Editing Plant physiology

{{for|the scientific journal of the same name|Plant Physiology (journal)}}
{{short description|Subdiscipline of botany}}[[Image:Kiemtafel (germination table).jpg|thumb|180x180px|A germination rate experiment]]'''Plant physiology''' is a subdiscipline of [[botany]] concerned with the functioning, or [[physiology]], of [[plant]]s.<ref name="Salisbury & Ross 1992">{{cite book| author = Frank B. Salisbury|author2=Cleon W. Ross | title = Plant physiology| year = 1992| publisher = Brooks/Cole Pub Co| isbn = 0-534-15162-0 }}</ref>

Plant physiologists study fundamental processes of plants, such as [[photosynthesis]], [[cellular respiration|respiration]], [[plant nutrition]], [[plant hormone]] functions, [[tropism]]s, [[nastic movements]], [[photoperiodism]], [[photomorphogenesis]], [[circadian rhythms]], [[environmental stress]] physiology, seed [[germination]], [[dormancy]] and [[stoma]]ta function and [[transpiration]]. Plant physiology interacts with the fields of [[plant morphology]] (structure of plants), plant [[ecology]] (interactions with the environment), [[phytochemistry]] ([[biochemistry]] of plants), [[cell biology]], genetics, biophysics and [[molecular biology]].

==Aims==
{{citations needed|section|date=January 2024}}
The field of plant physiology includes the study of all the internal activities of plants—those chemical and physical processes associated with [[life]] as they occur in plants.  This includes study at many levels of scale of size and time. At the smallest scale are [[molecule|molecular]] interactions of [[photosynthesis]] and internal [[diffusion]] of water, minerals, and nutrients.  At the largest scale are the processes of plant [[Developmental biology|development]], [[season]]ality, [[dormancy]], and [[reproductive]] control.  Major subdisciplines of plant physiology include [[phytochemistry]] (the study of the [[biochemistry]] of plants) and [[phytopathology]] (the study of [[disease]] in plants). The scope of plant physiology as a discipline may be divided into several major areas of research.

[[Image:Plant physiology.png|thumb|240px|Five key areas of study within plant physiology.]]
First, the study of [[phytochemistry]] (plant chemistry) is included within the domain of plant physiology.  To function and survive, plants produce a wide array of chemical compounds not found in other organisms.  [[Photosynthesis]] requires a large array of [[pigment]]s, [[enzyme]]s, and other compounds to function.  Because they cannot move, plants must also defend themselves chemically from [[herbivore]]s, [[pathogen]]s and competition from other plants.  They do this by producing [[toxin]]s and foul-tasting or smelling chemicals.  Other compounds defend plants against disease, permit survival during drought, and prepare plants for dormancy, while other compounds are used to attract [[pollinator]]s or herbivores to spread ripe seeds.

Secondly, plant physiology includes the study of biological and chemical processes of individual plant [[cell (biology)|cells]]. Plant cells have a number of features that distinguish them from cells of [[animal]]s, and which lead to major differences in the way that plant life behaves and responds differently from animal life.  For example, plant cells have a [[cell wall]] which maintains the shape of plant cells.  Plant cells also contain [[chlorophyll]], a chemical compound that interacts with [[light]] in a way that enables plants to manufacture their own nutrients rather than consuming other living things as animals do.

Thirdly, plant physiology deals with interactions between cells, [[tissue (biology)|tissues]], and organs within a plant.  Different cells and tissues are physically and chemically specialized to perform different functions.  [[Root]]s and [[rhizoid]]s function to anchor the plant and acquire minerals in the soil.  [[Leaf|Leaves]] catch light in order to manufacture nutrients. For both of these organs to remain living, minerals that the roots acquire must be transported to the leaves, and the nutrients manufactured in the leaves must be transported to the roots.  Plants have developed a number of ways to achieve this transport, such as [[vascular tissue]], and the functioning of the various modes of transport is studied by plant physiologists.

Fourthly, plant physiologists study the ways that plants control or regulate internal functions.  Like animals, plants produce chemicals called [[plant hormone|hormones]] which are produced in one part of the plant to signal cells in another part of the plant to respond.  Many [[flowering plant]]s bloom at the appropriate time because of light-sensitive compounds that respond to the length of the night, a phenomenon known as [[photoperiodism]].  The [[ripening]] of [[fruit]] and loss of leaves in the winter are controlled in part by the production of the gas [[Ethylene as a plant hormone|ethylene]] by the plant.

