Land‐Atmosphere Drivers of Landscape‐Scale Plant Water Content Loss

Andrew F. Feldman,Isabel F. Trigo,Daniel J. Short Gianotti,Guido D. Salvucci,Dara Entekhabi

doi:10.1029/2020gl090331

Abstract

AbstractPlant water content observations using microwave remote sensing measurements allow monitoring of landscape‐scale plant water stress. During soil drying following rainfall events, we use a Granger causality framework to quantify the degree to which environmental factors drive satellite‐based plant water content loss across Africa's diverse biomes. After soil drying into the water‐limited regime, satellite observations show that plants dry while solar radiation, vapor pressure deficit, and diurnal temperature amplitude increase. We find that soil drying primarily drives plant water content loss across African drylands, though with regional effects of diurnal temperature amplitude increases (found to indicate vapor pressure deficit increases here). We also detect interactions between these factors that reinforce plant drying during periods of soil moisture loss. Our results provide observational evidence across Africa that individual and interactive components of surface drying and heating can all drive plant water stress, especially during intermittent poststorm drying periods.

Highlights

Plant water content plays a fundamental role in whole‐plant function, such as in modulating root water uptake and transpiration loss and participating in carbohydrate transport
We address the debate on the degree to which soil moisture and air vapor pressure deficit (VPD) influence plant function at landscape scales
We show that soil moisture has the most widespread effects on plant water content which is consistent with previous studies that show dominant soil moisture effects on dryland vegetation

Summary

Introduction

Plant water content plays a fundamental role in whole‐plant function, such as in modulating root water uptake and transpiration loss and participating in carbohydrate transport. When plant water content is progressively lost due to increased transpiration demand and/or reduced root water uptake (Katul et al, 2012), predawn water potential becomes more negative, and typically photosynthesis decreases and mortality risk increases (Kramer & Boyer, 1995; McDowell et al, 2008). Given these considerations and its role as a state variable, plant water content dynamics carry information about plant water stress (Bartlett et al, 2012; Konings et al, 2019; Martínez‐Vilalta et al, 2019) beyond that of less direct indicators like soil moisture and carbon flux (Kennedy et al, 2019).

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Conclusion