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Another long one about carbon and Mycorrhizia and i will stop for now.
ORGANIC CARBON: FROM TREE LEAVES TO SOIL ORGANISMS
Donald H. Marx PhD.
Plant Health Care, Inc.
Frogmore, SC
FROM TREE LEAVES
Lets start this discussion off with describing the most important biochemical process on Earth photosynthesis!! This is the process by which energy from the sun is captured by the chloroplast in green leaves and used to make organic carbon the sugar glucose (the photosynthate) from inorganic carbon dioxide and water. The process releases oxygen from the splitting of the water molecule. When the water molecule is split, high-energy electrons are released and, after many biochemical reactions, they are transferred to and stored in phosphorus-containing organic compounds like ATP. The spending of this stored energy, that can be traced back to the sun, eventually leads to the production of the sugar, glucose. Glucose is found in all living cells of all plants, animals and microbes and, as glucose phosphate, serves as the major substrate for cellular respiration. Nearly all of the energy, sugar and oxygen used by the diverse forms of life plants, animals and microbes on Earth come from photosynthesis! Life as we know it could not exist without this biochemical reaction and its end products, organic carbon as glucose, the captured energy from the sun and oxygen! All life, whether it is the smallest microbe or the largest animal, is dependent on the availability and utilization of this carbon, oxygen and energy. Carbon is the most abundant organic chemical on Earth and serves as the building blocks for all life. Everything living contains carbon! None of the biochemical reactions in photosynthesis are spontaneous. All reactions are facilitated by a large diverse group of unique proteins- enzymes that are biological catalysts in virtually all biochemical reactions of all life forms.
The amount of sunlight and its duration has a controlling effect on photosynthesis. Leaves near the top of the tree canopy have a much higher photosynthetic rate than leaves near the bottom of the canopy. This is because there is more light saturation of the chloroplasts in direct sunlight. Inefficient lower branches with relatively few but highly shaded leaves of shade intolerant trees like ash, hickory (pecan), walnut, pine, birch, willow, etc., often do not contribute any new carbohydrates for growth of the main stem. The limited amounts produced in these shaded leaves are mainly used for maintenance of these specific leaves. Shade leaves are normally larger, but thinner, and have fewer stomates. Branches supporting these shade leaves normally shed, i.e. natural branch pruning, because of limited maintenance respiration. At low light intensities and for short durations, the rate of photosynthesis is higher in shade tolerant trees like maple, beech, buckeye, sugarberry and flowering dogwood, than in shade intolerant trees. That's why shade tolerant trees and shrubs can grow and thrive under the closed canopies of shade intolerant trees. These understory plants also benefit from the higher levels of respiratory carbon dioxide emitted from all the roots and organisms in the soil. This additional carbon dioxide somewhat compensates for the effects of reduced sunlight.
Sugar produced in leaves is translocated to the meristems, reproductive structures like seeds and other growth sinks where it is converted to energy (respiration) or to new tissue (protoplasm and cell walls). The main translocated sugar is sucrose a disaccharide which is glucose enzymatically combined with fructose, another sugar. Sugars and other carbohydrates are precursors to the synthesis of secondary or defensive chemicals (allelochemicals) and to all other biological reactions. What signals the tree to move these sugars? Very simply, the plant growth regulators (auxins, cytokinins, gibberellins, abscisic acid and ethylene) are considered to be the sugar traffic police in that they direct the flow of carbohydrates from their site of production to where they are needed for growth and respiration. Since new growth occurs at the meristems thats where most plant growth regulators are produced and concentrated. Trees and most other woody plants have three main meristematic areas stem tips, root tips and the cambium. They grow up, down and around. Basically, sucrose is translocated and allocated to these various plant parts by a carbohydrate source-sink relationship. This concentration gradient may extend hundreds if not thousands of feet away from the tree leaf where the sugar is made to the root tips where it eventually becomes new tissue.
Trees move carbon from its production site leaves to where it is needed most. On average, a healthy tree normally allocates about 70 % of its carbon sugar for growth and respiration above ground and about 30 % for below ground needs. If a soil or root stress occurs, the damaged tree may allocate very large amounts of carbohydrates below ground to replace and repair the damaged roots. This will be at the expense of carbohydrates normally allocated to the top. This is why symptoms of root damage are top dieback. Severe defoliation due to pests, major branch loss due to storms and severe pruning are top stresses. The most obvious effect of these top stresses is loss of leaves and, thereby, loss of current photosynthesis and the physical loss of stored foods and water in the larger branches. This will cause a carbohydrate deficiency to the root system because most of them will now stay in the top to repair this damage. Roots will dieback as a result of reduced carbon allocation below ground. This, in turn, causes a snowball effect. Reduced roots equal reduced absorption of soil resources (water, nitrogen and minerals), which equals a reduced supply of these resources above ground. The net result is a very unhealthy tree. Increases in soil nitrogen availability decreases carbon allocation to the roots. The air pollutant ozone disrupts the photosynthetic process which also causes a decrease in carbon allocation to the roots. On the other hand elevated carbon dioxide in the air increases carbon allocation to the root system and the rates of respiratory carbon dioxide emitted from the soil.
