Study of pollen and other acid-resistant microoscopic organic material
Pinepollen under the microscope A lateSiluriansporangium bearingtrilete spores. Such spores provide the earliest evidence of life on land.[1]Green: A spore tetrad.Blue: A spore bearing a trilete mark – the Y-shaped scar. The spores are about 30–35 μm across.
Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur insediments,sedimentary rocks, and even some metasedimentary rocks.Palynomorphs are the microscopic, acid-resistant organic remains and debris produced by a wide variety ofplants,animals, andProtista that have existed since the lateProterozoic.[2][3]
Palynology is quite useful in disciplines such asarcheology, in honey production, andcriminal andcivil law.[3][4] In archaeology, palynology is widely used to reconstruct ancient paleoenvironments and environmental shifts that significantly influenced past human societies and reconstruct the diet of prehistoric and historic humans.Melissopalynology, the study of pollen and other palynomorphs inhoney, identifies the sources of pollen in terms of geographical location(s) andgenera of plants. This not only provides important information on theecology of honey bees, it also an important tool in discovering and policing the criminal adultriation and mislabeling of honey and its products.Forensic palynology uses palynomorphs as evidence in criminal and civil law to prove or disprove a physical link between objects, people, and places.[4][5]
Palynomorphs are broadly defined as organic remains, includingmicrofossils, and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and range in size between 5 and 500micrometres. They are extracted from soils,sedimentary rocks andsediment cores, and other materials by a combination of physical (ultrasonic treatment andwet sieving) and chemical (acid digestion) procedures to remove the non-organic fraction. Palynomorphs may be composed of organic material such aschitin,pseudochitin andsporopollenin.[6]
Palynomorphs form ageological record of importance in determining the type ofprehistoric life that existed at the time the sedimentarystrata was laid down. As a result, these microfossils give important clues to the prevailingclimatic conditions of the time. Their paleontological utility derives from an abundance numbering in millions of palynomorphs per gram in organic marine deposits, even when such deposits are generally notfossiliferous. Palynomorphs, however, generally have been destroyed inmetamorphic or recrystallized rocks.[6]
Organic palynofacies considers all the acid insolubleparticulate organic matter (POM), includingkerogen andpalynomorphs in sediments and palynological preparations of sedimentary rocks. The sieved or unsieved preparations may be examined usingstrew mounts on microscope slides that may be examined using a transmitted light biological microscope orultraviolet (UV) fluorescence microscope. The abundance, composition and preservation of the various components, together with the thermal alteration of the organic matter is considered.
Palynomorph palynofacies considers the abundance, composition and diversity of palynomorphs in a sieved palynological preparation of sediments or palynological preparation ofsedimentary rocks. The ratio ofmarinefossilphytoplankton (acritarchs anddinoflagellate cysts), together withchitinozoans, to terrestrial palynomorphs (pollen andspores) can be used to derive a terrestrial input index in marine sediments.
The earliest reported observations of pollen under a microscope are likely to have been in the 1640s by the EnglishbotanistNehemiah Grew,[10] who described pollen and the stamen, and concluded that pollen is required for sexual reproduction in flowering plants.
Quantitative analysis of pollen began withLennart von Post's published work.[12] Although he published in the Swedish language, his methodology gained a wide audience through his lectures. In particular, hisKristiania lecture of 1916 was important in gaining a wider audience.[13] Because the early investigations were published in the Nordic languages (Scandinavian languages), the field of pollen analysis was confined to those countries.[14] The isolation ended with the German publication ofGunnar Erdtman's 1921 thesis. The methodology of pollen analysis became widespread throughoutEurope andNorth America and revolutionizedQuaternary vegetation andclimate change research.[13][15]
Earlier pollen researchers include Früh (1885),[16] who enumerated many common tree pollen types, and a considerable number ofspores andherb pollen grains. There is a study of pollen samples taken from sediments of Swedish lakes by Trybom (1888);[17]pine andspruce pollen was found in such profusion that he considered them to be serviceable as "index fossils".Georg F. L. Sarauw studied fossil pollen of middle Pleistocene age (Cromerian) from the harbour ofCopenhagen.[18] Lagerheim (in Witte 1905) and C. A.Weber (in H. A. Weber 1918) appear to be among the first to undertake 'percentage frequency' calculations.
