For example, here is a picture of the root systems for some prairie grasses: (Click image for higher-resolution PDF) from: http://www.conservationresearchinstitute.org/educational-offerings.html
How is it possible to follow one root thread 15 feet down? Especially when they are so densely packed in the top foot of soil that you couldn't dig at all without destroying roots.
You originally posted this question on the Garden and Landscaping Section - that's where I'm from, and though it was moved here instead, I'll answer it anyway:
That image you've shown isn't like a photograph, its an impression of what the roots are like. Usual method of working out root patterns on plants is to remove what's known as a monolith, or a block of soil where the plant is - the soil is then either carefully removed by hand, in the manner that archaeologists use, or air blasted, or soaked off in water to reveal as much of the roots as possible. For trees or plants with very large roots, newer methods include geophysical surveying by machine, or electric resistance surveying. Even this doesn't reveal everything - many roots may penetrate too far down, or run along cracks in rocks beneath the soil. The root length and distribution pattern vary according to local conditions, so its hard to be definite about where the roots of any particular plant are in a particular position in the landscape.
Reference and further reading:
Plant Physiological Ecology (ISBN 978-94-009-2221-1; Google books link)
Especially, check the Introduction on page No.367
… why do you assume that it's non-destructive? It's effectively performing an "archeological dig style" excavation, and the particular plant is not likely to survive it.
Here's a couple links to descriptions of "an improved method" along with a description of the "usual method" it's "improved" over, circa 1938 and 1940. jstor previews as these things do mostly get discussed in academic journals.
Origin Of Root Offshoots Revealed Possible Basis For New Ecological Agricultural Applications
VIB researchers at Ghent University have discovered the substance that governs the formation of root offshoots in plants, and how it works.
Root offshoots are vitally important for plants &ndash and for farmers. Plants draw the necessary nutrients from the soil through their roots. Because they do this best with a well-branched root system, plants must form offshoots of their roots at the right moment. The VIB researchers describe how this process is controlled in the prominent professional journal Science. A key player in this process is a protein called ACR4. Depending on the signals that it receives from its environment, this protein triggers the formation of a root offshoot.
Now that we know the control mechanism, we can begin to stimulate plant roots to form more, or fewer, offshoots. This can lead to a more ecological agriculture and to the production of better crops at the same time.
An efficient network
It is difficult to overstate the importance of plants in our lives &minus they are responsible for our oxygen and for food, clothing, energy, and countless other things. And in turn, the importance of a plant's roots is unquestionable: they provide the plant with necessary nutrients and moisture. The more the roots are subdivided, in breadth and depth, the better they can do their work. So, a well-coordinated, controlled formation of root offshoots is crucial to a plant. But, until now, how a plant determines when and where an offshoot should be formed was unknown.
Asymmetric cell division
The presence of stem cells is very important in the development of plants and animals. Stem cells are cells that can transform themselves into various types of cells. In animals, tissues and organs are formed before birth but in fully-grown plants, stem cells continue to play a major role in the formation of new organs or tissues, such as root offshoots.
These stem cells are found inside the root, and several of them will induce the formation of an offshoot. These 'root-founder' cells undergo an asymmetric cell division. In contrast to the usual cell division, which gives rise to two identical cells, asymmetric cell division produces two different cells: a stem cell that is identical to the original cell, and a cell that is ready to become a specialized cell &ndash in this case, a secondary root cell.
The decisive signal
With the aid of the mouse-ear cress (Arabidopsis thaliana), a frequently used model plant, Ive De Smet and Valya Vassileva in Tom Beeckman's group have been studying how a plant determines which cells will trigger offshoots. To do this, the VIB researchers in Ghent have employed a special technology that makes it possible to make synchronous offshoots develop at different moments. This allowed them to isolate the cells that induce the formation of offshoots. They found out which genes are active in these cells and compared them with the genes that are crucial to normal cell division. In this way, the researchers identified a specific set of genes that control asymmetric cell division and send the signal for the formation of offshoots.
ACR4: control over asymmetric division
The researchers then examined one of these genes more closely. The ACR4 gene contains the DNA code for a receptor, a protein that is often located on the exterior of a cell to pick up signals from the outside and transmit them to the controlling mechanisms within the cell. When the researchers disrupted the function of ACR4 in plant cells, the precisely orchestrated asymmetric cell division was also disturbed. From this finding, De Smet and Vassileva inferred that ACR4 plays a key role in the creation of offshoots. Because the protein has a receptor function, triggering the formation of offshoots depends on its reaction to signals from the environment.
Desired or undesired
With this research, the scientists have discovered a fundamental mechanism &minus fundamental for the plant, and very important for plant-breeders as well. This new knowledge enables us to promote, or retard, the formation of offshoots &minus both activities are useful in a large number of applications.
Promoting an extensive root system helps plants absorb nutrients more readily, and thus they need less fertilizer. Such plants can also grow more easily in dry or infertile soils. Furthermore, plants with a well-developed root system are more firmly anchored in the soil and can be used to counteract erosion.
On the other hand, slowing down secondary root formation can be advantageous in tuberous plants, like potatoes or sugar beets. This enables these food crops to invest all their energy in the production of nutrients. Fewer root offshoots also makes it easier for farmers to harvest these crops.
