Using the inter-relationships of stable isotopes in natural abundance as indicators of environmental stress and ecosystem vitality


Principal Investigator:

  Jonathon P. Comstock
Boyce Thompson Institute
Cornell University
Tower Road
Ithaca, NY 14853-1801
Phone: (607) 254-1380
John A. Laurence, Boyce Thompson Institute

Parks:  Sequoia/Kings Canyon National Park, Big Bend National Park, Glacier National Park


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)



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