CO2 fertilization effect

{{Main|Photosynthesis}}

Through photosynthesis, plants use CO₂ from the atmosphere, water from the ground, and energy from the sun to create sugars used for growth and fuel.{{cite report | vauthors = Calvin M, Benson AA | title = The Path of Carbon in Photosynthesis | url= https://escholarship.org/uc/item/9tk591mn | date = March 1948 | pages = 884–922 | publisher = Lawrence Berkeley National Laboratory |language=en}} While using these sugars as fuel releases carbon back into the atmosphere (photorespiration), growth stores carbon in the physical structures of the plant (i.e. leaves, wood, or non-woody stems).{{cite journal | vauthors = Walker AP, De Kauwe MG, Bastos A, Belmecheri S, Georgiou K, Keeling RF, McMahon SM, Medlyn BE, Moore DJ, Norby RJ, Zaehle S, Anderson-Teixeira KJ, Battipaglia G, Brienen RJ, Cabugao KG, Cailleret M, Campbell E, Canadell JG, Ciais P, Craig ME, Ellsworth DS, Farquhar GD, Fatichi S, Fisher JB, Frank DC, Graven H, Gu L, Haverd V, Heilman K, Heimann M, Hungate BA, Iversen CM, Joos F, Jiang M, Keenan TF, Knauer J, Körner C, Leshyk VO, Leuzinger S, Liu Y, MacBean N, Malhi Y, McVicar TR, Penuelas J, Pongratz J, Powell AS, Riutta T, Sabot ME, Schleucher J, Sitch S, Smith WK, Sulman B, Taylor B, Terrer C, Torn MS, Treseder KK, Trugman AT, Trumbore SE, van Mantgem PJ, Voelker SL, Whelan ME, Zuidema PA | display-authors = 6 | title = Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO₂ | journal = The New Phytologist | volume = 229 | issue = 5 | pages = 2413–2445 | date = March 2021 | pmid = 32789857 | doi = 10.1111/nph.16866 | doi-access = free | bibcode = 2021NewPh.229.2413W }} With about 19 percent of Earth's carbon stored in plants,{{cite web|title=Forests and Climate Change|url=http://www.fao.org/3/ac836e/AC836E03.htm#:~:text=At%20the%20global%20level,%2019,81%20percent%20in%20the%20soil|access-date=2021-03-24|website=www.fao.org}} plant growth plays an important role in storing carbon on the ground rather than in the atmosphere. In the context of carbon storage, growth of plants is often referred to as biomass productivity.{{cite journal | vauthors = Sivamani E, Bahieldin A, Wraith JM, Al-Niemi T, Dyer WE, Ho TD, Qu R | title = Improved biomass productivity and water use efficiency under water deficit conditions in transgenic wheat constitutively expressing the barley HVA1 gene | journal = Plant Science | volume = 155 | issue = 1 | pages = 1–9 | date = June 2000 | pmid = 10773334 | doi = 10.1016/S0168-9452(99)00247-2 | bibcode = 2000PlnSc.155....1S }}{{cite journal| vauthors = Singh SP, Adhikari BS, Zobel DB |date=1994|title=Biomass, Productivity, Leaf Longevity, and Forest Structure in the Central Himalaya |journal=Ecological Monographs|language=en|volume=64|issue=4|pages=401–421|doi=10.2307/2937143|jstor=2937143|bibcode=1994EcoM...64..401S |issn=1557-7015}} This term is used because researchers compare the growth of different plant communities by their biomass, amount of carbon they contain.