Finally, plant physiology includes the study of plant response to environmental conditions and their variation, a field known as [[#Environmental physiology|environmental physiology]].  Stress from water loss, changes in air chemistry, or crowding by other plants can lead to changes in the way a plant functions.  These changes may be affected by genetic, chemical, and physical factors.

==Biochemistry of plants==
[[Image:Latex dripping.JPG|thumb|[[Rubber|Latex]] being collected from a [[rubber tapping|tapped]] [[rubber tree]].]]
{{main|Phytochemistry}}
{{citations needed|section|date=January 2024}}
The [[chemical element]]s of which plants are constructed—principally [[carbon]], [[oxygen]], [[hydrogen]], [[nitrogen]], [[phosphorus]], [[sulfur]], etc.—are the same as for all other life forms: animals, fungi, [[bacteria]] and even [[virus]]es.  Only the details of their individual molecular structures vary.

Despite this underlying similarity, plants produce a vast array of chemical compounds with unique properties which they use to cope with their environment.  [[Pigment]]s are used by plants to absorb or detect light, and are extracted by humans for use in [[dye]]s. Other plant products may be used for the manufacture of commercially important [[rubber]] or [[biofuel]].  Perhaps the most celebrated compounds from plants are those with [[pharmacological]] activity, such as [[salicylic acid]] from which [[aspirin]] is made, [[morphine]], and [[digoxin]].  [[Drug company|Drug companies]] spend billions of dollars each year researching plant compounds for potential medicinal benefits.

===Constituent elements===
{{further|Plant nutrition}}

Plants require some [[nutrient]]s, such as [[carbon]] and [[nitrogen]], in large quantities to survive.  Some nutrients are termed [[Macronutrient (ecology)|macronutrients]], where the prefix ''macro-'' (large) refers to the quantity needed, not the size of the nutrient particles themselves.  Other nutrients, called [[micronutrient]]s, are required only in trace amounts for plants to remain healthy.  Such micronutrients are usually absorbed as [[ion]]s dissolved in water taken from the soil, though [[carnivorous plant]]s acquire some of their micronutrients from captured prey.

The following tables list [[chemical element|element]] nutrients essential to plants.  Uses within plants are generalized.

{| class="wikitable"
|-
|+ '''Macronutrients''' – necessary in large quantities
|-
| Element || Form of uptake || Notes
|-
| style="height:50px;"| [[Nitrogen]] || NO<sub>3</sub><sup>−</sup>, NH<sub>4</sub><sup>+</sup>|| Nucleic acids, proteins, hormones, etc.
|-
| [[Oxygen]]  || O<sub>2,</sub> H<sub>2</sub>O ||[[Cellulose]], [[starch]], other organic compounds
|-
| [[Carbon]] || CO<sub>2</sub>|| Cellulose, starch, other organic compounds
|-
| [[Hydrogen]] ||H<sub>2</sub>O || Cellulose, starch, other organic compounds
|-
| [[Potassium]] ||K<sup>+</sup>|| Cofactor in protein synthesis, water balance, etc.        
|-
| [[Calcium]] ||Ca<sup>2+</sup> || Membrane synthesis and stabilization
|-
| [[Magnesium]] || Mg<sup>2+</sup>|| Element essential for chlorophyll
|-
| style="height:50px;"| [[Phosphorus]] || H<sub>2</sub>PO<sub>4</sub><sup>−</sup>|| Nucleic acids, phospholipids, ATP
|-
| style="height:50px;"| [[Sulfur|Sulphur]] ||SO<sub>4</sub><sup>2−</sup>|| Constituent of proteins
|}