Plant research with medical possibilities?
This plant research sheds light on the control of asymmetric cell division &minus and this kind of cell division is similar to the cell division of stem cells in animals, too. So, these results can also provide greater insight into how animal stem cells specialize.
For example, irregular cell division plays a role in the development of various types of cancer, and similar control mechanisms might underlie this process as well. This is clearly an important area for future research.
Materials provided by VIB (the Flanders Institute for Biotechnology). Note: Content may be edited for style and length.
The Root of Plants (With Diagrams)| Botany
The root is the descending axis of the plant and the down­ward prolongation of the radicle. It is usually non-green in colour and grows away from light. The root has no nodes and internodes. It bears only similar mem­bers, i.e. only roots.
The main root developing from the radicle is called the pri­mary root which, in turn, produces many secondary and tertiary branches, thus forming a system of roots going inside the soil in different directions.
These branch roots develop from internal tissues of the pri­mary root, so they are endo­genous in origin. They are arranged in acropetal suc­cession, i.e. older roots near the base and smaller and smaller ones towards the tip.
Regions of the Root (Fig. 32):
A root has usually four regions, in order, from the apex toward the Fig. 32.
(i) Root Cap Region:
The extreme tip of the root is usually protected by a cap or thimble-shaped body called the root-cap. When the root pushes its way through the soil, the tender and soft tip runs the risk of being injured due to friction with soil particles.
The root-cap, serving as a buffer, protects the tip from that danger. Further, the cap secretes slimy mucilaginous matters which facilitate the course of the root through the soil. The root-cap is absent in many aquatic plants. In screw pine root- caps are multiple (Fig. 33).
(ii) Region of Active Growth and Elongation:
Next to the root-cap is the region of active growth. It is a very short region where cells divide actively. This merges into the region of elon­gation where the newly formed cells grow in length.
This region is found next and here the outer cells of the roots grow out as unicellular hairs. The uni­cellular root-hairs are responsible for the absorption of water and mineral matters dissolved in water from the soil.
By germinating mustard seeds on a piece of soaked blotting paper the dense root-hairs can be conveniently observed (Fig. 34). During the growth of the root old zone is exhausted and is replaced by new zones of root-hairs more and more towards the tip.
This is located higher up. Here secondary roots develop from the primary root. The branches also have four regions like the primary root.
Root Systems (Fig. 35):
In dicotyledonous plants the radicle produces the primary root which is quite prominent, that is, long and stout. This is called the tap root. The tap root bears many secondary and tertiary branches developing acropetally.
All these branches can be easily distinguished from the main root. The whole system is called the tap root system. In monocotyledons like maize and rice the radicle produces the primary root which soon aborts and is re­placed by a tuft of roots developing from the base of the stem. All of them are more or less similar and are called fibrous roots and the whole system is known as fibrous root system.
Normal and Adventitious Roots:
Roots that develop from the radicle (primary root) or branches of the roots from that origin, are called normal or true roots and roots growing from any position other than the normal point of origin, are called adventitious roots. So the tap root system, usually found in the dicotyledons, is normal and fibrous root system, common in the monocotyledons like grasses, is adventitious.
Normal Functions of the Root:
Roots perform two normal functions. First, they fix the plants to the soil and thus secure anchorage. Secondly, roots are responsible for the absorption of water and dissolved mineral matters from the soil through the delicate root-hairs. Water is ultimately conducted to the leaves.
The primary roots with their large number of secondary and tertiary branches in the dicoty­ledons, or the fibrous roots in the monocotyledons penetrate into the soil, spread out in different directions and thus effectively carry on the normal functions.
In common land plants the root system, in fact, equals to or even exceeds the aerial portions (shoot system) both in length and volume. The fixation or anchorage is the mechanical function of the root and absorption and conduction of water and dissolved mineral matters, are the chief physiological functions.
Besides these, roots may perform many special functions which will be discussed in connection with the modified roots.
Modifications of Roots:
Many roots undergo modifications for carrying on functions other than the normal ones. Some of the modified roots are normal, while many of them are adventitious.
1. Normal Roots Modified for Storage of Food:
Some roots become swollen and fleshy due to the storage of food matters and assume different shapes (Fig. 36):
Here the root with the hypocotyl becomes swollen. The swelling is maxi­mum in the middle. It gradually tapers to­wards the ends, i.e. base and apex, e.g. radish. Practically the whole swollen portion in radish is the hypocotyl.
Here also the root is fleshy it is broadest at the base and gradually tapers towards the apex like a cone, e.g. carrot.
It is very much swollen at the base (with the hypocotyl), but abruptly tapers towards the apex, as in beet and turnip.
2. Adventitious Roots Modified for Storage of Food:
In plants like sweet potato which grow on the surface of the soil, some of the ad­ventitious roots, deve­loping from the stem, become swollen and fleshy due to the storage of food. They do not have any re­gular shape. These are called tuberous root (Fig. 37).
(e) In Asparagus (B. Satamuli), Ruellia, etc., quite a good number of tuberous roots are produced from the stem, form­ing a bundle or fasci­cle. They are called fasciculated roots (Fig. 38).
