When you walk through the forest or the city, do you usually look up? The usual thing is to look at where we are going or where we put our feet, but if you find yourself in the middle of nature, do not forget to observe the trees, perhaps you find yourself with an image as beautiful as the cover of this post: you are observing the crown shyness.
A BOTANICAL PHENOMENON
Less than 100 years ago, back in 1920, a botanical phenomenon that give us beautiful and impressive images of certain forests was observed for the first time. In 1955, the botanist Maxwell R. Jacobs, described this phenomenon as “crown shyness” after studying various populations of eucalyptus. The crown shyness is also known as canopy disengagement, canopy shyness or intercrown spacing.
The furrows of sky that makes the crown shyness. Photo: Tom Cowey
This phenomenon consists in a limited growth of the canopy of the trees, in such a way that the leaves and branches of adjacent trees do not touch each other. This produces figures and patterns with the sky in the background when the trees are observed from the ground.
The canopy disengagement, among other themes, is explored in the documentary Once Upon a Forest.
WHY CROWN SHYNESS OCCURS?
The scientific community has not yet reached a consensus that explains the mechanism that gives rise to this phenomenon. A total of three hypotheses have tried to explain the crown shyness:
1. Friction hypothesis
The initial hypothesis of Maxwell R. Jacobs (currently barely accepted by the scientific community) explains that the friction of some branches with others, when the wind hits them, would limit the growth of the branches to avoid touching the neighboring trees, due to the damages produced by the abrasion.
2. Allelopathy hypothesis
The most supported hypothesis currently indicates that crown up has an allelopathic origin.
In botany, allelopathy is any effect that one plant transmits to another through the production of different chemical compounds, either causing a positive or negative effect on the other plant. These compounds are the so-called allelochemicals. In other words, plants and trees communicate with each other by chemical signals. This relationship occurs more frequently between trees and plants of the same species, although it also occurs between different species. To know in depth the process of allelopathy, we invite you to read the post Communication among plants: allelopathy.
Photo: airwii
3. Photoreceptors hypothesis
In addition to chemical signals, phytochrome photoreceptors (sensors of light capable of detecting the area of distant red light) possessed by trees and plants allow them to perceive the proximity of other individuals. Another type of photoreceptor detects blue light, which produces in plants and trees the avoidance of shadows produced by other individuals.
Plant photoreceptors and photoresponses. Credit: Christian Fleck
As a whole, the signals captured by these photoreceptors would provoke the response of the tree to move away from the adjacent one, which would allow it to obtain a greater quantity of light, which is essential for photosynthesis.
ARE ALL TREES “SHY“?
Crown shyness has been observed in certain European oak and pine species and tropical and subtropical species, such as some eucalyptus, species of the Dryobalanops genus, Pinus contorta, Avicennia germinans, Didymopanax pittieri, Clusia alata, Celtis spinosa,Pterocymbium beccarii, Picea sitchensis and Larix kaempferi.
Arboreal canopy of Dryobalanops aromatica in Kuala Lumpur. Photo: Patrice78500
In other species, the tops of the trees come to touch and even cross their branches, although the canopy (habitat that includes the tops of the trees) does not usually mix completely.
HYPOTHESIS ON THE ADVANTAGES OF THE CANOPY SHYNESS
The evolutionary sense of the timidity of the glass remains unknown, although botany has launched several hypotheses:
It allows a greater penetration of light in the forest to perform photosynthesis more efficiently.
It avoids damaging the branches and leaves when hit against each other in case of storm or gusts of wind.
It prevent diseases, larvae and insects that feed on leaves from spreading easily from one tree to another.
Ants build structures with their own bodies to move from one leaf to another. Photo: Rose Thumboor
For now, it seems that crown shyness is due to a relationship of collaboration between species for survival, rather than a competition (the popularly known as the “survival of thje fittest”). We will have to wait for future studies to shed a little more light on this still unknown phenomenon.
During million years the evolution leaded plants to develop different strategies to defence from natural enemies, giving rise to an evolutionary weaponry war in which the survival of ones and others depends into the ability to beat the other’s adaptations. It is inthat scenario where the high-level accumulation of heavy metals in plants plays an important role.
INTRODUCTION
Boyd (2012) commented that plant defences can be grouped in different categories:
mechanic: thorns, coverage, etc.
chemical: different organic and inorganic components.
visual: crypsis and mimicry .
behavioural: related with phenology’s modification.
and associative: symbiosis with other organisms, such is the case of the genus Cecropia, which has stablished a symbiotic relationship with ants of the genus Azteca, who protects these plants – to know more: Plants and animals can also live in marriage-.
Mechanic defence with thorns (Author: Karyn Christner, Flickr, CC).
It is known that chemical defence is ubiquitous, and thus, a lot of interactions among organisms can be explained for this reason. In this sense, some plants contains high levels of certain chemical elements, frequently metals or metallic components, which plays an important role in the defence, these plants are the heavy metal hyperaccumulating plants.
Heavy metal hyperaccumulating plants and their main characteristics
This plants belong to several families, thus hyperaccumulation is an independent acquisition occurring different times during the evolution. In all cases, hyperaccumulation allowed the ability to grow soils with high levels of heavy metals and to accumulate extraordinary amounts of heavy metals in aerial organs. It is known that the concentration of these chemical elements in hyperaccumulating plants can be 100 – 1000 times higher than in non-hypperaccumulating plants.
Generally, chemistry describes heavy metal as transition metals with atomic mass higher than 20 and with a relative density around 5. But, from a biological point of view, heavy metals or metalloids are elements which can be toxic in a low concentration. Even though, hyperaccumulating plants has become tolerant, i.e., they hypperacumulate this heavy metals without presenting phytotoxic effects (damage in plant tissues due toxicity).
In this sense, there are three main characteristics typically present in all hyperaccumulating plants:
Increased absorption rate of heavy metals.
Roots that perform translocation more quickly.
Great ability to detoxify and accumulate heavy metals in sheets.
Thus, hyperaccumulating plants are prepared to assimilate, translocate and accumulate high-levels of heavy metals in vacuoles or cellular wall. In part, it is due to the overexpression of genes codifying for membrane transporters.
The threshold values that allow to differentiate a hyperaccumulating plant from a non-hyperaccumulating one are related to the specific phytotoxicity of each heavy metal. According to this criterion, hyperaccumulating plants are plants that when grown on natural soils accumulate in the aerial parts (in grams of dry weight):
> 10 mg·g-1 (1%) of Mn or Zn,
> 1 mg·g-1 (0,1%) of As, Co, Cr, Cu, Ni, Pb, Sb, Se or Ti
THE ORIGIN OF HYPERACCULATING PLANTS AND THEIR IMPLICATIONS
Till the moment, several hypothesis has been proposed to explain why certain plants can hyperaccumulate heavy metals:
Tolerance and presence of metals in soils.
Resistance to drought.
Interference with other neighbouring plants.
Defence against natural enemies.
The most supported hypothesis is “Elemental defence”, which indicates that certain heavy metals could have a defensive role against natural enemies, such as herbivores and pathogens. So, in the case these organisms consume plants, they should present toxic effects, which would lead them to die or at least to reduce the intake of this plant in future. Even though heavy metals can act through their toxicity, this does not guarantee plants will not be damaged or attacked before the natural enemy is affected by them. For this reason, it is still necessary a more effective defence which allow to avoid the attack.
In contrast, according to a more modern hypothesis, the “Joint effects”, heavy metals could act along with other defensive organic components giving rise to a higher global defence. The advantages of inorganic elements, including heavy metals, are that they are not synthetized by plants, they are absorbed directly from the soil and thus a lower energetic cost is invested in defence, and also they cannot be biodegraded. Even though, some natural enemies can even avoid heavy metal effects by performing the chelation, i.e., using chelators (substances capable of binding with heavy metals to reduce their toxicity) or accumulating them in organs where their activity would be reduced. This modern hypothesis would justify the simultaneous presence of several heavy metals and defensive organic components in the same plant, with the aim to get a higher defence able to affect distinct natural enemies, which would be expected to do not be able to tolerate different element toxicity.