{| class="wikitable"
|-
|+ '''Micronutrients''' – necessary in small quantities
|-
|Element || Form of uptake || Notes
|-
| [[Chlorine]] || Cl<sup>−</sup> ||Photosystem II and stomata function
|-
| [[Iron]] || Fe<sup>2+</sup>, Fe<sup>3+</sup>||Chlorophyll formation and nitrogen fixation
|-
| [[Boron]]  || HBO<sub>3</sub> ||Crosslinking pectin
|-
| [[Manganese]] || Mn<sup>2+</sup>|| Activity of some enzymes and photosystem II
|-
| [[Zinc]] || Zn<sup>2+</sup>|| Involved in the synthesis of enzymes and chlorophyll
|-
| [[Copper]] || Cu<sup>+</sup>|| Enzymes for lignin synthesis
|-
| style="height:50px;"| [[Molybdenum]] || MoO<sub>4</sub><sup>2−</sup> || Nitrogen fixation, reduction of nitrates
|-
| [[Nickel]] || Ni<sup>2+</sup>|| Enzymatic cofactor in the metabolism of nitrogen compounds
|}

=== Pigments ===
[[Image:Chlorophyll-a-3D-vdW.png|thumb|Space-filling model of the [[chlorophyll]] molecule.]]
[[Image:orange violet pansies.jpg|thumb|[[Anthocyanin]] gives these [[pansies]] their dark purple pigmentation.]]
{{main|Biological pigment}}

Among the most important molecules for plant function are the [[pigment]]s.  Plant pigments include a variety of different kinds of molecules, including [[porphyrin]]s, [[carotenoid]]s, and [[anthocyanin]]s.  All [[biological pigment]]s selectively absorb certain [[wavelength]]s of [[light]] while [[Reflection (physics)|reflecting]] others.  The light that is absorbed may be used by the plant to power [[chemical reaction]]s, while the reflected wavelengths of light determine the [[color]] the pigment appears to the eye.

[[Chlorophyll]] is the primary pigment in plants; it is a [[porphyrin]] that absorbs red and blue wavelengths of light while reflecting [[green]].  It is the presence and relative abundance of chlorophyll that gives plants their green color.  All land plants and [[green alga]]e possess two forms of this pigment: chlorophyll ''a'' and chlorophyll ''b''.  [[Kelp]]s, [[diatom]]s, and other photosynthetic [[heterokont]]s contain chlorophyll ''c'' instead of ''b'',  [[red algae]] possess  chlorophyll ''a''.  All chlorophylls serve as the primary means plants use to intercept light to fuel [[photosynthesis]].

[[Carotenoid]]s are red, orange, or yellow [[tetraterpenoid]]s.  They function as accessory pigments in plants, helping to fuel [[photosynthesis]] by gathering wavelengths of light not readily absorbed by chlorophyll.  The most familiar carotenoids are [[carotene]] (an orange pigment found in [[carrot]]s), [[lutein]] (a yellow pigment found in fruits and vegetables), and [[lycopene]] (the red pigment responsible for the color of [[tomato]]es).  Carotenoids have been shown to act as [[antioxidant]]s and to promote healthy [[eyesight]] in humans.

[[Anthocyanin]]s  (literally "flower blue") are [[solubility|water-soluble]] [[flavonoid]] [[pigments]] that appear red to blue, according to [[pH]]. They occur in all [[Tissue (biology)|tissues]] of higher plants, providing color in [[leaf|leaves]], [[plant stem|stems]], [[root]]s, [[flower]]s, and [[fruit]]s, though not always in sufficient quantities to be noticeable. Anthocyanins are most visible in the [[petal]]s of flowers, where they may make up as much as 30% of the dry weight of the tissue.<ref>{{cite book| author = Trevor Robinson| title = The organic constituents of higher plants: their chemistry and interrelationships| year = 1963| publisher = Cordus Press| page = 183  }}</ref>  They are also responsible for the purple color seen on the underside of tropical shade plants such as ''[[Tradescantia zebrina]]''. In these plants, the anthocyanin catches light that has passed through the leaf and reflects it back towards regions bearing chlorophyll, in order to maximize the use of available light

[[Betalain]]s are red or yellow pigments.  Like anthocyanins they are water-soluble, but unlike anthocyanins they are [[indole]]-derived compounds synthesized from [[tyrosine]].  This class of pigments is found only in the [[Caryophyllales]] (including [[cactus]] and [[amaranth]]), and never co-occur in plants with anthocyanins. Betalains are responsible for the deep red color of [[beet]]s, and are used commercially as food-coloring agents.  Plant physiologists are uncertain of the function that betalains have in plants which possess them, but there is some preliminary evidence that they may have fungicidal properties.<ref>{{cite journal
| last= Kimler
| first= L. M.
| year=1975
| title=Betanin, the red beet pigment, as an antifungal agent
| journal= Botanical Society of America, Abstracts of Papers
| volume= 36 }}</ref>

