Essential Site Maintenance: Authorea-powered sites will be updated circa 15:00-17:00 Eastern on Tuesday 5 November.
There should be no interruption to normal services, but please contact us at [email protected] in case you face any issues.

loading page

How much does VPD drive tree water stress and forest disturbances?
  • +8
  • Nicolas Martin-StPaul,
  • Julien Ruffault,
  • Joannes Guillemot,
  • Renaud Barbero,
  • Hervé Cochard,
  • Maxime Cailleret,
  • Miquel De Caceres,
  • Jean-Luc Dupuy,
  • François Pimont,
  • José M. Torres-Ruiz,
  • Jean-Marc Limousin
Nicolas Martin-StPaul
INRA

Corresponding Author:[email protected]

Author Profile
Julien Ruffault
INRAE PACA
Author Profile
Joannes Guillemot
CIRAD Montpellier-Occitanie Research Centre
Author Profile
Renaud Barbero
INRAE PACA Site d'Aix Le Tholonet
Author Profile
Hervé Cochard
INRAE, PIAF research unit
Author Profile
Maxime Cailleret
INRAE
Author Profile
Miquel De Caceres
CTFC
Author Profile
Jean-Luc Dupuy
INRAE PACA
Author Profile
François Pimont
INRAE PACA
Author Profile
José M. Torres-Ruiz
INRAE
Author Profile
Jean-Marc Limousin
CNRS
Author Profile

Abstract

Vapor Pressure Deficit (VPD, atmospheric drought) and soil water potential (Ψsoil, soil drought) have both been reported to affect terrestrial plant water stress, plant functions (growth, stomatal conductance, transpiration) and vulnerability to ecosystem disturbances (mortality or vulnerability to wildfires). Which of atmospheric drought or soil drought has the greatest influence on these responses is yet an unresolved question. Using a state-of-the-art soil-plant-atmosphere hydraulic model, we conducted an in-silico experiment where VPD and Ψsoil were manipulated one at a time to quantify the relative importance of atmospheric vs soil drought on most critical plant functions. The model simulates the combined effects of soil drought and atmospheric drought on plant water potential (ΨPlant), a physiologically meaningful metric of plant water status driving plant turgor, stomatal conductance, hydraulic conductance or water content, and thus mortality and fire risks. Contrary to expectations, we showed that VPD had a weaker effect than Ψsoil on tree water stress and forest disturbances risk (i.e leaf moisture content). While physiological responses associated with low water stress such as stomatal closure or turgor loss could be driven by both VPD or soil drought, consequences of extreme water stress such as hydraulic failure, leaf desiccation and vulnerability to wildfires were almost exclusively driven by low Ψsoil. Our results therefore suggest that most plant functions are affected by VPD through its cumulative effect on Ψsoil via increased plant transpiration, rather than through a direct instantaneous effect on plant water potential. We argue that plant hydraulics provide a strong foundation for predicting tree and terrestrial ecosystem responses to climate changes and propose a list of explanations and testable hypotheses to reconcile plant hydraulic theory and observations of soil and atmospheric drought effects on plant functions.