Increased biomass productivity directly increases the amount of carbon stored in plants. And because researchers are interested in carbon storage, they are interested in where most of the biomass is found in individual plants or in an ecosystem. Plants will first use their available resources for survival and support the growth and maintenance of the most important tissues like leaves and fine roots which have short lives.{{cite journal | vauthors = De Kauwe MG, Medlyn BE, Zaehle S, Walker AP, Dietze MC, Wang YP, Luo Y, Jain AK, El-Masri B, Hickler T, Wårlind D, Weng E, Parton WJ, Thornton PE, Wang S, Prentice IC, Asao S, Smith B, McCarthy HR, Iversen CM, Hanson PJ, Warren JM, Oren R, Norby RJ | display-authors = 6 | title = Where does the carbon go? A model-data intercomparison of vegetation carbon allocation and turnover processes at two temperate forest free-air {{CO2}} enrichment sites | journal = The New Phytologist | volume = 203 | issue = 3 | pages = 883–99 | date = August 2014 | pmid = 24844873 | pmc = 4260117 | doi = 10.1111/nph.12847 }} With more resources available plants can grow more permanent, but less necessary tissues like wood.

If the air surrounding plants has a higher concentration of carbon dioxide, they may be able to grow better and store more carbon{{cite journal | vauthors = Walker AP, De Kauwe MG, Medlyn BE, Zaehle S, Iversen CM, Asao S, Guenet B, Harper A, Hickler T, Hungate BA, Jain AK, Luo Y, Lu X, Lu M, Luus K, Megonigal JP, Oren R, Ryan E, Shu S, Talhelm A, Wang YP, Warren JM, Werner C, Xia J, Yang B, Zak DR, Norby RJ | display-authors = 6 | title = Decadal biomass increment in early secondary succession woody ecosystems is increased by CO₂ enrichment | journal = Nature Communications | volume = 10 | issue = 1 | pages = 454 | date = February 2019 | pmid = 30765702 | pmc = 6376023 | doi = 10.1038/s41467-019-08348-1 | bibcode = 2019NatCo..10..454W }} and also store carbon in more permanent structures like wood. Evidence has shown this occurring for a few different reasons. First, plants that were otherwise limited by carbon or light availability benefit from a higher concentration of carbon.{{cite journal | vauthors = Lloyd J, Farquhar GD | title = Effects of rising temperatures and [{{CO2}}] on the physiology of tropical forest trees | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 363 | issue = 1498 | pages = 1811–7 | date = May 2008 | pmid = 18267901 | pmc = 2374913 | doi = 10.1098/rstb.2007.0032 }} Another reason is that plants are able use water more efficiently because of reduced stomatal conductance.{{cite journal| vauthors = Medlyn BE, Duursma RA, Eamus D, Ellsworth DS, Prentice IC, Barton CV, Crous KY, De Angelis P, Freeman M, Wingate L | display-authors = 6 |date=2011|title=Reconciling the optimal and empirical approaches to modelling stomatal conductance |journal=Global Change Biology|language=en|volume=17|issue=6|pages=2134–2144|doi=10.1111/j.1365-2486.2010.02375.x|bibcode=2011GCBio..17.2134M|hdl=10453/18084| s2cid = 51814113 |issn=1365-2486|hdl-access=free}} Plants experiencing higher CO₂ concentrations may benefit from a greater ability to gain nutrients from mycorrhizal fungi in the sugar-for-nutrients transaction.{{cite journal| vauthors = Fleischer K, Rammig A, De Kauwe MG, Walker AP, Domingues TF, Fuchslueger L, Garcia S, Goll DS, Grandis A, Jiang M, Haverd V | display-authors = 6 |date= September 2019 |title=Amazon forest response to CO₂ fertilization dependent on plant phosphorus acquisition |journal=Nature Geoscience|language=en|volume=12|issue=9|pages=736–741|doi=10.1038/s41561-019-0404-9|bibcode=2019NatGe..12..736F|s2cid=199448766|issn=1752-0908| url = http://nora.nerc.ac.uk/id/eprint/524958/1/N524958PP.pdf }} The same interaction may also increase the amount of carbon stored in the soil by mycorrhizal fungi.{{cite journal | vauthors = Orwin KH, Kirschbaum MU, St John MG, Dickie IA | title = Organic nutrient uptake by mycorrhizal fungi enhances ecosystem carbon storage: a model-based assessment | journal = Ecology Letters | volume = 14 | issue = 5 | pages = 493–502 | date = May 2011 | pmid = 21395963 | doi = 10.1111/j.1461-0248.2011.01611.x | bibcode = 2011EcolL..14..493O }}

