Plant Water Uptake Thresholds Inferred From Satellite Soil Moisture

Maoya Bassiouni,Chad W Higgins,Christopher J Still,Stephen P Good

doi:10.1029/2020gl087077

Abstract

AbstractEmpirical functions are widely used in hydrological, agricultural, and Earth system models to parameterize plant water uptake. We infer soil water potentials at which uptake is downregulated from its well‐watered rate and at which uptake ceases, in biomes with <60% woody vegetation at 36‐km grid resolution. We estimate thresholds through Bayesian inference using a stochastic soil water balance framework to construct theoretical soil moisture probability distributions consistent with empirical distributions derived from satellite soil moisture observations. The global median Nash–Sutcliffe efficiency between empirical soil moisture distributions and theoretical distributions using reference constants, inferred median parameters per biome, and spatially variable inferred parameters are 0.38, 0.59, and 0.8, respectively. Spatially variable thresholds capture location‐specific vegetation and climate characteristics and can be connected to biome‐level water uptake strategies. Results demonstrate that satellite soil moisture probability distributions encode information, valuable to understanding biome‐level ecohydrological adaptation and resistance to climate variability.

Highlights

Transpiration accounts for over 50% of the global transfer of water from the land back to the atmosphere (Good et al, 2015)
We estimate thresholds through Bayesian inference using a stochastic soil water balance framework to construct theoretical soil moisture probability distributions consistent with empirical distributions derived from satellite soil moisture observations
Inferred parameters Ψ0, Ψ*, and Emax/Ep construct theoretical descriptions of p(s) that are consistent with empirical p(s) derived from satellite soil moisture, and parameters are highly variable spatially (Figures 1a–1d)

Summary

Introduction

Transpiration accounts for over 50% of the global transfer of water from the land back to the atmosphere (Good et al, 2015). The driving force moving water from soils, through plant tissue, and to the atmosphere is the gradient in potential energy state of water (Tyree, 2003). Plant water uptake thresholds have been incorporated into soil water‐limitation constraints on evaporation (Feddes et al, 1976), often termed β functions, and are used in many hydrological (Laio et al, 2001; Westenbroek et al, 2018), agricultural (Hlavinka et al, 2011; Steduto et al, 2009), and Earth system (Baker et al, 2008; Clark et al, 2011; Niu et al, 2011; Oleson et al, 2013) models

Methods

Results

Conclusion