(f) In mango-ginger (B. Amada) the adventitious roots sud­denly become swollen at the tips. They are called nodulose roots (Fig. 39).
(g) In many grasses the swellings are often found at frequent intervals giving the root a beaded appearance. These peculiar roots are called moniliform (Fig. 39).
Adventitious Roots Modified:
Roots are normally underground organs. Some roots develop completely above ground and, so, are aerial. In the common banyan trees of our country roots are often found to hang freely in the air from the branches.
In course of time they reach the soil, become stouter and serve as so many extra supports or props. Thus they help the stem in bearing the weight of the heavy crown. These are called the prop roots (Fig.40).
These are also supporting roots. In plants like screw pine (B. Keya) quite a good number of adventitious roots develop from the basal part of the stem and go down­wards obliquely. These roots help the plant in maintaining the upright position. These are stilt roots (Fig. 41).
Weak climbing plants like betel, vine, Scindapsus (B. Gaj-pipul), etc., produce some adventitious roots which cling to the sup­ports and thus help the plants in climbing. They often sec­rete sticky juices or develop disc-like structures for that purpose (Fig. 42).
Many epiphytes, like orchids, pro­duce long roots which freely hang in air. They have sponge-like tissues, called velamen, at the ex­terior by means of which they can absorb moisture from the air (Fig. 43).
5. Sucking Roots or Haustoria:
Sucking roots or haustoria develop in the parasitic plants like Cuscuta or dodder (B. Swarnalata). These roots penetrate into the body of the host and draw nourishment from there without caring to manufacture their own food (Fig. 44, 2 & 3).
These roots are produced by the plants like Heritiera (B. Sundri), Rhizophora (B. Bora) growing in saline marshes or on the sea­shore where the soil is very poor in oxygen. Here some roots with pores at the tips come vertically surface of the soil and carry on the gaseous inter- with the change outer atmosphere. They are also called pneumatophores (Fig. 44—1).
In an aquatic plant fuissiaea (B. Keshar, dam) some peculiar, adventi­tious roots develop from the floating branches. They are light, soft and spongy due to the presence .of air­spaces. Besides faci­litating respiration, they give the plants buoyancy for float­ing on the surface of water (Fig. 45).
Roots of plants like Tinospora (B. Gulancha) hang freely in the air and. develop green colour. They can manu­facture food matters. The sub-merged roots of Trapanatans (water chest nut) coming out in pairs from the nodes are green and assimilatory in function.
Roots are also used for vegetative multiplication. Common vegetable plants like Trichosanthes dioica(B. Patol), sweet potato, etc., are propagated by means of roots. Many garden plants are also multiplied by root cuttings.
First Direct Observations of How Roots Grow
As scientists look at crops to find ways to help them deal with climate change stress and growing populations, a tool has emerged to give them a new perspective: the view from underground.
Plants are a lot like icebergs: A bulk of their mass is invisible to the naked eye, buried in their roots. Roots allow plants to compensate for their stationary role in life, hunting for nutrients and diving to mine for water in times of drought.
These are abilities food security researchers would like to be able to enhance to develop more durable crops, but laboratory conditions currently confine experiments to the first few days or weeks of a sprouting plant's life.
Alexander Bucksch, a computer scientist turned plant genetic mathematician, said he was driven to find a way to shed light on roots in his postdoctoral work at the Georgia Institute of Technology. He was struck by how little is known about their growth and how similar the scale, overlap and diversity of branching was to other systems he had created visual models for in his previous work.
"I had an immediate interest in going underground," he said. "We knew hardly anything about mature root systems, even less how to control traits. I realized I could take my technical side and apply it to biology, to get the best of both."
Bringing together specialists in root genetics, plant physiology and agro-ecology, Bucksch built a computer program that uses an algorithm to interpret digital images of mature roots extracted from the field. It allowed him to analyze enough root samples with a high degree of uniformity to allow statistically significant results. This could give future researchers the ability to manipulate traits of crops that have been concealed, explained Malcolm Bennett, a professor of plant sciences at the University of Nottingham in the United Kingdom.
"For 10,000 years we've selected for aerial traits directly, but we haven't directly been able to select for the hidden half, though we know roots can greatly impact the very things we're trying to select for," he said. "This is an impressive gain towards being able to do what we've wanted to for a long time."
Measuring the unseen in a standardized way
Understanding the challenges presented to root researchers is fairly easy, Bucksch explained. Current methods either grow seedlings in clay pots that can be analyzed using magnetic resonance imaging (MRI) or grow them in glass pots using a clear medium instead of soil. While these techniques are highly advanced, they observe only a small, unrepresentative portion of plant life, which restricts root study as many develop or are modified later in life.
"In maize [corn], you don't even see top roots grow within current studies," Bucksch said. "Before, the time scale people were working with was within a few weeks to a month at best now we're talking about being able to see the growth of months, maybe even more."
Bennett explained that this limited how quickly researchers could process their samples, which with a living subject that continues to grow makes comparing data collected days apart tricky.
"We just didn't have a high enough throughput to work with," Bennett said. "In the 1920s, we began learning how to study plant roots in laboratories and greenhouses, but ultimately you've got to get out into the field, and to do so you need an objective, quick way to look at your findings."
