Robust Estimation of Absorbing Root Surface Distributions From Xylem Water Isotope Compositions With an Inverse Plant Hydraulic Model

Frontiers in Forests and Global Change, vol. 4

Abstract

The vertical distribution of absorbing roots is one of the most influential plant traits determining plant strategy to access below ground resources. Yet little is known of natural variability in root distribution since collecting field data is challenging and labor-intensive. Studying stable water isotope compositions in plants could offer a cost-effective and practical solution to estimate the absorbing root surfaces distribution. However, such an approach requires developing realistic inverse modeling techniques that enable robust estimation of rooting distributions and associated uncertainty from xylem water isotopic composition observations. This study introduces an inverse modeling method that supports the assessment of the root allocation parameter (β) that defines the exponential vertical decay of a plants’ absorbing root surfaces distribution with soil depth. The method requires measurements obtained from xylem and soil water isotope composition, soil water potentials, and sap flow velocities when plants’ xylem water is sampled at a certain height above the rooting point. In a simulation study, we show that the approach can provide unbiased estimates of β and its associated uncertainty due to measuring errors and unmeasured environmental factors that can impact the xylem water isotopic data. We also recommend improving the accuracy and power of β estimation, highlighting the need for considering accurate soil water potential and sap flow monitoring. Finally, we apply the inverse modeling method to xylem water isotope data of lianas and trees collected in French Guiana. Our work shows that the inverse modeling procedure provides a robust analytical and statistical framework to estimate β. The method accounts for potential bias due to extraction errors and unmeasured environmental factors, which improves the viability of using stable water isotope compositions to estimate the distribution of absorbing root surfaces complementary to the assessment of relative root water uptake profiles.

Authors 7

1. Hannes De Deurwaerder corresponding

   Princeton University · Ghent University

   Affiliation as printed

   CAVElab–Computational and Applied Vegetation Ecology, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

   Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, United States

2. Marco D. Visser Aachen Institute of Environmental Sciences (CML)

   Leiden University · Princeton University

   Affiliation as printed

   Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, United States

   Institute of Environmental Sciences, Leiden University, Leiden, Netherlands

3. Félicien Meunier

   Ghent University

   Affiliation as printed

   CAVElab–Computational and Applied Vegetation Ecology, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

4. Matteo Detto

   Princeton University

   Affiliation as printed

   Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, United States

5. Pedro Hervé‐Fernández

   Adolfo Ibáñez University · Ghent University · University of Saskatchewan · Global Institute for Water Security

   Affiliation as printed

   Facultad de Artes Liberales, Universidad Adolfo Ibáñez, Santiago, Chile

   ISOFYS–Isotope Bioscience Laboratory, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

   School of Environment and Sustainability, Global Institute for Water Security, University of Saskatchewan, Saskatoon, SK, Canada

6. Pascal Boeckx

   Ghent University

   Affiliation as printed

   ISOFYS–Isotope Bioscience Laboratory, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

7. Hans Verbeeck

   Ghent University

   Affiliation as printed

   CAVElab–Computational and Applied Vegetation Ecology, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium