Spontaneous generation

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Spontaneous_generation

Spontaneous generation of seashells, according to Aristotle, varied with the nature of the seabed. Slime gave rise to oysters; sand, to scallops; and the hollows of rocks, to limpets and barnacles. People kept on wondering, though, whether the eggs of these animals might not be central to the generation process.

Spontaneous generation is a superseded scientific theory that held that living creatures could arise from nonliving matter and that such processes were commonplace and regular. It was hypothesized that certain forms, such as fleas, could arise from inanimate matter such as dust, or that maggots could arise from dead flesh. The doctrine of spontaneous generation was coherently synthesized by the Greek philosopher and naturalist Aristotle, who compiled and expanded the work of earlier natural philosophers and the various ancient explanations for the appearance of organisms. Spontaneous generation was taken as scientific fact for two millennia. Though challenged in the 17th and 18th centuries by the experiments of the Italian biologists Francesco Redi and Lazzaro Spallanzani, it was not discredited until the work of the French chemist Louis Pasteur and the Irish physicist John Tyndall in the mid-19th century.

Rejection of spontaneous generation is no longer controversial among biologists. By the middle of the 19th century, experiments by Pasteur and others were considered to have disproven the traditional theory of spontaneous generation. Attention has turned instead to the origin of life, since all life seems to have evolved from a single form around four billion years ago.

Description

"Spontaneous generation" means both the supposed processes by which different types of life might repeatedly emerge from specific sources other than seeds, eggs, or parents, and the theoretical principles presented in support of any such phenomena. Crucial to this doctrine are the ideas that life comes from non-life and that no causal agent, such as a parent, is needed. Supposed examples included the seasonal generation of mice and other animals from the mud of the Nile, the emergence of fleas from inanimate matter such as dust, or the appearance of maggots in dead flesh. Such ideas have something in common with the modern hypothesis of the origin of life, which asserts that life emerged some four billion years ago from non-living materials, over a time span of millions of years, and subsequently diversified into all the forms that now exist.

The term equivocal generation, sometimes known as heterogenesis or xenogenesis, describes the supposed process by which one form of life arises from a different, unrelated form, such as tapeworms from the bodies of their hosts.

Antiquity

Pre-Socratic philosophers

Active in the 6th and 5th centuries BCE, early Greek philosophers, called physiologoi in antiquity (Greek: φυσιολόγοι; in English, physical or natural philosophers), attempted to give natural explanations of phenomena that had previously been ascribed to the agency of the gods. The physiologoi sought the material principle or arche (Greek: ἀρχή) of things, emphasizing the rational unity of the external world and rejecting theological or mythological explanations.

Anaximander, who believed that all things arose from the elemental nature of the universe, the apeiron (ἄπειρον) or the "unbounded" or "infinite", was likely the first western thinker to propose that life developed spontaneously from nonliving matter. The primal chaos of the apeiron, eternally in motion, served as a platform on which elemental opposites (e.g., wet and dry, hot and cold) generated and shaped the many and varied things in the world. According to Hippolytus of Rome in the third century CE, Anaximander claimed that fish or fish-like creatures were first formed in the "wet" when acted on by the heat of the sun and that these aquatic creatures gave rise to human beings. The Roman author Censorinus, writing in the 3rd century, reported:

Anaximander of Miletus considered that from warmed up water and earth emerged either fish or entirely fishlike animals. Inside these animals, men took form and embryos were held prisoners until puberty; only then, after these animals burst open, could men and women come out, now able to feed themselves.

The Greek philosopher Anaximenes, a pupil of Anaximander, thought that air was the element that imparted life and endowed creatures with motion and thought. He proposed that plants and animals, including human beings, arose from a primordial terrestrial slime, a mixture of earth and water, combined with the sun's heat. The philosopher Anaxagoras, too, believed that life emerged from a terrestrial slime. However, Anaximenes held that the seeds of plants existed in the air from the beginning, and those of animals in the aether. Another philosopher, Xenophanes, traced the origin of man back to the transitional period between the fluid stage of the Earth and the formation of land, under the influence of the Sun.

In what has occasionally been seen as a prefiguration of a concept of natural selection, Empedocles accepted the spontaneous generation of life, but held that different forms, made up of differing combinations of parts, spontaneously arose as though by trial and error: successful combinations formed the individuals present in the observer's lifetime, whereas unsuccessful forms failed to reproduce.

Aristotle

Further information: Aristotle's biology

In his biological works, the natural philosopher Aristotle theorized extensively the reproduction of various animals, whether by sexual, parthenogenetic, or spontaneous generation. In accordance with his fundamental theory of hylomorphism, which held that every physical entity was a compound of matter and form, Aristotle's basic theory of sexual reproduction contended that the male's seed imposed form, the set of characteristics passed down to offspring on the "matter" (menstrual blood) supplied by the female. Thus female matter is the material cause of generation—it supplies the matter that will constitute the offspring—while the male semen is the efficient cause, the factor that instigates and delineates the thing's existence. Yet, Aristotle proposed in the History of Animals, many creatures form not through sexual processes but by spontaneous generation:

Now there is one property that animals are found to have in common with plants. For some plants are generated from the seed of plants, whilst other plants are self-generated through the formation of some elemental principle similar to a seed; and of these latter plants some derive their nutriment from the ground, whilst others grow inside other plants ... So with animals, some spring from parent animals according to their kind, whilst others grow spontaneously and not from kindred stock; and of these instances of spontaneous generation some come from putrefying earth or vegetable matter, as is the case with a number of insects, while others are spontaneously generated in the inside of animals out of the secretions of their several organs.

— Aristotle, History of Animals, Book V, Part 1

According to this theory, living things may come forth from nonliving things in a manner roughly analogous to the "enformation of the female matter by the agency of the male seed" seen in sexual reproduction. Nonliving materials, like the seminal fluid present in sexual generation, contain pneuma (πνεῦμα, "breath"), or "vital heat". According to Aristotle, pneuma had more "heat" than regular air did, and this heat endowed the substance with certain vital properties:

The power of every soul seems to have shared in a different and more divine body than the so called [four] elements ... For every [animal], what makes the seed generative inheres in the seed and is called its "heat". But this is not fire or some such power, but instead the pneuma that is enclosed in the seed and in foamy matter, this being analogous to the element of the stars. This is why fire does not generate any animal ... but the heat of the sun and the heat of animals does, not only the heat that fills the seed, but also any other residue of [the animal's] nature that may exist similarly possesses this vital principle.

— Aristotle, Generation of Animals, 736b29ff

Aristotle drew an analogy between the "foamy matter" (τὸ ἀφρῶδες, to aphrodes) found in nature and the "seed" of an animal, which he viewed as being a kind of foam itself (composed, as it was, from a mixture of water and pneuma). For Aristotle, the generative materials of male and female animals (semen and menstrual fluid) were essentially refinements, made by male and female bodies according to their respective proportions of heat, of ingested food, which was, in turn, a byproduct of the elements earth and water. Thus any creature, whether generated sexually from parents or spontaneously through the interaction of vital heat and elemental matter, was dependent on the proportions of pneuma and the various elements which Aristotle believed comprised all things. While Aristotle recognized that many living things emerged from putrefying matter, he pointed out that the putrefaction was not the source of life, but the byproduct of the action of the "sweet" element of water.

Animals and plants come into being in earth and in liquid because there is water in earth, and air in water, and in all air is vital heat so that in a sense all things are full of soul. Therefore living things form quickly whenever this air and vital heat are enclosed in anything. When they are so enclosed, the corporeal liquids being heated, there arises as it were a frothy bubble.

— Aristotle, Generation of Animals, Book III, Part 11

With varying degrees of observational confidence, Aristotle theorized the spontaneous generation of a range of creatures from different sorts of inanimate matter. The testaceans (a genus which for Aristotle included bivalves and snails), for instance, were characterized by spontaneous generation from mud, but differed based upon the precise material they grew in—for example, clams and scallops in sand, oysters in slime, and the barnacle and the limpet in the hollows of rocks.

