Stomatal response to humidity in a sugarcane field: simultaneous porometric and micrometeorological measurements*

Abstract

Abstract. Gas exchange data obtained with wellventilated leaf cuvettes provide clear evidence of a stomatal response to leaf‐air vapour pressure difference (V). In contrast, remotely sensed leaf temperatures with specific assumptions regarding canopy boundary layer characteristics, have been interpreted to mean that stomata do not respond to V. We address this apparent discrepancy in a sugarcane field by simultaneous application of a single‐leaf, porometric technique and a whole‐canopy, Bowen ratioenergy balance technique. These methods indicated significant stomatal response to V in well‐irrigated sugarcane. Stomatal responses to V in the field were obscured by strong covariance of major environmental parameters so that opening responses to light and closing responses to V tended to offset each other. Low boundary layer conductance significantly uncoupled V at the leaf surface (Vs) from V determined in the bulk atmosphere (Va). This reduced the range of the stimulus, Vs, thereby reducing the range of the stomatal response, without indicating low stomatal sensitivity to V. Stomatal responses to Va may be smaller than expected from V response curves in cuvettes, since Vs rather than the conventionally measured Va is analogous to V in a well‐stirred cuvette. Recently published conclusions that remotely sensed canopy temperatures are inconsistent with stomatal response to V may be based on erroneous estimates of canopy boundary layer conductance and thus of Vs, use of air saturation deficit rather than V to express evaporative demand, and investigation at higher levels of evaporative demand than those eliciting maximal stomatal response.

Root to leaf electrical signaling in avocado in response to light and soil water content

“…Stomatal conductance generally decreases as the soil water content falls below an adequate level to sustain normal plant water uptake (Khalil and Grace, 1992). In dry soils, where gs is low, it generally increases immediately after the beginning of an irrigation event (Grantz and Meinzer, 1990). Stomata open and close very rapidly, in scales from minutes to hours, in response to changes in soil water conditions (Novak and Osmolovskaya, 1997;Kopyt et al, 2001;Meinzer, 2002;Gurovich and Gratacós, 2003;Zavala, 2004).…”

Evaluating stomatal models and their atmospheric drought response in a land surface scheme: A multibiome analysis

“…At the ecosystem level, leaf boundary and atmospheric resistances can be a considerable component in the overall vegetation‐atmosphere resistance pathway and lead to a partial decoupling of the canopy from the atmosphere [e.g., Meinzer et al , ; Magnani et al , ]. This can lead to a significant deviation of the temperature and humidity conditions at the notional canopy surface from those in the free air stream [ Grantz and Meinzer , ; McNaughton and Jarvis , ], which affects estimates of eddy covariance derived g 1 differently than leaf level estimates. Further possible reasons are related to uncertainties in the derivation of G c (equation ) and G a resulting from uncertainties in surface roughness estimation and energy balance nonclosure [ Wilson et al , ].…”

Climate change impacts on sugarcane attainable yield in southern Brazil

“…Although derived for sweet corn, the method compared well with sugarcane stomatal diffusion resistances measured under ambient atmospheric [CO 2 ] by Venkataramana et al (1986), Grantz and Meinzer (1990), Souza et al (2008), and Vu and Allen (2009).…”