The termpalynology was introduced by Hyde and Williams in 1944, following correspondence with the SwedishgeologistErnst Antevs, in the pages of thePollen Analysis Circular (one of the first journals devoted to pollen analysis, produced byPaul Sears in North America). Hyde and Williams chosepalynology on the basis of theGreek wordspaluno meaning 'to sprinkle' andpale meaning 'dust' (and thus similar to theLatin wordpollen).[19] The archive-based background to the adoption of the termpalynology and to alternative names (e.g.paepalology,pollenology) has been exhaustively explored.[20] It has been argued there that the word gained general acceptance once used by the influential Swedish palynologistGunnar Erdtman.
Pollen analysis in North America stemmed fromPhyllis Draper, an MS student under Sears at the University of Oklahoma. During her time as a student, she developed the first pollen diagram from a sample that depicted the percentage of several species at different depths at Curtis Bog. This was the introduction of pollen analysis in North America;[21] pollen diagrams today still often remain in the same format with depth on the y-axis and abundances of species on the x-axis.
Pollen analysis advanced rapidly in this period due to advances in optics and computers. Much of the science was revised byJohannes Iversen andKnut Fægri in their textbook on the subject.[22]
Chemical digestion follows a number of steps.[23] Initially the only chemical treatment used by researchers was treatment withpotassium hydroxide (KOH) to removehumic substances; defloculation was accomplished through surface treatment or ultra-sonic treatment, although sonification may cause the pollen exine to rupture.[14] In 1924, the use ofhydrofluoric acid (HF) to digestsilicateminerals was introduced by Assarson and Granlund, greatly reducing the amount of time required to scan slides for palynomorphs.[24]
Palynological studies using peats presented a particular challenge because of the presence of well-preserved organic material, including fine rootlets, moss leaflets and organic litter. This was the last major challenge in the chemical preparation of materials for palynological study.Acetolysis was developed by Gunnar Erdtman and his brother to remove these fine cellulose materials by dissolving them.[25] In acetolysis the specimen is treated withacetic anhydride andsulfuric acid, dissolvingcellulistic materials and thus providing better visibility for palynomorphs.[26]
Some steps of the chemical treatments require special care for safety reasons, in particular the use of HF which diffuses very fast through the skin and, causes severe chemical burns, and can be fatal.[27]
Another treatment includes kerosene flotation forchitinous materials.
Once samples have been prepared chemically, they are mounted onmicroscope slides using silicon oil, glycerol or glycerol-jelly and examined using lightmicroscopy or mounted on a stub forscanning electron microscopy.
Researchers will often study either modern samples from a number of unique sites within a given area, or samples from a single site with a record through time, such as samples obtained frompeat or lake sediments. More recent studies have used the modern analog technique in which paleo-samples are compared to modern samples for which the parent vegetation is known.[28]
When the slides are observed under a microscope, the researcher counts the number of grains of each pollen taxon. This record is next used to produce apollen diagram. These data can be used to detectanthropogenic effects, such as logging,[29] traditional patterns of land use[30] or long term changes in regional climate[31]
Organicpalynofacies studies, which examine the preservation of the particulate organic matter andpalynomorphs provides information on the depositional environment of sediments and depositional palaeoenvironments ofsedimentary rocks.
Taxonomy andevolutionary studies. Involving the use of pollen morphological characters as source of taxonomic data to delimit plant species under same family or genus. Pollen apertural status is frequently used for differential sorting or finding similarities between species of the same taxa. This is also called Palynotaxonomy.
