Editing Soil pH (section)

=== Acid soils ===
High levels of aluminium occur near mining sites; small amounts of aluminium are released to the environment at the coal-fired power plants or [[Incineration|incinerators]].<ref name="ATSDR Public Health">{{cite web |url=https://www.atsdr.cdc.gov/ToxProfiles/tp22-c1-b.pdf |title=Public health statement for aluminum |website=www.atsdr.cdc.gov |language=en |date=September 2008 |access-date=12 March 2023 |archive-date=12 December 2016 |archive-url=https://web.archive.org/web/20161212212014/https://www.atsdr.cdc.gov/phs/phs.asp?id=1076&tid=34 |url-status=live}}</ref> Aluminium in the air is washed out by the rain or normally settles down but small particles of aluminium remain in the air for a long time.<ref name="ATSDR Public Health" />

Acidic [[precipitation]] is the main natural factor to mobilize aluminium from natural sources<ref name="Piero3">{{cite journal |last=Dolara |first=Piero |date=21 July 2014 |title=Occurrence, exposure, effects, recommended intake and possible dietary use of selected trace compounds (aluminium, bismuth, cobalt, gold, lithium, nickel, silver) |journal=[[International Journal of Food Sciences and Nutrition]] |volume=65 |issue=8 |pages=911–24 |doi=10.3109/09637486.2014.937801 |issn=1465-3478 |pmid=25045935 |s2cid=43779869 |url=https://lib-nhwjx7zkiyjoeipfyn7m37ed.late.re/book/35772390/5dc19c |access-date=12 March 2023}}</ref> and the main reason for the environmental effects of aluminium;<ref name="RosselandEldhuset1990">{{cite journal |last1=Rosseland |first1=Bjorn Olav |last2=Eldhuset |first2=Toril Drabløs |last3=Staurnes |first3=Magne |year=1990 |title=Environmental effects of aluminium |journal=Environmental Geochemistry and Health |volume=12 |issue=1–2 |pages=17–27 |doi=10.1007/BF01734045 |pmid=24202562 |bibcode=1990EnvGH..12...17R |s2cid=23714684 |issn=0269-4042 |url=https://www.researchgate.net/publication/258348898 |access-date=12 March 2023}}</ref> however, the main factor of presence of aluminium in salt and freshwater are the industrial processes that also release aluminium into air.<ref name="Piero3" /> Plants grown in acid soils can experience a variety of stresses including [[aluminium]]&nbsp;(Al), [[hydrogen]]&nbsp;(H), and/or [[manganese]]&nbsp;(Mn) toxicity, as well as nutrient deficiencies of [[calcium]]&nbsp;(Ca) and [[magnesium]]&nbsp;(Mg).<ref>{{cite book |title=The nature and properties of soils, global edition |edition=15th |year=2016 |last1=Weil |first1=Raymond R. |last2=Brady |first2=Nyle C. |isbn=9781292162232 |url=https://lib-nhwjx7zkiyjoeipfyn7m37ed.late.re/book/3515307/f40531 |access-date=19 March 2023 |publisher=[[Pearson Education]] |location=London, United Kingdom}}</ref>

