Editing Weathering (section)

===Biological===
Mineral weathering can also be initiated or accelerated by soil microorganisms. Soil organisms make up about 10&nbsp;mg/cm<sup>3</sup> of typical soils, and laboratory experiments have demonstrated that [[albite]] and [[muscovite]] weather twice as fast in live versus sterile soil. [[Lichens]] on rocks are among the most effective biological agents of chemical weathering.{{sfn|Blatt|Middleton|Murray|1980|p=250}} For example, an experimental study on hornblende granite in New Jersey, US, demonstrated a 3x – 4x increase in weathering rate under lichen covered surfaces compared to recently exposed bare rock surfaces.<ref>{{cite journal|doi=10.1016/j.chemgeo.2011.10.009|title=Effect of lichen colonization on chemical weathering of hornblende granite as estimated by aqueous elemental flux|date=2012|last1=Zambell|first1=C.B.|last2=Adams|first2=J.M.|last3=Gorring|first3=M.L.|last4=Schwartzman|first4=D.W.|journal=Chemical Geology|volume=291|pages=166–174|bibcode=2012ChGeo.291..166Z}}</ref>

[[File:lava z14.jpg|thumb|right|Biological weathering of [[basalt]] by [[lichen]], [[La Palma]]]]
The most common forms of biological weathering result from the release of [[chelating]] compounds (such as certain organic acids and [[siderophore]]s) and of carbon dioxide and organic acids by plants. Roots can build up the carbon dioxide level to 30% of all soil gases, aided by adsorption of {{CO2}} on clay minerals and the very slow diffusion rate of {{CO2}} out of the soil.<ref>{{cite journal |last1=Fripiat |first1=J. J. |title=Interlamellar Adsorption of Carbon Dioxide by Smectites |journal=Clays and Clay Minerals |date=1974 |volume=22 |issue=1 |pages=23–30 |doi=10.1346/CCMN.1974.0220105|bibcode=1974CCM....22...23F |s2cid=53610319 |url=http://www.clays.org/journal/archive/volume%2022/22-1-23.pdf |url-status=dead |archive-url=https://web.archive.org/web/20180603022725/http://www.clays.org/journal/archive/volume%2022/22-1-23.pdf |archive-date= Jun 3, 2018 }}</ref> The {{CO2}} and organic acids help break down [[aluminium]]- and [[iron]]-containing compounds in the soils beneath them. Roots have a negative electrical charge balanced by protons in the soil next to the roots, and these can be exchanged for essential nutrient cations such as potassium.{{sfn|Blatt|Middleton|Murray|1980|pp=251}} [[Bacterial decay|Decaying]] remains of dead plants in soil may form organic acids which, when dissolved in water, cause chemical weathering.<ref>{{cite book|last=Chapin III|first=F. Stuart|author2=Pamela A. Matson |author3=Harold A. Mooney |title=Principles of terrestrial ecosystem ecology |url=https://books.google.com/books?id=OOH1H779-7EC&pg=PA54 |date=2002|publisher=Springer|location=New York|isbn=9780387954431|pages=54–55|edition=[Nachdr.]}}</ref> Chelating compounds, mostly low molecular weight organic acids, are capable of removing metal ions from bare rock surfaces, with aluminium and silicon being particularly susceptible.{{sfn|Blatt|Tracy|1996|p=233}} The ability to break down bare rock allows lichens to be among the first colonizers of dry land.{{sfn|Blatt|Middleton|Murray|1980|pp=250-251}} The accumulation of chelating compounds can easily affect surrounding rocks and soils, and may lead to [[podsol]]isation of soils.<ref>{{Cite journal|last1=Lundström|first1=U. S.|last2=van Breemen|first2=N.|last3=Bain|first3=D. C.|last4=van Hees|first4=P. A. W.|last5=Giesler|first5=R.|last6=Gustafsson|first6=J. P.|last7=Ilvesniemi|first7=H.|last8=Karltun|first8=E.|last9=Melkerud|first9=P. -A.|last10=Olsson|first10=M.|last11=Riise|first11=G.|date=2000-02-01|title=Advances in understanding the podzolization process resulting from a multidisciplinary study of three coniferous forest soils in the Nordic Countries|url=http://www.sciencedirect.com/science/article/pii/S0016706199000774|journal=Geoderma|language=en|volume=94|issue=2|pages=335–353|doi=10.1016/S0016-7061(99)00077-4|bibcode=2000Geode..94..335L|issn=0016-7061}}</ref><ref>{{cite book|last=Waugh|first=David|title=Geography : an integrated approach|date=2000|publisher=[[Nelson Thornes]]|location=Gloucester, U.K.|isbn=9780174447061|page=272|edition=3rd}}</ref>

The symbiotic [[Mycorrhiza|mycorrhizal fungi]] associated with tree root systems can release inorganic nutrients from minerals such as apatite or biotite and transfer these nutrients to the trees, thus contributing to tree nutrition.<ref>{{cite journal|author=Landeweert, R. |author2=Hoffland, E. |author3=Finlay, R.D. |author4=Kuyper, T.W. |author5=van Breemen, N. |author-link5=Nico van Breemen|pmid=11301154|date=2001|title=Linking plants to rocks: Ectomycorrhizal fungi mobilize nutrients from minerals|volume=16|issue=5|pages=248–254|journal=Trends in Ecology & Evolution|doi=10.1016/S0169-5347(01)02122-X}}</ref>  It was also recently evidenced that bacterial communities can impact mineral stability leading to the release of inorganic nutrients.<ref>{{cite journal|author=Calvaruso, C.|author2=Turpault, M.-P.|author3=Frey-Klett, P.|doi=10.1128/AEM.72.2.1258-1266.2006|title=Root-Associated Bacteria Contribute to Mineral Weathering and to Mineral Nutrition in Trees: A Budgeting Analysis|date=2006|journal=Applied and Environmental Microbiology|volume=72|issue=2|pages=1258–66|pmid=16461674|pmc=1392890 |bibcode=2006ApEnM..72.1258C}}</ref> A large range of bacterial strains or communities from diverse genera have been reported to be able to colonize mineral surfaces or to weather minerals, and for some of them a plant growth promoting effect has been demonstrated.<ref>{{cite journal|author=Uroz, S.|author2=Calvaruso, C.|author3=Turpault, M.-P.|author4=Frey-Klett, P.|title=Mineral weathering by bacteria: ecology, actors and mechanisms|journal=Trends Microbiol|date= 2009|volume=17|issue=8|pages=378–87|doi=10.1016/j.tim.2009.05.004|pmid=19660952}}</ref>  The demonstrated or hypothesised mechanisms used by bacteria to weather minerals include several oxidoreduction and dissolution reactions as well as the production of weathering agents, such as protons, organic acids and chelating molecules.