In the 1980s, image-based techniques were applied to the study of roots to better predict how they might grow, but this process still didn't allow the kind of certainty needed for genetic study and was very time-consuming.
In 2011, Jonathan Lynch from Pennsylvania State University, now part of Bucksch's team, helped create an alternative, a way to standardize root sampling and generate more precise results, which he called "shovelomics." It called for roots to be extracted, washed and then measured against a protractor board for classification in a specific manner.
But there were still subjective factors that remained a problem. "Each person brings with them different levels of expertise, field knowledge and training into their interpretation, making scores subjective," Bucksch said. "We wanted to take counting and measuring out of the researcher's hands altogether to avoid this."
Speaking the same language
The new method, published last week in Plant Physiology, has researchers photographing their root samples against a black background board alongside a circle to scale the image. This image is then uploaded to a computer that uses the algorithm to analyze fine and large-scale aspects of the samples. For many root systems, this was previously impossible given their high degree of complexity.
Within these additions also come the tools to match the visible traits of the plant with the genetic makeup of the trait. This was needed to unlock and explore root adaptive potential.
"What we can learn now is how plants change to meet their environment," Bucksch said. "What things have worked in the past for the plant is reflected in the angle, the branching and the dynamics of its root system."
Bennett added that he admired the range of factors the team, from both Penn State and Georgia Tech, took into consideration when working on the technology, ensuring it would be simplistic enough for use in developing countries.
"Their process costs cents to process, requires no huge input expense and is fast enough to make possible sequencing and eventually genomic insight," he said. "That's a huge gain for the field and a step towards helping us finally chisel out and incorporate ideal phenotypes into future crops."
Bucksch, who is confident their method will offer all types of researchers a new way to observe elements of mature plant life, said he never really doubted they would be successful, even though many different specialists were needed to create the final product.
"Biology is all about processes, and that is exactly what algorithms describe the two have just developed different languages because they have grown in isolation from one another," he said. "Breaking down this initial barrier was probably the most difficult part of the entire project, but once we had done it, we knew we had something we could all work with."
CELLULAR MECHANISMS OF ROOT EXUDATION
Subcellular Trafficking of Exuded Metabolites
Despite the ecophysiological significance of plant-secreted compounds and the large number of compounds that plant cells produce, very little is currently known about the molecular mechanisms for the trafficking of phytochemicals. In at least some plants, channels are likely to be involved in the secretion of organic acids normally present at high levels in the cytoplasm. A good example is provided by the exudation of citrate, malate, and related organic acids by maize and wheat (Triticum aestivum) in response to high Al 3+ concentrations ( Ma et al., 2001). However, plants have the potential to express 100,000 compounds, primarily derived from secondary metabolism ( Verpoorte, 2000), many of them with cytotoxic activities that would prevent their accumulation in the cytoplasm. The speculation that phytochemicals are transported from the site of synthesis to the site of storage by vesicles or specialized organelles is gaining momentum as evidence accumulates regarding the presence of intracellular bodies in plant cells induced to accumulate large quantities of secondary metabolites ( Grotewold, 2001). For example, it has long been known that specific steps of the isoquinoline alkaloid biosynthetic pathway are sequestered in alkaloid vesicles and that pathway intermediates must traffic from one subcellular compartment to another by mechanisms that prevent their free diffusion in the cytosol ( Facchini, 2001). Subcellular inclusions that accumulate 3-deoxy anthocyanidin flavonoid phytoalexins are observed in sorghum leaves infected by the fungusColletotrichum graminicola ( Snyder and Nicholson, 1990). These inclusions are similar to the anthocyanoplasts observed in maize cells expressing the C1 and R regulators of anthocyanin accumulation ( Grotewold et al., 1998).
Root exudates often include phenylpropanoids and flavonoids, presumably synthesized on the cytoplasmic surface of the endoplasmic reticulum (ER Winkel-Shirley, 2001). For example, the flavone luteolin, secreted by alfalfa (Medicago sativa) seedlings and seed coats, provides one of the signals that induces the nodulation genes in R. meliloti ( Peters et al., 1986). Cytotoxic and antimicrobial catechin flavonoids are secreted by the roots of knapweed plants ( Bais et al., 2002c). Although the mechanisms by which these compounds are transported from the ER to the plasma membrane are not known, it is possible that they are transported by ER-originating vesicles that fuse to the cell membrane and release their contents.
Vesicles with the above-described properties and containing green autofluorescent compounds have been identified in maize cells ectopically expressing the P regulator of 3-deoxy flavonoid biosynthesis ( Grotewold et al., 1998). These vesicles are likely to originate from the ER, as suggested by the presence of green fluorescence inside specific regions of the ER after treatment with brefeldin A. The vesicles fuse and form large green fluorescent bodies that migrate to the surface of the cell and fuse to the cell membrane and release the green fluorescent compound to the cell wall ( Grotewold et al., 1998). Interestingly, the accumulation of the green fluorescence in the cell wall is increased by treatment with Golgi-disrupting agents, such as brefeldin A or monensin, suggesting a trans-Golgi network-independent pathway for the secretion of these compounds. Cultured cells of maize ectopically expressing P also accumulate increased quantities of yellow autofluorescent compounds that are targeted to the central vacuole by subcellular structures that resemble anthocyanoplasts ( Grotewold et al., 1998). The use of these autofluorescent compounds, or the fluorescent β-carbolines present in exudates ofO. tuberosa roots ( Bais et al., 2002a), should greatly increase the opportunities available to study the molecular mechanisms underlying the secretion of phytochemicals.