On the other hand, it has been shown that certain herbivores have the ability to avoid the intake of plants with high levels of heavy metals, doing what is called “taste for metals“. Although this is known to occur, the exact mechanism of this alert and avoidance process is still uncertain.
Solanum nigrum, cadmium hyperaccumulating plant (Autor: John Tann, Flickr, CC).
Additionaly, even tough heavy metal concentration in plant are really high, some herbivores manage to surpass this defense by being tolerant, i.e., their diet allows them to intake high dosis of metals and, thus, consume the plant. This could lead to think some herbivores could become specialist in the intake of hyperaccumulating plants, and, thus, this type of defence would be reduced to organisms with varied diets, which are called generalists. It has been demonstrated to not be true, as generalists herbivores sometimes present a higher preference and tolerance for hyperaccumulating plants than specialist organisms.
For all these reasons, it can be said that evolution is still playing an important role in this wonderful weaponry war.
REFERENCES
Boyd, R., Davis, M.A., Wall, M.A. & Balkwill K. (2002). Nickel defends the South African hyperaccumulator Senecio coronatus (Asteraceae) against Helix aspersa (Mollusca: Pulmonidae). Chemoecology 12, p. 91–97.
Boyd, R. (2007). The defense hypothesis of elemental hyperaccumulation: status, challenges and new directions. Plant soil 293, p. 153-176.
Boyd, R. (2012). Elemental Defenses of Plants by Metals. Nature Education Knowledge 3 (10), p. 57.
Laskowski, R. & Hopkin, S.P. (1996). Effect of Zn, Cu, Pb and Cd on Fitness in Snails (Helix aspersa). Ecotoxicology and environmentak safety 34, p. 59-69.
Marschner, P. (2012). Mineral Nutrition of Higher Plants (3). Chennai: Academic Press.
Noret, N., Meerts, P., Tolrà, R., Poschenrieder, C., Barceló, J. & Escarre, J. (2005). Palatability of Thlaspi caerulescens for snails: influence of zinc and glucosinolates. New Phytologist 165, p. 763-772.
Prasad, A.K.V.S.K. & Saradhi P.P. (1994).Effect of zinc on free radicals and proline in Brassica and Cajanus. Phytochemistry 39, p. 45-47.
Rascio, N. & Navari-Izzo, F. (2011). Heavy metal hyperaccumulating plants: How and why do they do it? And what makes them so interesting?. Plant Science 180 (2),p. 169-181.
Shiojiri, K., Takabayashi, J., Yano, S. & Takafuji, A. (2000) Herbivore-species-specific interactions between crucifer plants and parasitic wasps (Hymenoptera: Braconidae) that are mediated by infochemicals present in areas damaged by herbivores. Applied Entomology and Zoology 35, p. 519–524.
Solanki, R. & Dhankhar, R. (2011). Biochemical changes and adaptive strategies of plants under heavy metalstress. Biologia 66 (2), p. 195-204.
Verbruggen, N., Hermans, C. & Schat, H. (2009). Molecular mechanisms of metal hyperaccumulation in plants. New Phytologist 181 (4), p. 759–776.
Wenzel, W.W. & Jockwer F. (1999). Accumulation of heavy metals in plants grown on mineralised soils of the Austrian Alps. Environmental pollution 104, p. 145-155.
We often hear that epiphytes plants live on the air and it really seems like this, because they don’t nearly need soil to develop. They grow on trunks taking advantage of his height in search of the source of energy much wanted in tropical forests: the sun. In this article we describe epiphytes adaptations and the most common epiphytic groups of these amazing plants.
Epiphytes adaptations
The epiphytes live on other plants without parasitize them or damaging any of its organs or functions. Epiphytes take advantage of other plants structures as physical support to grow into the shaded forest canopy, using the trunks and branches of older trees to reach more height and catch the sunlight. Epiphytes never touch the ground; they are adapted to live on the air!
Epiphytic plants including Cactaceae, Bromeliaceae and ferns growink on a trunk. Source: Barres Fotonatura.
They have amazing adaptations as a result of this habit, such as:
• The ability to capture water and nutrients from the air, the rain and the small amount of soil or organic debris that may remain in the trees trunk where they root.
• Their roots are much more adapted to anchor to the trunks that to absorve water and nutrients.
• Frequently, they develop structures to accumulate moisture.
Although epiphyte plants depend on its host to obtain their nutrients, sometimes they grow so much that overload their host and end up killing their support. This is the case of some Ficus (Moraceae), called “strangler fig” that develop aerial roots around other trees without letting them grow.
Hollow structure left by a stranges fig after killing its hoste. Source: Wikipedia.
Thanks to the epiphytes contribution we can say that tropical rain forest is organized in a vertical gradient along the trees trunks, where we find organism diversity organized according to their distance to the ground. Epiphytes are largely responsible for the extremely rich biodiversity that makes tropical rainforests the most complex ecosystems on Earth. Besides providing different layers of vegetation along height, epiphytes provide shelter and nutrients to different insects and amphibians; who use water stored in the epiphytes leaves as a shelter or nest in the refuge generated in the middle of the trunk.
Water accumulated on a Bromeliad. Source: Otávio Nogueira, Creative Commons.
Epiphytes are found mostly in tropical rainforests, where dozens epiphytes have recorded on a single tree. However, in temperate climates or even deserts we can also found drought tolerant epiphytic species.
Epiphytes diversity
Currently, approximately 25,000 species are epiphytes. Most common and known epiphytes are Bromeliaceae and Orchidaceae families and ferns. Epiphytism has appeared several times throughout evolution and we found examples in other tropical spermatophytes (plants with seed and trunk) like Ericaceae, Gesneriaceae, Melastomataceae, Moraceae and Piperaceae and also in seedless plants (lichens, mosses and liver) of temperate climates.
Orchids
Orchids have the highest number of epiphytic in the world, with 20 tropical epiphytic genera. The genus with much epiphytes species number are Bulbophyllum (1800) and Dendrobium (1200). The genus of epiphytic orchids Phalaenopsis (60 species) is cultivated worldwide because of its beauty. In fact, many plants used in interior gardening are epiphytes because they have few nutrients and water requirements.
Among orchids, we wanted to highlight a species known for a different reason: the vanilla (Vanilla planifolia), native to Mexico and Central America, where it was consumed with cocoa. It was imported to Reunion island and Madagascar (currently first world producers) by the Spaniards when they discovered their amazing flavor. The vanilla crops imitate their naturally grow on trees, and vanilla plants are not grown on ground, but on logs. The part of the vanilla plant that is consumed is the still immature fruit, after a curing process.
Vanilla cultivation on logs. Source: pixabay.com
Orchids have one of the most complex pollination systems throughout the plant world, with several cases of monospecific coevolution systems linked to insects and hummingbirds. Vanilla is another example, as it is only pollinated by Mexican native bees and hummingbirds, so pollination does not occur naturally in the cultivation areas and it must be done by hand. Normally, women and children still practice this handmade technique pollinating each vanilla flower to get its precious fruit. In fact, vanilla is the world’s most expensive crop, by weight.
Vanilla flower. Source: Wikipedia.com.