Latin and early Christian sources

Athenaeus dissented towards spontaneous generation, claiming that a variety of anchovy did not generate from roe, as Aristotle stated, but rather, from sea foam.

As the dominant view of philosophers and thinkers continued to be in favour of spontaneous generation, some Christian theologians accepted the view. The Berber theologian and philosopher Augustine of Hippo discussed spontaneous generation in The City of God and The Literal Meaning of Genesis, citing Biblical passages such as "Let the waters bring forth abundantly the moving creature that hath life" (Genesis 1:20) as decrees that would enable ongoing creation.

Middle Ages

Barnacles turning into geese, in the 1552 Cosmographia

 

The goose barnacle

 

The barnacle goose

 

In the Middle Ages, it was thought that the goose barnacle gave birth to the barnacle goose, supporting the virgin birth of Jesus.

From the fall of the Roman Empire in 5th century to the East–West Schism in 1054, the influence of Greek science declined, although spontaneous generation generally went unchallenged. New descriptions were made. Of the beliefs, some had doctrinal implications. In 1188, Gerald of Wales, after having traveled in Ireland, argued that the barnacle goose myth was evidence for the virgin birth of Jesus. Where the practice of fasting during Lent allowed fish, but prohibited fowl, the idea that the goose was in fact a fish suggested that its consumption be permitted during Lent. The practice was eventually prohibited by decree of Pope Innocent III in 1215.

After Aristotle’s works were reintroduced to Western Europe, they were translated into Latin from the original Greek or Arabic. They reached their greatest level of acceptance during the 13th century. With the availability of Latin translations, the German philosopher Albertus Magnus and his student Thomas Aquinas raised Aristotelianism to its greatest prominence. Albert wrote a paraphrase of Aristotle, De causis et processu universitatis, in which he removed some commentaries by Arabic scholars and incorporated others. The influential writings of Aquinas, on both the physical and metaphysical, are predominantly Aristotelian, but show numerous other influences.

Claude Duret's 1605 Histoire admirable des plantes et herbes esmerueillables et miraculeuses en nature... illustrated numerous supposed examples of spontaneous generation, such as this tree generating both fishes and birds

Spontaneous generation is described in literature as if it were a fact well into the Renaissance. Shakespeare wrote of snakes and crocodiles forming from the mud of the Nile:

Lepidus: You’ve strange serpents there?
Antony: Ay, Lepidus.
Lepidus: Your serpent of Egypt is bred now of your mud by the operation of your sun; so is your crocodile.
Antony: They are so.

Shakespeare: Antony and Cleopatra: Act 2, scene 7

The author of The Compleat Angler, Izaak Walton repeats the question of the origin of eels "as rats and mice, and many other living creatures, are bred in Egypt, by the sun's heat when it shines upon the overflowing of the river...". While the ancient question of the origin of eels remained unanswered and the additional idea that eels reproduced from corruption of age was mentioned, the spontaneous generation of rats and mice stirred up no debate.

The Dutch biologist and microscopist Jan Swammerdam rejected the concept that one animal could arise from another or from putrification by chance because it was impious; he found the concept of spontaneous generation irreligious, and he associated it with atheism.

Previous beliefs

• Frogs were believed to have spontaneously generated from mud.
• Mice were believed to become pregnant though the act of licking salt, or grew from the moisture of the earth.
• Barnacle geese were thought to have emerged from a crustacean, the goose barnacle (see the barnacle goose myth).
• Snakes could generate from the marrow of the human spine, and had previously generated from the blood of Medusa.
• Eels had multiple stories. Aristotle claimed that eels emerged from earthworms, and were lacking in sex and milt, spawn and passages for these. Later authors dissented. The Roman author and natural historian Pliny the Elder did not argue against the anatomic limits of eels, but stated that eels reproduce by budding, scraping themselves against rocks, liberating particles that become eels. The Greek author Athenaeus described eels as entwining and discharging a fluid which would settle on mud and generate life.
• Bookworms could generate from excessive wind. Vitruvius, a Roman architect and writer of the 1st century BCE, advised that to stop their generation, libraries be placed facing eastwards to benefit from morning light, but not towards the south or the west as those winds were particularly offensive.
• Bees were generated in decomposing cows, through a process known as bugonia. Samson's riddle led some to believe they could also generate through the body of a lion.
• Wasps could be generated from decomposing horses.
• Cicada were generated from the spittle of the cuckoo.

Experimental approach

Early tests

The Brussels physician Jan Baptist van Helmont described a recipe for mice (a piece of dirty cloth plus wheat for 21 days) and scorpions (basil, placed between two bricks and left in sunlight). His notes suggest he may have attempted to do these things.

Where Aristotle held that the embryo was formed by a coagulation in the uterus, the English physician William Harvey showed by way of dissection of deer that there was no visible embryo during the first month. Although his work predated the microscope, this led him to suggest that life came from invisible eggs. In the frontispiece of his 1651 book Exercitationes de Generatione Animalium (Essays on the Generation of Animals), he denied spontaneous generation with the motto omnia ex ovo ("everything from eggs").

Illustration of Redi's 1668 experiment to refute spontaneous generation

The ancient beliefs were subjected to testing. In 1668, the Italian physician and parasitologist Francesco Redi challenged the idea that maggots arose spontaneously from rotting meat. In the first major experiment to challenge spontaneous generation, he placed meat in a variety of sealed, open, and partially covered containers. Realizing that the sealed containers were deprived of air, he used "fine Naples veil", and observed no worms on the meat, but they appeared on the cloth. Redi used his experiments to support the preexistence theory put forth by the Catholic Church at that time, which maintained that living things originated from parents. In scientific circles Redi's work very soon had great influence, as evidenced in a letter from the English natural theologian John Ray in 1671 to members of the Royal Society of London, in which he calls the spontaneous generation of insects "unlikely".

Pier Antonio Micheli, c. 1729, observed that when fungal spores were placed on slices of melon, the same type of fungi were produced that the spores came from, and from this observation he noted that fungi did not arise from spontaneous generation.

In 1745, John Needham performed a series of experiments on boiled broths. Believing that boiling would kill all living things, he showed that when sealed right after boiling, the broths would cloud, allowing the belief in spontaneous generation to persist. His studies were rigorously scrutinized by his peers, and many of them agreed.

Lazzaro Spallanzani modified the Needham experiment in 1768, where he attempted to exclude the possibility of introducing a contaminating factor between boiling and sealing. His technique involved boiling the broth in a sealed container with the air partially evacuated to prevent explosions. Although he did not see growth, the exclusion of air left the question of whether air was an essential factor in spontaneous generation. But attitudes were changing; by the start of the 19th century, a scientist such as Joseph Priestley could write that "There is nothing in modern philosophy that appears to me so extraordinary, as the revival of what has long been considered as the exploded doctrine of equivocal, or, as Dr. Darwin calls it, spontaneous generation."

In 1837, Charles Cagniard de la Tour, a physicist, and Theodor Schwann, one of the founders of cell theory, published their independent discovery of yeast in alcoholic fermentation. They used the microscope to examine foam left over from the process of brewing beer. Where the Dutch microscopist Antonie van Leeuwenhoek described "small spheroid globules", they observed yeast cells undergo cell division. Fermentation would not occur when sterile air or pure oxygen was introduced if yeast were not present. This suggested that airborne microorganisms, not spontaneous generation, was responsible.

However, although the idea of spontaneous generation had been in decline for nearly a century, its supporters did not abandon it all at once. As James Rennie wrote in 1838, despite Redi's experiments, "distinguished naturalists, such as Blumenbach, Cuvier, Bory de St. Vincent, R. Brown, &c." continued to support the theory.

Pasteur and Tyndall

Louis Pasteur's 1859 experiment showed that a boiled nutrient broth did not give rise spontaneously to new life, but that if direct access to air was permitted, the broth decomposed, implying that small organisms (in modern terms, microbial spores) had fallen in and started to grow in the broth.

