Nocturnal responses of stomata to changes in VPD in air and HELOX

I have built a new gas exchange system that allows us to investigate how stomata respond to changes in vapour pressure deficit (VPD). This system is novel in that we can switch the carrier gas from nitrogen to helium, and vice-versa, with the flick of a switch. This will allow us to instantaneously change the VPD whilst maintaining constant leaf temperature and ambient humidity. This project aims to build on the work of Mott and Parkhurst in the early 1990s, carried out under saturating light conditions, by looking at nocturnal responses of stomata to changes in VPD.


The mechanisms by which leaf stomata respond to changes in VPD are not fully understood. However, Mott and Parkhurst (1991) showed that stomata in illuminated leaves respond normally when VPD is changed by switching the carrier gas from nitrogen/oxygen (normal air) to helium/oxygen (helox, in which vapor diffuses 2.33 times faster than in nitox) while holding ambient humidity and leaf temperature constant. This seminal experiment indicated that the VPD response is not governed by humidity as such, whether outside or inside the leaf, but instead by something coupled to the rate of water loss. However, the Mott/Parkhurst experiment has never been performed in non-illuminated leaves, so the mechanism of VPD responses in nocturnally-open stomata remains unknown. This project aims to repeat the helox experiments on dark-opened stomata, as well as illuminated leaves of a range of species. This work is part of an ARC Discovery project entitled “Are plants wasting water in the dark?”. T. Buckley, 2017

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