was an acceptable sampling time, and the adsorbing capacity of the glass traps would not be exceeded.
Jewell Cozort
Effects of grazing and soil nutrients on the competition between Prosopis glandulosa and Buchloe dactyloides
Prosopis glandulosa var. glandulosa Torr. (honey mesquite) is a woody plant found in the American southwest which has increased in density over the last 150 years. Buchloe dactyloides (Nutt.) Engelm. (buffalo grass) is a key element of upland short-grass prairies and can be found growing in the same areas as P. glandulosa. Both species have been shown to increase in density on heavily grazed areas. Previous studies have shown that B. dactyloides competes more successfully than P. glandulosa for soil resources. A greenhouse experiment was conducted to study the effects of simulated grazing of B. dactyloides and soil nutrients, on the competition between P. glandulosa and B. dactyloides. Two levels of simulated grazing were tested - no clipping and clipping at 10 cm above the soil surface. Two levels of soil nutrients were tested – a native soil low in soil nutrients and native soil amended with Hoagland nutrient mixture. Each species was grown alone or in mixture with each other. Buchloe dactyloides dry mass was reduced when grown with P. glandulosa, in low soil nutrients, or when clipped. Nutrient additions had a greater effect when B. dactyloides was not clipped. Prosopis glandulosa growth was greatest when grown with clipped B. dactyloides, which was not significantly different than growth alone. In addition, growth with clipped B. dactyloides was significantly greater than growth with unclipped B. dactyloides. Soil nutrients had the greatest effect on P. glandulosa when grown alone and a smaller effect when grown with clipped B. dactyloides. Evaluating the competitive abilities of B. dactyloides and P. glandulosa during simulated grazing and altered soil nutrients allowed a better understanding of factors which may contribute to changes in grassland communities in the southwestern United States.
Rachel Grotte
Role of Abiotic Factors on Foraging Activity Patterns of Western Harvester Ant Genus Pogonomyrmex
Effects of abiotic factors on activity patterns of Pogonomyrmex spp. were observed in the Gila Wilderness Area of New Mexico. Previous studies indicated that certain abiotic factors affect time of foraging activity, clearing of vegetation from mound, and mound structure for Pogonomyrmex. Data was collected at Lake Roberts in the Gila Wilderness of New Mexico over a 24 hour period from 10 am to 10 am on 6/2/09-6/3/09 at 4 different mounds. Air, soil surface, and at sub-surface temperature (10cm below) were measured every hour. Also measured every hour were relative humidity, light intensity, and ant activity. Average mound population size was ~1672. The Pearson product-moment correlation coefficients between all pairs of abiotic factors were significant (P < 0.0001). All temperature measurements were positively correlated with each other. All temperature measurements were inversely related to relative humidity and positively related to light intensity. Relative humidity and light intensity were inversely related. Forty-percent of the variation in ant activity could be explained by a six factor equation including the quadratic transformation of surface temperature, air temperature, relative humidity, and the quadratic transformation of light intensity. Fourteen percent of the variation in ant activity was explained by air temperature and an additional 16% by the addition of the quadratic transformation of surface temperature. It is shown that Pogonomyrmex spp. utilizes a bimodal activity pattern for foraging activity with highest average activity at ~10 am and ~4 pm where average temperature was 28°C.
Jennifer Guerrero
In vivo analysis of the Tomato Golden Mosaic virus AL2 promoter
Tomato Golden Mosaic virus (TGMV) is a member of the Geminiviridae family of single stranded (ss) DNA viruses plant viruses. TGMV belongs to the genus Begomovirus with two genome components, named A and B. DNA component A directs expression of the AL2 and AL3 genes, while DNA B directs expression of genes required for the movement of the virus in plants. AL2 directs coat protein expression and AL3 directs expression of a replication enhancing protein. Promoters for transcripts initiating at nucleotides 1935 and 1629 regulate expression of AL2 and AL3, as determined using promoter::ß-D-glucuronidase (GUS) fusions in transient leaf assays. We have generated transgenic N.benthamiana plants harboring the AL1935 and AL1629 promoter::GUS fusions to determine tissue specificity of each promoter. Plants will be analyzed using histochemical staining to determine whether each promoter is expressed in mesophyll cells and/or phloem cells.