Stored chemical energy is released by the enzymatic oxidation of carbon-based chemicals like glucose. The process is called respiration. There are two main forms of respiration. Growth respiration provides energy needed to synthesize new tissues at meristems and other carbon sinks. Maintenance respiration provides energy needed to keep existing tissues alive and healthy. These respiratory activities can utilize from 30 to 60 % of the daily production of photosynthate. Sugars are mainly synthesized in green leaves but they are consumed by respiration in every living cell of the plant. New growth occurs when the rate of photosynthesis, which creates sugar and oxygen, exceeds the rate of respiration, which burns the sugar, releasing energy, CO2 and water. Most of the glucose is enzymatically converted into hundreds of other organic chemicals, i.e., other carbohydrates, proteins, amino acids, fats, lipids, hormones, growth regulators, etc., needed by trees and all other plants. Much is converted into cellulose, hemicellulose and lignin wood! Some organic carbon is stored, as insoluble starch and lipids, to be used later. Wood is simply many glucose molecules attached to each other in a specific pattern. Starch is also many glucose molecules but they are attached differently than those comprising wood. Starch is made in most living cells but doesnt move from cell to cell because its insoluble. How can it be used then as an energy source or building block? It must be enzymatically converted back to simple glucose which is used directly by that cell or translocated across membranes and utilized by other cells for growth and respiration? Trees and other woody plants use both stored and currently produced carbohydrates, often at the same time, for growth and respiration.
It is obvious that plant growth is the results of its' ability to fix carbon in photosynthesis, to allocate it to the meristems where it is incorporated into protoplasm and cell walls, and to release the energy via respiration to fuel the needs of the chemical reactions and growth. The partitioning of growth between above and below ground tree parts is a function of the photosynthetic potential of the leaves and the absorptive potential of the roots for essential soil resources. Any factor affecting green leaf area or leaf function will reduce the rate of photosynthesis and reduce the allocation of the carbohydrates to the roots.
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Use for sidebars
v land plants produce about 100,000,000,000 metric tons of carbon each year of which two-thirds is produced by trees? This exceeds that of the entire world by a factor of four, and that of agricultural plants by a factor of more than two.
v one acre of young plantation trees removes about three-fourths of a ton of carbon each year. Old growth forests and their soils emit as much respiratory CO2 as their leaves fix in photosynthesis. You and I each add (via breathing, automobiles, heat, electricity, etc.) about 5 tons of carbon each year!! That means it takes over 6 acres of young productive forests to recycle the CO2 each of us produces!
v trees and other land plants capture about 40% and the ocean about 50% of the annual CO2 produced by industry (coal combustion and cement production). Eighty % of CO2 in the atmosphere comes from combustion of fossil fuels 60% from industrialized nations. Between 1750 and today CO2 has increased 30 % in our atmosphere.
v trees are also important commercially! They produce more than 5,000 wood and paper products everything from baby food to rayon, and toothpaste to football helmets. Oil and coal are simply very, very old dead trees! Ecologically, trees are essential to land stability and hydrology. Imagine a world without trees look at Haiti!!
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By now you know that organic carbon in its various forms is essential to all life. This means that every living organism must find enough carbon to sustain and reproduce itself. Lets look at that another way, all other things being equal, when you find a population of organisms, whether they are fish, elephants, butterflies, earthworms or soil bacteria, it is because they have satisfied their carbon-based dietary requirements. They wouldnt be where you found them long without food, i.e. organic carbon in its many forms.
TO SOIL ORGANISMS
This leads us now belowground. What happens to the organic carbon that is shed aboveground (branches, leaves, flowers, bark, etc.) forming the forest floor. This is natures mulch. What happens to the carbon that is shed by the root system? Roots shed whatever tissue is no longer functioning (old fine roots and bark) and exude spent organic compounds just like the aboveground tree parts. These are recycled by various organisms. The number of species of organisms involved in this belowground carbon cycle is staggering! Because of this great diversity it is nearly impossible to isolate individual groups of soil organisms and identify precisely their part in the carbon nutrient cycle. This carbon cycle is a chain of events, each event with a different cast of characters (or organisms). Its a succession. Each stage is based on the chemical form of organic carbon now available. Each group of organisms eats what they can, they leave or die and then another group follows and eats and on and on until all of the carbon is converted back to CO2 and H2O! Were now back at the starting line for the carbon cycle to repeat itself! However, this may take a thousand years before the toughest carbon compounds, like lignin, are reduced to their original component parts. Soil organisms as a group may only represent about 5% of the total living and dead organic matter in forest soils, but are the gate keepers of the carbon-cycle responsible for the transformation and decomposition of all soil organic carbon.
Soils organisms do not photosynthesize as do green plants and are, therefore, dependent on external supplies of carbon energy like we are. Basically, you can separate these soil organisms into groups by how they obtain their organic carbon nutrition. By far the largest group is the saprophytes. They gain their carbon nutrition directly from usually long-dead organic matter, i.e., by decay or decomposition. Examples are fungi in wood decay, bacteria and fungi in compost piles and the litter in the forest floor, bread mold, bacteria in septic tanks and coliform bacteria in your digestive system.
Another group is the pathogens and predators. They gain their carbon nutrition directly from living hosts causing a physiological dysfunction (disease) of that host or by killing and eating them directly, i.e. predation. Examples of pathogens are fungi causing Dutch elm and oak wilt diseases, bacteria in crown gall and fire blight diseases and Pythium/Phytophthora causing fine root diseases. Examples of predators are beneficial nematodes, amoebae and other protozoa that ingest bacteria, fungi and algae.
