Editing Stoma (section)

===Inferring stomatal behavior from gas exchange===
The degree of stomatal resistance can be determined by measuring leaf gas exchange of a leaf. The [[transpiration]] rate is dependent on the [[diffusion]] resistance provided by the stomatal pores and also on the [[humidity]] gradient between the leaf's internal air spaces and the outside air. Stomatal resistance (or its inverse, [[stomatal conductance]]) can therefore be calculated from the transpiration rate and humidity gradient. This allows scientists to investigate how stomata respond to changes in environmental conditions, such as light intensity and concentrations of gases such as water vapor, carbon dioxide, and [[ozone]].<ref>{{cite journal |first=Michael |last=Hopkin |title=Carbon sinks threatened by increasing ozone |journal=Nature |volume=448 |pages=396–397 |date=2007-07-26 |bibcode=2007Natur.448..396H |doi=10.1038/448396b |issue=7152 |pmid=17653153|doi-access=free }}</ref> Evaporation (''E'') can be calculated as<ref name=calculations>{{cite web |url=http://4e.plantphys.net/article.php?ch=9&id=134 |title=Calculating Important Parameters in Leaf Gas Exchange |work=Plant Physiology Online |publisher=Sinauer |access-date=2013-02-24 |archive-date=2008-06-16 |archive-url=https://web.archive.org/web/20080616013217/http://4e.plantphys.net/article.php?ch=9&id=134 |url-status=dead }}</ref>

: <math>E = \frac{e_\text{i} - e_\text{a}}{Pr},</math>

where ''e''<sub>i</sub> and ''e''<sub>a</sub> are the partial pressures of water in the leaf and in the ambient air respectively, ''P'' is atmospheric pressure, and ''r'' is stomatal resistance.
The inverse of ''r'' is conductance to water vapor (''g''), so the equation can be rearranged to<ref name=calculations/>

: <math>E = (e_\text{i} - e_\text{a})g / P</math>

and solved for ''g'':<ref name=calculations/>

: <math>g = \frac{EP}{e_\text{i} - e_\text{a}}.</math>

Photosynthetic CO<sub>2</sub> assimilation (''A'') can be calculated from

: <math>A = \frac{(C_\text{a} - C_\text{i})g}{1.6P},</math>

where ''C''<sub>a</sub> and ''C''<sub>i</sub> are the atmospheric and sub-stomatal partial pressures of CO<sub>2</sub> respectively{{clarify|reason=what is "1.6"?|date=March 2023}}. The rate of evaporation from a leaf can be determined using a [[photosynthesis system]]. These scientific instruments measure the amount of water vapour leaving the leaf and the vapor pressure of the ambient air. Photosynthetic systems may calculate [[water use efficiency]] (''A''/''E''), ''g'', intrinsic water use efficiency (''A''/''g''), and ''C''<sub>i</sub>. These scientific instruments are commonly used by plant physiologists to measure CO<sub>2</sub> uptake and thus measure photosynthetic rate.<ref>{{cite journal
|journal=Photosynthesis Research
|volume=9
|issue=3
|date=January 1986
|pages=345–357
|title=A system for measuring leaf gas exchange based on regulating vapour pressure difference
|author=Waichi Agata
|author2=Yoshinobu Kawamitsu
|author3=Susumu Hakoyama
|author4=Yasuo Shima
|doi=10.1007/BF00029799
|issn=1573-5079
|pmid=24442366
|bibcode=1986PhoRe...9..345A
|s2cid=28367821
}}</ref><ref>{{citation
|title=Portable Gas Exchange Fluorescence System GFS-3000. Handbook of Operation
|date=March 20, 2013
|url=http://www.walz.com/downloads/manuals/gfs-3000/gfs-3000_Manual_8a.pdf
|access-date=October 20, 2014
|archive-date=December 15, 2017
|archive-url=https://web.archive.org/web/20171215121153/http://www.walz.com/downloads/manuals/gfs-3000/gfs-3000_Manual_8a.pdf
|url-status=dead
}}</ref>