==Signals and regulators==
[[Image:Auxin.jpg|thumb|A [[mutation]] that stops ''[[Arabidopsis thaliana]]'' responding to [[auxin]] causes abnormal growth (right)]]
Plants produce hormones and other growth regulators which act to signal a physiological response in their tissues.  They also produce compounds such as [[phytochrome]] that are sensitive to light and which serve to trigger growth or development in response to environmental signals.

===Plant hormones===
{{main|Plant hormone}}
{{citations needed|section|date=January 2024}}
[[Plant hormone]]s, known as plant growth regulators (PGRs) or phytohormones, are chemicals that regulate a plant's growth. According to a standard animal definition, [[hormone]]s are signal molecules produced at specific locations, that occur in very low concentrations, and cause altered processes in target cells at other locations. Unlike animals, plants lack specific hormone-producing tissues or organs.  Plant hormones are often not transported to other parts of the plant and production is not limited to specific locations.

Plant hormones are [[chemical]]s that in small amounts promote and influence the [[cell growth|growth]], [[morphogenesis|development]] and [[cellular differentiation|differentiation]] of cells and tissues. Hormones are vital to plant growth; affecting processes in plants from flowering to [[seed]] development, [[dormancy]], and [[germination]]. They regulate which tissues grow upwards and which grow downwards, leaf formation and stem growth, fruit development and ripening, as well as leaf [[abscission]] and even plant death.

The most important plant hormones are [[abscissic acid]] (ABA), [[auxin]]s, [[ethylene]], [[gibberellin]]s, and [[cytokinin]]s, though there are many other substances that serve to regulate plant physiology.

===Photomorphogenesis===
{{main|Photomorphogenesis}}

While most people know that [[light]] is important for photosynthesis in plants, few realize that plant sensitivity to light plays a role in the control of plant structural development ([[morphogenesis]]).  The use of light to control structural development is called [[photomorphogenesis]], and is dependent upon the presence of specialized [[Photopigment|photoreceptors]], which are chemical [[pigment]]s capable of absorbing specific [[wavelength]]s of light.

Plants use four kinds of photoreceptors:<ref name="Salisbury & Ross 1992" /> [[phytochrome]], [[cryptochrome]], a [[UV-B]] photoreceptor, and [[protochlorophyllide|protochlorophyllide ''a'']].  The first two of these, phytochrome and cryptochrome, are [[photoreceptor protein]]s, complex molecular structures formed by joining a [[protein]] with a light-sensitive pigment.  Cryptochrome is also known as the UV-A photoreceptor, because it absorbs [[ultraviolet]] light in the long wave "A" region.  The UV-B receptor is one or more compounds not yet identified with certainty, though some evidence suggests [[carotene]] or [[riboflavin]] as candidates.<ref name="Fosket 1994">{{cite book| last = Fosket| first = Donald E.| title = Plant Growth and Development: A Molecular Approach| year = 1994| publisher = Academic Press| location = San Diego| isbn = 0-12-262430-0| pages = 498–509 }}</ref>  Protochlorophyllide ''a'', as its name suggests, is a chemical precursor of [[chlorophyll]].

The most studied of the photoreceptors in plants is [[phytochrome]].  It is sensitive to light in the [[red]] and [[far-red]] region of the [[visible spectrum]]. Many flowering plants use it to regulate the time of [[flower]]ing based on the length of day and night ([[photoperiodism]]) and to set circadian rhythms. It also regulates other responses including the germination of seeds, elongation of seedlings, the size, shape and number of leaves, the synthesis of chlorophyll, and the straightening of the [[epicotyl]] or [[hypocotyl]] hook of [[dicot]] seedlings.