The third group is the symbionts. They gain their carbon nutrition directly from their beneficial organic union with living hosts in which the hosts are not harmed but gain from the mutualistic partnership. Examples are fungi in mycorrhizae and lichens and the bacteria in N-fixing nodules of legumes.
The smallest and most numerous organisms in soil are the bacteria. These single-celled microbes are the simplest, smallest and most abundant forms of life on earth. Saprophytic soil bacteria are found in greatest numbers in the upper 12 of soil where their food, i.e. carbon in organic matter and in nutrients on and near roots is the most prevalent and where aeration, soil water, inorganic mineral elements, pH and temperature are adequate to satisfy their needs. A thimble of productive soil may contain up to 6 billion bacteria representing some 4,000 different species that count nearly exceeds the entire worlds human population!
Bacteria perform many important processes in soil that are essential to all life on Earth. They decompose organic matter including the cellulose and lignin in wood. Certain bacteria have been used to bioremediate soil and water contaminated with pesticides, gasoline, crude oil, jet fuel, TNT, and other man-made hydrocarbons. Some of these bacterial soil processes require free oxygen (aerobic), some require intermediate amounts of free oxygen (microaerophilic) and others require no free oxygen (anaerobic). Soils productive for land plants are aerobic but most also contain microsites which are anaerobic and/or microaerophilic.
Many species of soil bacteria are opportunistic and live freely in soil colonizing particles of organic matter. Some are primarily decomposers of simple carbohydrates, organic acids and amino acids. Some species, called rhizobacteria, have adapted themselves to nonwoody absorbing roots where their food, i.e. organic chemical exudates and sloughed cells from growing roots, called rhizodeposition, are present. Rhizobacterial associations have been found on all plants. Rhizobacteria can increase mineral element (P, K, Ca, etc.) solubility from insoluble mineral sources, recycle inorganic nutrients especially nitrogen from organic forms, fix atmospheric nitrogen, reduce (by antagonism or competition) many root disease pathogens, and produce plant-growth regulators (auxins, gibberelins and cytokinins) which contribute to improved root growth and functions. Recently, certain bacteria have been found to increase mycorrhizal development (mycorrhizae helper bacteria); how they do this is not fully understood. They occupy and function in the rhizosphere of mycorrhizae (mycorrhizosphere). Recently, bacteria that fix nitrogen have been discovered actually growing inside the hyphae of mycorrhizal fungi revealing a tripartite symbiosis. Basically, all of these bacteria, carrying out all of the different soil and root processes, are collectively referred to as plant growth promoting bacteria.
Gaseous nitrogen can be fixed symbiotically by nodulating bacteria (as with legumes) or fixed by free-living bacteria in the soil. The nodulating bacteria obtain their organic carbon nutrition directly from their organic union with plant host. The free-living bacteria obtain their carbon nutrition from the organic matter in the soil or from sloughed root cells or root exudates (i.e. rhizodeposition). The nitrogen fixed by these specific bacteria is eventually released as either ammonium or nitrate into the soil. These are the main forms of nitrogen absorbed by plant roots. This fixation of atmospheric nitrogen is the main way that new nitrogen is added naturally to plant ecosystems. Nitrogen is essential to the total organic carbon decomposition process. Carbon: nitrogen ratios in the soil between 15 and 30 to 1 are ideal. Greater ratios, like that found in raw wood chips (300:1), actually cause loss of nitrogen (denitrification) from the soil when applied as a mulch.
Actinomycetes are a unique group of microbes that actually link the bacteria and the fungi. They are saprophytic and decompose organic matter. Many live exclusively in the rhizosphere and give soil the earthy odor. Many have been isolated from soil and found to produce antibiotics. Streptomycin comes from the actinomycete, Streptomyces and actionomycin comes from Actinomyces. Their main functions in soil health are the antibiotics affecting root disease pathogens and their ability to decompose organic matter.
Other microbes, involved in this belowground carbon cycle, are fungi. Fungi are especially significant in acidic soils because many bacteria are adversely affected by acid soils. They produce enzymes more capable of decomposing structural components of the shed plant material like cellulose and lignin in woody debris than do most bacteria. There are thousands of these wood decaying, saprophytic fungi. Many produce large conks on living trees and on woody debris on the forest floor. Bacteria are also intimately involved with these fungi in a succession resulting in wood decay. Thousands of other fungi, like the molds Penicillium and Aspergillus, are saprophytes also. They decompose the simple carbon compounds like sugars in various organic matter in soil. Some produce antibiotics, like penicillin, that can reduce the populations of harmful bacteria and fungi. Others, like species of Trichoderma and Gliocladium, may produce effective antibiotics but also may directly attack and parasitize mycelia of pathogenic fungi and, thus reduce the incidence of root disease.
Algae represent another population of soil microbes that have important functions in soil. However, their numbers are far fewer than bacteria and fungi. They occur mostly in moist soils and their numbers decrease rapidly with soil depth because sunlight and photosynthesis is reduced except on the soil surface. They are highly susceptible to soil disturbance. Some algae fix atmospheric nitrogen and produce mucigel that contributes to soil aggregation.