Bromeliads
Bromeliaceae includes more than 3,000 neotropical species, most of them epiphytic. The most species rich genera are Tillandsia (450), Pitcairnia (250), Vriesia (200), Aechmea (150) and Puya (150). The leaves of bromeliads grow in rosette facilitating the accumulation of water. The cultivation of bromeliads has been prohibited in Brazil (where we found 43% of Bromeliaceae native species) by ignorance, because it was thought that this water favored the reproduction of Aedes aegypti, mosquito transmitter of Zika, dengue and chikungunya virus. Actually, bromeliads have secondary compounds that prevent the proliferation of this mosquito eggs and larvae while the water inside the leaves creates a micro-habitat that accumulates nutrients that feed other insects, amphibians and native birds that can help fighting it. Bromeliaceae flowers have bright colors and are accompanied by showy bracts also attracting the attention of pollinators, especially hummingbirds and bats. Many bromeliads are used as ornamental plants, especially Tillandsia and Guzmania.
Tillandsia sp. Source: Barres Fotonatura.
Epiphytes from temperate climates
One of the most incredible epiphytic ferns is the staghorn fern (Platycerium bifurcatum), widely used as an ornamental plant. The staghorn fern is native to Australia but is found in all tropical areas used for gardening. This fern develops two leaf shapes: the first kind is kidney-shaped and does not produce spores; its function is to anchor to the trunk. These leaves eventually acquire a brown coloration and form a base from which the second kind of leaves grow; which are fertile and therefore produce spores. The fertile leaves are long and bifurcated and can grow up to 90 cm long. The spores of this fern are produced at the leaves apex that gain a velvet appearance.
The two kinds of leaves in Platycerium bifurcatum. Source: Barres Fotonatura.
At temperate forests, the most common epiphytes are lichens. Among lichens, we want to highlight Usnea or old’s men beard. It is a cosmopolitan genus growing on conifers and deciduous trees. This grayish fruticose lichen grow as curtain shape hanging from trees. Curiously, there is a species of epiphytic bromeliads that reminds Usnea because they share this particular growth form. Its called Spanish moss (Tillandsia usneoides) but is neither a moss or lichen, but a bromeliad with very small leaves growing chained to the ground. Nor is Spanish but lives in America.
Usnea lichen growing as a curtain on temperate climates (left) and Tillandsia usneoides of tropical climates (right): Source: Barres Fotonatura and Wikipedia.com.
The epiphytes are still little known because climbing techniques in tropical rainforest have only been developed recently so we still known a little about compared with carnivorous or parasitic plants. Many are still to discover!
REFERENCES
Benzing, D.H. 1990. Vascular Epiphytes: General Biology and Related Biota. Cambridge: Cambridge University Press.
Smith N., Mori S. A., Henderson, A., Stevenson D. W. & Heald, S. V. 2004. Flowering Plants of the Neotropics. New Jersey, USA: The New York Botanical Garden, Princeton university press.
Have you ever wondered which are the longest-lived organisms of the seas and oceans of the Earth? The sea turtles are well known to have long lives. But, ¿which is the oldest organism of the ocean (and the planet)?
BOWHEAD WHALES
The bowhead whales (Balaena mysticetus), also called Arctic right whales, live most of the year associated with sea ice in the Arctic ocean. These marine mammals are among the largest animals on Earth, weighing up to 75-100 tons and with a length of 14-17 m on males and 16-18 m on females.
More than 20 years ago, in 1993, it was discovered by chance that bowhead whales have a longer life than previously thought. Their lifespan was considered to be about 50 years, but the unexpected discovery let to know that they live more than 100 years. In fact, some individuals are known to have lived for about 200 years.
Which was that fortuitous discovery? An Alaskan Eskimo hunted an individual with the tip of a harpoon inside its blubber. This harpoon was created with a technique not used for 100 years.
They are among the mammals that get much older, even among other whales. And the explanation to this fact lies on the extreme cold of their habitat: they have to invest so much energy in maintaining the body temperature that their first pregnancy is usually at 26 years and, therefore, they have a long life expectancy.
SEA TURTLES
In the famous Disney movie Finding Nemo, Marlin, Nemo’s father, meets Crush, a 150-year-old sea turtle. However, do sea turtles live so much?
Sea turtles have long lives, but their age is unknown (Picture: Key West Aquarium).
It is well-known that sea turtles have a long life, but their ages are barely known. It has been confirmed that growth lines in some turtle bones are laid down annually, but due to growing at different rates depending on the age, this cannot be used to estimate their age.
However, scientist believe that these awesome reptiles may live long like whales. Those turtles that outlive the first stages of life can expect to live at least 50 years. In addition, biological aging is nearly suspended for these animals.
Despite unknowing the age of the oldest wild sea turtle, it is said to be a 400-year-old captive sea turtle in China.
THE OLDEST KNOWN ANIMALS
Black corals are the oldest known animals on Earth. Notwithstanding, they are not the oldest organisms on the planet.
Leiopathes sp. is a genus of black corals that can live several millenniums (Picture: CBS News).
These coal-dark-skeleton corals grow a great deal less than a millimetre per year, such as the Mediterranean red coral. Despite its name, they usually show yellow, red, brown and green colours. Although they are considered deep-sea corals, they are found worldwide and at all depths.
Research in 2009 demonstrated that a Hawaiian black coral individual included in the Leiopathes glaberrima species had been living and growing since the building of Egyptian pyramids; 4,600 years ago.
Like sea turtles, in case an individual survives the first century of age, there is every likelihood of living for a millennium or more.
THE IMMORTAL JELLYFISH
It is a fact of life that all living beings die; except for Turritopsis nutricula, the immortal jellyfish. This small (4.5 mm) bell-shaped jellyfish is immortal owing to the fact that possess the capability to age in reverse.
The immortal jellyfish, Turritopsis nutricula (Picture: Bored Panda).
This species starts its life being a mass of polyps growing in the seafloor, which in some point produce jellyfishes that develop gonads to create the following generation of polyps, and then die. This has nothing special in comparison with other jellyfishes. Learn more about these beautiful animals here.
This cnidarian species, under the presence of a stressor or injury, transforms all its cells into larval forms. It is that changes from an adult to a larva. Then, every single larva can transform into a new adult. That process is named transdifferentiation. Little do scientists know about this process in the wild.
Transdifferentiation in Turritopsis nutricula (Picture: Bored Panda).
THE OLDEST ORGANISM ON EARTH
The oldest organism on Earth is neither an animal, algae nor a microorganism. The most elderly organism in the planet is a plant. In concrete, a marine plant known as Posidonia oceanica, commonly known as Neptune Grass or Mediterranean tapeweed. Do you want to know the reason why the Posidonia ecosystems are considered the marine jungles?
Spanish researchers found out that in Formentera (Balearic Islands) there is a 100,000-year-old Posidonia clone. This means this is the longest-living organism on the biosphere.
The key to understand its age is the clonal growth: it is based on the constant division of cells placed in the meristems and on the extremely slow growth of its stalk (rhizomes).
REFERENCES
Arnaud-Haond S, Duarte CM, Diaz-Almela E, Marba` N, Sintes T, et al. (2012) Implications of Extreme Life Span in Clonal Organisms: Millenary Clones in Meadows of the Threatened Seagrass Posidonia oceanica. PLoS ONE 7(2): e30454. doi:10.1371/journal.pone.0030454
Rugh, D.J. & Shelden, K.E.W. (2009). Bowhead whale. Balaena mysticetus. In Perrin, W.F; Würsig, B & Thewissen, J.G.M. Encyclopedia of Marine Mammals. Academic Press (2 ed).
Schiffman, J & Breen, M (2008). Comparative oncology: what dogs and other species can teach us about humans with cancer. The Royal Society Publishing. DOI: 10.1098/rstb.2014.0231
Brazil is one of the richest country of the world in terms of biodiversity. The Amazon rainforest, often known as the world’s lungs, is recognized as the world’s most diverse region. Is it really so? Brazil hides many more biomes as richer as the tropical rainforest, but much more unknown and with a high degree of threates that affect its conservation. In this post I will explain the main characteristics of the six Brazil biomes and I will review different crops that have been introduced into the country since historical times affecting the natural balance of its ecosystems, from sugar and coffee to soybeans.