Louis Pasteur's 1859 experiment is widely seen as having settled the question of spontaneous generation. He boiled a meat broth in a swan neck flask; the bend in the neck of the flask prevented falling particles from reaching the broth, while still allowing the free flow of air. The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth quickly became clouded. However, minority objections were persistent and not always unreasonable, given that the experimental difficulties were far more challenging than the popular accounts suggest. The investigations of the Irish physician John Tyndall, a correspondent of Pasteur and an admirer of his work, were decisive in disproving spontaneous generation. All the same, Tyndall encountered difficulties in dealing with microbial spores, which were not well understood in his day. Like Pasteur, he boiled his cultures to sterilize them, and some types of bacterial spores can survive boiling. The autoclave, which eventually came into universal application in medical practice and microbiology to sterilise equipment, was introduced after these experiments.

In 1862, the French Academy of Sciences paid special attention to the issue, establishing a prize "to him who by well-conducted experiments throws new light on the question of the so-called spontaneous generation" and appointed a commission to judge the winner. Pasteur and others used the term biogenesis as the opposite of spontaneous generation, to mean that life was generated only from other life. Pasteur's claim followed the German physician Rudolf Virchow's doctrine Omnis cellula e cellula ("all cells from cells"), itself derived from the work of Robert Remak. After Pasteur's 1859 experiment, the term "spontaneous generation" fell out of favor. Experimentalists used a variety of terms for the study of the origin of life from nonliving materials. Heterogenesis was applied to the generation of living things from once-living organic matter (such as boiled broths), and the English physiologist Henry Charlton Bastian proposed the term archebiosis for life originating from non-living materials. Disliking the randomness and unpredictability implied by the term spontaneous generation, in 1870 Bastian coined the term biogenesis for the formation of life from nonliving matter. Soon thereafter, however, the English biologist Thomas Henry Huxley proposed the term abiogenesis for this same process, and adopted biogenesis for the process by which life arises from existing life.

Vitalism

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Vitalism

 

Vitalism is a belief that starts from the premise that "living organisms are fundamentally different from non-living entities because they contain some non-physical element or are governed by different principles than are inanimate things." Where vitalism explicitly invokes a vital principle, that element is often referred to as the "vital spark", "energy", "élan vital" (coined by vitalist Henri Bergson), "vital force", or "vis vitalis", which some equate with the soul. In the 18th and 19th centuries, vitalism was discussed among biologists, between those who felt that the known mechanics of physics would eventually explain the difference between life and non-life and vitalists who argued that the processes of life could not be reduced to a mechanistic process. Vitalist biologists such as Johannes Reinke proposed testable hypotheses meant to show inadequacies with mechanistic explanations, but their experiments failed to provide support for vitalism. Biologists now consider vitalism in this sense to have been refuted by empirical evidence, and hence regard it either as a superseded scientific theory, or, since the mid-20th century, as a pseudoscience.

Vitalism has a long history in medical philosophies: many traditional healing practices posited that disease results from some imbalance in vital forces.

History

Ancient times

The notion that bodily functions are due to a vitalistic principle existing in all living creatures has roots going back at least to ancient Egypt. In Greek philosophy, the Milesian school proposed natural explanations deduced from materialism and mechanism. However, by the time of Lucretius, this account was supplemented, (for example, by the unpredictable clinamen of Epicurus), and in Stoic physics, the pneuma assumed the role of logos. Galen believed the lungs draw pneuma from the air, which the blood communicates throughout the body.

Medieval

In Europe, medieval physics was influenced by the idea of pneuma, helping to shape later aether theories.

Early modern

Vitalists included English anatomist Francis Glisson (1597–1677) and the Italian doctor Marcello Malpighi (1628–1694). Caspar Friedrich Wolff (1733–1794) is considered to be the father of epigenesis in embryology, that is, he marks the point when embryonic development began to be described in terms of the proliferation of cells rather than the incarnation of a preformed soul. However, this degree of empirical observation was not matched by a mechanistic philosophy: in his Theoria Generationis (1759), he tried to explain the emergence of the organism by the actions of a vis essentialis (an organizing, formative force). Carl Reichenbach (1788–1869) later developed the theory of Odic force, a form of life-energy that permeates living things.

In the 17th century, modern science responded to Newton's action at a distance and the mechanism of Cartesian dualism with vitalist theories: that whereas the chemical transformations undergone by non-living substances are reversible, so-called "organic" matter is permanently altered by chemical transformations (such as cooking).

As worded by Charles Birch and John B. Cobb, "the claims of the vitalists came to the fore again" in the 18th century: "Georg Ernst Stahl's followers were active as were others, such as the physician genius Francis Xavier Bichat of the Hotel Dieu." However, "Bichat moved from the tendency typical of the French vitalistic tradition to progressively free himself from metaphysics in order to combine with hypotheses and theories which accorded to the scientific criteria of physics and chemistry." John Hunter recognised "a 'living principle' in addition to mechanics."

Johann Friedrich Blumenbach was influential in establishing epigenesis in the life sciences in 1781 with his publication of Über den Bildungstrieb und das Zeugungsgeschäfte. Blumenbach cut up freshwater Hydra and established that the removed parts would regenerate. He inferred the presence of a "formative drive" (Bildungstrieb) in living matter. But he pointed out that this name,

like names applied to every other kind of vital power, of itself, explains nothing: it serves merely to designate a peculiar power formed by the combination of the mechanical principle with that which is susceptible of modification.

19th century

Further information: Alternatives to Darwinism

The synthesis of urea in the early 19th century from inorganic compounds was counterevidence for the vitalist hypothesis that only organisms could make the components of living things.

Jöns Jakob Berzelius, one of the early 19th century founders of modern chemistry, argued that a regulative force must exist within living matter to maintain its functions. Berzelius contended that compounds could be distinguished by whether they required any organisms in their synthesis (organic compounds) or whether they did not (inorganic compounds). Vitalist chemists predicted that organic materials could not be synthesized from inorganic components, but Friedrich Wöhler synthesised urea from inorganic components in 1828. However, contemporary accounts do not support the common belief that vitalism died when Wöhler made urea. This Wöhler Myth, as historian Peter Ramberg called it, originated from a popular history of chemistry published in 1931, which, "ignoring all pretense of historical accuracy, turned Wöhler into a crusader who made attempt after attempt to synthesize a natural product that would refute vitalism and lift the veil of ignorance, until 'one afternoon the miracle happened'".

Between 1833 and 1844, Johannes Peter Müller wrote a book on physiology called Handbuch der Physiologie, which became the leading textbook in the field for much of the nineteenth century. The book showed Müller's commitments to vitalism; he questioned why organic matter differs from inorganic, then proceeded to chemical analyses of the blood and lymph. He describes in detail the circulatory, lymphatic, respiratory, digestive, endocrine, nervous, and sensory systems in a wide variety of animals but explains that the presence of a soul makes each organism an indivisible whole. He claimed that the behaviour of light and sound waves showed that living organisms possessed a life-energy for which physical laws could never fully account.

Louis Pasteur argued that only life could catalyse fermentation. Painting by Albert Edelfelt, 1885

Louis Pasteur (1822–1895) after his famous rebuttal of spontaneous generation, performed several experiments that he felt supported vitalism. According to Bechtel, Pasteur "fitted fermentation into a more general programme describing special reactions that only occur in living organisms. These are irreducibly vital phenomena." Rejecting the claims of Berzelius, Liebig, Traube and others that fermentation resulted from chemical agents or catalysts within cells, Pasteur concluded that fermentation was a "vital action".

20th century

Hans Driesch (1867–1941) interpreted his experiments as showing that life is not run by physicochemical laws. His main argument was that when one cuts up an embryo after its first division or two, each part grows into a complete adult. Driesch's reputation as an experimental biologist deteriorated as a result of his vitalistic theories, which scientists have seen since his time as pseudoscience. Vitalism is a superseded scientific hypothesis, and the term is sometimes used as a pejorative epithet. Ernst Mayr (1904–2005) wrote:

It would be ahistorical to ridicule vitalists. When one reads the writings of one of the leading vitalists like Driesch one is forced to agree with him that many of the basic problems of biology simply cannot be solved by a philosophy as that of Descartes, in which the organism is simply considered a machine... The logic of the critique of the vitalists was impeccable.

