Intraspecific Variation in Nickel Hyperaccumulation in Populations of Psychotria grandis From Serpentine and Non-Serpentine Soils of Puerto Rico
Metal hyperaccumulators are plants that store heavy metals or metalloids in their leaves, often to concentrations much higher than in the soil. Most hyperaccumulators are obligate, occurring only on metalliferous soils, but a few species are facultative, occurring on both metalliferous and nonmetalliferous soils. Psychotria grandis (Rubiaceae) ranges from Central America through the Caribbean on many soil types, and is known to hyperaccumulate nickel on serpentine (ultramafic) soils in several locations. In this study, three Puerto Rican populations of P. grandis, one from serpentine soil, one from non-serpentine soil, and one from a geologically heterogeneous area were sampled to determine differences in foliar Ni concentration between populations, and between trees within populations. Approximately ten trees were examined at each site, with leaves from multiple branches collected from each tree. Nickel concentration in leaves was measured by atomic absorption spectrometry. There were significant differences in mean Ni concentration among the three sites. Unsurprisingly, the non-serpentine site was lowest (4,000 μg/g). The heterogeneous site had a mean Ni concentration of 2,224 μg/g, so it also exceeds the 1000 μg/g criterion for hyperaccumulation. There were significant differences in Ni concentration among trees within each of the three sites, with especially wide variation in the geologically heterogeneous site. A greenhouse propagation protocol was developed to allow rooting of semi-woody stem cuttings of P. grandis, and future studies will compare accumulation capacity of the three populations under uniform conditions.
1 Dept of Biology, Furman University, Greenville, SC; 2 Departamento de Biologia, Universidad de Puerto Rico, Mayaguez, PR
112 • Andrew E. Rosselot, Blake W. Nelson, Andrew J. Jajack, Jay A. Yoder
Common Treatments Applied to Honey Bee Colonies and Their Implications for Rise of Lethal Chalkbrood Disease
Chalkbrood is a fungal disease afflicting bee larvae; larvae turning into mummified, dried-out shells that result from a takeover by the fungus (Ascosphaeraapis) from inside out characterize the disease. Beekeepers have observed a trend within their colonies of increased chalkbrood symptoms being present while they are using treatments that promote bee health, carbohydrate feeding supplements, antibiotics, and miticides. This was an invitro fungal growth study, and we made it applicable to a field setting by using crushed bee larvae in agar growth media as a mock infection, strong chalkbrood-inducing temperature conditions (implementing cold- and heat-shocks that incite the disease), and treatment concentrations that beekeepers use, to explore whether colony treatments promote growth and establishment, leading to infection by A. apis. Growth of A. apis increased steadily from 25oC - 35oC, without a burst in growth, even in the presence, or absence of a cold- or heat-shock cue. Fumagillin, oxytetracycline, and tylosin antibiotics, seven different brands of high fructose corn syrup, and sucrose syrup, alone and in combination, did not accentuate or slow down fungal growth compared to water-treated controls. Formic acid and oxalic acid miticides severely inhibited growth of A. apis. We have no evidence that colony treatments trigger chalkbrood. The need for treatment is a sign of stress already present within the colony, and this stress allows for chalkbrood to perpetuate, which puts a priority on keeping bees healthy.
113 • Hayden Summers, Kel Arlinghaus, Timothy Griffith
Will Geographic Range Shifts Impact Rates of Photosynthesis? a Study of Extended Day Lengths on Leaf Photosynthesis of a Commercial Corn Variety
As global temperatures continue to increase, the geographic range of commercially grown crops will shift towards higher latitudes. With a shifted geographic range comes longer day lengths that could potentialy alter vital vegetative developmental processes. More specifically, little is known about how differing day length cues will effect common crop varieties leaf development and resulting photosynthetic rates. Truckers favorite white corn variety was grown under three different day lengths corresponding to a southern portion, northern portion, and edge of the range. As day length was increased, the rates of photosynthesis also increased- a 46% increase in photosynthesis was observed from the southern day length to the range-edge day length. However, under longer day lengths, there was also a slight increase in rates of transpiration. These changes in rates of photosynthesis are associated with changes in leaf architecture. As stomatal indexes (number of stomata compared to epidermal cells) increased there was a significant increase in rates of photosynthesis, as well as higher rates of transpiration. This experiment is consistant with our previously conducted studies on other native species that show that increases in day length increase stomatal densities. Our results raise the possibility that as crop ranges shift north in response to global climate change, alterations in rates of photosynthesis and water loss may impact sustainable plant growth and yield.