Now lets discuss the major symbionts of plants mycorrhizal fungi. Over 95 percent of the green plants of the world form symbiotic relationships with mycorrhizal fungi. These unique, root-inhabiting fungi colonize either the outside of fine absorbing roots (ectomycorrhizae) or the inside of the roots (endomycorrhizae). Ectomycorrhizae occur on about 10 percent of the world flora or about 2000 species of woody plants. Pine, fir, larch, spruce, hemlock, oak, chestnut, beech, alder, birch, basswood, poplar, willow, hickory and pecan, Eucalyptus, Arbutus, and a few others form ectomycorrhizae. In North America there are more than 2,100 species of fungi that form ectomycorrhizae with specific trees; worldwide, there are over 5,000 species. Most of these fungi produce mushrooms or puffballs. Billions of spores are disseminated by wind, insects, and small animals from these fruiting bodies that spread the fungi to new locations. Ectomycorrhizae are only found on trees; they dont occur on nonwoody plants. Most ectomycorrhizae can be recognized with the naked eye since they occur in different shapes, sizes and colors.
Endomycorrhizae are the most widespread of all mycorrhizal types and comprises three general groups. Ericaceous endomycorrhizae occur on four or five families in the Ericales and include Rhododendron, mountain laurel, cranberry and blueberry. Orchidaceous endomycorrhizae are another type that occurs only in the plant family Orchidaceae. These two groups will not be discussed further. Vesicular- arbuscular mycorrhizae (VAM) is the third group of endomycorrhizae. Vesicles and/or arbuscules are structures produced by these fungi in or on colonized roots. VAM have been observed in roots of over 1,000 genera of plants representing some 200 plant families. It has been estimated that over 85 percent of the 300,000 species of vascular plants in the world form VAM. These include agricultural crops (except the cabbage family Brassica), most wild and cultivated grasses, fruit and nut trees (except pecan), many hardwoods, vines, desert plants, flowers, and most ornamentals. VAM fungi are ubiquitous in all natural soils that are or have recently supported their host plants. However, their population density (i.e. number of spores and other propagules) and species diversity vary greatly in different soils supporting different plants. Degraded soils like those in our urban landscapes are low in organic matter, have poor physical structure, and are usually compacted. These characteristics limit plant growth and cannot support significant populations of VAM fungi. Healthy forest, desert and grassland soils with high plant density contain many of them. There are about 150 total species of VAM fungi identified, to date, worldwide. More are being discovered every year. VAM roots are not changed in either color or shape from nonmycorrhizal roots as are ectomycorrhizae. VAM can only be confirmed microscopically and thus, cannot be identified with the unaided eye. These fungi produce large spores on their vegetative threads (mycelia) either in or growing from roots in the soil. Because of their location and large size, spores are disseminated very slowly to new areas by soil animals and insects. VAM fungal spores are 10 to 20 times larger in diameter and volume than the smaller spores of ectomycorrhizal fungi produced in puffballs and mushrooms.
The host plants supply mycorrhizal fungi with organic carbon in the form of sugars and other essential organics, such as certain vitamins and amino acids derived directly or indirectly from photosynthesis. Since these mycorrhizal fungi cannot obtain these essential dietary carbon nutrients from any other source they are totally dependent on the photosynthates translocated to roots of their plant hosts for their survival and growth. This means, very simply, that the mycorrhizal fungi cannot grow and develop unless they obtain their dietary carbon from the roots of their plant hosts thats their restaurant! In return, the fungi extend mycelia far into the soil, significantly increasing the surface area of the roots (up to 700 % more) to improve absorption of water, nitrogen and essential mineral elements for its plant host. Thats why its called a symbiosis both partners give and take in the association.
Lets put this another way. In order to develop and maintain a significant complement of mycorrhizae, a plant will allocate between 4 and 15 % of its sugar made in photosynthesis to satisfy the sugar needs of the fungi in the symbiotic association. The expense of this sugar tax assures the plant of longer-lived (several months) mycorrhizal roots capable of satisfying the plants requirements of essential soil resources. A plant with few or no mycorrhizae will spend as much or more sugar tax producing and replacing (rapid turnover rate) the short-lived (1 6 wks.) nonmycorrhizal absorbing roots which are also significantly less efficient than mycorrhizae in acquiring these essential resources from the soil for the plant. Without significant mycorrhizal development the plant would waste carbon energy theyre too efficient to do this, thus mycorrhizae! Few plants in their native habitat are without mycorrhizae. Research has shown that most plants, especially trees, have an obligate requirement for mycorrhizae without them they die!
Recently, VAM fungi were reported to produce a glycoprotein exudate while in the mycorrhizal association. This organic chemical, called glomalin after the VAM fungal genus Glomus, plays a significant role in soil aggregate stability and can represent 4 to 5 % of total soil carbon and nitrogen in forest soils. This glycoprotein can form a continuous bridge between essential elements in soil solution in the rhizosphere and the plant root. This organic adds to the total rhizodeposition.