===Photoperiodism===
[[Image:Poinsettia 2.jpg|thumb|The [[poinsettia]] is a short-day plant, requiring two months of long nights prior to blooming.]]
{{main|Photoperiodism}}

Many [[flowering plant]]s use the pigment phytochrome to sense seasonal changes in [[day]] length, which they take as signals to flower. This sensitivity to day length is termed [[photoperiodism]]. Broadly speaking, flowering plants can be classified as long day plants, short day plants, or day neutral plants, depending on their particular response to changes in day length.  Long day plants require a certain minimum length of daylight to start flowering, so these plants flower in the spring or summer. Conversely, short day plants flower when the length of daylight falls below a certain critical level. Day neutral plants do not initiate flowering based on photoperiodism, though some may use temperature sensitivity ([[vernalization]]) instead.

Although a short day plant cannot flower during the long days of summer, it is not actually the period of light exposure that limits flowering.  Rather, a short day plant requires a minimal length of uninterrupted darkness in each 24-hour period (a short daylength) before floral development can begin.  It has been determined experimentally that a short day plant (long night) does not flower if a flash of phytochrome activating light is used on the plant during the night.

Plants make use of the phytochrome system to sense day length or photoperiod.  This fact is utilized by [[florist]]s and [[greenhouse]] gardeners to control and even induce flowering out of season, such as the [[poinsettia]] (''Euphorbia pulcherrima'').

==Environmental physiology==
[[Image:Arabidopsis thaliana.jpg|thumb|[[Phototropism]] in ''[[Arabidopsis thaliana]]'' is regulated by blue to UV light.<ref>{{Cite web |url=http://www.plantphys.net/article.php?id=266 |title=plantphys.net |access-date=2007-09-22 |archive-url=https://web.archive.org/web/20060512073313/http://www.plantphys.net/article.php?id=266 |archive-date=2006-05-12 |url-status=dead }}</ref>]]
{{main|Ecophysiology}}

Paradoxically, the subdiscipline of environmental physiology is on the one hand a recent field of study in plant ecology and on the other hand one of the oldest.<ref name="Salisbury & Ross 1992" /> Environmental physiology is the preferred name of the subdiscipline among plant physiologists, but it goes by a number of other names in the applied sciences. It is roughly synonymous with [[ecophysiology]], crop ecology, [[horticulture]] and [[agronomy]]. The particular name applied to the subdiscipline is specific to the viewpoint and goals of research. Whatever name is applied, it deals with the ways in which plants respond to their environment and so overlaps with the field of [[ecology]].

Environmental physiologists examine plant response to physical factors such as [[radiation]] (including [[light]] and [[ultraviolet]] radiation), [[temperature]], [[fire]], and [[wind]]. Of particular importance are [[water]] relations (which can be measured with the [[Pressure bomb]]) and the stress of [[drought]] or [[flood|inundation]], exchange of gases with the [[atmosphere]], as well as the cycling of nutrients such as [[nitrogen]] and [[carbon]].

Environmental physiologists also examine plant response to biological factors.  This includes not only negative interactions, such as [[competition (biology)|competition]], [[herbivory]], [[disease]] and [[parasitism]], but also positive interactions, such as [[Mutualism (biology)|mutualism]] and [[pollination]].

While plants, as living beings, can perceive and communicate physical stimuli and damage, they do not feel [[pain]] as members of the [[Animal|animal kingdom]] do simply because of the lack of any [[pain receptors]], [[nerves]], or a [[brain]],<ref name="EncyBrit"/> and, by extension, lack of [[consciousness]].<ref>{{cite journal| last1 = Draguhn| first1 = Andreas | last2 = Mallatt| first2 = Jon M. | last3 = Robinson| first3 = David G. | author-link = | title = Anesthetics and plants: no pain, no brain, and therefore no consciousness| journal = Protoplasma| volume = 258| issue = 2| pages = 239–248| publisher = Springer | date = 2021| language = | jstor = | issn = | doi = 10.1007/s00709-020-01550-9| pmid = 32880005 | pmc = 7907021 | bibcode = 2021Prpls.258..239D | id = 32880005| mr = | zbl = | jfm = }}</ref> Many plants are known to perceive and respond to mechanical stimuli at a cellular level, and some plants such as the [[venus flytrap]] or [[Mimosa pudica|touch-me-not]], are known for their "obvious sensory abilities".<ref name="EncyBrit"/> Nevertheless, the plant kingdom as a whole do not feel pain notwithstanding their abilities to respond to sunlight, gravity, wind, and any external stimuli such as insect bites, since they lack any nervous system. The primary reason for this is that, unlike the members of the [[Animal|animal kingdom]] whose evolutionary successes and failures are shaped by suffering, the evolution of plants are simply shaped by life and death.<ref name="EncyBrit">{{cite web
| url = https://www.britannica.com/story/do-plants-feel-pain
| title = Do Plants Feel Pain?
| last = Petruzzello
| first = Melissa
| date = 2016
| website = Encyclopedia Britannica
| access-date = 8 January 2023
| quote = Given that plants do not have pain receptors, nerves, or a brain, they do not feel pain as we members of the animal kingdom understand it. Uprooting a carrot or trimming a hedge is not a form of botanical torture, and you can bite into that apple without worry.}}</ref>