Allergy studies andpollen counting. Studies of the geographic distribution and seasonal production of pollen, can be used to forecast pollen conditions, helping sufferers of allergies such ashay fever.
Archaeological palynology examines human uses of plants in the past. This can help determine seasonality of site occupation, presence or absence of agricultural practices or products, and 'plant-related activity areas' within an archaeological context.Bonfire Shelter is one such example of this application.
^Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds., 2005,Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp.ISBN0-922152-76-4
^abcdWilliams, G., Fensome, R.A., Miller, M. and Bujak, J., 2020.Microfossils: palynology. In Sorkhabi, R., ed., 15 pp.,Encyclopedia of Petroleum Geoscience. Geneva, Switzerland, Springer Nature. 1000 pp.
^abcdKneller, M., and Fowell, F., 2009.Palynology. In Gornitz, V., ed., pp. 766-768.,Encyclopedia of Paleoclimatology and Ancient Environments. Geneva, Switzerland, Springer Dordrecht. 1049 pp.
^Laurence, A.R., and Bryant, V.M., 2009.Forensic Palynology. In Bruinsma, G., and Weisburd, D., ed., pp. 1471-1754.,Encyclopedia of Criminology and Criminal Justice. New York, New York, Springer Science+Business Media. 5632 pp.
^abcTraverse, A., 2007,Paleopalynology (2nd ed.). Amsterdam, the Netherlands, Springer-Dordrecht. 813 pp.ISBN978-1-4020-5609-3
^Fonseca, Carolina; Mendonça Filho, João Graciano; Lézin, Carine; Duarte, Luís V.; Fauré, Phillipe (April 2018). "Organic facies variability during the Toarcian Oceanic Anoxic Event record of the Grands Causses and Quercy basins (southern France)".International Journal of Coal Geology.190:218–235.Bibcode:2018IJCG..190..218F.doi:10.1016/j.coal.2017.10.006.
^Fonseca, Carolina; Oliveira Mendonça, Joalice; Mendonça Filho, João Graciano; Lézin, Carine; Duarte, Luís V. (March 2018). "Thermal maturity assessment study of the late Pliensbachian-early Toarcian organic-rich sediments in southern France: Grands Causses, Quercy and Pyrenean basins".Marine and Petroleum Geology.91:338–349.Bibcode:2018MarPG..91..338F.doi:10.1016/j.marpetgeo.2018.01.017.
^Traverse, Alfred and Sullivan, Herbert J. "The Background, Origin, and Early History of the American Association of Stratigraphic Palynologists" Palynology 7: 7-18 (1983)
^abFaegri, Knut (1973). "In memoriam O. Gunnar E. Erdtman".Pollen et Spores.15:5–12.
^von Post, L (1918) "Skogsträdpollen i sydsvenska torvmosslagerföljder", Forhandlinger ved de Skandinaviske naturforskeres 16. møte i Kristiania 1916: p. 433
^Früh, J (1885) "Kritische Beiträge zur Kenntnis des Torfes", Jahrb.k.k.Geol.Reichsanstalt 35
^Trybom, F (1888) "Bottenprof fran svenska insjöar", Geol.Foren.Forhandl.10
^Fægri, K. & Iversen, J. (1989)Textbook of pollen analysis. 4th ed. John Wiley & Sons, Chichester. 328 p.
^Bennett, K.D.; Willis, K.J. (2001). "Pollen". In Smol, John P.; Birks, H. John B.; Last, William M. (eds.).Tracking Environmental Change Using Lake Sediments. Volume 3: Terrestrial, algal, and siliceous indicators. Dordrecht: Kluwer Academic Publishers. pp. 5–32.
^Assarson, G. och E.; Granlund, E. (1924). "En metod for pollenanalys av minerogena jordarter".Geologiska Föreningen i Stockholm Förhandlingar.46 (1–2):76–82.doi:10.1080/11035892409444879.