Vitalism has become so disreputable a belief in the last fifty years that no biologist alive today would want to be classified as a vitalist. Still, the remnants of vitalist thinking can be found in the work of Alistair Hardy, Sewall Wright, and Charles Birch, who seem to believe in some sort of nonmaterial principle in organisms.

Other vitalists included Johannes Reinke and Oscar Hertwig. Reinke used the word neovitalism to describe his work, claiming that it would eventually be verified through experimentation, and that it was an improvement over the other vitalistic theories. The work of Reinke influenced Carl Jung.

John Scott Haldane adopted an anti-mechanist approach to biology and an idealist philosophy early on in his career. Haldane saw his work as a vindication of his belief that teleology was an essential concept in biology. His views became widely known with his first book Mechanism, life and personality in 1913. Haldane borrowed arguments from the vitalists to use against mechanism; however, he was not a vitalist. Haldane treated the organism as fundamental to biology: "we perceive the organism as a self-regulating entity", "every effort to analyze it into components that can be reduced to a mechanical explanation violates this central experience". The work of Haldane was an influence on organicism. Haldane stated that a purely mechanist interpretation could not account for the characteristics of life. Haldane wrote a number of books in which he attempted to show the invalidity of both vitalism and mechanist approaches to science. Haldane explained:

We must find a different theoretical basis of biology, based on the observation that all the phenomena concerned tend towards being so coordinated that they express what is normal for an adult organism.

By 1931, biologists had "almost unanimously abandoned vitalism as an acknowledged belief."

Emergentism

Main article: Emergentism

Contemporary science and engineering sometimes describe emergent processes, in which the properties of a system cannot be fully described in terms of the properties of the constituents. This may be because the properties of the constituents are not fully understood, or because the interactions between the individual constituents are important for the behavior of the system.

Whether emergence should be grouped with traditional vitalist concepts is a matter of semantic controversy. According to Emmeche et al. (1997):

On the one hand, many scientists and philosophers regard emergence as having only a pseudo-scientific status. On the other hand, new developments in physics, biology, psychology, and cross-disciplinary fields such as cognitive science, artificial life, and the study of non-linear dynamical systems have focused strongly on the high level 'collective behaviour' of complex systems, which is often said to be truly emergent, and the term is increasingly used to characterize such systems.

Mesmerism

Main article: Animal magnetism

Franz Mesmer proposed the vitalist force of magnétisme animal in animals with breath.

A popular vitalist theory of the 18th century was "animal magnetism", in the theories of Franz Mesmer (1734–1815). However, the use of the (conventional) English term animal magnetism to translate Mesmer's magnétisme animal can be misleading for three reasons:

• Mesmer chose his term to clearly distinguish his variant of magnetic force from those referred to, at that time, as mineral magnetism, cosmic magnetism and planetary magnetism.
• Mesmer felt that this particular force/power only resided in the bodies of humans and animals.
• Mesmer chose the word "animal," for its root meaning (from Latin animus="breath") specifically to identify his force as a quality that belonged to all creatures with breath; viz., the animate beings: humans and animals.

Mesmer's ideas became so influential that King Louis XVI of France appointed two commissions to investigate mesmerism; one was led by Joseph-Ignace Guillotin, the other, led by Benjamin Franklin, included Bailly and Lavoisier. The commissioners learned about Mesmeric theory, and saw its patients fall into fits and trances. In Franklin's garden, a patient was led to each of five trees, one of which had been "mesmerized"; he hugged each in turn to receive the "vital fluid," but fainted at the foot of a 'wrong' one. At Lavoisier's house, four normal cups of water were held before a "sensitive" woman; the fourth produced convulsions, but she calmly swallowed the mesmerized contents of a fifth, believing it to be plain water. The commissioners concluded that "the fluid without imagination is powerless, whereas imagination without the fluid can produce the effects of the fluid."

Medical philosophies

Vitalism has a long history in medical philosophies: many traditional healing practices posited that disease results from some imbalance in vital forces. In the Western tradition founded by Hippocrates, these vital forces were associated with the four temperaments and humours; Eastern traditions posited an imbalance or blocking of qi or prana. One example of a similar notion in Africa is the Yoruba concept of ase. Today forms of vitalism continue to exist as philosophical positions or as tenets in some religious traditions.

Complementary and alternative medicine therapies include energy therapies, associated with vitalism, especially biofield therapies such as therapeutic touch, Reiki, external qi, chakra healing and SHEN therapy. In these therapies, the "subtle energy" field of a patient is manipulated by a practitioner. The subtle energy is held to exist beyond the electromagnetic energy produced by the heart and brain. Beverly Rubik describes the biofield as a "complex, dynamic, extremely weak EM field within and around the human body...."

The founder of homeopathy, Samuel Hahnemann, promoted an immaterial, vitalistic view of disease: "...they are solely spirit-like (dynamic) derangements of the spirit-like power (the vital principle) that animates the human body." The view of disease as a dynamic disturbance of the immaterial and dynamic vital force is taught in many homeopathic colleges and constitutes a fundamental principle for many contemporary practising homeopaths.

Criticism

The 17th century French playwright Molière mocked vitalism in his 1673 play Le Malade imaginaire.

Vitalism has sometimes been criticized as begging the question by inventing a name. Molière had famously parodied this fallacy in Le Malade imaginaire, where a quack "answers" the question of "Why does opium cause sleep?" with "Because of its dormitive virtue (i.e., soporific power)." Thomas Henry Huxley compared vitalism to stating that water is the way it is because of its "aquosity". His grandson Julian Huxley in 1926 compared "vital force" or élan vital to explaining a railroad locomotive's operation by its élan locomotif ("locomotive force").

Another criticism is that vitalists have failed to rule out mechanistic explanations. This is rather obvious in retrospect for organic chemistry and developmental biology, but the criticism goes back at least a century. In 1912, Jacques Loeb published The Mechanistic Conception of Life, in which he described experiments on how a sea urchin could have a pin for its father, as Bertrand Russell put it (Religion and Science). He offered this challenge:

"... we must either succeed in producing living matter artificially, or we must find the reasons why this is impossible." (pp. 5–6)

Loeb addressed vitalism more explicitly:

"It is, therefore, unwarranted to continue the statement that in addition to the acceleration of oxidations the beginning of individual life is determined by the entrance of a metaphysical "life principle" into the egg; and that death is determined, aside from the cessation of oxidations, by the departure of this "principle" from the body. In the case of the evaporation of water we are satisfied with the explanation given by the kinetic theory of gases and do not demand that to repeat a well-known jest of Huxley the disappearance of the "aquosity" be also taken into consideration." (pp. 14–15)

Bechtel states that vitalism "is often viewed as unfalsifiable, and therefore a pernicious metaphysical doctrine." For many scientists, "vitalist" theories were unsatisfactory "holding positions" on the pathway to mechanistic understanding. In 1967, Francis Crick, the co-discoverer of the structure of DNA, stated "And so to those of you who may be vitalists I would make this prophecy: what everyone believed yesterday, and you believe today, only cranks will believe tomorrow."

While many vitalistic theories have in fact been falsified, notably Mesmerism, the pseudoscientific retention of untested and untestable theories continues to this day. Alan Sokal published an analysis of the wide acceptance among professional nurses of "scientific theories" of spiritual healing. (Pseudoscience and Postmodernism: Antagonists or Fellow-Travelers?). Use of a technique called therapeutic touch was especially reviewed by Sokal, who concluded, "nearly all the pseudoscientific systems to be examined in this essay are based philosophically on vitalism" and added that "Mainstream science has rejected vitalism since at least the 1930s, for a plethora of good reasons that have only become stronger with time."