ATP-Binding Cassette (ABC) Transporter as an Alternative to Vesicular Trafficking
The previous section highlighted the possibility of vesicular trafficking and fusion as a cellular mechanism responsible for root exudation, but could other mechanisms also be responsible once the compounds reach the membrane? For example, the involvement of membrane transporters such as the ABC transporters might be responsible for the secretion of root-secreted compounds. The ABC superfamily of membrane transporters is one of the largest protein families, and its members can be found in animals, bacteria, fungi, and plants. ABC transporters use ATP hydrolysis to actively transport chemically and structurally unrelated compounds from cells ( Martinoia et al., 2002). The recent completion of the Arabidopsis genome research project ( Arabidopsis Genome Initiative, 2000) revealed that Arabidopsis contains 53 putative ABC transporter genes. However, the protein localization and function of most of these genes are largely unknown ( Martinoia et al., 2002). Most of the plant ABC transporters characterized to date have been localized in the vacuolar membrane and are believed to be responsible for the intracellular sequestration of cytotoxins ( Theodoulou, 2000).
Currently, very little is known about plant plasma membrane ABC transporters, but the Arabidopsis AtPGP1, localized to the plasma membrane ( Sidler et al., 1998), has been shown to be involved in cell elongation by actively pumping auxin from its site of synthesis in the cytoplasm to appropriate cells ( Noh et al., 2001). Working on the assumption that plasma membrane ABC transporters might be involved in the secretion of defense metabolites, and their expression may be regulated by the concentration of these metabolites, Jasinski et al. (2002) identified a plasma membrane ABC transporter (NpABC1) from Nicotiana plumbaginifolia by treating cell cultures with various secondary metabolites. Interestingly, addition of sclareolide, an antifungal diterpene produced at the leaf surface of Nicotiana spp. ( Baily et al., 1975), resulted in the expression of NpABC1 ( Jasinski et al., 2002). These findings suggest that NpABC1 and likely other plasma membrane ABC transporters are involved in the secretion of secondary metabolites involved in plant defense, but further studies are required to positively identify plasma membrane ABC transporters involved in root exudation of specific compounds.
RESPONSES TO ABIOTIC STRESSES
Several papers examine how roots respond to abiotic stresses, including nutritional limitations, elemental toxicities, waterlogging and physical constraints. Soil acidity affects more than 30 % of arable land and continues to limit agricultural productivity globally. Aluminium and manganese toxicities are largely responsible for poor plant growth but nutrient deficiencies also contribute. Many species have evolved strategies to cope with these stresses, and Rao et al. (2016) comprehensively review the adaptive changes in root structure and function that provide protection from these hostile soils. They encourage further breeding strategies to select for additional root traits. Líška et al. (2016) demonstrate how exposure of roots to air, or to toxic metals such as cadmium, influences the development of suberin lamella. Suberin is a wax-like cell-wall polymer that provides a barrier to the movement of water and solutes. They find that suberin is preferentially deposited on the side of the root exposed to these treatments, presumably as a means of protecting the plant from these stresses. Metabolic responses to phosphorus deficiency in rice (O.sativa) were investigated by Zhu et al. (2016). This paper examines phosphorus recycling from roots to the shoots, where the phosphorus supply is restricted, and reports that ethylene regulates this process. Raising ethylene concentrations in phosphorus-deficient rice plants increased cell wall pectin content and the expression of the phosphate transporter OsPT2 both of these changes accelerated phosphorus release from the root cell walls, which increased phosphorus translocation to the shoots. Compaction is another major soil constraint that affects root penetration and final rooting depth. Popova et al. (2016) studied the effect of soil strength on elongation rate and diameter of maize (Zea mays) roots. Their paper describes how final root shape and tortuosity in compacted soil results not only from mechanical deflections but also from tropic responses via touch stimuli. Mechanical stress is also the topic of a study by De Zio et al. (2016). They examined roots of the woody perennial Populus nigra and compared the anatomy, lignin content and hormone concentrations on the convex and concave sides of roots forced to turn a tight corner. Lignin content and xylem thickness increased on the concave side whereas more lateral roots appeared on the convex side. Hormone analysis indicates that auxin and abscisic acid concentrations were likely to be responsible for regulating these changes. Interestingly, the responses of roots to mechanical stress contrasts with the modifications known to occur in the stems of poplar plants ( Plomion et al., 2001).
Waterlogging presents a number of physical and chemical stresses to plants but the reduction in oxygen availability can limit growth and survival. Some species, such as alligator weed (Alternanthera philoxeroides), are well adapted to flooded conditions because they have evolved specific mechanisms to overcome this limitation, and consequently have become a major threat to wetlands, rivers and irrigation systems around the world. Alligator weed is a perennial, growing vigorously and forming an intricate root system of adventitious roots that suspend in water. Ayi et al. (2016) investigated the adventitious roots that develop on alligator weed in submerged conditions. They measured the oxygen gradients in the unstirred layers adjacent to these roots and provide evidence that they are capable of absorbing oxygen from the water. They also demonstrate that oxygen concentration within stem nodes having adventitious roots increased compared with stem nodes without adventitious roots, suggesting that oxygen may intimately regulate their development, possibly helping to supply carbohydrate for vigorous root growth. It remains to be shown whether the development of these adventitious roots offers alligator weed greater capacity to absorb oxygen from water than similar roots in other species.
