Editing Stoma (section)

==Stomata and climate change==
===Response of stomata to environmental factors===
[[Photosynthesis]], plant water transport ([[xylem]]) and gas exchange are regulated by stomatal function which is important in the functioning of plants.<ref name="Rico-2013">{{cite journal | last1 = Rico | first1 = C | last2 = Pittermann | first2 = J | last3 = Polley | first3 = HW | last4 = Aspinwall | first4 = MJ | last5 = Fay | first5 = PA | year = 2013 | title = The effect of subambient to elevated atmospheric CO2 concentration on vascular function in Helianthus annuus: implications for plant response to climate change | journal = New Phytologist | volume = 199 | issue = 4| pages = 956–965 | doi=10.1111/nph.12339| pmid = 23731256 | doi-access = free | bibcode = 2013NewPh.199..956R }}</ref>

Stomata are responsive to light with [[Visible spectrum|blue light]] being almost 10 times as effective as [[Red|red light]] in causing stomatal response. Research suggests this is because the light response of stomata to blue light is independent of other leaf components like [[chlorophyll]]. Guard cell [[protoplasts]] swell under blue light provided there is sufficient availability of [[potassium]].<ref>{{cite book |last=McDonald |first=Maurice S. |title=Photobiology of Higher Plants |publisher=Wiley |date=2003 |page=293 |isbn=978-0-470-85523-2}}</ref> Multiple studies have found support that increasing potassium concentrations may increase stomatal opening in the mornings, before the photosynthesis process starts, but that later in the day [[sucrose]] plays a larger role in regulating stomatal opening.<ref>{{cite book |editor-first1=Konrad |editor-last1=Mengel |editor-first2=Ernest A. |editor-last2=Kirkby |editor-first3=Harald |editor-last3=Kosegarten |editor-first4=Thomas |editor-last4=Appel |title=Principles of Plant Nutrition |publisher=Springer |date=2001 |page=205 |isbn=978-94-010-1009-2 |doi=10.1007/978-94-010-1009-2|s2cid=9332099 }}</ref> [[Zeaxanthin]] in guard cells acts as a blue light photoreceptor which mediates the stomatal opening.<ref name="KochharKaur2020">{{cite book |last1=Kochhar |first1=S. L. |last2=Gujral |first2=Sukhbir Kaur |title=Plant Physiology: Theory and Applications |date=2020 |publisher=Cambridge University Press |isbn=978-1-108-48639-2 |pages=75–99 |edition=2 |doi=10.1017/9781108486392.006 |chapter=Transpiration}}</ref> The effect of blue light on guard cells is reversed by green light, which isomerizes zeaxanthin.<ref name="KochharKaur2020"/>

[[Stomatal density]] and aperture (length of stomata) varies under a number of environmental factors such as atmospheric CO<sub>2</sub> concentration, light intensity, air temperature and photoperiod (daytime duration).
<ref name="Buckley-2013">{{cite journal | last1 = Buckley | first1 = TN | last2 = Mott | first2 = KA | year = 2013 | title = Modelling stomatal conductance in response to environmental factors | journal = Plant, Cell and Environment | volume = 36 | issue = 9| pages = 1691–1699 | doi=10.1111/pce.12140| pmid = 23730938 | doi-access = free | bibcode = 2013PCEnv..36.1691B }}</ref><ref name="Rogiers-2011">{{cite journal | last1 = Rogiers | first1 = SY | last2 = Hardie | first2 = WJ | last3 = Smith | first3 = JP | year = 2011 | title = Stomatal density of grapevine leaves (Vitis Vinifera L.) responds to soil temperature and atmospheric carbon dioxide | journal = Australian Journal of Grape and Wine Research | volume = 17 | issue = 2| pages = 147–152 | doi=10.1111/j.1755-0238.2011.00124.x| doi-access =  }}</ref>

Decreasing stomatal density is one way plants have responded to the increase in concentration of atmospheric CO<sub>2</sub> ([CO<sub>2</sub>]<sub>atm</sub>).<ref name="Ceccarelli-2010">{{cite journal | last1 = Ceccarelli | first1 = S | last2 = Grando | first2 = S | last3 = Maatougui | first3 = M | last4 = Michael | first4 = M | last5 = Slash | first5 = M | last6 = Haghparast | first6 = R | last7 = Rahmanian | first7 = M | last8 = Taheri | first8 = A | last9 = Al-Yassin | first9 = A | last10 = Benbelkacem | first10 = A | last11 = Labdi | first11 = M | last12 = Mimoun | first12 = H | last13 = Nachit | first13 = M | year = 2010 | title = Plant breeding and climate changes | journal = The Journal of Agricultural Science | volume = 148 | issue = 6| pages = 627–637 | doi=10.1017/s0021859610000651| s2cid = 86237270 | doi-access = free }}</ref> Although changes in [CO<sub>2</sub>]<sub>atm</sub> response is the least understood mechanistically, this stomatal response has begun to plateau where it is soon expected to impact [[transpiration]] and photosynthesis processes in plants.<ref name="Rico-2013" /><ref>{{cite journal | last1 = Serna | first1 = L | last2 = Fenoll | first2 = C | year = 2000 | title = Coping with human CO2 emissions | journal = Nature | volume = 408 | issue = 6813| pages = 656–657 | doi=10.1038/35047202| pmid = 11130053 | s2cid = 39010041 }}</ref>