Mycorrhizae are able to absorb, accumulate and transfer essential elements and water to plants more rapidly and for longer periods of time than nonmycorrhizal roots. From a practical perspective, it would require approximately 100 times more sugars and energy from photosynthesis for a tree to form enough nonmycorrhizal absorbing roots to produce the same surface area formed by the mycelia of mycorrhizal fungi and the mycorrhizae. Trees and other plants are simply not able to produce 100 times more photosynthate; thus, they evolved a dependency on mycorrhizae. Mycorrhizae live and function longer than nonmycorrhizal absorbing roots, increase the tolerance of their tree host to drought, soil compaction, high soil temperatures, heavy metals, soil salinity, organic and inorganic soil toxins and extremes of soil pH. They also depress many root diseases caused by pathogenic fungi and nematodes. Recently, mycorrhizal plants were found to suppress the attacks by certain foliar insects by increasing the natural defense chemicals produced by healthy plants. Mycorrhizal fungi of any type do not significantly decompose soil organic matter but may acquire certain elements, such as nitrogen and phosphorus, from the organic matter and share them with their plant host. An important prerequisite to remember for mycorrhizal development is that nonwoody, susceptible roots must be preformed before they can be colonized by the fungi and become mycorrhizae. Susceptibility means that the simple sugars required by these fungi are available to them in these roots. Remember, everything is based on availability of essential carbon.
In natural forests and grasslands, many species of mycorrhizal fungi share common plant hosts and form a continuous, interconnecting network of mycelia on roots between the plants. It has been shown that dominant forest trees in full sunlight will actually transfer sugars through a common ectomycorrhizal fungal mycelial network to roots of adjacent understory trees that are shaded and produce less photosynthate. The dominant trees can function as nurse trees to the understory trees and improve growth and competitive abilities of the smaller trees. Photosynthate transfer between grasses sharing a common VAM fungal mycelial network has also been reported.
TO YOUR UNDERSTANDING
The preceding discussion was an attempt to describe the foliar and soil processes that support normal growth and development of plants in their native habitats. Note that I used the word normal. Thats deliberate. If you dont know what normal is, how can you possibly recognize abnormal? You must be able to recognize a healthy plant before you can judge one to be unhealthy. You also have to identify what contributes to normal growth and what growth looks like without it.
By now you have a better understanding of the importance of the organic carbon cycle to the world. Also, you should have a greater appreciation for the importance of the biological factory that produces most of the worlds energy, oxygen and organic-based sugars green leaves! All life on Earth is dependent on this factory and its products, including the diverse life in the soil. I bet you didnt know you walked over such abundant and diverse populations of soil microbes that are so critically important to soil and plant health thru the soil processes they drive. Even through they represent only about 5% of the total organic carbon (living and dead) in soil, over 95% of the essential inorganic elements (N, P, K, etc.) pass through these microbes before these elements are passed on to plants.
Compared to natural soils, the soils in most manmade landscapes have little periodically renewed and recyclable high quality, native organic matter needed to drive natural soil processes, are compacted with poor aeration and low water storage capacity, and frequently have a creeping soil pH caused by alkaline or effluent irrigation water or fertilizer and lime treatments of turf. Trees and other plants growing on these sites must have the capacity to produce new functional absorbing roots, the soil must contain effective inocula of mycorrhizal fungi needed to form abundant mycorrhizae on the new roots and the soil must contain the proper organic matter and associated microbes to carry out all of the essential natural soil processes. If not, you have abnormal or inhibited growth. You are then forced to maintain these trees with a row crop mentality that involves the abundant use of pesticides and inorganic fertilizers. These chemicals, when used in excess, can inhibit beneficial microbes, delay normal root function and natural soil processes and may actually increase the susceptibility of the tree and other plants to pests. Many states have already banned or have limited the use of many of these synthetic chemicals because of their purported damaging effects to the environment.
We have domesticated forest trees and other plants, by removing them from their natural environments and by growing them in commercial tree plantations, fruit and nut tree orchards, yards in subdivisions, manicured parks and golf courses, roadsides, sidewalk cutouts and other unnatural landscapes. Trees commonly occur in these various manmade landscapes by one of two events. Either they existed as a forest tree in the area before manmade development or they were transplanted after development. Roots of preexisting trees are routinely damaged during construction by trenching utilities, by drain fields, by grading for drainage, by compaction from vehicles, and by the ever-present urban forest floor of concrete/asphalt roads, driveways and sidewalks.
There is an old forestry saying build the roots and the tops will follow. Transplanted trees are routinely moved to their new environment with less than 10 percent of their original root system developed in the nursery but yet they are expected to maintain a normal growth rate on their new planting site. In reality these transplanted trees, if they survive, may need 10 years to replace the original lateral and absorbing root systems, if ever. Roots not only need large soil volumes for proper development but also they must have favorable soil conditions (oxygen, proper temperature, available soil water, soluble nitrogen and essential minerals) that allow them to develop. Remember, that with all of this, these plants must have a healthy green and dense canopy to produce the photosynthates (sugars) and energy needed for growth and respiration. Since photosynthesis and the allocation pattern of the photosynthate is essential to plant growth, it is obvious that the most important single indicator of plant health, especially trees, is the health of the canopy. Protect the factory!!
If your job is to manage trees and other plants then you must understand the belowground traits acquired by these plants from their former natural environment and design management practices in manmade landscapes to satisfy these requirements. Good quality organic matter in soil, an organic mulch over the rooting area of shrubs and trees, the largest possible volume of quality soil (preferred pH, good water storage and physical properties, high reserve of mineral elements) for maximum root expanse, and adequate populations of mycorrhizal fungi and beneficial rhizobacteria are a few prerequisites to healthy and normal root development and function. Inoculants of mycorrhizal fungi and rhizobacteria can be introduced to roots and soil in the nursery, at planting or during maintenance of turf, flowers, shrubs and trees. Use of these microbial and natural inoculants has been shown to improve the establishment and normal growth of these plants and also to improve the below and aboveground health and function of established mature trees in diverse manmade landscapes.