Phenotypic screens for single, abiotic soil constraints, such as those in the studies summarized above, can reveal the genetic and physiological basis of tolerance mechanisms. Similar studies have identified many new membrane transport proteins that regulate the uptake of nutrients and the exclusion of toxic ions through specific root exudates ( Schroeder et al., 2013). The next step will be to combine these treatments and score performance with the multiple stresses encountered in the field. This will accelerate progress towards improving agricultural production and provide management options for forestry and natural systems ( Rich and Watt, 2013).
What the scientists did
Plant roots grow downward by sensing gravity using tiny, stone-like starch balls — called granules — in their cells. When gravity pulls the granules to the “bottom” of a cell, it triggers signals that tell the plant “this way is down.”
But if a root hits a rock or senses nutrients in another direction, a separate signal will switch on and tell it to turn. How quickly and frequently the root changes directions determines how deep, versus how spread out, the roots will grow over time.
Scientists had previously surmised the plant hormone auxin was involved in the root turning process because it controls most aspects of plant growth, but they didn’t know which gene was responsible.
So the researchers turned to the weed-like plant Arabidopsis to study root behavior. Think of Arabidopsis as the floral version of a lab mouse — it is commonly studied in laboratories to decipher plant genetics.
Busch’s team gave 215 plants a low dose of a chemical known to block the auxin hormone, and watched for drastic changes in the roots.
Arabidopsis thaliana, otherwise known as the thale cress or mouse-ear cress, is a popular research tool in plant biology. Photo by lehic/via Adobe Stock
Genetic dissection of maize seedling root system architecture traits using an ultra-high density bin-map and a recombinant inbred line population
Maize (Zea mays) root system architecture (RSA) mediates the key functions of plant anchorage and acquisition of nutrients and water. In this study, a set of 204 recombinant inbred lines (RILs) was derived from the widely adapted Chinese hybrid ZD958(Zheng58 × Chang7-2), genotyped by sequencing (GBS) and evaluated as seedlings for 24 RSA related traits divided into primary, seminal and total root classes. Significant differences between the means of the parental phenotypes were detected for 18 traits, and extensive transgressive segregation in the RIL population was observed for all traits. Moderate to strong relationships among the traits were discovered. A total of 62 quantitative trait loci (QTL) were identified that individually explained from 1.6% to 11.6% (total root dry weight/total seedling shoot dry weight) of the phenotypic variation. Eighteen, 24 and 20 QTL were identified for primary, seminal and total root classes of traits, respectively. We found hotspots of 5, 3, 4 and 12 QTL in maize chromosome bins 2.06, 3.02-03, 9.02-04, and 9.05-06, respectively, implicating the presence of root gene clusters or pleiotropic effects. These results characterized the phenotypic variation and genetic architecture of seedling RSA in a population derived from a successful maize hybrid.
Keywords: Maize QTL bin map genotyping by sequencing (GBS) root system architecture.
© 2015 The Authors. Journal of Integrative Plant Biology published by Wiley Publishing Asia Pty Ltd on behalf of Institute of Botany, Chinese Academy of Sciences.
Biologists Discover How Salt Stops Plant Growth
It has not been clear how salt halts the growth of the plant-root system, until now. According to an international study published in the journal Plant Cell, an inner layer of tissue in the branching roots that anchor the plant is sensitive to salt and activates a stress hormone, which stops root growth.
This is a microscope image of a branching root, the cell boundaries are in red and the GFP fluorescent signal marks the endodermis (José Dinneny)
Salt accumulates in irrigated soils due to the evaporation of water, which leaves salt behind. Roots are intimately associated with their environment and develop highly intricate branched networks that enable them to explore the soil. The branching roots grow horizontally off the main root and are important for water and nutrient uptake.
“An important missing piece of the puzzle to understanding how plants cope with stressful environments is knowing when and where stressors act to affect growth,” said study senior author Dr José Dinneny of Carnegie Institution for Science.
The biologists grew seedlings of a laboratory plant (Arabidopsis) that is a relative of mustard using a custom imaging system, which enabled them to measure the dynamic process of root growth throughout the salt response.
This ability to track root growth in real time led the researchers to observe that branching roots entered a dormant phase of growth as salt was introduced. To determine how dormancy might be regulated, they surveyed the role of different plant hormones in this process and found that a critical plant hormone called abscisic acid was the key signaling molecule.
“We are familiar with how animals use a fight or flight strategy to face external challenges. While plants can’t run for safety, they can control how much they grow into dangerous territory. It turns out that abscisic acid, a stress hormone produced in the plant when it is exposed to drought or salty environments, is important in controlling the plant equivalent of fight or flight,” Dr Dinneny said.
