Vol 31, Part I - forums.sou.edu • Index page - Southern Oregon ...

ABSTRACTS – Contributed Posters
177 Petrologic and Geochemical Evolution of Lower
Oligocene to Lower Miocene Volcanic Rocks of the Western
Cascades Volcanic Series, Southwest Oregon, JAD A
D’ALLURA (Department of Chemistry, Physics, Materials,
and Engineering, Southern Oregon University, 1250 Siskiyou
Boulevard, Ashland, OR 97520; rockit@dishmail.net).
Western Cascade volcanism in Southwest Oregon
exhibits distinct trends from oldest (early Oligocene; ~33Ma)
to youngest (early Miocene; ~23Ma) lavas and related
volcaniclastic rocks. Petrologic and geochemical trends
support complex histories yet are typical of eruptions through
continental crust associated with subduction. Long residence
time within magma chambers is reflected in the abundance
of phenocrysts (normally 20-35%), complex zoning of
minerals, and reaction rims. These features commonly are
coupled with textures indicating periods of rapid growth and
local devolitization during ascent. Assimilation fabrics and
strikingly different generations of plagioclase are evident in
many rocks.
Geochemical relations are consistent with evolving
calc-alkaline trends dominated by fractional crystallization.
Increasing silica and alkali content as well as increasing
Rb, Cs, Ba, Pb and Th and decreasing Ti, Zr, Nb, Ta, Cr,
Ni, and Sc are consistent with maturation of succeeding
magmas. Trends, from tholeiitic to calc-alkaline rocks,
follow decreasingly curved paths on AFM diagrams rather
than the typical straight-line “Cascade” trend suggesting
eruption through thickening and evolving crust. In general,
the geochemistry of clasts in breccias units mirror trends in
the lavas. Older tuffaceous rocks are dacitic while younger
tuffs are rhyolitic showing variable but increasing alkali
content. Atypical variations in trace elements that defy a
simple fractionation model are due to assimilation of crustal
material or complexities within magma chambers. Lower
Miocene rocks contain a higher Mg, Cr, and Ni content
and slightly fewer phenocrysts, suggesting crustal thinning,
opening of conduits caused by faulting, or rapid rise of
magma.
ECOLOGY, ORGANISMAL BIOLOGY,
and ENVIRONMENTAL SCIENCES
178 Characterizing a Local Model System for Studies
of Ecological Stoichiometry of Trophic Interactions,
CAROLYN F WEBER, JEFFREY P HILL, and
AMOEBA (Department of Biological Sciences, Idaho State
University, 921 South 8th Avenue, Stop 8007, Pocatello, ID
83209-8007; webecaro@isu.edu).
The elemental stoichiometry of biomass and available
resources play an important role in controlling how organisms
interact with each other and their habitats, but the relationship
between these two stoichiometries is poorly understood
in terrestrial ecosystems. A first step in understanding this
100
relationship is studying the physiological homeostasis of
organisms in isolation and in mixed communities across a
range of environmentally relevant resource stoichiometries.
Mesocosm studies conducted in a controlled laboratory
setting can potentially provide such insights, but require
well-characterized and small-scale model systems. We
are currently using mesocosms to characterize feedingbehaviors
of organisms associated with soil mosses that
are abundant in local sagebrush steppe. Physical separation
and antibiotic applications have isolated a soil nematode
species, and several bacterial species that can serve as
their food source. Based on DNA sequencing of ribosomal
RNA genes, the nematode and bacteria isolated thus far
are most closely related to Panagrolaimus detritophagus
and four undescribed members of the genus Pseudomonas,
respectively. Efforts to obtain axenic cultures from two
species of moss protonema have revealed the presence of
a persistent fungal associate; coarse manipulations of light
and organic carbon availability influenced the balance of
moss-fungus relationships indicating that varied ecological
stoichiometries exert significant control over the type of
interactions (e.g. mutualistic, parasitic) between these two
organisms. Identifying the nutritional requirements and
elemental stoichiometries of individual organisms will
provide the foundation for understanding of how nutrient
availability and trophic flux of key elements contribute to
species composition in local soil moss communities.
179 Defining Microalgae Growth Conditions That
Eliminate Competitive Exclusion and Maximize Lipid
Production for the Purpose of Biofuel Production,
HERBERT A POLLARD IV*, WILLIAM HEWITT*,
and LUKE SUGDEN* (Department of Biology, Boise
State University, 1910 University Drive, Boise, ID 83725;
bioinfo@boisestate.edu).
It has been long recognized by population ecologists
that greater species diversity allows for greater biomass
productions. Currently, DOE projections of algal based
biofuels rest on calculation of only single species culture.
Our work investigates the use of mixed species microalgae
cultures to enhance potential for biomass production vs.
single species cultures. We assessed microbial conditions
that permit two microalgae species to grow without
competitive exclusion taking place. Our approach is unique
in that we will use uniculture growth constants on a limiting
growth substrate gradient to determine the concentrations
in which mixed-culture growth can be maintained. Our
work utilizes Monod’s model of growth rate on a single
growth controlling substrate to define the conditions of
mixed culture growth, but also investigate whether the
stage of high lipid production between two microalgae
can be induced at the same range of nitrogen limitation.
If this condition is met, it will allow for the comparison
of net lipid yields of stable mixed cultures vs. single