SurEau: a mechanistic model of plant water relations under extreme drought

Hervé Cochard,François Pimont,Julien Ruffault,Nicolas Martin-Stpaul

doi:10.1007/s13595-021-01067-y

Abstract

Key messageA new process-based model,SurEau, is described. It predicts the risk of xylem hydraulic failure under drought.ContextThe increase in drought intensity due to climate change will accentuate the risk of tree mortality. But very few process-based models are currently able to predict this mortality risk.AimsWe describe the operating principle of a new mechanistic model SurEau that computes the water balance, water relations, and hydraulics of a plant under extreme drought.MethodsSurEau is based on the formalization of key physiological processes of plant response to water stress. The hydraulic and hydric functioning of the plant is at the core of this model, which focuses on both water flows (i.e., hydraulic) and water pools (i.e., hydric) using variable hydraulic conductances. The model considers the elementary flow of water from the soil to the atmosphere through different plant organs that are described by their symplasmic and apoplasmic compartments. For each organ, the symplasm is described by a pressure-volume curve and the apoplasm by its vulnerability curve to cavitation. The model is evaluated on mature oak trees exposed to water stress.ResultsOn the tested oak trees, the model captures well the observed soil water balance, water relations, and level of embolism. A sensitivity analysis reveals that the level of embolism is strongly determined by air VPD and key physiological traits such as cuticular transpiration, resistance to cavitation, and leaf area.ConclusionThe process-based SurEau model offers new opportunities to evaluate how different species or genotypes will respond to future climatic conditions.

Highlights

Numerous models have been developed to simulate the water relations and gas exchanges of plants under well-watered or limiting hydric conditions (Sperry et al 1998; Venturas et al 2018; Mackay et al 2012; Christofforsen et al 2016; Tuzet et al 2017; De Cáceres et al 2021)
A few years ago, we identified that there were few mechanistic models taking into account the water relations of plants under conditions of extreme water stress, i.e., when the plant reaches its survival limit (Xu et al 2016; Venturas et al 2018)
Cavitation events accentuate in the apoplasm of the different organs, decreasing the amount of water stored in the vessels

Summary

Introduction

Numerous models have been developed to simulate the water relations and gas exchanges of plants under well-watered or limiting hydric conditions (Sperry et al 1998; Venturas et al 2018; Mackay et al 2012; Christofforsen et al 2016; Tuzet et al 2017; De Cáceres et al 2021). These models are based either on empirical relationships or on more mechanistic bases, i.e., based on a physical representation of the physiological processes. This model has already been used in a number of recent studies (Martin-StPaul et al 2017, 2020; Scoffoni et al 2018; Duursma et al 2019; Cochard 2020a; Brodribb et al 2019; Brodribb et al 2020; Dayer et al 2020; Lamarque et al 2020; Lopez et al 2021), but never formally described as here

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