Joseph C. Keating, Jr. discusses vitalism's past and present roles in chiropractic and calls vitalism "a form of bio-theology." He further explains that:

"Vitalism is that rejected tradition in biology which proposes that life is sustained and explained by an unmeasurable, intelligent force or energy. The supposed effects of vitalism are the manifestations of life itself, which in turn are the basis for inferring the concept in the first place. This circular reasoning offers pseudo-explanation, and may deceive us into believing we have explained some aspect of biology when in fact we have only labeled our ignorance. 'Explaining an unknown (life) with an unknowable (Innate),' suggests chiropractor Joseph Donahue, 'is absurd'."

Keating views vitalism as incompatible with scientific thinking:

"Chiropractors are not unique in recognizing a tendency and capacity for self-repair and auto-regulation of human physiology. But we surely stick out like a sore thumb among professions which claim to be scientifically based by our unrelenting commitment to vitalism. So long as we propound the 'One cause, one cure' rhetoric of Innate, we should expect to be met by ridicule from the wider health science community. Chiropractors can't have it both ways. Our theories cannot be both dogmatically held vitalistic constructs and be scientific at the same time. The purposiveness, consciousness and rigidity of the Palmers' Innate should be rejected."

Keating also mentions Skinner's viewpoint:

"Vitalism has many faces and has sprung up in many areas of scientific inquiry. Psychologist B.F. Skinner, for example, pointed out the irrationality of attributing behavior to mental states and traits. Such 'mental way stations,' he argued, amount to excess theoretical baggage which fails to advance cause-and-effect explanations by substituting an unfathomable psychology of 'mind'."

According to Williams, "[t]oday, vitalism is one of the ideas that form the basis for many pseudoscientific health systems that claim that illnesses are caused by a disturbance or imbalance of the body's vital force." "Vitalists claim to be scientific, but in fact they reject the scientific method with its basic postulates of cause and effect and of provability. They often regard subjective experience to be more valid than objective material reality."

Victor Stenger states that the term "bioenergetics" "is applied in biochemistry to refer to the readily measurable exchanges of energy within organisms, and between organisms and the environment, which occur by normal physical and chemical processes. This is not, however, what the new vitalists have in mind. They imagine the bioenergetic field as a holistic living force that goes beyond reductionist physics and chemistry."

Such a field is sometimes explained as electromagnetic, though some advocates also make confused appeals to quantum physics. Joanne Stefanatos states that "The principles of energy medicine originate in quantum physics." Stenger offers several explanations as to why this line of reasoning may be misplaced. He explains that energy exists in discrete packets called quanta. Energy fields are composed of their component parts and so only exist when quanta are present. Therefore, energy fields are not holistic, but are rather a system of discrete parts that must obey the laws of physics. This also means that energy fields are not instantaneous. These facts of quantum physics place limitations on the infinite, continuous field that is used by some theorists to describe so-called "human energy fields". Stenger continues, explaining that the effects of EM forces have been measured by physicists as accurately as one part in a billion and there is yet to be any evidence that living organisms emit a unique field.

Vitalistic thinking has been identified in the naive biological theories of children: "Recent experimental results show that a majority of preschoolers tend to choose vitalistic explanations as most plausible. Vitalism, together with other forms of intermediate causality, constitute unique causal devices for naive biology as a core domain of thought."

Seaweed fertiliser

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Seaweed_fertiliser

Seaweed fertiliser (or fertilizer) is organic fertilizer made from seaweed that is used in agriculture to increase soil fertility and plant growth. The use of seaweed fertilizer dates back to antiquity and has a broad array of benefits for soils. Seaweed fertilizer can be applied in a number of different forms, including refined liquid extracts and dried, pulverized organic material. Through its composition of various bioactive molecules, seaweed functions as a strong soil conditioner, bio-remediator, and biological pest control, with each seaweed phylum offering various benefits to soil and crop health. These benefits can include increased tolerance to abiotic stressors, improved soil texture and water retention, and reduced occurrence of diseases.

On a broader socio-ecological scale, seaweed aquaculture and fertilizer development have significant roles in biogeochemical nutrient cycling through carbon storage and the uptake of nitrogen and phosphorus. Seaweed fertilizer application to soils can also alter the structure and function of microbial communities. Seaweed aquaculture has the potential to yield ecosystem services by providing a source of nutrition to human communities and a mechanism for improving water quality in natural systems and aquaculture operations. The rising popularity of organic farming practices is drawing increased attention towards the various applications of seaweed-derived fertilizers and soil additives. While the seaweed fertilizer industry is still in its infancy, it holds significant potential for sustainable economic development as well as the reduction of nutrient runoff in coastal systems. There are however ongoing challenges associated with the use and production of seaweed fertilizer including the spread of diseases and invasive species, the risk of heavy-metal accumulation, and the efficiency and refinement of production methods.

Nomenclature and taxonomy

“Seaweed" is one of the common names given to multicellular macroalgae, such as green algae (Chlorophyta), brown algae (Phaeophyceae), and red algae (Rhodophyta). The term, seaweed is sometimes used to refer to microalgae and plants as well. Seaweeds are typically benthic organisms which have a structure called a holdfast, that keeps them anchored to the sea floor; they also have a stipe, otherwise known as a stem, and blade-shaped foliage. Sargassum seaweed is one exception to this anatomy and function, as it does not attach to the benthic environment. The color of seaweeds generally follows depth/light, with green seaweeds, brown seaweeds, and red seaweeds corresponding to shallow, moderate, and deeper waters respectively; red seaweeds are sometimes found up to 30 meters in depth. The smallest seaweeds grow only a few millimeters in height, while the largest seaweeds can grow up to 50 meters in height. There are an estimated 1,800 green, 1,800 brown, and 6,200 red seaweed species in existence. Brown seaweeds are generally known as kelp, but are also known by other common names such as rockweed and wracks. Red seaweeds are the most diverse group of seaweed, and along with green seaweeds, are most closely related to terrestrial plants, whereas brown seaweeds are the most distantly related to terrestrial plants. Seaweeds are found extensively in shallow natural environments, and farmed both in the ocean and in land-based aquaculture operations. Most brown seaweeds that are found in the wild are from the genera Laminaria, Undaria, Hizikia, whereas most brown seaweeds that are farmed for uses such as fertilizer and heavy metal indication, are from the species Ascophyllum, Ecklonia, Fucus, Sargassum. Green seaweeds that are used as bioindicators, for heavy metal indication for example, are from the genera Ulva and Enteromorpha. Red seaweed from the genus Poryphora, is commonly used for human food.

History

The first written record of agricultural use seaweed was from ancient Greek and Roman civilizations in the 2nd century, where foraged beach castings were used to feed livestock and wrap plant roots for preservation. However, stable isotope analysis of prehistoric sheep teeth in the Orkneys indicate that early peoples used seaweed as livestock fodder over 5,000 years ago, and researchers speculate that foraged seaweed was also used as fertilizer because ashed remnants of seaweed were found in archeological sites. Such agricultural techniques might have been key to the survival of early settlements in Scotland. Historical records and archaeological evidence of seaweed fertilizer use in the coastal Atlantic are vast and scattered, ranging from Scandinavia to Portugal, from the neolithic period through the 20th century. Most details of seaweed fertilizer use come from the British Isles, Channel Islands, Normandy and Brittany (France), where a variety of application techniques were used over the centuries, and some continue to this day. Ireland has a long history (12th century) of harvesting seaweed for fertilizing nutrient-poor post glacial soils using composted manure as enrichment and the increased agricultural productivity allowed the Irish population to grow substantially. The Channel Islands (12th century) used a dried blend of red and brown seaweeds, called "Vraic" or "wrack", to spread over potato fields during the winter months to enrich before planting the crop in the spring. Similarly, coastal people in Normandy and Brittany have been collecting "wrack" using wood rakes since the neolithic period, though the fertilizer composition originally included all marine debris that washed ashore. In 17th–19th century Scotland, Fucus spp. were cultivated by placing rocky substrate in the intertidal zones to encourage seaweed settlement. The seaweed biomass was then used in composted trenches, where crops (potatoes, oats, wheat, onions) were grown directly in the sandy fertilizer mixture. This ‘lazy bed’ method afforded minimal crop rotation and allowed rugged landscape and acidic soils to be farmed, where plant growth was otherwise unsuitable. The high value of seaweed in these regions caused political disputes over harvesting rights and in Ireland such rights were established before the country itself. These early applications of seaweed fertilizer were limited to coastlines, where the macroalgae could be harvested from the intertidal or collected after a storm washed it to shore. However, dried wrack mixtures or ashed ‘fucus’ potash could be transported further inland because it weighs less than wet seaweed.