WHAT IS A BIOME?
In this post I will discuss the different biomes of Brazil. But what is a biome? It is a group of ecosystem with a common history and climate and therefore being characterized by the same animals and plants. Biome concept includes all living beings of a community but in practice biomes are defined by the vegetation general appearance. Is a unit of biological classification used to classify major geographic regions of the world. Thera are ten recognized biomes in the world: polar desert, tundra, taiga, temperate deciduous forest, laurel forest, rainforest, steppe, savannah, desert and Mediterranean.
BIOLOGY OF BRAZIL
Brazil is recognized as the country with largest biodiversity in the world, followed by China, Indonesia, Mexico and South Africa. Brazil, according to recent scientific publications, is the country with the richest flora in the world, with 46,100 species of plants, fungi and algae described, 43% of them being endemic. This number increases every year since many Brazil biodiversity is still unknown. In fact it is estimated that 20,000 species have not been described yet. Botanists describe about 250 new species of plants every year in Brazil. So if you are taxonomist willing to contribute, there’s people lacking in Brazil!
Another amazing fact is that, 57% of the 8900 seed plant species in Brazil are endemic.
BRAZILIAN BIOMES
Nowadays, six different types of biomes are defined in Brazil: Amazon, Atlantic Forest, Cerrado, Caatinga, Pampa and Pantanal. This classification has little changed since the first attempt to classify the Brazilian vegetation in floristic domains elaborated by Martius in 1824, who gave names of Greek nymphs to the five domains detected.He chose the Nayades, nymphs of lakes, rivers and fountains to call the Amazon.For the cerrado, he took the Oreades, nymphs of the mountains, companions of Diana, the hunt Goddess.He named the Atlantic forest under the Dryades, the nymphs protective of oaks and trees in general.He considered pampas and araucarias forests under the Napeias dominion, nymphs of valleys and meadows and finally Hamadryades, nymphs protectors each one of a particular tree, were used to designate the caatinga.
Brazil is one of the few countries in the world including two hotspots for the conservation of biodiversity: the Atlantic Forest and the Cerrado.
Cattinga in the only biome exclusive from Brazil, tough other Cerrado-like savannahs are found in South America and the Atlnatic Forest, out from Brazil, is only found in North-East Argentina and East Paraguay.
Map with the distribution of the six brazilian biomes.
1. AMAZON
The Amazon basin area is the world’s largest forest and the most biodiverse biome in Brazil. It occupies almost 50% of the country and is seriously threatened due to the deforestation caused by logging industries and soybean crops. Currently it is estimated that 16% of the amazon rainforest is under anthropic pressure.
Aerial view of the Amazon rainforest (Source: Commons Wikimedia).
The origin of the Amazon diversity remains a mystery. Recent scientific studies explain that the rise of the Andes, which began at least 34 million years ago originated this biological richness. The Andes were formed by the collapse of the American tectonic plate under the Pacific oceanic plate. This geological process changed the wind regime in the area, affecting the rainfall patterns in the eastern side of the Andes. This also changed the Amazon River direction that before flew into the Pacific Ocean but due to this gemountain range rise was redirected to the Atlantic ocean.
These geological and climatic phenomena originated the formation of a large area of wetlands in the eastern part of the Andes, causing the appearance of many new species. The Amazon is an enclosed tropical rain forest with a sandy soil, poor in nutrients. The undergrowth is nonexistent and organisms are distributed along the canopy.
We found pantropical plant families like Fabaceae, Rubiaceae or Orchidaceae, and other of Amazonian origin; as Lecythidaceae (one of its most famous species is the Brazil nut tree, Bertholletia excelsa) or Vochysiaceae.
Bertholletia excelsa, the Brazil nut producer, typical from the Amazon rainforest (Source: Flickr and Commons Wikimedia).
2. ATLANTIC FOREST
Atlantic forest is a tropical forest covering the coastal region of Brazil and therefore it is characterized by humid winds coming from the sea and steep reliefs. It is composed of a variety of ecosystems because a high variety of altitudes, latitudes and therefore, climates ranging from semideciduous seasonal forests to open mountain fields and Araucaria’s forests in the south.
Araucaria forest, ecoregion considered in the Atlantic forest domain in south Brazil (Source: Wikipedia).
Although much more less known than the Amazon rainforest, the Atlantic forest has the largest diversity of angiosperms, pteridophytes and fungi in the country; with a very high level of endemism (50% of its species are exclusive) and is in a worst level of conservation. In fact until the arrival of the Europeans, it was the largest tropical forest worldwide. Today remains only 10% of its original length due to anthropogenic pressure. One of the first exploitation of this biome was the pau-brasil (Caesalpinia echinata), valued because of its wood and the red dye of its resin, that gave name to the country. Pau-Brasil was then followed by others human impacts as sugar cane and coffee cultivation and gold mining. But it was not until the twentieth century that the degradation of the environment worsened, given that the major economic and historical capitals like Sao Paulo, Rio de Janeiro and Salvador are within its domain.
Typical landscape of the Atlanic rainforest (Source: Commons Wikimedia).
However, we must be optimistic. The Atlantic Forest biome is the region with more conservation units in South America.
3. CERRADO
It is the second largest biome of South American covering 22% of Brazil.
It is considered the richest savannah in the world in terms of species number. It contains a high level of endemic species and it is considered one of the global hotspots in terms of biodiversity. Containing 11,627 species of plants (of which 40% are endemic) and 200 animal species, 137 of which are threatened to extinction.
Cerrado is in interior areas of Brazil with two well marked seasons (rain and dry season). It includes different types of habitats such as campo sujo, campo limpo or cerradão. It is composed of small trees with deep roots and leaves with trichomes and an undergrowth composed of sedges and grasses. Cerrado soils are sandy and nutrient-poor with reddish colors featuring the high iron content.
Typical landscape of the Cerrado (Source: pixabay).
Vochysia and Qualea (Vochysiaceae) genera dominate the savannah landscape of the cerrado. Representatives of the Asteraceae, Fabaceae and Orchidaceae are the most frequent in terms of species number.
It is in second position in terms of degradation in Brazil recent decades. The origin of this destruction is the development of the agricultural industry: approximately 40% of soybean crops (Brazil is the largest producer of soybeans in the world) and 70% of beef are produced in cerrado areas. Half of the cerrado biome has been destroyed in only the past 50 years. Despite this risk only 8% of its area is legally protected.
Soybean monoculture inside the cerrado domain in Tocantins (Source: barres fotonatura).
4. CAATINGA
It is the only exclusively Brazilian biome and occupies 11% of the country. Its name comes from a native language of Brazil, the Tupi-Guarani and means white forest. However, this biome is the most undervalued and little known because of its aridity.
The climate of the caatinga is semi arid and soils are stony. The vegetation is steppe and savannah like and is characterized by a great adaptation to aridity (xerophyte vegetation) often prickly. The caatinga trees lose their leaves during dry season, leaving a landscape full of whitish trunks.
Typical landscape of the Caatinga (Source: Commons Wikimedia).
Plant families predominating caatinga landscape are Cactaceae (Cereus, Melocactus or Pilosocereus genera are common), Bromeliaceae and Euphorbiaceae, but representatives from Asteraceae, Malvaceae and Poaceae can also been found. A typical native caatinga species is Juazeiro (Ziziphus joazeiro, Rhamnaceae).
Melocactus sp. (Cactaceae), a very comon genus in the caatinga (Source: barres fotonatura).
The caatinga conservation status is also critical. About 80% of the caatinga is already anthropizated. The main motive for this degradation is the food industry and mining.