===Tropisms and nastic movements===
{{main|Tropism|Nastic movement}}

Plants may respond both to directional and non-directional [[Stimulus (physiology)|stimuli]].  A response to a directional stimulus, such as [[gravity]] or [[light|sun light]], is called a tropism.  A response to a nondirectional stimulus, such as [[temperature]] or [[humidity]], is a nastic movement.

[[Tropism]]s in plants are the result of differential [[cell (biology)|cell]] growth, in which the cells on one side of the plant elongates more than those on the other side, causing the part to bend toward the side with less growth.  Among the common tropisms seen in plants is [[phototropism]], the bending of the plant toward a source of light.  Phototropism allows the plant to maximize light exposure in plants which require additional light for photosynthesis, or to minimize it in plants subjected to intense light and heat. [[Geotropism]] allows the roots of a plant to determine the direction of gravity and grow downwards.  Tropisms generally result from an interaction between the environment and production of one or more plant hormones.

[[Nastic movement]]s results from differential cell growth (e.g. epinasty and hiponasty), or from changes in [[turgor pressure]] within plant tissues (e.g., [[nyctinasty]]), which may occur rapidly.  A familiar example is [[thigmonasty]] (response to touch) in the [[Venus fly trap]], a [[carnivorous plant]].  The traps consist of modified leaf blades which bear sensitive trigger hairs. When the hairs are touched by an insect or other animal, the leaf folds shut.  This mechanism allows the plant to trap and digest small insects for additional nutrients.  Although the trap is rapidly shut by changes in internal cell pressures, the leaf must grow slowly to reset for a second opportunity to trap insects.<ref>{{cite book| author = Adrian Charles Slack|author2=Jane Gate | title = Carnivorous Plants| year = 1980| publisher = Cambridge, Massachusetts : MIT Press| isbn = 978-0-262-19186-9| page = 160 }}</ref>

===Plant disease===
[[Image:Powdery mildew.JPG|thumb|[[Powdery mildew]] on crop leaves]]
{{main|Phytopathology}}

Economically, one of the most important areas of research in environmental physiology is that of [[phytopathology]], the study of [[disease]]s in plants and the manner in which plants resist or cope with infection.  Plant are susceptible to the same kinds of disease organisms as animals, including [[virus]]es, [[bacteria]], and [[fungi]], as well as physical invasion by [[insect]]s and [[roundworm]]s.

Because the biology of plants differs with animals, their symptoms and responses are quite different.  In some cases, a plant can simply shed infected leaves or flowers to prevent the spread of disease, in a process called abscission.  Most animals do not have this option as a means of controlling disease.  Plant diseases organisms themselves also differ from those causing disease in animals because plants cannot usually spread infection through casual physical contact.  Plant [[pathogen]]s tend to spread via [[spore]]s or are carried by animal [[Vector (epidemiology)|vectors]].