Drought inhibits stomatal opening, but research on soybeans suggests moderate drought does not have a significant effect on stomatal closure of its leaves. There are different mechanisms of stomatal closure. Low humidity stresses guard cells causing [[turgor]] loss, termed hydropassive closure. Hydroactive closure is contrasted as the whole leaf affected by drought stress, believed to be most likely triggered by [[abscisic acid]].<ref>{{cite book |editor-first1=Konrad |editor-last1=Mengel |editor-first2=Ernest A. |editor-last2=Kirkby |editor-first3=Harald |editor-last3=Kosegarten |editor-first4=Thomas |editor-last4=Appel |title=Principles of Plant Nutrition |publisher=Springer |date=2001 |page=223 |isbn=978-94-010-1009-2 |doi=10.1007/978-94-010-1009-2|s2cid=9332099 }}</ref>

===Future adaptations during climate change===
It is expected that [CO<sub>2</sub>]<sub>atm</sub> will reach 500–1000 ppm by 2100.<ref name="Rico-2013" /> 96% of the past 400,000 years experienced below 280 ppm CO<sub>2</sub>. From this figure, it is highly probable that [[genotype]]s of today’s plants have diverged from their pre-industrial relatives.<ref name="Rico-2013" />

The gene ''HIC'' (high carbon dioxide) encodes a negative regulator for the development of stomata in plants.<ref name="Gray-2000">{{cite journal | last1 = Gray | first1 = J | last2 = Holroyd | first2 = G | last3 = van der Lee | first3 = F | last4 = Bahrami | first4 = A | last5 = Sijmons | first5 = P | last6 = Woodward | first6 = F | last7 = Schuch | first7 = W | last8 = Hetherington | first8 = A | year = 2000 | title = The ''HIC'' signalling pathway links CO<sub>2</sub> perception to stomatal development | journal = Nature | volume = 408 | issue = 6813| pages = 713–716 | bibcode = 2000Natur.408..713G | doi = 10.1038/35047071 | pmid = 11130071 | s2cid = 83843467 }}</ref> Research into the ''HIC'' gene using'' [[Arabidopsis thaliana]]'' found no increase of stomatal development in the dominant [[allele]], but in the ‘wild type’ [[recessive allele]] showed a large increase, both in response to rising CO<sub>2</sub> levels in the atmosphere.<ref name="Gray-2000" /> These studies imply the plants response to changing CO<sub>2</sub> levels is largely controlled by genetics.

===Agricultural implications===

The CO<sub>2 </sub>fertiliser effect has been greatly overestimated during [[Free-air concentration enrichment|Free-Air Carbon dioxide Enrichment]] (FACE) experiments where results show increased CO<sub>2</sub> levels in the atmosphere enhances photosynthesis, reduce transpiration, and increase [[Water-use efficiency|water use efficiency]] (WUE).<ref name="Ceccarelli-2010" /> Increased [[biomass]] is one of the effects with simulations from experiments predicting a 5–20% increase in crop yields at 550 ppm of CO<sub>2</sub>.<ref name="Tubiello-2007">{{cite journal | last1 = Tubiello | first1 = FN | last2 = Soussana | first2 = J-F | last3 = Howden | first3 = SM | year = 2007 | title = Crop and pasture response to climate change | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 50| pages = 19686–19690 | doi=10.1073/pnas.0701728104| pmid = 18077401 | pmc = 2148358 | bibcode = 2007PNAS..10419686T | doi-access = free }}</ref> Rates of leaf photosynthesis were shown to increase by 30–50% in [[C3 carbon fixation|C3]] plants, and 10–25% in [[C4 carbon fixation|C4]] under doubled CO<sub>2</sub> levels.<ref name="Tubiello-2007" /> The existence of a [[feedback mechanism]] results a [[phenotypic plasticity]] in response to [CO<sub>2</sub>]<sub>atm</sub> that may have been an adaptive trait in the evolution of plant respiration and function.<ref name="Rico-2013" /><ref name="Rogiers-2011" />

Predicting how stomata perform during adaptation is useful for understanding the productivity of plant systems for both natural and [[agricultural systems]].<ref name="Buckley-2013" /> Plant breeders and farmers are beginning to work together using evolutionary and participatory plant breeding to find the best suited species such as heat and drought resistant crop varieties that could naturally evolve to the change in the face of food security challenges.<ref name="Ceccarelli-2010" />