Seaweed fertilizer spread inland when a kelp industry developed in Scotland, Norway, and Brittany in the 18th and 19th century. The industry developed out of demand for ashed soda, or potash, which was used to create glass and soap, and led to shortages for agricultural applications in traditional coastal communities. Potash is a water-soluble potassium rich concentrate made from plant matter, so it was also exported as a fertilizer. Coastal communities in the seaweed industry both expanded and struggled to keep up with the demand. Early commercial kelp export in Scotland devastated traditional agriculture in the region because intensive labor was needed during the seaweed growing season to harvest and process the kelp, which led to a labor transition from farming to kelp processing. Additionally, exploitation of kelp resources for potash production left little kelp behind for local fertilizer and coastal land became more desirable than inland regions. The Scottish seaweed industry went through multiple boom and bust cycles, employing 10,000 families and producing 3,000 tonnes of ash per year during its peak. The export price of kelp ash dropped in 1822, leading to a sudden emigration from the area because the crop was no longer profitable enough to support such a large industry. Kelp exploitation and toxic ash processing caused ecological and economic damage in Orkney and left many people sick and blinded. The kelp industry picked up again for iodine production in 1845, and alginate (a thickening agent) production in the early 1900s, which reinvigorated kelp harvest.

Global production of seaweed fertilizer largely phased out when chemical fertilizers were developed in the 1920s, due to the cheaper production cost. Chemical fertilizers revolutionized the agriculture industry and allowed the human population to grow far beyond the limits of traditional food production methods. Synthetic fertilizers are still the predominant global source for commercial agricultural applications due to the cheap cost of production and widespread access. However, small scale organic farmers and coastal communities continued traditional seaweed techniques in regions with a rich seaweed history. The first industrial kelp liquid fertilizer, Maxicrop, was created by Reginald Milton in 1947. The creation of liquid fertilizer has allowed for more widespread application of seaweed-derived fertilizer to inland regions and sparked a growing agronomic interest in seaweed for a variety of agricultural applications, including foliage spray, biostimulants, and soil conditioning. Interestingly, the historic rise of seaweed aquaculture did not align with fertilizer production because the European countries that produce seaweed fertilizer haven't developed a significant aquaculture industry; seaweed farming is also currently dominated by China and Indonesia, where the crop is grown for food and other lucrative uses.

Aquaculture

A satellite image of seaweed aquaculture off the southern coast of South Korea. The dark squares displayed in the image are fields of seaweed growing.

The development of modern seaweed mariculture/aquaculture has allowed the expansion of seaweed fertilizer research and improved processing methods since the 1950s. Seaweed has been cultivated in Asian countries for food production for centuries, but seaweed aquaculture is now growing rapidly across the world for specialty use in biofuel, agar, cosmetics, medicine, and bioplastics. The nascent agricultural seaweed sector, including animal feed, soil additives, and agrochemicals, makes up less than 1% of the overall global value of seaweed aquaculture. However, significant interest in agricultural applications of the crop has increased dramatically since 1950, as specialty agrochemical uses for seaweed materials have been demonstrated through scientific research. Increased concern over the depletion and degradation of marine resources in the past century, coupled with the threats of climate change, has increased global interest in sustainable solutions for blue economic development of the oceans. Seaweed aquaculture is promoted as a solution to expand novel industry development and food security while simultaneously restoring damaged ecosystems. Unlike terrestrial crops, growing seaweed requires no land, feed, fertilizers, pesticides, and water resources. Different seaweeds also offer a variety of ecosystem services (discussed below), which contribute to the growing popularity of seaweed as a bioremediation crop. Fertilizer plays and important role in sustainable seaweed aquaculture development because seaweed farming can help alleviate excess nutrient loading associated with terrestrial chemical fertilizer run-off and applying organic seaweed fertilizer on soil closes the nutrient loop between land and sea. Additionally, seaweed fertilizer can be produced using by-products from other industries or raw materials that are unsuitable for human consumption, such as rotting or infected biomass or biowaste products from carrageenan processing methods. Seaweed aquaculture is also important for supporting sustainble growth of the seaweed fertilizer industry because it limits the potential for exploitation of native seaweed for commercial interests. However, the nascent seaweed aquaculture industry faces a number of challenges to sustainable development, as discussed below. Environmental impacts of seaweed harvest and production need to be carefully scrutinized to protect coastal communities and maintain the socioeconomic benefits of using seaweed resources in industry.

Ecosystem services

Seaweed mariculture for purposes including fertilizer production, has the potential to improve environmental conditions in coastal habitats, especially with regards to toxic algal blooms, as mariculture seaweeds uptake excess nutrients that have resulted from runoff, thereby inhibiting the growth of toxic algal blooms that harm local ecosystems. Seaweed fertilizers can also be more biodegradable, less toxic, and less hazardous than chemical fertilizers, depending on the type of seaweed fertilizer. Seaweeds are used in aquaculture operations to uptake fish waste as nutrients and improve water quality parameters. Humans use seaweeds nutritionally as food, industrially for animal feed and plant fertilizer, and ecologically to improve environmental conditions. Seaweeds have been consumed by humans for centuries because they have excellent nutritional profiles, contain minerals, trace elements, amino acids, and vitamins, and are high in fiber and low in calories. Red seaweeds have the highest protein content and brown seaweeds have the lowest protein content. Of all the red seaweeds, Porphyra, is the genus most frequently used for human consumption. Brown seaweeds are so plentiful that they most used for industrial animal feeds and fertilizers. Furthermore, seaweeds are currently being investigated as a potential source of sustainable biofuel, as well as being investigated as a potential component of wastewater treatment, because some species are able to absorb and remove heavy metals and other toxicants from water bodies, and also generally serve as water quality indicators.

Ecosystem impacts

Any ecosystem impacts of using seaweed for plant and crop fertilizer are primarily due to how the seaweed is harvested. Large-scale, unsustainable seaweed farming can lead to the displacement and alteration of native habitats due to the presence of farming infrastructure in the water, and day-to-day anthropogenic operations in the area. Seaweed is currently harvested from farmed sources, wild sources, and from beach collection efforts. Harvesting wild seaweed will tend to have negative impacts on local ecosystems, especially if existing populations are overexploited and rendered unable to provide ecosystem services. There is also a risk that large, industrial scale seaweed monocultures will be established in natural benthic environments, leading to the competitive exclusion of native seaweeds and sea grasses, which inhabit the depths underneath seaweed farms. Furthermore, large, industrial scale seaweed farming can alter the natural benthic environment that they are established in, by altering environmental parameters such as light availability, the movement of water, sedimentation rates and nutrient levels, and due to the general, overall stress caused by anthropogenic factors.

Production and application methods

The composition of various minerals found in three different species of seaweed.

Brown seaweeds are most commonly used for fertilizer production, at present and historically. Seaweed fertilizer can be used as a crude addition to soil as mulch, composted to break down the hardy raw material, or dried and pulverized to make the nutrients more bioavailable to plant roots. Compost fertilization is a technique that any small-scale organic farm can readily use if they have access to seaweed, though extracts are more common for large-scale commercial applications. Commercial manufacturing processes are often more technical than traditional techniques using raw biomass and use different biochemical processes to concentrate and extract the most beneficial nutrients from seaweed.