To understand how Abscisic Acid controls growth, the biologists devised a strategy to inhibit the response to this hormone in different tissue layers of the root. They developed several mutants in which the response to the hormone was suppressed in different root layers. They found that a significant portion of the salt response was dependent upon how a single cell layer sensed the hormone. The live imaging allowed them to watch what happened to root growth in these mutant plants.
Lead author Dr Lina Duan, also of Carnegie Institution for Science, said: “Interestingly, the ‘inner-skin’ of the root, called the endodermis, was most critical for this process. This tissue layer is particularly important as it acts like a semipermeable barrier limiting which substances can enter the root system from the soil environment.”
“Our results mean that in addition to acting as a filter for substances in the soil, the endodermis also acts as a guard, with abscisic acid, to prevent a plant from growing in dangerous environments,” Dr Dinneny concluded. “Irrigation of agricultural land is a major contributor to soil salinity. And as sea levels rise with climate change, understanding how plants, particularly crops, react to salt might allow us to develop plant varieties that can grow in the saltier soils that will likely occur in coastal zones.”
Bibliographic information: Duana L et al. Endodermal ABA Signaling Promotes Lateral Root Quiescence during Salt Stress in Arabidopsis Seedlings. The Plant Cell, published online before print January 2013 doi: 10.1105/tpc.112.107227
Talking Trees—Secrets of Plant Communication
Forests are nurseries of health and well-being. New discoveries are showing that this doesn’t happen by accident. The trees are working together.
Come with me on an imaginary journey through a woodland wonderland. As we wind down the shaded path, damp moss on the forest floor brushes our bare feet. The scent of white cedar tickles our noses, while filtered morning light enchants our eyes. A gray squirrel chatters overhead in the ancient oaks, and nearby a white-breasted nuthatch chitters to its mate.
What a special place to retreat from our hectic, dysfunctional world and experience peace and tranquility! But there’s more to the forest than meets our eyes (and noses, ears, and feet).
The psalmist declared, “ Let the field be joyful, and all that is in it. Then all the trees of the woods will rejoice before the Lord ” ( Psalm 96:12 ). It’s poetry, certainly, emphasizing that God’s creation yearns for the Lord to return and restore peace on earth.
Stresses constantly threaten to destroy the forest’s surface harmony, and yet modern scientific research is revealing how marvelously the Creator has equipped His woodlands to respond to these stresses, keeping alive these reminders of harmony that once existed and will be restored someday through Christ.
Researchers are discovering that trees form communities that “talk” to each other, sharing their needs and providing mutual assistance. Yes, you heard me correctly. It’s mindboggling, even for someone like me who has spent his life studying nature’s wonders (forest ecology in particular).
Now, it’s important to remember that forests aren’t human or alive in any sense like animals (they lack the “breath” of life, or nephesh, according to God ’s Word). Unfortunately, some current researchers blur the line, imbuing plants with animal or human attributes, such as feelings and consciousness, which they don’t have. The science itself is fascinating, without any need to make trees sound human-like.
When the Bible proclaims that “the trees of the woods” give glory to God , this metaphor may be a reality in unexpected ways.
Trees can’t run from danger or visit their neighbors to ask for a cup of sugar like we can. To sidestep peril and meet their changing needs in a fallen world, cursed because of man’s rebellion against God, their Creator imbued trees with unique abilities. They can communicate with other trees and with other creatures, seeking help. Why would this be necessary, if the Lord made plants to provide food and shelter for animals and people (see Genesis 1:29–30 )? Well, for one thing, they need to survive—no matter what abuses they suffer at the hands of heedless clearcutters or unrestrained insects in our fallen world—to meet the needs of future generations.
One of their defenses against being overeaten is producing chemicals that make them taste bad. At the same time, other chemicals warn nearby trees that a swarm of voracious beetles or other animals have invaded. These chemicals are specifically tailored for this purpose.
In addition to chemical warnings, some oak and beech leaves and spruce needles will produce electrical signals when an insect predator eats them. Electrical impulses generate messages to the rest of the tree so that, within an hour, the tree will hopefully taste so bad that the insects flee.
Experiments in the African savannah suggest that when a giraffe arrives and starts ingesting acacia leaves, plants will soon be inedible but will also warn nearby trees. Leaves send out the warning gas ethylene, and other trees in the vicinity detect the scent and start producing their own defense chemicals before the giraffe arrives. How do plants “smell” the gas and then mount their own defense before the giraffe begins eating them? More research is needed.
To avoid being overeaten when giraffes begin munching on them, acacia trees can change the flavor of their leaves and also warn other trees to do the same.
As hungry insects salivate on elms and pines, the trees can chemically analyze the insects’ saliva, reproduce it in mass quantities, and broadcast the chemical to the forest community. This cry for help alerts predators who like to eat the insects. They promptly come flying to the location, eliminating the insects that are attacking the tree.
It’s easy to imagine why God originally designed systems to produce chemicals with many different smells—to bless other creatures in the forest. Many woodland scents are still just as pleasant to animals as they are to us. In fact, the trees that produce flowers and fruit purposefully send out sweet-scented messages in a wide variety of colors, patterns, and perfumes to invite animals to come, explore, and partake.