ORGANIC CARBON: FROM TREE LEAVES TO SOIL ORGANISMS
Donald H. Marx PhD.
Plant Health Care, Inc.
Frogmore, SC
FROM TREE LEAVES
Lets start this discussion off with describing the most important biochemical process on Earth photosynthesis!! This is the process by which energy from the sun is captured by the chloroplast in green leaves and used to make organic carbon the sugar glucose (the photosynthate) from inorganic carbon dioxide and water. The process releases oxygen from the splitting of the water molecule. When the water molecule is split, high-energy electrons are released and, after many biochemical reactions, they are transferred to and stored in phosphorus-containing organic compounds like ATP. The spending of this stored energy, that can be traced back to the sun, eventually leads to the production of the sugar, glucose. Glucose is found in all living cells of all plants, animals and microbes and, as glucose phosphate, serves as the major substrate for cellular respiration. Nearly all of the energy, sugar and oxygen used by the diverse forms of life plants, animals and microbes on Earth come from photosynthesis! Life as we know it could not exist without this biochemical reaction and its end products, organic carbon as glucose, the captured energy from the sun and oxygen! All life, whether it is the smallest microbe or the largest animal, is dependent on the availability and utilization of this carbon, oxygen and energy. Carbon is the most abundant organic chemical on Earth and serves as the building blocks for all life. Everything living contains carbon! None of the biochemical reactions in photosynthesis are spontaneous. All reactions are facilitated by a large diverse group of unique proteins- enzymes that are biological catalysts in virtually all biochemical reactions of all life forms.
The amount of sunlight and its duration has a controlling effect on photosynthesis. Leaves near the top of the tree canopy have a much higher photosynthetic rate than leaves near the bottom of the canopy. This is because there is more light saturation of the chloroplasts in direct sunlight. Inefficient lower branches with relatively few but highly shaded leaves of shade intolerant trees like ash, hickory (pecan), walnut, pine, birch, willow, etc., often do not contribute any new carbohydrates for growth of the main stem. The limited amounts produced in these shaded leaves are mainly used for maintenance of these specific leaves. Shade leaves are normally larger, but thinner, and have fewer stomates. Branches supporting these shade leaves normally shed, i.e. natural branch pruning, because of limited maintenance respiration. At low light intensities and for short durations, the rate of photosynthesis is higher in shade tolerant trees like maple, beech, buckeye, sugarberry and flowering dogwood, than in shade intolerant trees. That's why shade tolerant trees and shrubs can grow and thrive under the closed canopies of shade intolerant trees. These understory plants also benefit from the higher levels of respiratory carbon dioxide emitted from all the roots and organisms in the soil. This additional carbon dioxide somewhat compensates for the effects of reduced sunlight.
Sugar produced in leaves is translocated to the meristems, reproductive structures like seeds and other growth sinks where it is converted to energy (respiration) or to new tissue (protoplasm and cell walls). The main translocated sugar is sucrose a disaccharide which is glucose enzymatically combined with fructose, another sugar. Sugars and other carbohydrates are precursors to the synthesis of secondary or defensive chemicals (allelochemicals) and to all other biological reactions. What signals the tree to move these sugars? Very simply, the plant growth regulators (auxins, cytokinins, gibberellins, abscisic acid and ethylene) are considered to be the sugar traffic police in that they direct the flow of carbohydrates from their site of production to where they are needed for growth and respiration. Since new growth occurs at the meristems thats where most plant growth regulators are produced and concentrated. Trees and most other woody plants have three main meristematic areas stem tips, root tips and the cambium. They grow up, down and around. Basically, sucrose is translocated and allocated to these various plant parts by a carbohydrate source-sink relationship. This concentration gradient may extend hundreds if not thousands of feet away from the tree leaf where the sugar is made to the root tips where it eventually becomes new tissue.
Trees move carbon from its production site leaves to where it is needed most. On average, a healthy tree normally allocates about 70 % of its carbon sugar for growth and respiration above ground and about 30 % for below ground needs. If a soil or root stress occurs, the damaged tree may allocate very large amounts of carbohydrates below ground to replace and repair the damaged roots. This will be at the expense of carbohydrates normally allocated to the top. This is why symptoms of root damage are top dieback. Severe defoliation due to pests, major branch loss due to storms and severe pruning are top stresses. The most obvious effect of these top stresses is loss of leaves and, thereby, loss of current photosynthesis and the physical loss of stored foods and water in the larger branches. This will cause a carbohydrate deficiency to the root system because most of them will now stay in the top to repair this damage. Roots will dieback as a result of reduced carbon allocation below ground. This, in turn, causes a snowball effect. Reduced roots equal reduced absorption of soil resources (water, nitrogen and minerals), which equals a reduced supply of these resources above ground. The net result is a very unhealthy tree. Increases in soil nitrogen availability decreases carbon allocation to the roots. The air pollutant ozone disrupts the photosynthetic process which also causes a decrease in carbon allocation to the roots. On the other hand elevated carbon dioxide in the air increases carbon allocation to the root system and the rates of respiratory carbon dioxide emitted from the soil.