[[Aluminium#Environmental effects|Aluminium toxicity]] is the most widespread problem in acid soils.  Aluminium is present in all soils to varying degrees, but dissolved Al<sup>3+</sup> is toxic to plants; Al<sup>3+</sup> is most soluble at low pH; above pH&nbsp;5.0, there is little Al in soluble form in most soils.<ref name="Kopittke2016">{{cite journal |last1=Kopittke |first1=Peter M. |last2=Menzies |first2=Neal W. |last3=Wang |first3=Peng |last4=Blamey |first4=F. Pax C. |title=Kinetics and nature of aluminium rhizotoxic effects: a review |journal=[[Journal of Experimental Botany]] |date=August 2016 |volume=67 |issue=15 |pages=4451–67 |doi=10.1093/jxb/erw233 |pmid=27302129 |url=https://articles-pdjrj4ripo5k3r4j2r4mhmo5.late.re/book/55935402/d61ab1 |access-date=19 March 2023}}</ref><ref>{{cite journal |last1=Hansson |first1=Karna |last2=Olsson |first2=Bengt A. |last3=Olsson |first3=Mats |last4=Johansson |first4=Ulf |last5=Kleja |first5=Dan Berggren |title=Differences in soil properties in adjacent stands of Scots pine, Norway spruce and silver birch in SW Sweden |journal=[[Forest Ecology and Management]] |date=August 2011 |volume=262 |issue=3 |pages=522–30 |doi=10.1016/j.foreco.2011.04.021 |url=https://www.academia.edu/16589041 |access-date=19 March 2023}}</ref> Aluminium is not a plant nutrient, and as such, is not actively taken up by the plants, but enters plant roots passively through [[osmosis]]. Aluminium can exist in many different forms and is a responsible agent for limiting growth in various parts of the world. Aluminium tolerance studies have been conducted in different plant species to see viable thresholds and concentrations exposed along with function upon exposure.<ref>{{cite journal |last1=Wright |first1=Robert J. |title=Soil aluminum toxicity and plant growth |journal=Communications in Soil Science and Plant Analysis |date=September 1989 |volume=20 |issue=15–16 |pages=1479–97 |doi=10.1080/00103628909368163 |bibcode=1989CSSPA..20.1479W |url=https://articles-pdjrj4ripo5k3r4j2r4mhmo5.late.re/book/21233659/9e6a73 |access-date=19 March 2023}}</ref> Aluminium inhibits root growth; lateral roots and root tips become thickened and roots lack fine branching; root tips may turn brown. In the root, the initial effect of Al<sup>3+</sup> is the inhibition of the expansion of the cells of the [[rhizodermis]], leading to their rupture; thereafter it is known to interfere with many physiological processes including the uptake and transport of calcium and other essential nutrients, cell division, cell wall formation, and enzyme activity.<ref name="Kopittke2016"/><ref>{{cite journal |last1=Rout |first1=Gyana Ranjan |last2=Samantaray |first2=Sanghamitra |last3=Das |first3=Premananda |title=Aluminium toxicity in plants: a review |journal=Agronomie |date=January 2001 |volume=21 |issue=1 |pages=3–21 |doi=10.1051/agro:2001105 |bibcode=2001AgSD...21....3R |url=https://hal.science/hal-00886101/document |access-date=19 March 2023}}</ref>

Proton (H<sup>+</sup> ion) stress can also limit plant growth. The [[proton pump]], H<sup>+</sup>-ATPase, of the [[plasmalemma]] of root cells works to maintain the near-neutral pH of their [[cytoplasm]]. A high proton activity (pH within the range 3.0–4.0 for most plant species) in the external growth medium overcomes the capacity of the cell to maintain the cytoplasmic pH and growth shuts down.<ref name="Shavrukov2016">{{cite journal |last1=Shavrukov |first1=Yuri |last2=Hirai |first2=Yoshihiko |title=Good and bad protons: genetic aspects of acidity stress responses in plants |journal=[[Journal of Experimental Botany]] |date=January 2016 |volume=67 |issue=1 |pages=15–30 |doi=10.1093/jxb/erv437 |pmid=26417020 |doi-access=free}}</ref>

In soils with a high content of [[manganese]]-containing minerals, Mn toxicity can become a problem at pH 5.6 and lower.  Manganese, like aluminium, becomes increasingly soluble as pH drops, and Mn toxicity symptoms can be seen at pH levels below 5.6.  Manganese is an essential plant nutrient, so plants transport Mn into leaves.  Classic symptoms of Mn toxicity are crinkling or cupping of leaves.<ref>{{cite journal |last=Ramakrishnan |first=Palayanoor Sivaswamy |title=Nutritional requirements of the edaphic ecotypes in ''Melilotus alba'' Medic. II. Aluminium and manganese |journal=[[New Phytologist]] |date=April 1968 |volume=67 |issue=2 |pages=301–08 |doi=10.1111/j.1469-8137.1968.tb06385.x |doi-access=free}}</ref>