Abstracts of Papers - Harvard Forest - Harvard University

in relation to insect herbivory and carbon-
allocation.
Carbon allocation and energy budgets are useful
concepts *for predicting and examining the responses
of organisms to environmental resources and
stresses. Ecological processes are potentially
amenable to this approach assuming many organisms
have limited carbon or energy incomes and are
therefore subject to at least some constraints in
the allocation of these incomes. The allocation
of plant resources to defense against herbivores
can be approached by focussing on variation of
secondary chemical production. Recent instrumen-
tation improvements, particularly in gas and high
pressure liquid chromatography, have facilitated
a shift from pre,ence/absence information toward
quantitative measurement of leaf secondary chemi-
cals. Variation in production of such chemicals
within and among plants is examined in regard to
ecological constraints which may influence patterns
of carbon allocation. These include conditions
which may: (a) directly influence chemical pro-
duction, e.g. differing levels of herbivory, (b)
influence plant carbon income, e.g. physical or
chemical limitations on photosynthesis, or (c)
affect both budgetary components, such as leaf
nitrogen content. The implications of these
variations will be examined within a plant-centered
consideration of current models of the "cost" of
plant antiherbivore chemicals.
PITELKA, LOUIS F.* and JEFFREY W. ASHMUN, Bates
College, Lewiston, Maine 04240. -The use of
carbon-14 and other radioisotopes to study
resource allocation in field populations.
C-14 and other radioisotopes have long been employed
to follow the movement of photosynthate or other
metabolites. Experiments using such tracers can be
conducted quite easily in the field on natural
populations. These techniques represent a useful
tool for addressing problems of interest to
population biologists. For instance, C-14 may be
used to reveal spatial or temporal patterns of
resource allocation that are difficult to detect with
biomass or calorific analyses. By labelling plants
at different times in a season or by harvesting
plants at increasing intervals after labelling,
seasonal patterns of resource allocation and
reallocation can be analyzed. Especially in
perennials, the role of stored reserves vs. current
assimilation in supporting new growth or
reproduction may be compared. A more specific use
of tracers is seen in studies of connections between
plants. In clonal plants, C-14 can be used to assess
the degree to which persistent connections remain
active and connected ramets function as single
physiological units. Functional connections may
affect how individual ramets respond to competition
and herbivory and how they accomodate the demands and
risks of reproduction. The use of isotopes other
than C-14 may show that the movement of other
resources differs from that of photosynthate.
Connections can also exist among unrelated plants
(same or different species) as a result of root
grafts or fungal associations. Radioistopes reveal
how these function. This in turn should increase
our understanding of the ecologically important
costs and benefits of such connections.
PRIMACK, RICHARD B. * and CHARLES K. LEVY, Biology
Department, Boston University, Boston, MA 02215.
Radionuclide labeling of seeds to assess fitness
in plants.
Ecological Section 37
One of the primaty problems in estimating individual
fitness in plant populations has been the difficulty
of following seeds from one generation to the next.
Individual adult plants can be characterized for
traits which may be related to fitness, but we have
little ability to identify individuals which actually
leave more surviving offspring into the next genera-
tion. In this project, we are exploring techniques
for tagging seeds with selected combinations of
gamma-emitting radionuclides (60Co, 137Cs, 54Mn,
etc.). These labels are not harmful to either the
plants or the investigators due to the extreme sensi-
tivity of the crystal scintillation equipment. Our
preliminary studies with radishes, beans, Impatiens,
Bidens, and Polygonum have shown that these labels
can be injected into the stem of the adult plant and
are rapidly taken up by the developing seeds. In the
lab, the labels are present in the cotyledons of the
young seedlings. Following dispersal and germinatiorn
the maternal parent of the seedling can potentially
be identified in the field without killing the seed-
ling by sampling a small piece of the cotyledon.
This technique will potentially allow us to determine
the heritability of life history characters under
field conditions, changes in genotype frequency with
time, the dispersal and distribution of seedling
families within the population, and the longevity of
seeds in the soil. The fate of introduced or novel
genotypes in a population can be studied experimental-
ly by adding labeled seeds to a population. We are
determining whether this technique can be used to
label pollen of different plants to determine the
male parent of a seed.
SCHAAL, BARBARA A. Department of Biology, Washington
University, St. Louis MO 63130.
Variation of DNA seguences in plant populations.
Genetic variation among individuals is essential for
the evolutionary process, yet absolute levels of
variation are known for very few species. The development
of nucleic acid technologies, such as restriction
fragment analyses and hybridization to cloned
probes, has allowed the analysis of variation in
specific DNA sequences. Analysis of the DNA sequences
which code for ribosomal RNA (rDNA) show variation
among individuals for DNA nucleotide sequence, variation
in the length of the rDNA sequence, and variation
for total gene copy number. Variability
viduals within species is predominantly
among indiin
the nontranscribed
spacer region of rDNA. Variation among
taxa occurs in the evolutionarily conservative 17 S
and 26 S coding regions. These molecular data are
providing precise measures of variation within and
among plant species.
STRAIN, B.R.*l, J.D. GOESCHL2, Y. FARES?-2 C.E.
MAGNUSON2, C.E. NELSON3, C.H. JAEGER1, and E.G.
BILPUCH3. lDepartment of Botany, Duke University,
Durham, NC 27706, 2Biosystems Research Division,
Texas A&M University, College Station, TX 77843,
and 3Department of Physics, Duke University,
Durham, NC 27706. - Use of carbon-li for
continuous non-destructive monitoring of photosynthate
movement.
A system has been developed at the Duke University
Phytotron which allows the study of carbon flow
dynamics in plants without destructive sampling of
tissues. The system utilizes the short half life
(20.3 min) carbon-ll isotope continuously supplied to
the plants as 11CO2. The isotope is produced continuously
with a dedicated 4 MeV Van de Graaff
accelerator in the nearby ( < 100) m) physics department..
As a tracer, hGc has several advantages. lIt