Stored chemical energy is released by the enzymatic oxidation of carbon-based chemicals like glucose. The process is called respiration. There are two main forms of respiration. Growth respiration provides energy needed to synthesize new tissues at meristems and other carbon sinks. Maintenance respiration provides energy needed to keep existing tissues alive and healthy. These respiratory activities can utilize from 30 to 60 % of the daily production of photosynthate. Sugars are mainly synthesized in green leaves but they are consumed by respiration in every living cell of the plant. New growth occurs when the rate of photosynthesis, which creates sugar and oxygen, exceeds the rate of respiration, which burns the sugar, releasing energy, CO2 and water. Most of the glucose is enzymatically converted into hundreds of other organic chemicals, i.e., other carbohydrates, proteins, amino acids, fats, lipids, hormones, growth regulators, etc., needed by trees and all other plants. Much is converted into cellulose, hemicellulose and lignin wood! Some organic carbon is stored, as insoluble starch and lipids, to be used later. Wood is simply many glucose molecules attached to each other in a specific pattern. Starch is also many glucose molecules but they are attached differently than those comprising wood. Starch is made in most living cells but doesnt move from cell to cell because its insoluble. How can it be used then as an energy source or building block? It must be enzymatically converted back to simple glucose which is used directly by that cell or translocated across membranes and utilized by other cells for growth and respiration? Trees and other woody plants use both stored and currently produced carbohydrates, often at the same time, for growth and respiration.
It is obvious that plant growth is the results of its' ability to fix carbon in photosynthesis, to allocate it to the meristems where it is incorporated into protoplasm and cell walls, and to release the energy via respiration to fuel the needs of the chemical reactions and growth. The partitioning of growth between above and below ground tree parts is a function of the photosynthetic potential of the leaves and the absorptive potential of the roots for essential soil resources. Any factor affecting green leaf area or leaf function will reduce the rate of photosynthesis and reduce the allocation of the carbohydrates to the roots.
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Use for sidebars
v land plants produce about 100,000,000,000 metric tons of carbon each year of which two-thirds is produced by trees? This exceeds that of the entire world by a factor of four, and that of agricultural plants by a factor of more than two.
v one acre of young plantation trees removes about three-fourths of a ton of carbon each year. Old growth forests and their soils emit as much respiratory CO2 as their leaves fix in photosynthesis. You and I each add (via breathing, automobiles, heat, electricity, etc.) about 5 tons of carbon each year!! That means it takes over 6 acres of young productive forests to recycle the CO2 each of us produces!
v trees and other land plants capture about 40% and the ocean about 50% of the annual CO2 produced by industry (coal combustion and cement production). Eighty % of CO2 in the atmosphere comes from combustion of fossil fuels 60% from industrialized nations. Between 1750 and today CO2 has increased 30 % in our atmosphere.
v trees are also important commercially! They produce more than 5,000 wood and paper products everything from baby food to rayon, and toothpaste to football helmets. Oil and coal are simply very, very old dead trees! Ecologically, trees are essential to land stability and hydrology. Imagine a world without trees look at Haiti!!
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By now you know that organic carbon in its various forms is essential to all life. This means that every living organism must find enough carbon to sustain and reproduce itself. Lets look at that another way, all other things being equal, when you find a population of organisms, whether they are fish, elephants, butterflies, earthworms or soil bacteria, it is because they have satisfied their carbon-based dietary requirements. They wouldnt be where you found them long without food, i.e. organic carbon in its many forms.
TO SOIL ORGANISMS
This leads us now belowground. What happens to the organic carbon that is shed aboveground (branches, leaves, flowers, bark, etc.) forming the forest floor. This is natures mulch. What happens to the carbon that is shed by the root system? Roots shed whatever tissue is no longer functioning (old fine roots and bark) and exude spent organic compounds just like the aboveground tree parts. These are recycled by various organisms. The number of species of organisms involved in this belowground carbon cycle is staggering! Because of this great diversity it is nearly impossible to isolate individual groups of soil organisms and identify precisely their part in the carbon nutrient cycle. This carbon cycle is a chain of events, each event with a different cast of characters (or organisms). Its a succession. Each stage is based on the chemical form of organic carbon now available. Each group of organisms eats what they can, they leave or die and then another group follows and eats and on and on until all of the carbon is converted back to CO2 and H2O! Were now back at the starting line for the carbon cycle to repeat itself! However, this may take a thousand years before the toughest carbon compounds, like lignin, are reduced to their original component parts. Soil organisms as a group may only represent about 5% of the total living and dead organic matter in forest soils, but are the gate keepers of the carbon-cycle responsible for the transformation and decomposition of all soil organic carbon.
Soils organisms do not photosynthesize as do green plants and are, therefore, dependent on external supplies of carbon energy like we are. Basically, you can separate these soil organisms into groups by how they obtain their organic carbon nutrition. By far the largest group is the saprophytes. They gain their carbon nutrition directly from usually long-dead organic matter, i.e., by decay or decomposition. Examples are fungi in wood decay, bacteria and fungi in compost piles and the litter in the forest floor, bread mold, bacteria in septic tanks and coliform bacteria in your digestive system.