5. PAMPA
Pampa is a biome that occupies a single state in Brazil, Rio Grande do Sul covering only 2% of the country. Pampa biome is also very well represented in Uruguay and northern Argentina. It includes a large diversity of landscapes, ranging from plains, mountains and rocky outcrops, but the more typical are grass fields with hills and isolated trees nearby water courses.
About 1,900 species of flowering plants have been catalogated in the Pampa, of which 450 are from the grass family (Poaceae) and 141 from Cyperaceae. Also Compositae (Asteraceae) and legumes (Fabaceae) species are frequent. In the areas of rocky outcrops we can found a large number of Cactaceae and Bromeliaceae.
Typical landscape of Pampa biome (Source: Flickr).
Regarding the fauna, there are up to 300 species of birds and 100 of mammals, with the emblematic species rhea, vicuña (South American camelids) or Cavia (rodents near the capybaras).
The pampas region has a very typical cultural heritage, shared with the pampas inhabitants of Argentina and Uruguay and developed by gaucho people.
The most developed economic activities are agriculture and livestock, which came along with Iberian colonization, displacing much of the native vegetation. According to estimates of habitat loss, in 2008 only 36% of the native vegetation remained . Only 3% of the pampa is protected under some form of conservation unit.
6. PANTANAL
Pantanal biome is a flooded forest steppe occupying the alluvial plain of the Paraguay River and its tributaries. It is therefore a wet plain which floods during the rainy season, from November to April. These floods favor a high biodiversity. It occupies only 1.75% of Brazil and is therefore the less extensive biome in the country.
When floods occur, a lot of organic matter emerges, since water carries all traces of vegetation and decaying animals favoring soil fertilization.
Grasses fields (Poaceae) configure the typical landscape in Pantanal. Not flooded areas are occupied by shrubs and even trees. About 2,000 different species of plants have been cataloged in Pantanal. Some of the more representative are palms (Arecaceae) and aquatic macrophytes (Lentibularaceae, Nymphaeaceae, Pontederiaceae).
Victoria regia (Nymphaeaceae) in the pantanal from Mato Grosso state (Source: Flickr).
Pantanal contains a high diversity of fishes (263 species), amphibians (41 species), reptiles (113 species), birds (650 species) and mammals (132 species), being the hyacinth macaw, the alligator or the black jaguar its most emblematic species.
After the Amazon, it is the second most preserved biome in Brazil since 80% of its extension retains its native vegetation. However, human activity also has made a great impact, especially with farming activities. Fishing and cattle are the most developed economic activities in the Pantanal. Also the establishment of hydroelectric plants is threatening the ecological balance of the environment, because if the flooding regime is broken, wildlife will be affected.
REFERENCES
Guraim Neto, G. 1991. Plantas do Brasil, angiospermas do estado de Mato Grosso, Pantanal. Acta Botánica Brasileira 5: 25-47.
Hoorn, C. et al. 2010. Amazonia through time: andean uplift, climate change, landscape evolution, and biodiversity. Science 330: 927.
Martius, C.P.F. von. 1824. Tabula geographica Brasilie et terrarum adjacentium. Tabula geographica quinque provicias florae Brasiliensis illustrans. In: Martius, C.P.F. von ed. Flora Brasiliensis, Vol. 1, Part 1, Fasc. 21. Monacchi et Lipsiae.
When we think about the life of plants it is difficult to imagine without interaction with the animals, as they establish different symbiotic relationships day after day. These symbiotic relationships include all the herbivores, or in the contradictory way, all the carnivorous plants. But there are many other super important interactions between plants and animals, such as the relationships that allow them to help each other and to live together. So, this time I want to present mutualism between plants and animals.
And, what is mutualism? it is the relationship established between two organisms in which both benefit from living together, i.e., the two get a reward when they live with the other. This relationship increase their biological effectiveness (fitness), so there is a tendency to live always together.
According to this definition, both pollination and seed dispersal by animals are cases of mutualism. Let’s see.
POLLINATION BY ANIMALS
Many plants are visited by animals seeking to feed on nectar, pollen or other sugars they produce in their flowers and, during this process, the animals carry pollen from one flower to others, allowing it reaches the stigma in a very effective way. Thus, the plant gets the benefit of fertilization with a lower cost of pollen production, which would be higher if it was dispersed through the air. And the animals, in exchange, obtain food. Therefore, a true relationship of mutualism is stablished between the two organisms.
“Video:The Beauty of Pollination” – Super Soul Sunday – Oprah Winfrey Network (www.youtube.com)
The extreme mutualism occurs when the species evolve depending on the other organism, i.e., when there is coevolution. We define the coevolution such as these evolutionary adaptations that allow two or more organisms to establish a deep relationship of symbiosis, due that the evolutionary adaptations of one specie influence the evolutionary adaptations of another organism. For example, this occurs between various orchids and their pollinators, as is the well- known case of Darwin’s orchid. But there are many other plants that also have co-evolved with their pollinators, as a fig tree or cassava.
In no way, this should be confused with the trickery produced by some plants to their pollinators, that is, when they do not obtain any direct benefit. For example, some orchids can attract their pollinators through odours (pheromones) and their curious forms that resemble female pollinator, stimulating them to visit their flowers. The pollinators will be impregnated with pollen, which will be transported to other flowers due to the same trickery.
Bee orchid (Ophrys apifera) (Autnor: Bernard DUPONT, flickr).
SEED DISPERSAL BY ANIMALS
The origin of seed dispersal by animals probably had occurred thanks to a co-evolutionary process between animals and mechanisms of seed dispersal in which both plants and animals obtain a profit. The most probably is that this process began in the Carboniferous (~ 300MA), as it is believed that some plants like cycads developed a false fleshy fruits that could be consumed by primitive reptiles that would act as seed dispersers. This process could have intensified the diversification of flowering plants (angiosperms), small mammals and birds during the Cretaceous (65-12MA).
The mutualism can occur in two ways within the seed dispersal by animals.
The first case is carried out by animals that eat seeds or fruits. These seeds or some parts of the fruits (diaspores) are expelled without being damaged, by defecation or regurgitation, allowing the seed germination. In this case, diaspores are carriers of rewards or lures that result very attractive to animals. That is the reason why fruits are usually fleshy, sweet and often have bright colours or emit scents to attract them.
For example, the red-eyed wattle (Acacia cyclops) produces seeds with elaiosomes (a very nutritive substance usually made of lipids) that are bigger than the own seed. This suppose an elevated energy cost to the plant, because it doesn’t only have to produce seeds, as it has to generate the award too. But in return, the rose-breasted or galah cockatoo (Eolophus roseicapillus) transports their seeds in long distances. Because when the galah cockatoo eats elaiosomes, it also ingest seeds which will be transported by its flight until they are expelled elsewhere.
On the left, Galah cockatoo (Eolophus roseicapillus) (Autnor: Richard Fisher, flickr) ; On the right, red-eyed wattle’s seeds (black) with the elaiosome (pink) ( Acacia cyclops) (Autnor: Sydney Oats, flickr).
And the other type of seed dispersal by animals that establishes a mutualistic relationship occurs when the seeds or fruits are collected by the animal in times of abundance and then are buried as a food storage to be used when needed. As long as not all seed will be eaten, some will be able to germinate.
A squirrel that is recollecting som nuts (Author: William Murphy, flickr)
But this has not finished yet, since there are other curious and less well-known examples that have somehow made that both animals and plants can live together in a perfect “marriage.” Let’s see examples:
Azteca and Cecropia
Plants of the genus Cecropia live in tropical rain forests of Central and South America and they are very big fighters. The strategy that allow them to grow quickly and capture sunlight, avoiding competition with other plants, resides in the strong relationship they have with Azteca ants. Plants provide nests to the ants, since their stems are normally hollow and with separations, allowing ants to inhabit inside. Furthermore, these plants also produce Müllerian bodies, which are small but very nutritive substances rich in glycogen that ants can eat. In return, the ants protect Cecropia from vines and lianas, allowing them to success as a pioneer plants.