A simple liquid fertilizer can be created by fermenting seaweed leaves in water, though the process is intensified and hastened industrially through heat and pressure. Other methods for liquid extraction include a soft-extraction with low temperature milling to suspend fine particles in water, heating the raw material with alkaline sodium or potassium to extract nutrients, and the addition of enzymes to aid in biochemical decomposition.Extraction of bioavailable nutrients from raw seaweed is achieved by breaking down the hardy cell walls through physical techniques, such as ultrasound extraction, boiling, or freeze-thaw. Biological fermentation techniques are also used to degrade the cells. Physical extraction techniques are often faster, but more expensive and result in poorer crop yield in trials. Since seaweed extract has chelating properties that maintain trace metal ions bioavailability to plants, additional micronutrients are often added to solution to increase the fertilization benefit to specific crops. Organic fertilization techniques have lower environmental consequences in comparison to the production of artificial chemical fertilizers, because they use no harsh caustic or organic solvents to produce fertilizer and the seaweed raw material is a renewable resource, as opposed to mineral deposits and fossil fuels needed to synthesize chemical fertilizer. Large-scale agricultural use of synthetic fertilizer depletes soil fertility and increases water hardness over time, so recent trends in agricultural development are following an organic approach to sustain food production through improved soil management and bio-fertilization techniques. Seaweed extracts are bio-fertilizers that can also be used as biostimulants, which are applied to enhance nutrient efficiency and abiotic stress tolerance. New extraction technologies are being developed to improve efficiency and target the isolation of specific compounds for specialized applications of seaweed biostimulants, though specific extraction techniques are frequently trade secrets. Additionally, many liquid fertilizer extraction processes can complement other industrial uses for seaweed, such as carrageenan production, which increases the economic benefit of the same seaweed crop.

Nutrient cycling

To support a growing seaweed aquaculture industry many studies have evaluated the nutrient cycle dynamics of different seaweed species in addition to exploring co-production applications including bioremediation and carbon sequestration. Seaweeds can form highly productive communities in coastal regions, dominating the nutrient cycles within these ecosystems. As primary producers, seaweeds incorporate inorganic carbon, light, and nutrients (such as nitrogen and phosphorus), into biomass through photosynthesis. Harvesting seaweed from marine environments results in the net removal of these elements from these ecosystems in addition to the removal of heavy metals and contaminants.

For photosynthesis, seaweeds utilize both inorganic nitrogen, in the forms of nitrate (NO₃⁻) and ammonium (NH₄⁺), and organic nitrogen in the form of urea. Primary production using nitrate is generally considered new production because nitrate is externally supplied through upwelling and riverine input, and often has been converted from forms of nitrogen that are released from biological respiration. However, primary production using ammonium is denoted as recycled production because ammonium is internally supplied through regeneration by heterotrophs within ecosystems. For example, the ammonium excreted by fish and invertebrates within the same coastal ecosystems as seaweeds can support seaweed production through providing a nitrogen source. Phosphorus is supplied inorganically as phosphate (PO₄^3-) and generally follows similar seasonal patterns to nitrate. Additionally, seaweeds require inorganic carbon, typically supplied from the environment in the form of carbon dioxide (CO₂) or bicarbonate (HCO₃⁻).

Similar to other marine photosynthesizing organisms like phytoplankton, seaweeds also experience nutrient limitations impacting their ability to grow. Nitrogen is the most commonly found limiting nutrient for seaweed photosynthesis, although phosphorus has also been found to be limiting. The ratio of inorganic carbon, nitrogen, and phosphorus is also important to ensure balanced growth. Generally the N:P ratio for seaweeds is 30:1, however, the ratio can differ significantly among species and requires experimental testing to identify the specific ratio for a given species. Exploring the relationship between nutrient cycling and seaweed growth is vital to optimizing seaweed aquaculture and understanding the functions and benefits of seaweed applications, including its use as a fertilizer, bio-remediator, and in the blue economy.

Coastal eutrophication

A growing population and intensification of industry and agriculture have increased the volume of wastewater discharged into coastal marine ecosystems. These waters typically contain high concentrations of nitrogen and phosphorus, and relatively high heavy metal concentrations, leading to eutrophication of many coastal ecosystems. Eutrophication results from the excessive nutrient load within these ecosystems resulting from the pollution of waters entering the oceans from industry, animal feed, and synthetic fertilizers, and thus over-fertilizes these systems. Eutrophication leads to high productivity in coastal systems, which can result in coastal hypoxia and ocean acidification, two major concerns for coastal ecosystems. A notable service of seaweed farming is its ability to act as a bio-remediator through uptake and removal of excessive nutrients in coastal ecosystems with their application to land uses. Brown algae, due in part to their large size, have been noted for their high productivity and corresponding high nutrient uptake in coastal ecosystems. Additionally, studies have focused on how brown algae growth can be optimized to increase biomass production and therefore increase the quantity of nutrients removed from these ecosystems. Studies have also explored the potential of brown algae to sequester large volumes of carbon (blue carbon).

Bio-remediation in eutrophic ecosystems

Seaweeds have received significant attention for their potential to mitigate eutrophication in coastal ecosystems through nutrient uptake during primary production in integrated multi-trophic aquaculture (IMTA). Bioremediation involves the use of biological organisms to lower the concentrations of nitrogen, phosphorus, and heavy metal concentrations in marine ecosystems. The bioremediation potential of seaweeds depends, in part, on their growth rate which is controlled by numerous factors including water movement, light, desiccation, temperature, salinity, life stage, and age class. It has also been proposed that in eutrophic ecosystems phosphorus can become limiting to seaweed growth due to the high N:P ratio of the wastewater entering these ecosystems. Bioremediation practices have been widely used due to their cost-effective ability to reduce excess nutrients in coastal ecosystems leading to a decrease in harmful algal blooms and an oxygenation of the water column. Seaweeds have also been studied for their potential use in the biosorption and accumulation of heavy metals in polluted waters, although the accumulation of heavy metals may impact algal growth.

Blue carbon

Blue carbon methods involve the use of marine ecosystems for carbon storage and burial. Seaweed aquaculture shows potential to act as a CO₂ sink through the uptake of carbon during photosynthesis, transformation of inorganic carbon into biomass, and ultimately the fixation of carbon which can later be exported and buried. Duarte et al. (2017) outline a potential strategy for a seaweed farming blue carbon initiative. However the contribution of seaweed to blue carbon has faced controversy over the ability of seaweed to act as a net sink for atmospheric carbon. Krause-Jensen et al., (2018) discuss two main criteria for seaweed farming to be considered a blue carbon initiative: it must be both extensive in size and sequestration rate and possess the ability to be actionable by humans, that the sequestration rate can be managed by human action. Seaweed farming, including the use of seaweed as fertilizer could become an important contributor in climate mitigation strategies through carbon sequestration and storage.

The positive impacts conferred by seaweed fertilizer on crops.

Functions and benefits of seaweed fertilizer

Fertilization

Seaweed functions as an organic bio-fertilizer. Because seaweed is rich in micro and macronutrients, humic acids, and phytohormones, it enhances soil fertility. In addition, seaweed-derived fertilizers contain polysaccharides, proteins, and fatty acids which improve the moisture and nutrient retention of soil, contributing to improved crop growth. More trace minerals are found in seaweed than those produced with animal byproducts.

The application of seaweed fertilizers can also result in enhanced tolerance to abiotic stressors that generally inhibit crop growth and yield such as low moisture, high salinity, and freezing temperatures. These stress tolerance benefits appear to be driven by physiological changes induced in crops by the seaweed, including improved energy storage, enhanced root morphology, and greater metabolic potential, enhancing the plant's ability to survive unfavorable conditions. Kappaphycus alvarezzi extracts have also resulted in considerable reductions in the leakage of electrolytes, as well as enhanced chlorophyll and carotenoid production, and water content. Research has also demonstrated that wheat plants treated with seaweed extracts have accumulated key osmoprotectants such as proline, other amino acids, and total protein.