From 2002 to 2014, plants appear to have gone into overdrive, starting to pull more CO₂ out of the air than they have done before.{{cite web |date=2016-11-08 |title=Study: Carbon-Hungry Plants Impede Growth Rate of Atmospheric {{CO2}} {{!}} Berkeley Lab |url=http://newscenter.lbl.gov/2016/11/08/atmospheric-co2-pause/ |access-date=2016-11-11 |website=News Center |vauthors=Krotz D}} The result was that the rate at which CO₂ accumulates in the atmosphere did not increase during this time period, although previously, it had grown considerably in concert with growing greenhouse gas emissions.

A 1993 review of scientific greenhouse studies found that a doubling of {{CO2}} concentration would stimulate the growth of 156 different plant species by an average of 37%. Response varied significantly by species, with some showing much greater gains and a few showing a loss. For example, a 1979 greenhouse study found that with doubled {{CO2}} concentration the dry weight of 40-day-old cotton plants doubled, but the dry weight of 30-day-old maize plants increased by only 20%.{{cite web | vauthors = Poorter H |title=Interspecific variation in the growth response of plants to an elevated ambient {{CO2}} concentration |url=http://www.science.poorter.eu/1993_poorter_vegetatio.pdf}}{{cite journal | vauthors = Wong SC |date=December 1979 |title=Elevated Partial Pressure of {{CO2}} and Plant Growth |journal=Oecologia |volume=44 |issue=1 |pages=68–74 |bibcode=1979Oecol..44...68W |doi=10.1007/BF00346400 |pmid=28310466 |s2cid=24541633}}

In addition to greenhouse studies, field and satellite measurements attempt to understand the effect of increased {{co2}} in more natural environments. In free-air carbon dioxide enrichment (FACE) experiments plants are grown in field plots and the {{CO2}} concentration of the surrounding air is artificially elevated. These experiments generally use lower {{CO2}} levels than the greenhouse studies. They show lower gains in growth than greenhouse studies, with the gains depending heavily on the species under study. A 2005 review of 12 experiments at 475–600 ppm showed an average gain of 17% in crop yield, with legumes typically showing a greater response than other species and C4 plants generally showing less. The review also stated that the experiments have their own limitations. The studied {{CO2}} levels were lower, and most of the experiments were carried out in temperate regions.{{cite journal | vauthors = Ainsworth L |author-link1=Lisa Ainsworth |date=February 2005 |title=What have we learned from 15 years of free-air {{CO2}} enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising {{CO2}}. |journal=New Phytol. |volume=165 |issue=2 |pages=351–71 |doi=10.1111/j.1469-8137.2004.01224.x |pmid=15720649 |doi-access=free}} Satellite measurements found increasing leaf area index for 25% to 50% of Earth's vegetated area over the past 35 years (i.e., a greening of the planet), providing evidence for a positive CO₂ fertilization effect.{{Cite journal | vauthors = Zhu Z, Piao S, Myneni RB, Huang M, Zeng Z, Canadell JG, Ciais P, Sitch S, Friedlingstein P, Arneth A, Cao C | display-authors = 6 |date=August 2016 |title=Greening of the Earth and its drivers |url=http://www.escholarship.org/uc/item/8mc6q011 |journal=Nature Climate Change |volume=6 |issue=8 |pages=791–95 |bibcode=2016NatCC...6..791Z |doi=10.1038/nclimate3004 |issn=1758-6798 |quote=We show a persistent and widespread increase of growing season integrated LAI (greening) over 25% to 50% of the global vegetated area, whereas less than 4% of the globe shows decreasing LAI (browning). Factorial simulations with multiple global ecosystem models suggest that {{CO2}} fertilization effects explain 70% of the observed greening trend |s2cid=7980894}}{{Cite news | vauthors = Hille K |date=2016-04-25 |title=Carbon Dioxide Fertilization Greening Earth, Study Finds |work=NASA |url=https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth |access-date=2018-02-04}}