Ant Plants: Cecropia – Azteca Symbiosis (www.youtube.com)
Marcgravia and Bats
Few years ago, an interesting plant has been discovered in Cuba. This plant is pollinated by bats, and it has evolved giving rise to modified leaves that act as satellite dish for echolocation performed by these animals. That is, their shape allow bats to locate them quickly, so they can collect nectar more efficiently. And at the same time, bats also pollinate plants more efficiently, as these animals move very quickly each night to visit hundreds of flowers to feed.
In general, we see that the life of plants depends largely on the life of animals, since they are connected in one way or another. All the interactions we have presented are part of an even larger set that make life a more complex and peculiar one, in which one’s life cannot be explained without the other’s life. For this reason, we can say that life of some animals and some plants resembles a marriage.
REFERENCES
Notes from the Environmental Biology degree (Universitat Autònoma de Barcelona) and the Master’s degree in Biodiversity (Universitat de Barcelona).
Bascompte, J. & Jordano, P. (2013) Mutualistic Networks (Chapter 1. Biodiversity and Plant-Animal Coevolution). Princeton University Press, pp 224.
Dansereau, P. (1957): Biogeography: an Ecological Perspective. The Ronald Press, New York., pp. 394.
Fenner M. & Thompson K. (2005). The Ecology of seeds. Cambridge: Cambridge University Press, 2005. pp. 250.
Font Quer, P. (1953): Diccionario de Botánica. Editorial Labor, Barcelona.
Izco, J., Barreno, E., Brugués, M., Costa, M., Devesa, J. A., Fernández, F., Gallardo, T., Llimona, X., Parada, C., Talavera, S. & Valdés, B. (2004) Botánica ªEdición. McGraw-Hill, pp. 906.
Murray D. R. (2012). Seed dispersal. Academy Press. 322 pp.
Tiffney B. (2004). Vertebrate dispersal of seed plants through time. Annual Review of Ecology, Evolution and Systematics. 35:1-29.
Willis, K.J. & McElwain, J.C. (2014) The Evolution of Plants (second edition). Oxford University Press, pp. 424.
Has anyone ever seen a fig flower? Surely even if you really look for it, you will not find any of them. In fact, neither Linnaeus, the great Swedish botanist, could discover the enigma of fig flowers and when he described the species and gave him a scientific name (Ficus carica L.), he said the fig had no flowers! But then how does the fig reproduce himself and origins its delicious summer fruit; the fig?
The flowers of the fig tree cannot be seen as they grow hidden inside the receptacle that supports them, the fig. They have developed a close relationship of mutualism with their pollinators so they don’t need to bloom externally offering sweet rewards. Indeed, each species of Ficus (including 750 species in family Moraceae) is pollinated by a unique wasp species (family Agaonidae; Blastophaga psenes in the case of the Mediterranean fig). It is a very complex case of coevolution between a plant and its pollinator in which neither species could survive without the other.
The mechanism of fig pollination works as a perfect gear. Female wasps are the first to visit the fig, where they arrive attracted by the smell of the mature female flowers. The female wasps possess special adaptations to penetrate the fig and achieve their ultimate goal: to leave their eggs inside. They have inverted teeth in the jaws and special hooks in the legs that let them to advance into the fruit. However, they have only one opportunity to deposit their eggs since most wasps lose their wings and antennae once they have entered the fig and therefore can no longer look for another. Once the eggs hatch, the wasp larvae feed on the contents of the fig. The male wasp larvae are the first to complete its development and when they reach sexual maturity, they seek female wasps, fertilize them and die inside the fig. The female wasps leave the figs a few days later, coinciding with the male flowers maturation and thus favoring that their exit will be carrying pollen. These fertilized and full of pollen wasps will look for a fig fruit again where to leave the pollen and eggs. Then the cycle begins again.
The fig is actually an infructescence (an ensemble of fruits that act as a single unit to facilitate the dispersion) with a special morphology called syconium. The syconium is a type of pear-shaped receptacle, thickened and fleshy with a small opening, the ostiole, that allows the entry of pollinators. Both male and female flowers (fig is monoecious) are together in the syconium, enveloped by bracts (white filaments found in the fig), but each one maturates in different time to avoid autopollination. Once the flowers are fertilized, the fruits originate within the same structure, thus flowers and fruits mix up.
Fig with the ostiole, hole by which wasps get into the flowers (Foto: barresfotonatura)
WHERE DO THE FIGS COME FROM?
Who would have said that the fig tree would have a so complex fructification mechanism? In fact, the fig tree is native to Asia but is now naturalized in the Mediterranean since prehistoric times. There is evidence of its consumption and cultivation from the Neolithic. The fig tree is considered as one of the first plants cultivated by mankind. In spring it produces fertilized figs (breba), increasing its production with two harvests per year.
Main Ficus species grow in tropical climates. In temperate areas, some of this species were brought for its interest in gardening. Many cities have grown these giants in their public gardens because their dramatic appearance. They can reach up to 30 meters high and they develop aerial roots that end up reaching the ground acting as buttress that hold their weight. The have become unique elements of our urban landscape; such as in the Parque Genovés, Cadiz or the magnificent specimen of Ficus rubiginosa located in the Botanic Garden of Barcelona.
Ornamental fig tree at the Parque Genovés, Cadiz (Foto: barresfotonatura)Ficus socotrana with aerial roots in Ethiopia (Foto: barresfotonatura)
REFERENCES
Byng W (2014). The Flowering Plants Handbook: A practical guide to families and genera of the world. Plant Gateway Ltd., Hertford, UK.
Cruaud A, Cook J, Da-Rong Y, Genson G, Jabbour-Zahab R, Kjellberg F et al. (2011). Fig-fig wasp mutualism, the fall of the strict cospeciation paradigm? In: Patiny, S., ed., Evolution of plant-pollinator relationships. Cambridge: Cambridge University Press, pp. 68–102.
Font Quer P (1953). Diccionario de Botánica. Ed. Labor
Machado CA, Robbins N, Gilbert MTP & Herre EA (2005). Critical review of host specificity and its coevolutionary implications in the fig/fig-wasp mutualism. Proceedings of the National Academy of Sciences of the USA 102: 6558–6565.
Since a few years ago, we have heard about the climate change. Nowadays, it is already evident and also a concern. This not only affects to us, the humans, but to all kind of life. It has been talked enough about the global warming, but perhaps, what happens to the vegetation has not been much diffused. There are many things affected by climate change and vegetation is also one of them. In addition, the changes in this also affect us. But, what are these changes? how can the vegetation regulate them? And how we can help to mitigate them through plants?
CHANGES ON PLANTS
Biomes distribution
In general, due to climate change, an increase of precipitations in some parts of the world are expected, while in others a decrease is awaited. A global temperature increment is also denoted. This leads to an alteration in the location of the biomes, large units of vegetation (e.g.: savannas, tropical forests, tundras, etc.).
Biome triangle classified by latitude, altitude and humidity (Author: Peter Halasaz).
On the other hand, there is an upward trend in the distribution of species in the high latitudes and a detriment in the lower latitudes. This has serious associated problems; the change in the species distribution affects their conservation and genetic diversity. Consequently, the marginal populations in lower latitudes, which have been considered very important for the long-term conservation of genetic diversity and due their evolutionary potential, are threatened by this diversity loss. And conversely, the populations in high latitudes would be affected by the arrival of other competing species that could displace those already present, being as invasive.
