Project Summary:
We propose to relate
the pattern of occurrence of natural abundance stable isotope ratios
for five key elements (C, N, O, S, and H) in tree rings, roots, and
leaves of plants to the environmental conditions under which the plants
grow. These isotopes are naturally occurring, non-radioactive tracers.
Plant material will be sampled across gradients of nitrogen deposition,
ozone exposure, and elevation in three national parks. The technique
is based on the fact that natural materials are often made of atoms
which have different numbers of neutrons but the same number of protons.
This gives them almost identical chemical properties, but slightly different
masses. Variation in isotopic composition originates in biogeochemical
processes discriminating against the heavy isotopes, and can occur at
the ecosystem level resulting in naturally labeled resource pools upon
which different species may specialize, or on a small scale within organisms
due to individual physiology. Analysis of stable isotope composition
of plants can therefore yield information about resource capture, physiological
specialization, and altered metabolism under stress. Use of stable isotopes
of single elements to analyze discrete questions in water relations
(D and O), photosynthetic physiology (C) and nutrient capture (N and
S) are now becoming commonplace. Sometimes isotopes of two or (rarely)
three elements have been analyzed simultaneously to unravel the mechanisms
of ecosystem function. However, we believe that in addition to the established
patterns of isotope discrimination associated with single environmental
resources, isotope "fingerprints" resulting from multivariate analyses
of D/H, 13C/12C, 15N/14N,
34S/32S, and 18O/16O will
be associated with the complex variation of multiple resource gradients
and their interactions. Including these interactions in a single multivariate
analysis will generate hitherto unrealized resolution of both ecotypes
and spatial/temporal distribution of unique stress syndromes. Furthermore,
isotope abundance ratios laid down during growth are retained in old
biomass fractions, and by looking at materials that may be dated, such
as tree rings, historical patterns of resource utilization and physiological
behavior can be determined. By examining the isotope ratios in tree
rings, we should, for example, be able to detect changes in nitrogen
deposition over time, and relate those changes not only to the record
of altered nutrient relationships, but the indirect effects on water
and carbon metabolism as well.
Final Report: Using
the Inter-Relationships of Stable Isotopes in Natural Abundance as Indicators
of Environmental Stress and Ecosystem Vitality (Comstock)
Final Report: Steady-state
isotopic fractionation in branched pathways using plant uptake of NO3
as an example (Comstock)
2000 PRIMENet Presentation: Using
the inter-relationships of stable isotopes in natural abundance as indicators
of environmental stress and ecosystem vitality (Jonathan Comstock
and John Laurence)
Back to PRIMENet Research Projects