Depending on environment, there are differential responses to elevated atmospheric CO₂ between major 'functional types' of plant, such as {{c3}} and {{c4}} plants, or more or less woody species; which has the potential among other things to alter competition between these groups.{{Cite journal |last1=Giam |first1=Xingli |last2=Bradshaw |first2=Corey J.A. |last3=Tan |first3=Hugh T.W. |last4=Sodhi |first4=Navjot S. |date=July 2010 |title=Future habitat loss and the conservation of plant biodiversity |url=http://dx.doi.org/10.1016/j.biocon.2010.04.019 |journal=Biological Conservation |volume=143 |issue=7 |pages=1594–1602 |doi=10.1016/j.biocon.2010.04.019 |bibcode=2010BCons.143.1594G |issn=0006-3207}}{{cite journal |author1=Jeffrey S. Dukes |author2=Harold A. Mooney |date=April 1999 |title=Does global change increase the success of biological invaders? |journal=Trends Ecol. Evol. |volume=14 |issue=4 |pages=135–9 |doi=10.1016/S0169-5347(98)01554-7 |pmid=10322518}} Increased CO₂ can also lead to increased Carbon : Nitrogen ratios in the leaves of plants or in other aspects of leaf chemistry, possibly changing herbivore nutrition.{{cite journal |author=Gleadow RM |display-authors=etal |year=1998 |title=Enhanced CO₂ alters the relationship between photosynthesis and defence in cyanogenic Eucalyptus cladocalyx F. Muell. |journal=Plant Cell Environ. |volume=21 |issue=1 |pages=12–22 |doi=10.1046/j.1365-3040.1998.00258.x |doi-access=free|bibcode=1998PCEnv..21...12G }} Studies show that doubled concentrations of CO₂ will show an increase in photosynthesis in C3 plants but not in C4 plants.{{Cite journal |last=HAMIM |date=December 2005 |title=Photosynthesis of C3 and C4 Species in Response to Increased CO 2 Concentration and Drought Stress |journal=HAYATI Journal of Biosciences |volume=12 |issue=4 |pages=131–138 |doi=10.1016/s1978-3019(16)30340-0 |issn=1978-3019 |doi-access=free}} However, it is also shown that {{C4}} plants are able to persist in drought better than the {{C3}} plants.{{Cite journal |last1=Sternberg |first1=Marcelo |last2=Brown |first2=Valerie K. |last3=Masters |first3=Gregory J. |last4=Clarke |first4=Ian P. |date=1999-07-01 |title=Plant community dynamics in a calcareous grassland under climate change manipulations |url=https://doi.org/10.1023/A:1009812024996 |journal=Plant Ecology |language=en |volume=143 |issue=1 |pages=29–37 |doi=10.1023/A:1009812024996 |bibcode=1999PlEco.143...29S |issn=1573-5052 |s2cid=24847776}}

The effects of {{CO2}} enrichment can be most simply attained in a greenhouse (see {{section link|Greenhouse|Carbon dioxide enrichment}} for its agricultural use). However, for experimentation, the results obtained in a greenhouse would be doubted due to it introducing too many confounding variables. Open-air chambers have been similarly doubted, with some critiques attributing, e.g., a decline in mineral concentrations found in these {{CO2}}-enrichment experiments to constraints put on the root system. The current state-of-the art is the FACE methodology, where {{CO2}} is put out directly in the open field.{{cite journal |vauthors=Loladze I |date=May 2014 |title=Hidden shift of the ionome of plants exposed to elevated CO₂ depletes minerals at the base of human nutrition |journal=eLife |volume=3 |pages=e02245 |doi=10.7554/elife.02245 |pmc=4034684 |pmid=24867639 |doi-access=free }} Even then, there are doubts over whether the results of FACE in one part of the world applies to another.