Species distribution
Within the scenario of climate change, species have some ability to adjust their distribution and to adapt to this.
But, what type of species may be responding more quickly to this change? It appears that those with a faster life cycle and a higher dispersion capacity will be showing more adaptability and a better response. This could lead to a loss of some plants with slower rates.
The Purple milk Thistle (Galactites tomentosa) is a plant with a fast life cycle and high distribution capacity (Author: Ghislain118).
One factor that facilitates adjustment in the distribution is the presence of wildlife corridors: these are parts of the geographical area that enable connectivity and movement of species from one population to another. They are important because they prevent that some species can remain isolated and because they can also allow the movement to new regions.
Another factor is the altitudinal gradient, which provides shelter for many species, facilitates the presence of wildlife corridors and permits redistribution of species along altitude. Therefore, in those territories where there is greater altitudinal range, the conservation is favored.
In short, the ability of species to cope with climate changedepends on the plant characteristics and the territory attributes. And, conversely, the species vulnerability to climate change occurs when the speed to displace their distribution or adapt their lives is less than the climate change velocity.
At internal level
Climate change also affects the plant as an organism, as it causes changes in their metabolism and phenology (periodic or seasonal rhythms of the plant).
One of the effects that pushes the climate change is the carbon dioxide (CO2) concentration increase in the atmosphere. This could produce a fertilization phenomenon of vegetation. Due the CO2 increase in the atmosphere it also increases the uptake by plants, thus increasing the photosynthesis and allowing greater assimilation. But, this is not all advantages, because for this an important water loss occurs due that the stomata (structures that allow gas exchange and transpiration) remain open long time to incorporate CO2. So, there are opposing effects and fertilization will depend on the plant itself, but the local climate will also determine this process. Many studies have shown that various plants react differently to the CO2 increase, since the compound affects various physiological processes and therefore there are not unique responses. Then, we find a factor that alters the plant metabolism and we cannot predict what will be the effects. Furthermore, this fertilizer effect is limited by the nutrients amount and without them production slows.
On the other hand, we must not forget that climate change also alters the weather and that this affects the vegetation growth and its phenology. This can have even an impact on a global scale; for example, could produce an imbalance in the production of cultivated plants for food.
PLANTS AS CLIMATE REGULATORS
Although one cannot speak of plants as regulators of global climate, it is clear that there is a relationship between climate and vegetation. However, this relationship is somewhat complicated because the vegetation has both effects of cooling and heating the weather.
The vegetation decreases the albedo; dark colours absorb more solar radiation and, in consequence, less sunlight is reflected outward. And besides, as the plants surface is usually rough, the absorption is increased. Consequently, if there is more vegetation, local temperature (transmitted heat) intensifies.
But, on the other hand, by increasing vegetation there is more evapotranspiration (set of water evaporation from a surface and transpiration through the plant). So, the heat is spent on passing the liquid water to gas, leading to a cooling effect. In addition, evapotranspiration also helps increase local rainfall.
Therefore, it is an ambiguous process and in certain environments the cooling effect outweighs, while in others the heating effect has more relevance.
MITIGATION
Nowadays, there are several proposals to reduce climate change, but, in which way can the plants cooperate?
Plant communities can act as a sinks, carbon reservoirs, because through CO2 assimilation, they help to offset carbon emissions. Proper management of agricultural and forest ecosystems can stimulate capture and storage of carbon. On the other hand, if deforestation were reduced and protection of natural habitats and forests increased, emissions would be diminished and this would stimulate the sink effect. Still, there is a risk that these carbon sinks may become emission sources; for example, due to fire.
Finally, we must introduce biofuels: these, unlike fossil fuels (e.g. petroleum), are renewable resources, since they are cultivated plants for use as fuels. Although they fail to remove CO2 from the atmosphere or reduce carbon emissions, they get to avoid this increase in the atmosphere. For this reason, they may not become a strict mitigation measure, but they can keep neutral balance of uptake and release. The problem is that they can lead to side effects on social and environmental level, such as increased prices for other crops or stimulate deforestation to establish these biofuel crops, what should not happen.
Sugarcane crop (Saccharum officinarum) in Brazil to produce biofuel (Author: Mariordo).
REFERENCES
Notes of Plant Physiology, Science of the Biosphere and Analysis of vegetation, Degree of Environmental Biology, UAB
Hample & R. J. Petit. 2005. Conserving biodiversity under climate change: the rear edge matters. Ecology letters 8 (5): 461-467.
As always have been said, plants are unable to speak. But, even if they don’t speak, this does not mean they do not communicate with each other. Relatively few years ago, during the period from 1930 to 1940, it was discovered that plants also transmit certain stimuli to others. But, what kind of communication exist among them? What are their words and how are pronounced? And what involves this interaction?
INTRODUCTION
In 1937, Molisch introduced the term allelopathy referring to the two Latin words “Allelon” and “Pathos”, which mean “another” and “suffering”, respectively. But, the actual meaning of the word was determined by Rice in 1984. Allelopathy now means any effect that a plant transmits to another directly or indirectly through production of different metabolism compounds, causing either a positive or negative effect on the other organism. These compounds are called allelochemicals.
The allelochemicals are released on the environment by plants. But, they are not directly aimed to the action site, thus it is a passive mechanism. To be effective, allelopathic interaction needs that these substances are distributed along the ground or the air and that they reach the other plant. Once inside the recipient plant, this one may have defense and degradation mechanisms of the compounds while avoiding the effect, or conversely, it will suffer a pathological effect.
The release of allelochemicals can be 4 main ways:
Leaching: the aerial part of the plant lets go substances by rain effect. Then, they can fall on other plants or on the ground. Therefore, it can be direct or indirect effect, depending on whether they falls on another plant or not. Although, in principle, it is considered indirect.
Decomposition: the plants drop their leftovers on the ground, where they decomposed under the microorganisms action, which help the release of the compounds. The plant leftovers range from leaves to branches or roots. The substances found there may be inactive until coming into contact with moisture or microorganisms, or can be active and then be inactivated by the microorganisms activity or by being retained on the ground. So, it is an indirect way. The decomposition is very important because the most of allelochemicals are released this way.
Volatilization: the substances are released by the stomata (structures that allow the exchange of gas and transpiration). These are volatile and water-soluble, thus can be absorbed by other plant’s stomata or be dissolved in water. Commonly, plants using these pathways occur in temperate and warm climates. It is considered a direct route.
Exudation: the plants can also release allelochemicals directly by live roots. The exudation system depends especially of roots state, of the kind of roots and of their growing level (if they are growing or not).
The 4 main pathways of allelochemical releasing: volatilization (V), leaching (L), descomposition (D) and root exudation (E). (Adapted image of OpenClips)
REGULATORY FACTORS
Factors influencing the release of allelochemicals are normally abiotic, such as high radiation, low humidity, unsuitable pH, ultraviolet light, temperature, nutrient deficiency, pollution or contamination (including pesticides ). The higher is the stress caused by this factors to the plant, highest is the allelochemicals amount released from secondary metabolic routes.
This is important for research and pharmacy: for generating relevant oils many plants are grown under stressful conditions, as it is thanks to the production of these secondary metabolites that they can survive.
Furthermore, biotic factors also take part, such as insects, herbivores or competition with other plant species. These activate the plant defenses and then the organism is stimulated to secrete bitter substances, or substances that harden the tissues, that are toxic or give off unpleasant odors, etc.
Finally, each plant has its own genome and this makes synthesize those or other substances. But, they are also determined by the phenology (life stages) and the development (if the size of the plant is bigger, it can release more allelochemicals).
ACTION MODE
The allelochemicals are very diverse and, therefore, it’s difficult to establish a general action model; since it depends on the compound type, the receiving plants and how it acts.
