A new, vapour‐phase mechanism for stomatal responses to humidity and temperature

Abstract

A new mechanism for stomatal responses to humidity and temperature is proposed. Unlike previously-proposed mechanisms, which rely on liquid water transport to create water potential gradients within the leaf, the new mechanism assumes that water transport to the guard cells is primarily through the vapour phase. Under steady-state conditions, guard cells are assumed to be in near-equilibrium with the water vapour in the air near the bottom of the stomatal pore. As the water potential of this air varies with changing air humidity and leaf temperature, the resultant changes in guard cell water potential produce stomatal movements. A simple, closed-form, mathematical model based on this idea is derived. The new model is parameterized for a previously published set of data and is shown to fit the data as well as or better than existing models. The model contains mathematical elements that are consistent with previously-proposed mechanistic models based on liquid flow as well as empirical models based on relative humidity. As such, it provides a mechanistic explanation for the realm of validity for each of these approaches.

Stomatal conductance increases with rising temperature

“…Very little is known about the direct effect of temperature on stomatal conductance (g s ) 6 which may exist independently from indirect mechanisms. 7,8 Results of experiments that examined the direct dependence of stomatal conductance on temperature have not been consistent. Previous studies have reported a complete range of responses to increased temperature, including stomatal opening, [9][10][11][12] no significant response, [13][14][15][16] stomatal closure, [17][18][19] peaked response with maximum g s at temperatures optimal for photosynthesis 20 or more complex responses.…”

Mechanisms of water supply and vegetation demand govern the seasonality and magnitude of evapotranspiration in Amazonia and Cerrado

“…The conclusions of syntheses of eddy covariance measures of the seasonality of E in the Amazon have largely emphasized the secondary role of vegetation demand across a range of forest types (Costa et al, 2004;Juarez et al, 2007;da Rocha et al, 2002da Rocha et al, , 2009Fisher et al, 2009), but recent work suggests that forests indeed exhibit varying degrees of control on the seasonal exchange of water in their canopies (Costa et al, 2010). Much of what is known about the functioning of stomata remains phenomenological; at the leaf-level, attempts at forming a solid mechanistic basis of stomatal function have proven to be a challenge (Buckley, 2005;Peak and Mott, 2011).…”

Stomatal Response to Humidity: Blurring the Boundary between Active and Passive Movement

“…In a recent paper, Wang et al (2017) take this approach and, in the process, unify the macroscopic water relations and evapotranspiration of the whole plant with the microscopic events of subcellular transport in the guard cells. They extend the quantitative OnGuard systems platform by incorporating the concept of a VPD gradient that extends through the stomatal pore and into the substomatal cavity adjacent to the guard cells (Peak and Mott, 2011). OnGuard is a proven computational platform for modeling stomatal physiology that encompasses guard cell transport, signaling, and homeostasis, and has predicted stomatal behavior across species (Chen et al, 2012;Wang et al, 2012).…”