{{Main|Free-air concentration enrichment}}

The ORNL conducted FACE experiments where {{CO2}} levels were increased above ambient levels in forest stands.{{cite web |url=https://face.ornl.gov/expdes.html |title=Oak Ridge Experiment on {{CO2}} Enrichment of Sweetgum: Experimental design |author= |date=Jun 29, 2009 |publisher=ORNL |access-date=Nov 23, 2019 |archive-date=January 9, 2018 |archive-url=https://web.archive.org/web/20180109100001/http://face.ornl.gov/expdes.html |url-status=dead }} These experiments showed:{{cite web |url=https://climatechangescience.ornl.gov/content/free-air-co2 |title=Free-Air {{CO2}} Enrichment (FACE) | vauthors = Norby R |publisher=ORNL |access-date=Nov 23, 2019 }}

• Increased root production stimulated by increased {{CO2}}, resulting in more soil carbon.
• An initial increase of net primary productivity, which was not sustained.
• Faster decline in nitrogen availability in increased {{CO2}} forest plots.
• Change in plant community structure, with minimal change in microbial community structure.{{cite journal| vauthors = Norby RJ, Zak DR |s2cid=85977324 |title=Ecological Lessons from Free-Air {{CO2}} Enrichment (FACE) Experiments|journal=Annual Review of Ecology, Evolution, and Systematics|volume=42|issue=1|year=2011|pages=181–203|issn=1543-592X|doi=10.1146/annurev-ecolsys-102209-144647}}
• Enhanced {{CO2}} cannot significantly increase the leaf carrying capacity or leaf area index of an area.

FACE experiments have been criticized as not being representative of the entire globe. These experiments were not meant to be extrapolated globally. Similar experiments are being conducted in other regions such as in the Amazon rainforest in Brazil.{{cite web |url=https://face.ornl.gov/AmazonFACE.html |title=Amazon FACE Experiment |author= |website=Mar 28, 2015 |publisher=ORNL |access-date=Nov 23, 2019 |archive-date=August 9, 2017 |archive-url=https://web.archive.org/web/20170809093154/http://face.ornl.gov/AmazonFACE.html |url-status=dead }}

Duke University did a study where they dosed a loblolly pine plantation with elevated levels of {{CO2}}.{{cite web |date=16 August 2000 |title=Duke Study Shows Carbon Dioxide Boosts Pine Tree Reproduction |url=https://www.sciencedaily.com/releases/2000/08/000811062434.htm |access-date=9 March 2013 |publisher=Sciencedaily.com}} The studies showed that the pines did indeed grow faster and stronger. They were also less prone to damage during ice storms, which is a factor that limits loblolly growth farther north. The forest did relatively better during dry years. The hypothesis is that the limiting factors in the growth of the pines are nutrients such as nitrogen, which is in deficit on much of the pine land in the Southeast. In dry years, however, the trees do not bump up against those factors since they are growing more slowly because water is the limiting factor. When rain is plentiful trees reach the limits of the site's nutrients and the extra {{CO2}} is not beneficial. Most forest soils in Southeastern region are deficient in nitrogen and phosphorus as well as trace minerals. Pine forests often sit on land that was used for cotton, corn or tobacco. Since these crops depleted originally shallow and infertile soils, tree farmers must work to improve soils.

{{excerpt|Effects of climate change on agriculture#Reduced nutritional value of crops}}

• Effects of climate change on agriculture

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{{Reflist}}

• [http://www.fao.org/docrep/w5183e/w5183e06.htm 4. The CO₂ fertilization effect: higher carbohydrate production and retention as biomass and seed yield]
• [http://www.realclimate.org/index.php/archives/2004/11/co_2-fertilization CO₂ fertilization]

Category:Atmosphere of Earth

Category:Carbon dioxide

Category:Greenhouse gases

Category:Mineral deficiencies