The dual C and O isotope – gas exchange model: A concept review for
understanding plant responses to the environment and its application in
tree rings
Abstract
The combined study of C and O isotopes in plant organic matter has
emerged as a powerful tool for understanding plant functional response
to environmental change. The approach relies on established
relationships between leaf gas exchange and isotopic fractionation to
derive a series of model scenarios that can be used to draw inferences
about changes in photosynthetic assimi-lation and stomatal conductance
driven by changes in environmental parameters (CO2, water availability,
air humidity, temperature, nutrients). We review the mechanistic basis
for model and research to date, and discuss where isotopic observations
don’t match our current under-standing of plant physiological response
to environment. We demonstrate that 1) the model has been applied
successfully in many, but not all studies, and 2), while originally
conceived for leaf isotopes, the model has been applied extensively to
tree ring isotopes in the context of tree phys-iology and
dendrochronology. Where isotopic observations deviate from
physiologically plau-sible conclusions, this mismatch between
gas-exchange and isotope response provides valuable insights on
underlying physiological processes. Overall, we found that isotope
responses can be grouped into situations of increasing resource
limitation versus higher resource availability. Thus, the dual isotope
model helps to interpret plant responses to a multitude of environmental
factors.