Editing Root (section)

==Environmental interactions==
[[File:Cycas revoluta coralloid roots.JPG|thumb|Coralloid roots of ''[[Cycas revoluta]]'']]
Light has been shown to have some impact on roots, but it's not been studied as much as the effect of light on other plant systems. Early research in the 1930s found that light decreased the effectiveness of [[Indole-3-acetic acid]] on adventitious root initiation. Studies of the pea in the 1950s shows that lateral root formation was inhibited by light, and in the early 1960s researchers found that light could induce positive [[gravitropic]] responses in some situations. The effects of light on root elongation has been studied for [[monocotyledonous]] and [[dicotyledonous]] plants, with the majority of studies finding that light inhibited root elongation, whether pulsed or continuous. Studies of ''[[Arabidopsis]]'' in the 1990s showed negative [[phototropism]] and inhibition of the elongation of root hairs in light sensed by [[phyB]].<ref name=jpp1997>{{cite journal |last1=Kurata |first1=Tetsuya |title=Light-stimulated root elongation in Arabidopsis thaliana |journal=Journal of Plant Physiology |date=1997 |volume=151 |issue=3 |pages=345–351|doi=10.1016/S0176-1617(97)80263-5 |bibcode=1997JPPhy.151..346K |hdl=2115/44841 |hdl-access=free }}</ref>

Certain plants, namely [[Fabaceae]], form [[root nodules]] in order to associate and form a symbiotic relationship with nitrogen-fixing bacteria called [[rhizobia]]. Owing to the high energy required to fix nitrogen from the atmosphere, the bacteria take carbon compounds from the plant to fuel the process. In return, the plant takes nitrogen compounds produced from ammonia by the bacteria.<ref>{{cite book |author=Postgate, J. |year=1998 |title=Nitrogen Fixation |edition=3rd |publisher=Cambridge University Press |location=Cambridge, UK}}</ref>

Soil temperature is a factor that effects [[root initiation]] and length. Root length is usually impacted more dramatically by temperature than overall mass, where cooler temperatures tend to cause more lateral growth because downward extension is limited by cooler temperatures at subsoil levels. Needs vary by plant species, but in temperate regions cool temperatures may limit root systems. Cool temperature species like [[oats]], [[rapeseed]], [[rye]], [[wheat]] fare better in lower temperatures than summer [[Annual plant|annuals]] like [[maize]] and [[cotton]]. Researchers have found that plants like cotton develop wider and shorter [[taproot]]s in cooler temperatures. The first root originating from the seed usually has a wider diameter than root branches, so smaller root diameters are expected if temperatures increase root initiation. Root diameter also decreases when the root elongates.<ref name=encyclopedia>{{Cite book|last=Lal|first=Rattan|url=https://books.google.com/books?id=627Qopsj7bsC|title=Encyclopedia of Soil Science|date=2006|publisher=CRC Press|isbn=978-0-8493-5054-2|language=en}}</ref>