Foliar applications of seaweed fertilizer extract have been shown to improve the uptake of nitrogen, phosphorus, potassium, and sulfur in soybeans such as Glycine max. Research has also demonstrated that brown algae seaweed extracts can improve tomato plant growth, overall crop yield, and resistance to environmental stressors. Additional documented benefits of using seaweed as a fertilizer include reduced transplant shock, increased leaf surface area, and increased sugar content.

Soil conditioning

As a soil conditioner, seaweed fertilizer can improve the physical qualities of soil, such as aeration and water retention. Clay soils that lack organic matter and porosity benefit from the humic acid and soluble alginates found in seaweed. These compounds bond with metallic radicals which cause the clay particles to aggregate, thereby improving the texture, aeration, and retention of the soil by stimulating clay disaggregation. The degradation of alginates also supplements the soil with organic matter, enhancing its fertility. In particular, brown seaweeds such as Sargassum are known to have valuable soil conditioning properties. This seaweed contains soluble alginates as well as alginic acid, which catalyzes the bacterial decomposition of organic matter. This process improves soil quality by enhancing populations of nitrogen-fixing bacteria and by supplementing the soil with additional conditioners through the waste products produced by these bacteria.

Bio-remediation of polluted soils

Seaweed functions as a bio-remediator through its adsorption of harmful pollutants. Functional groups on the algal surface such as ester, hydroxyl, carbonyl amino, sulfhydryl, and phosphate groups drive the biosorption of heavy metal ions. Seaweeds such as Gracilaria corticata varcartecala and Grateloupia lithophila effectively remove a wide variety of heavy metals, including chromium (III) and (IV), mercury (II), lead (II), and cadmium (II) from their environment. In addition, Ulva spp. and Gelidium spp. have been shown to enhance the degradation of DDT in polluted soils and may reduce its bioavailability. Although there is significant potential for seaweed to serve as a bio-remediator for polluted soils, more research is needed to fully develop the mechanisms for this process in the context of agriculture. Heavy metals accumulated by seaweed fertilizer may transfer to crops in some cases, causing significant implications for public health.

The application of biochar is another strategy that can remediate and enhance infertile soils. Seaweed can be transformed into biochar and used as a means of increasing the organic matter and nutrient content of the soil. Different types of seaweed appear to yield unique nutrients and parameters; red seaweeds, for example, create biochar that is rich in potassium and sulfur and is more acidic than biochar generated from brown seaweeds. While this is a new field of research, current data shows that targeted breeding of seaweeds may result in biochars that can be tailored to different types of soil and crops.

Integrated pest management

The addition of seaweed to soil can increase crop health and resistance to diseases. Seaweeds contain a diverse array of bioactive molecules that can respond to diseases and pests, including steroids, terpenes, acetogenins, and amino acid-derived polymers. The application of seaweed extracts reduces the presence of harmful pests including nematodes and insects. While the application of seaweed seems to reduce the harmful effects of nematode infestation, the combination of seaweed application and carbofuran, a chemical nematocide, seems to be most effective. In addition, several species of seaweed appear to hinder the early growth and development of numerous detrimental insects, including Sargassum swartzii, Padina pavonica, and Caulerpa denticulata.

Soil microbial response to seaweed fertilizer treatment

Shifts in bacterial and fungal communities, in response to seaweed fertilizer treatment, have only recently been studied. Soil Microbial community composition and functionality is largely driven by underlying soil health and abiotic properties. Many DNA sequencing and omics-based approaches, combined with greenhouse experiments, have been used to characterize microbial responses to seaweed fertilizer treatment on a wide variety of crops. Deep 16S ribosomal RNA (rRNA) amplicon sequencing of the bacteria found in the soils of tomato plots, treated with a Sargassum horneri fermented seaweed fertilizer, showed a large shift in alpha diversity and beta diversity indices between untreated soils and soils after 60 days. This shift in community composition was correlated with a 1.48-1.83 times increase in tomato yield in treated soils. Though dominant bacterial phyla remained similar between treatment groups, changes in the abundance of the class, Bacilli and family, Micrococcaceae were noted. Enzyme assays also displayed an increase in protease, polyphenol oxidase, dehydrogenase, invertase, and urease activity, which was thought to be induced by microbial community alterations. Each of the microbial and enzymatic results listed above were noted to improve the nutrient turnover and quality in soils treated with fertilizer. To investigate interactions between plant growth-promoting rhizobacteria (PGPR) and seaweed-derived extract, Ngoroyemoto et al. treated Amaranthus hybridus with both Kelpak and PGPR and measured impacts on plant growth. It was found that the treatment of plants with Kelpak® and the bacteria, Pseudomonas fluorescens and Bacillus licheniformis, decreased plant stress responses and increased production. The most recently mentioned study provides implications for crop benefits when the application of seaweed fertilizer to soils favors the growth of PGPR.

Wang et al. found that apple seedlings treated with seaweed fertilizer differed markedly in fungal diversity and species richness, when compared to no-treatment control groups. These findings were complemented by increases in soil quality and enzyme activities in treated soil groups, which supports the hypothesis that the fertilizer promoted the growth of plant-beneficial fungal species. With the use of 16S rRNA and fungal internal transcribed spacer (ITS) sequencing, Renaut et al. examined the effect of Ascophyllum nodosum extract treatment on the rhizospheres of pepper and tomato plants in greenhouses. This group found that bacterial and fungal species composition and community structures differed based on treatment. A rise of the abundance of certain amplicon sequence variants (ASVs) were also directly correlated with increases in plant health and growth. These ASVs included fungi in the family, Microascaceae, the genus, Mortierella spp., and several other uncultured ASVs. A large diversity of bacterial ASVs were identified to be positively correlated with growth in this same study, including Rhizobium, Sphingomonas, Sphingobium, and Bradyrhizobium.

Resistance to plant pathogens

The application of seaweed fertilizer may also increase resistance to plant pathogens. In greenhouse samples, Ali et al. tested the treatment of Ascophyllum nodosum extract on tomato and sweet pepper crops and found that it both increased plant health and reduced the incidence of plant pathogens. Further investigation showed that the up-regulation of pathogen defense-related enzymes led to the reduction of the pathogens, Xanthomonas campestris pv. vesicatoria and Alternaria solani. Chen et al. found that Ascophyllum nodosum treatment positively impacted the community composition of maize rhizospheres. This may have critical implications for plant health because the structure of rhizosphere microbial communities can aid in the resistance of plants to soil-borne pathogens.

Other pathogen reductions include the mitigation of carrot foliar fungal diseases following Ascophyllum nodosum treatment and inoculation with the fungal pathogens, Alternaria radicina and Botrytis cinerea. Reduced disease severity was noted at 10 and 20 days post-inoculation in comparison to control plants, and the seaweed treatment was found to be more effective at reducing disease pathology than salicylic acid, a known plant protector from biotic and abiotic stresses. Islam et al. had similar results when treating Arabidopsis thaliana with brown algal extracts, followed by inoculation with the fungal pathogen Phytophthora cinnamomi. This group analyzed plant RNA transcripts and found that the seaweed extract primed A. thaliana to defend against the fungal pathogen before its inoculation, which led to increased host survival and decreased susceptibility to infection.

Fewer studies have analyzed the impact of seaweed fertilizer treatment on plant resistance to viral pathogens, however limited auspicious results have been demonstrated. It has been shown that green, brown, and red seaweeds contain polysaccharides that illicit pathogen response pathways in plants, which primes defense against viruses, along with bacteria and fungi. Specifically, defense enzymes, including phenylalanine ammonia lyase and lipoxygenase, are activated and lead to viral defense. Aqueous and ethanolic extracts from the brown alga, Durvillaea antarctica was shown to decrease pathological symptoms of tobacco mosaic virus (TMV) in tobacco leaves. Another study done on tobacco plants found that sulfated fucan oligosaccharides, extracted from brown algae, induced local and systemic acquired resistance to TMV. Based on the above results, it can be stated that the application of seaweed fertilizers has considerable potential to provide broad benefits to agricultural crops and resistance to bacterial, fungal, and viral plant pathogens.