Nicolas Morales
The Effects of Soil Salinity and Soil Moisture on the Growth of Agalinis calycina
Agalinis calycina, a hemiparasitic species in the snapdragon family, was believed to be extinct until rediscovery in a salt marsh downstream of the Diamond Y Spring in Pecos County, Texas. This salt marsh has a unique mineral composition that may influence the growth of this species and its potential competitors. Twenty-six of the forty North American species of Agalinis are considered imperiled or critically imperiled in at least one state in which they occur. The US Fish and Wildlife Service listed Agalinis calycina as a species of concern with a global and state (Texas) rank of 1. A greenhouse study is being conducted to determine the effects on soil salinity and soil moisture on the growth of Agalinis calycina. Several hundred seeds have been treated with 5 mM gibberellic acid to stimulate germination, and placed on moistened filter paper in Petri dishes in the dark. Past studies showed a 20% germination rate with gibberellic acid treatment. After germination, seedlings will be transplanted to pots containing native soil. Three levels of salinity (0, 1, 10 g/liter) will be created using the ions found in the Diamond Y Spring water. There will be three water treatments – field capacity, 50% field capacity, and 33% field capacity. Aboveground and belowground dry mass will be measured to determine the effects of soil salinity and soil moisture on the growth of A. calycin. These results should lead to a better understanding of factors which may be important for the management and preservation of this threatened species.
Former Fellows
Marcus Guerrero
Pinus ponderosa Age and Growth Rate in a Dendrochronology Field Study in the Coronado National Forest, AZ
Dendrochronology is a useful technique of scientific dating based on the evaluation of tree-ring growth patterns. We hypothesize that the age of Pinus ponderosa can be estimated based on circumference. Furthermore, we hypothesize that historical annual temperature and precipitation will affect the width of P. ponderosa tree rings. A field survey was conducted in the Coronado National Forest, Arizona on June 12, 2009 to measure the circumference and age of P. ponderosa. A total of 21 samples were collected ranging from 31.4 to 148 cm in circumference. Pinus ponderosa tree cores were taken and circumference measured at 1.37 m using an increment borer. After core extraction, cores were sanded and number of rings (age) determined. The trees ranged in age from 24 years (46.5 cm in circumference) – 85 years (141.5 cm in circumference). Six cores over the range measured were selected to measure the width of each ring using a micrometer under a dissecting microscope. The resulting width of each ring was compared to historical temperature and precipitation data which was collected from three weather stations located less than 16 km from the sampled P. ponderosa. If a correlation is found between the rate of growth of P. ponderosa and annual precipitation and/or temperature data in Southeast Arizona, we can predict the rate of new growth based on recent precipitation and/or temperature data. Establishing relationships between P. ponderosa tree ring growth and climate data may provide a useful tool in evaluating past climates in the southwestern United States.
Matthew Mueller
Survey of Benthic Macro-Invertebrates in Cibolo Creek Nature Preserve
A biomonitoring assessment of the taxa diversity of freshwater macro-invertebrates in Cibolo Creek inside the Cibolo Creek Nature Preserve, in Boerne, Texas (Kendall County) was performed in mid-May 2009. Enumerations of the macro-invertebrate community were used to determine the health of the creek downstream of the Boerne Municipal Water Treatment Plant discharge area. Samples were collected from the sediment with a cylinder 10 cm in diameter driven approximately 7.6 cm into the sediment. At sampling locations, samples were taken along the streambed perpendicular to the water flow with samples being taken along both stream bank and within the center of the stream. Samples where then transported to the laboratory where they were preserved in 70% ethyl alcohol. Samples were hand sorted under a dissection microscope at 25x magnification. Organisms were identified to family and where possible genus. Samples sorted thus far have a high concentration of mollusks, as well as a species of mayfly, an unidentified oligochete, a number of unidentified arthropods, and two genera of gastropods. While sampling is incomplete, biomonitoring is an important approach to the measurement of the lands watershed health. It gives insight into not only the chemical makeup of a water source but an idea as to how the ecosystem is reacting and adapting to any chemical changes in the water.
Tina Shippy
Potential Allelopathic Effects of Juniperus ashei on Germination and Growth of Bouteloua curtipendula
A laboratory experiment was conducted to determine the potential allelopathic effects of Juniperus ashei (Ashe juniper) on the germination and growth of the C4 grass, Bouteloua curtipendula (side-oats grama), through the growing season. Previous studies showed a reduction in the germination of B. curtipendula in the presence of J. ashei leaves. The "sandwhich agar method"’ was used to test the effects of J. ashei leaves on the germination and growth of B. curtipendula. Additionally, the effects of two concentrations of camphor were evaluated (0.00625 g/ml and 0.01250 g/ml). Previous studies indicate camphor is the most abundant potentially allelopathic compound found in J. ashei leaves. In May there were no significant differences between germination, leaf length, and root length of B. curtipendula between the control, 0.0062 g/ml camphor, 0.0125 g/ml camphor, and J. ashei leaves (P > 0.05). Leaves of J. ashei collected in July significantly reduced germination, leaf length, and root length of B. curtipendula when compared to the control (P < 0.05). Data confirms previous studies indicating an inhibitory affect of J. ashei on B. curtipendula germination. Additionally, results indicate a negative influence of J. ashei leaves on leaf and root growth of B. curtipendula, which has not been previously documented. This suggests that the inhibitory effects may change throughout the growing season. Identifying the potential inhibitory effects of J. ashei on B. curtipendula and other native grasses can give a better understanding of the interactions of species and how these interactions may shape plant communities.