Communication is happening below our feet as it is above. If we could carefully remove the loam at the base of a forest tree, we’d see a root system that spreads out twice as far as the canopy above our heads. This root system reaches depths of 1–5 feet (0.3–1.5 m), depending on the location. More astonishingly, roots may connect directly with the roots of other trees. Trees can distinguish members of their own kind and establish connections with them.
This reality contradicts the old view that woodland trees simply competed in a life-and-death struggle for limited light and nutrients. Though plants do compete in forests, current research suggests that more often, trees may be cooperating and assisting each other. When one tree is sick, nearby trees may share nutrients through their roots to help it get well again. If a lodgepole pine sapling springs up in the shade of a thick forest, older trees somehow sense that it doesn’t get enough sunlight to make food for itself, so they may share their bounty. They even change their root structure to open space for saplings.
How do plants talk in the soil? They may have several options. For example, researchers have found evidence that plants are communicating by sound. Though this sounds crazy, vibrations emanating from seedlings in laboratory settings have been detected by special instruments and measured at 220 hertz. In experiments, roots direct other roots to grow toward this low frequency. Much more research must be done, but these experiments suggest one intriguing possibility for the way plants communicate.
Trees also communicate with chemical messages, but they aren’t just talking to each other. They talk to their other soil neighbors, too. Microorganisms, such as bacteria and fungi, gather water and nutrients that the trees need. So roots produce nutritious substances, such as sugars and proteins, to attract these organisms. One researcher described this chemical advertisement as trees producing “cakes” and “cookies” to attract microbes to come and enjoy.
Special fungi recognize these chemical messages and not only partake, but also interact with roots to form partnerships. Fungi, for example, will inform the tree when they need to enter a root, and the tree will respond by softening a place in its root wall where the fungus can enter.
Fungal microbes receive all the food (sugar) they need to build their bodies, and in return they help trees obtain water and minerals, protect them from drought, absorb toxic heavy metals, and help undernourished and young trees. Trees couldn’t build their tall trunks without a steady supply of minerals from microbes that mine the soil and transport them to the tree.
This underground network of root/fungus communication acts in many ways like an underground internet. These special fungi called mycorrhizae (“fungus root”) spread a tangled highway of long microscopic tubes, called fungal hyphae, through the soil from tree root to tree root. Literally miles of tiny tubes are found within a single cubic foot of soil between two tree roots.
Trees communicate so intensely via these networks that it has been called the “underground internet” and the “wood wide web.” Electrical impulses pass through nerve-like cells from root tip to root tip, and these signals may be broadcasting news about drought conditions, predator attack, and heavy metal contamination.
Working together by means of complex communication tools such as sound, chemicals, and electricity, every member in the forest benefits. These complex relationships help maintain a healthy forest system, as the trees moderate temperature extremes, store groundwater and carbon more efficiently, produce plenty of oxygen, and provide a healthy habitat for other forest denizens.
I have not met anyone who wasn’t amazed by these findings. No matter what their religious or political view, people around the world are recognizing forests as places that promote emotional, spiritual, and physical health. Trees filter dust, pollen, pollutants, bacteria, and viruses from the air. Taking a deep breath in a virgin forest is literally a healthy experience. Research is confirming that, when stressed and driven people visit the forest, they find not only rest but lower blood pressure and an increased sense of peace.
There is no question that these phenomena have been overstated at times and greatly anthropomorphized (described in human-like terms). So how should followers of Christ make sense of these findings?
When we study the forest, we find mutually beneficial relationships, lavish provision, and steady communication. Are these not attributes of the Creator? Are they not evidence that God wants to display some of these wonderful attributes, even in nonthinking organisms?
Romans 1:20 proclaims, “ Since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse. ” The Bible highlights many of God’s attributes, including the fact that He is relational ( Genesis 2 1 Corinthians 12 ) and is a communicator ( John 1:1 Hebrews 1 ). In His creation we can see visible and finite hints of His invisible and infinite characteristics, if we have eyes to see.
All forest ecologists see the amazing relationships and interconnections within the forest. As a result, some have called the forest-and-earth biosphere a living organism. But we know from Scripture that a loving Creator is behind them. Christ the Word has filled His creation with organisms that communicate with chemicals, sounds, and electrical impulses. The recipient is designed to listen and respond in kind. What an amazing reminder that God desires to communicate with us, and He expects us to respond to His Word and help one another, too.
Yet we live in a broken world full of sickness and unhealthy relationships. Even the forest suffers from genetic defects, blight, and wanton destruction. The potential harmony of the forest reminds us about what once was, before man’s rebellion against the Creator brought corruption into the world. But the Creator, Jesus Christ the Son of God, came to earth as a man to restore all things, and He will complete this restoration when He comes again ( John 1:1–14 Revelation 21:1–7 ).
Spending time in the forest is a wonderful way to meditate on God and get our life priorities back in line. Scripture proclaims, “ Seek the Lord while He may be found. . . . For you shall go out with joy, and be led out with peace the mountains and the hills shall break forth into singing before you, and all the trees of the field shall clap their hands ” ( Isaiah 55:6, 12 ).
Source: The Hidden Life of Trees: What They Feel, How They Communicate by Peter Wohlleben. (This book often overstates the human-like qualities of trees, so use biblical discernment when reading it.)