Reconstructing Plant Root Area and Water Uptake Profiles
Kiona Ogle1 and Robert L. Wolpert2,3 and James
F. Reynolds1,3
Duke University Department of Biology1,
Institute of Statistics and Decision Sciences2, and
Nicholas School of the Environment and Earth Sciences3
March 2003
A major challenge in plant ecology is quantifying how roots interact
with the soil to obtain water and nutrients. A stable isotope analysis
of hydrogen and oxygen bound in plant and soil water is one of the best
and leat destructive methods for elucidating plant-soil interactions.
Plant roots obtain water from various depths in the soil and the
isotopic signature of plant stem water reflects the soil water sources.
However, current methods for inferring plant water sources based on
stable isotopes ("simple linear mixing models") are limited. First,
their formulation restricts the number of water sources to a maximum of
three (e.g., surface, intermediate, deep soil water); estimation of
additional sources leads to an identifiability problem. Second, simple
linear mixing models do not appropriately reflect uncertainty, and most
importantly, they cannot be employed to elucidate behavior of the root
system itself such as root activity for water uptake. This study
introduces the RAPID (Root Area Profile and Isotope Deconvolution)
algorithm, a novel and powerful approach for reconstructing plant water
update and root area profiles. The RAPID algorithm overcomes the
nonidentifiability problem by incorporating a biophysical model for root
water uptake into a Bayesian framework such that the biophysics and
prior distributions place biologically realistic constraints on the
profiles. Posterior distributions for the proportions of active root
area and water acquired from each soil layer are obtained via Markoov
chain Monte Carlo. Finally, RAPID is applied to cata collected for a
desert shrub and employed to examine sampling implications.
Keywords:
dD;
d180;
Larrea tridentata;
Bayesian;
MCMC;
RAPID;
creosotebush;
deconvolution;
identifiability;
inverse problem;
plant water relations;
soil texture;
soil water;
water uptake.
The manuscript is available in PostScript (1.97mb) and
PDF (785kb) formats. It is scheduled to appear in
the July 2004 issue of Ecology. Cite as:
@Article{ogle:wolp:reyn:2004,
Author = "Kiona Ogle and Robert L. Wolpert and James F. Reynolds",
Title = "Reconstructing Plant Root Area and Water Uptake Profiles",
Journal = "Ecology",
Year = 2004,
Month = jul,
Volume = 85,
Number = 7,
Pages = "1967--1978",
URL = "http://ftp.stat.duke.edu/pub/WorkingPapers/03-06.html",
}