One of the most important advances in the control of plant disease was the discovery of [[Bordeaux mixture]] in the nineteenth century.  The mixture is the first known [[fungicide]] and is a combination of [[copper sulfate]] and [[lime (mineral)|lime]].  Application of the mixture served to inhibit the growth of [[downy mildew]] that threatened to seriously damage the [[France|French]] [[wine]] industry.<ref>{{cite book| author = Kingsley Rowland Stern|author2=Shelley Jansky | title = Introductory Plant Biology| year = 1991| publisher = WCB/McGraw-Hill| isbn = 978-0-697-09948-8| page = 309 }}</ref>

==History==
{{Further|History of botany}}

===Early history===
[[Image:Portrait of J.B. van Helmont, Aufgang...1683 Wellcome L0003194.jpg|thumb|[[Jan Baptist van Helmont]].]]
[[Francis Bacon]] published one of the first plant physiology experiments in 1627 in the book, ''Sylva Sylvarum.'' Bacon grew several terrestrial plants, including a rose, in water and concluded that soil was only needed to keep the plant upright. [[Jan Baptist van Helmont]] published what is considered the first quantitative experiment in plant physiology in 1648. He grew a willow tree for five years in a pot containing 200 pounds of oven-dry soil. The soil lost just two ounces of dry weight and van Helmont concluded that plants get all their weight from water, not soil. In 1699, [[John Woodward (naturalist)|John Woodward]] published experiments on growth of [[spearmint]] in different sources of water. He found that plants grew much better in water with soil added than in distilled water.

[[Stephen Hales]] is considered the Father of Plant Physiology for the many experiments in the 1727 book, ''Vegetable Staticks'';<ref>Hales, Stephen. 1727. ''Vegetable Staticks'' http://www.illustratedgarden.org/mobot/rarebooks/title.asp?relation=QK711H341727</ref> though [[Julius von Sachs]] unified the pieces of plant physiology and put them together as a discipline. His ''Lehrbuch der Botanik'' was the plant physiology bible of its time.<ref>{{cite book| author = Duane Isely| title = 101 Botanists| year = 1994| publisher = Iowa State Press| isbn = 978-0-8138-2498-7| pages = [https://archive.org/details/onehundredonebot00isel/page/216 216–219]| url-access = registration| url = https://archive.org/details/onehundredonebot00isel/page/216}}</ref>

Researchers discovered in the 1800s that plants absorb essential mineral nutrients as inorganic ions in water. In natural conditions, soil acts as a mineral nutrient reservoir but the soil itself is not essential to plant growth. When the mineral nutrients in the soil are dissolved in water, plant roots absorb nutrients readily, soil is no longer required for the plant to thrive. This observation is the basis for [[hydroponics]], the growing of plants in a water solution rather than soil, which has become a standard technique in biological research, teaching lab exercises, crop production and as a hobby.

==Economic applications==

=== Food production ===
{{further|Agriculture|Horticulture}}

In [[horticulture]] and [[agriculture]] along with [[food science]], plant physiology is an important topic relating to [[fruit]]s, [[vegetable]]s, and other consumable parts of plants.  Topics studied include: ''climatic'' requirements, fruit drop, nutrition, [[ripening]], fruit set.  The production of food crops also hinges on the study of plant physiology covering such topics as optimal planting and harvesting times and post harvest storage of plant products for human consumption and the production of secondary products like drugs and cosmetics.

Crop physiology steps back and looks at a field of plants as a whole, rather than looking at each plant individually. Crop physiology looks at how plants respond to each other and how to maximize results like food production through determining things like optimal [[plant density|planting density]].

==See also==
{{portal|Biology|Ecology|Environment}}
* [[Biomechanics]]
* [[Hyperaccumulator]]
* [[Phytochemistry]]
* [[Plant anatomy]]
* [[Plant morphology]]
* [[Plant secondary metabolism]]
* [[Branches of botany]]

==References==
{{reflist}}

===Further reading===
*{{cite book| last = Lambers| first = H.| title = Plant physiological ecology| year = 1998| publisher = Springer-Verlag| location = New York| isbn = 0-387-98326-0 }}
* {{cite book| last = Larcher| first = W.| title = Physiological plant ecology| edition = 4th| year = 2001| publisher = Springer| isbn = 3-540-43516-6 }}
* {{cite book| author = Frank B. Salisbury|author2=Cleon W. Ross | title = Plant physiology| year = 1992| publisher = Brooks/Cole Pub Co| isbn = 0-534-15162-0 }}
* Lincoln Taiz, Eduardo Zeiger, Ian Max Møller, Angus Murphy: ''Fundamentals of Plant Physiology''. Sinauer, 2018.
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