acanthochronology

{{Short description|Study of cactus spines and the chronology of their growth}}

Acanthochronology is the study of cactus spines or Euphorbia thorns grown in time ordered sequence (i.e. in series). Physical, morphological or chemical characteristics and information about the relative order or absolute age of the spines or thorns is used to study past climate or plant physiology.

File:Time ordered spines.jpg cactus in Tucson, Arizona. The numbers written on the cactus in black ink denote the order that the spines grew - youngest towards the apex, oldest towards the base.]]

For example, columnar cactus spines grow from the apex of the plant. After several weeks the spines stop growing and have been moved to the side of the stem. The old spines remain in place for decades as new spines are created at the continually growing apex.{{cite journal |doi=10.1093/aob/mcl133 |pmid=16820405 |title=Structure-Function Relationships in Highly Modified Shoots of Cactaceae |journal=Annals of Botany |volume=98 |issue=5 |pages=901–926 |year=2006 |last1=Mauseth |first1=J. D |pmc=2803597 }} The result is that along each external "rib" of the cactus is a series of spines arranged in the order they grew in – the oldest spines are at the bottom and the youngest spines are at the top. These spines can be dated using bomb-spike{{cite journal |doi=10.1017/s0033822200033142 |journal=Radiocarbon |volume=46 |issue=3 |pages=1273–1298 |year=2004 |last1=Hua |first1=Quan |title=Review of Tropospheric Bomb 14C Data for Carbon Cycle Modeling and Age Calibration Purposes |last2=Barbetti |first2=Mike |bibcode=2004Radcb..46.1273H |doi-access=free }} Carbon-14 and isotopes of carbon (Carbon-13) and oxygen (Oxygen-18) may be used to infer past climate{{cite journal |doi=10.1007/s00442-007-0832-x |title=Past climate changes and ecophysiological responses recorded in the isotope ratios of saguaro cactus spines |journal=Oecologia |volume=154 |issue=2 |pages=247–258 |year=2007 |last1=English |first1=Nathan B |last2=Dettman |first2=David L |last3=Sandquist |first3=Darren R |last4=Williams |first4=David G |pmid=17724618 |bibcode=2007Oecol.154..247E |s2cid=282478 }} (e.g. precipitation or temperature), plant stem growth{{cite journal |doi=10.1017/RDC.2016.25 |title=On the Age and Growth Rate of Giant Cacti: Radiocarbon Dating of the Spines of Cardon (Pachycereus Pringlei) |journal=Radiocarbon |volume=58 |issue=3 |pages=479–490 |year=2016 |last1=Delgado-Fernández |first1=Mariana |last2=Garcillán |first2=Pedro P |last3=Ezcurra |first3=Exequiel |bibcode=2016Radcb..58..479D |s2cid=130664993 }} or plant physiology (e.g. photosynthetic processes).{{cite journal |doi=10.1093/jxb/erz320 |title=Giant cacti: isotopic recorders of climate variation in warm deserts of the Americas |journal=Journal of Experimental Botany |volume= 70|issue= 22|pages= 6509–6519|year=2019 |last1=Hultine |first1=Kevin R |last2=Dettman |first2=David L |last3=English |first3=Nathan B |last4=Williams |first4=David G |pmid=31269200 }} Alternatively, the width of small transverse bands{{cite journal |doi=10.1029/2009JG001008 |title=Daily to decadal patterns of precipitation, humidity, and photosynthetic physiology recorded in the spines of the columnar cactus, Carnegiea gigantea |journal=Journal of Geophysical Research: Biogeosciences |volume=115 |year=2010 |last1=English |first1=Nathan B |last2=Dettman |first2=David L |last3=Sandquist |first3=Darren R |last4=Williams |first4=David G |issue=G2 |pages=n/a |bibcode=2010JGRG..115.2013E |url=http://repository.uwyo.edu/cgi/viewcontent.cgi?article=1025&context=botany_facpub |hdl=20.500.11919/768 |hdl-access=free }} in the spine may be used to infer daily information about cloud cover or plant productivity, although this remains to be tested. It has also been shown that regular waxy banding on the sides of a Costa Rican cactus (Lemaireocereus aragonii) indicate annual growth and can be used as temporal chronometers.{{cite journal |doi=10.2307/2388815 |jstor=2388815 |title=Annual Waxy Bands on a Costa Rican Cactus |journal=Biotropica |volume=26 |issue=2 |pages=229 |year=1994 |last1=Buskirk |first1=Ruth E |last2=Otis |first2=Gard W }}

File:Transverse banding on cactus spine.jpg. Each band (1 couplet of thick white and thin red lines) represents one day of spine growth. Each square in the bottom scale = 1 centimeter.]]

This sub-discipline of paleoclimatology and ecophysiology is relatively new. Acanthochronology is closely related to dendrochronology, dendroclimatology and isotope geochemistry and borrows many of the methods and techniques from these sub-disciplines of the Earth Sciences. It also draws heavily from the field of ecophysiology, a branch of Biology, to ascribe spine or thorn characteristics to particular environmental or physiological variables.{{citation needed|date=August 2018}}

The first peer-reviewed article to present and explain an isotope spine series was from a saguaro cactus in Tucson, Arizona. This and other work shows that radiocarbon and isotope time-series derived from spines can be used for demographic or palaeoclimate studies.

File:Isotope spine series from a saguaro cactus.jpg