Vapour pressure deficit is the main driver of tree canopy conductance across biomes

How much does VPD drive tree water stress and forest disturbances?

“…In particular, rising VPD induced a decrease of up to 50% in these functions in the absence of soil drought. This is consistent with empirical observations that VPD negatively influence stomatal conductance (López et al 2021) and with the widely reported negative effects of VPD on primary productivity (Novick et al 2016;Yuan et al 2019;Dannenberg et al 2022;Flo et al 2022;Fu et al 2022b;Grünig et al 2022) or growth (Trotsiuk et al 2021). However, our results suggest that this effect operates only in the first phase of the drought (moderately negative water potential): as ysoil decrease and stomatal conductance and turgor become close to nill, no further influences of soil or atmospheric drought were observed for turgor and stomatal conductance (Figure 2A to 2D).…”

“…While pioneer studies mainly focused on plant responses to reduced precipitation or soil moisture deficit ("soil drought", Beier et al, 2004;Bréda et al, 2006;Limousin et al, 2009;Pangle et al, 2015;Weltzin et al, 2003), the impact of recent massive heat-waves on plants has favored the emergence of the "globalchange-type drought" concept (Breshears et al 2005) and shed light on the key role of "atmospheric drought" (or vapor pressure deficit, VPD) on plant functioning (Park Williams et al 2012;Trenberth et al 2014;McDowell et al , 2022Yuan et al 2019;Grossiord et al 2020). Major efforts are currently underway to unravel the respective roles of VPD and soil drought on the different facets of plant functioning (e.g., gas exchanges, growth, mortality, vulnerability to wildfire) in studies ranging from controlled experiments (Grossiord et al 2017a, b;Schönbeck et al 2022) to analyses of climate impacts at regional (Trotsiuk et al 2021;Dannenberg et al 2022;Grünig et al 2022) and continental scales (Seager et al 2015;Humphrey et al 2021;Bauman et al 2022;Flo et al 2022;Fu et al 2022b, a). In these studies the predominant role of VPD is most of the time invoked as the main driver of plant responses (Grossiord et al 2017a, b;Flo et al 2021Flo et al , 2022Humphrey et al 2021;Bauman et al 2022;Fu et al 2022b, a;Grünig et al 2022;Schönbeck et al 2022).…”

“…Major efforts are currently underway to unravel the respective roles of VPD and soil drought on the different facets of plant functioning (e.g., gas exchanges, growth, mortality, vulnerability to wildfire) in studies ranging from controlled experiments (Grossiord et al 2017a, b;Schönbeck et al 2022) to analyses of climate impacts at regional (Trotsiuk et al 2021;Dannenberg et al 2022;Grünig et al 2022) and continental scales (Seager et al 2015;Humphrey et al 2021;Bauman et al 2022;Flo et al 2022;Fu et al 2022b, a). In these studies the predominant role of VPD is most of the time invoked as the main driver of plant responses (Grossiord et al 2017a, b;Flo et al 2021Flo et al , 2022Humphrey et al 2021;Bauman et al 2022;Fu et al 2022b, a;Grünig et al 2022;Schönbeck et al 2022). These conclusions may seem in contradiction with observational evidence from agricultural irrigation or natural riparian forests in arid zones showing that root access to soil water is a stronger predictor of plant productivity than VPD (Sousa et al 2022).…”

Simple Models Outperform More Complex Big‐Leaf Models of Daily Transpiration in Forested Biomes

“…We hypothesized that f SM constraints were competing with VPD constraints, confirmed through additional examination of the relationship between f SM and VPD constraints below the critical soil moisture stress threshold of −0.5 (Section S8, Figures S6, and S7 in Supporting Information S1 ). The fact that VPD was sufficiently constraining supports findings reported elsewhere (Flo et al., 2021 ; Lu et al., 2022 ; Novick et al., 2016 ) about the relative importance of atmospheric moisture demand over soil moisture supply in constraining T in non‐arid biomes.…”

“…As another example, the value that various individual environmental constraints provide to a global model is also unclear. For instance, it has been posited that soil moisture (SM) supply may be less containing than atmospheric moisture demand in many biomes (Flo et al., 2021 ; Lu et al., 2022 ; Novick et al., 2016 ), suggesting that a constraint based on atmospheric demand (i.e., as vapor pressure deficit (VPD)) may be more effective than one based on SM for a model that is to be applied at the global scale. Complicating model evaluation further are the different ways of representing key behavior for the same individual stress (or constraint) functions, particularly for SM supply (Verhoef & Egea, 2014 ) and atmospheric moisture demand (C. Lin et al., 2018 ).…”