When we talk about how the allelochemicals can act at internal level, there is a large number of physiological parameters that can be affected. They have action on the cellular membrane, disrupt the activity of different enzymes or structural proteins or alter hormonal balance. They can also inhibit or reduce cellular respiration and chlorophyll synthesis, leading to a reduction in vitality, growth and overall development of the plant. Furthermore, these substances can also reduce seed germination or seedling development, or affect cell division, pollen germination, etc.
On the other hand, at external level, the allelochemicals may be related to the release or limitation of nutrients that are found in the soil. Others act on microorganisms, leading to a perturbation on the symbiotic relationships they establish. In addition, these substances have great importance into the generations succession, as they determine certain competition tendencies and also act on the habitat ecology. Even so, it is a successive competition, as they do not directly compete to obtain the main resources.
EXAMPLES
One of the best known allelochemicals is the juglone, produced by the Eastern black walnut (Juglans nigra). Juglone, once released to soil, can inhibit the other plants growth around the tree. This allows the issuing organism to get more resources, avoiding competition.
Eastern black walnut (Juglans nigra) (Photo taken by Hans Braxmeier)
A very curious case is that of the acacias (Acacia). These plants synthesize a toxic alkaloid that migrates to the leaves when the body is attacked by a herbivore. This substance’s toxicity is high, because it damages with the contact and ingestion, becoming deadly even for large herbivores.In addition, this alkaloid is volatile and transferred by air to other nearby acacias, acting as an alarm. When the other acacias receive this signal, this component is segregated to leaves, making them darker. Even so, the effect is temporary. This makes animals like giraffes have to constantly move to eat a few leaves of each acacia, and always against the wind, to avoid toxicity.
A. Aguilella & F. Puche. 2004. Diccionari de botànica. Col·leció Educació. Material. Universitat de València: pp. 500.
A. Macías, D. Marín, A. Oliveros-Bastidas, R.M. Varela, A.M. Simonet, C. Carrera & J.M.G. Molinillo. 2003. Alelopathy as a new strategy for sustainable ecosystems development. Biological Sciences in Space 17 (1).
J. Ferguson, B. Rathinasabapathi & C. A. Chase. 2013. Allelopathy: How plants suppresss other plants. University of Florida, IFAS Extension HS944
Notes of Phanerogamae, Applied Plant Physiology and Analisi of vegetation, Degree of Environmental Biology, UAB
This week I’m going to talk about how plants can survive in cold environments. The two biomes where cold is the main restrictive factor of the plant growth are tundra and alpine. In these places, the temperature can be under 0⁰C. Therefore, how do plants do to survive there?
INTRODUCTION
The cold is a restrictive factor to plant growth. It can be caused for two main reasons: height and high latitudes. When the height raises, the cold also does it; for each 100 meters of height, temperature gets down 1ºC. And in high latitudes, cold is caused by low insolation (only a little amount of sun’s heat is received). Plants can live until certain limits in high mountains, originating the alpine biome, and even become an ecosystem above the polar circle in the northern hemisphere, forming the tundra biome. Therefore, plants can survive in these cold ecosystems somehow. But, what kind of plants are and how do they do it?
On the left, tundra zone; and on the right, alpine zone (Image by Terpsichores).
VEGETATION STRUCTURE
First of all, we need to know what kind of plants are living in these places.
The trees’ growth is very restricted in both biomes. Indeed, trees are missing in tundra and only can be found in subalpine zone in the high mountains, between 1.600m and 2.400m; even so, the biggest height where trees can occur depends of different climatic factors and of the topographic relief. Once there are no trees, so there is no forest, we talk about alpine zone in high mountains.
On the other hand, shrubs are uncommon in both biomes, being the most of them smaller and creeping. That way, they can protect themselves against heavy frosts and cold winds, because they get covered of snow during the unfavourable period. Cranberry bush (Vaccinium vitis-idaea) is a good example of this kind of shrubs.
Cranberry bush (Vaccinium vitis-idaea) (Photo taken by Arnstein Rønning).
The herbs, bryophytes (e.g. mosses) and lichentogether, are the most dominant of these two biomes, because they are the most abundant.
On the left, tundra in Siberia (Photo taken by Dr. Andreas Hugentobler); on the right, alpine zone in Monte Blanco (Photo taken by Gnomefillier)
PLANT ADAPTATIONS
Due to cold weather and other restrictive factors of these biomes, plants have had to adapt in different ways. In these two biomes, the summer is the favourable season and is when plants can develop themselves. But in winter, unfavourable period, they can only remain dormant in the form of seeds or reducing their activity to a minimum, thus avoiding own energy consumption.
For all these, these plants produce storage organs below ground, where they are protected from cold temperatures. Examples are rhizomes (underground stems, usually elongated and with horizontal growth, root-like) and bulbs (short and thick stem, covered with more or less developed fleshy leaves). These bodies ensure sufficient energy reserves during the unfavourable period. Furthermore, their roots are thick and can also accumulate reserves.
On the left, iris rhizome (Iris) (Photo taken by David Monniaux); On the right, lily bulb (Lilium) (Photo taken by Denis Barthel).
On the other hand, their capacity to reach new zones to live, new habitats, depends more of the vegetative reproductionor asexual reproduction, that is, the emission of buds, underground organs, etc. And, in particularly, it is favoured by a high number of buds (plant organ that, when is developed, forms a stem, branch or flower).
A very curious adaptation, that can also protects against the wind, is that some plants are cushion-shaped. This morphology allows moisture and temperature to increase within the plant, and therefore stimulates the development and facilitates photosynthesis.
Cushion-shaped plant (Minuartia arcica) (Photo taken by Σ64).
Knowing that the favourable season is brief, plants usually are evergreen, that is, they have leaves during all year; and, that way, they don’t use energy to regenerate new leaves. Also, plant cells don’t freeze because they produce high concentrations of monosaccharides (simple sugars). So, it makes very difficult to freeze the perennial parts (those living all year).
Lucile's Glory-of-the-snow (Chionodoxa luciliae) (Photo taken by Ruhrfisch).
Moreover, their life cycle is also affected. The favourable period is so brief that it is often impossible to grow, forming flowers and fruits in the same year. Therefore, the plants usually live longer than a year and tend to perform only one of these three functions during the favourable season. Then remain dormant during unfavourable weather. So, its cycle is affected and it’s very impossible to live there to annual plants
Thanks to all these adaptations, plants have managed to live in such extraordinary places like these biomes, as incredible survivors. Remember, if you liked this article, you should not forget to share it. Thank you very much for your interest.
REFERENCES
Notes of Botany, Phanerogamae, Science of the biosphere and Analysis of vegetation, Degree of Environmental Biology, UAB.
Enciclopedia Catalana 1993-98. Biosfera. Volums. 9 Tundra i insularitat V. Krvazhimskii; A. N. Danilov. 2000. Reindeer in tundra ecosystems: the challenges of understanding System complexity. Publicat a tundra ecosystems: the challenges of understanding system complexity, V. 19, 107-110 pp.
Walter H. 1998 Vegetació i zones climàtiques del món. L’estructuració ecològica de la geobiosfera. 2ªed cat. Promocions i Publ Univ SA, Barcelona
On the left, tundra zone; and on the right, alpine zone (Image by 
Trees on subalpine zone (Photo taken by 
Cranberry bush (Vaccinium vitis-idaea) (Photo taken by 
On the left, tundra in Siberia (Photo taken by Dr. Andreas Hugentobler); on the right, alpine zone in Monte Blanco (Photo taken by 
On the left, iris rhizome (Iris) (Photo taken by 
Cushion-shaped plant (Minuartia arcica) (Photo taken by 
Lucile's Glory-of-the-snow (Chionodoxa luciliae) (Photo taken by 
All you need is Biology 