Another group is the pathogens and predators. They gain their carbon nutrition directly from living hosts causing a physiological dysfunction (disease) of that host or by killing and eating them directly, i.e. predation. Examples of pathogens are fungi causing Dutch elm and oak wilt diseases, bacteria in crown gall and fire blight diseases and Pythium/Phytophthora causing fine root diseases. Examples of predators are beneficial nematodes, amoebae and other protozoa that ingest bacteria, fungi and algae.
The third group is the symbionts. They gain their carbon nutrition directly from their beneficial organic union with living hosts in which the hosts are not harmed but gain from the mutualistic partnership. Examples are fungi in mycorrhizae and lichens and the bacteria in N-fixing nodules of legumes.
The smallest and most numerous organisms in soil are the bacteria. These single-celled microbes are the simplest, smallest and most abundant forms of life on earth. Saprophytic soil bacteria are found in greatest numbers in the upper 12 of soil where their food, i.e. carbon in organic matter and in nutrients on and near roots is the most prevalent and where aeration, soil water, inorganic mineral elements, pH and temperature are adequate to satisfy their needs. A thimble of productive soil may contain up to 6 billion bacteria representing some 4,000 different species that count nearly exceeds the entire worlds human population!
Bacteria perform many important processes in soil that are essential to all life on Earth. They decompose organic matter including the cellulose and lignin in wood. Certain bacteria have been used to bioremediate soil and water contaminated with pesticides, gasoline, crude oil, jet fuel, TNT, and other man-made hydrocarbons. Some of these bacterial soil processes require free oxygen (aerobic), some require intermediate amounts of free oxygen (microaerophilic) and others require no free oxygen (anaerobic). Soils productive for land plants are aerobic but most also contain microsites which are anaerobic and/or microaerophilic.
Many species of soil bacteria are opportunistic and live freely in soil colonizing particles of organic matter. Some are primarily decomposers of simple carbohydrates, organic acids and amino acids. Some species, called rhizobacteria, have adapted themselves to nonwoody absorbing roots where their food, i.e. organic chemical exudates and sloughed cells from growing roots, called rhizodeposition, are present. Rhizobacterial associations have been found on all plants. Rhizobacteria can increase mineral element (P, K, Ca, etc.) solubility from insoluble mineral sources, recycle inorganic nutrients especially nitrogen from organic forms, fix atmospheric nitrogen, reduce (by antagonism or competition) many root disease pathogens, and produce plant-growth regulators (auxins, gibberelins and cytokinins) which contribute to improved root growth and functions. Recently, certain bacteria have been found to increase mycorrhizal development (mycorrhizae helper bacteria); how they do this is not fully understood. They occupy and function in the rhizosphere of mycorrhizae (mycorrhizosphere). Recently, bacteria that fix nitrogen have been discovered actually growing inside the hyphae of mycorrhizal fungi revealing a tripartite symbiosis. Basically, all of these bacteria, carrying out all of the different soil and root processes, are collectively referred to as plant growth promoting bacteria.
Gaseous nitrogen can be fixed symbiotically by nodulating bacteria (as with legumes) or fixed by free-living bacteria in the soil. The nodulating bacteria obtain their organic carbon nutrition directly from their organic union with plant host. The free-living bacteria obtain their carbon nutrition from the organic matter in the soil or from sloughed root cells or root exudates (i.e. rhizodeposition). The nitrogen fixed by these specific bacteria is eventually released as either ammonium or nitrate into the soil. These are the main forms of nitrogen absorbed by plant roots. This fixation of atmospheric nitrogen is the main way that new nitrogen is added naturally to plant ecosystems. Nitrogen is essential to the total organic carbon decomposition process. Carbon: nitrogen ratios in the soil between 15 and 30 to 1 are ideal. Greater ratios, like that found in raw wood chips (300:1), actually cause loss of nitrogen (denitrification) from the soil when applied as a mulch.
Actinomycetes are a unique group of microbes that actually link the bacteria and the fungi. They are saprophytic and decompose organic matter. Many live exclusively in the rhizosphere and give soil the earthy odor. Many have been isolated from soil and found to produce antibiotics. Streptomycin comes from the actinomycete, Streptomyces and actionomycin comes from Actinomyces. Their main functions in soil health are the antibiotics affecting root disease pathogens and their ability to decompose organic matter.
Other microbes, involved in this belowground carbon cycle, are fungi. Fungi are especially significant in acidic soils because many bacteria are adversely affected by acid soils. They produce enzymes more capable of decomposing structural components of the shed plant material like cellulose and lignin in woody debris than do most bacteria. There are thousands of these wood decaying, saprophytic fungi. Many produce large conks on living trees and on woody debris on the forest floor. Bacteria are also intimately involved with these fungi in a succession resulting in wood decay. Thousands of other fungi, like the molds Penicillium and Aspergillus, are saprophytes also. They decompose the simple carbon compounds like sugars in various organic matter in soil. Some produce antibiotics, like penicillin, that can reduce the populations of harmful bacteria and fungi. Others, like species of Trichoderma and Gliocladium, may produce effective antibiotics but also may directly attack and parasitize mycelia of pathogenic fungi and, thus reduce the incidence of root disease.
Algae represent another population of soil microbes that have important functions in soil. However, their numbers are far fewer than bacteria and fungi. They occur mostly in moist soils and their numbers decrease rapidly with soil depth because sunlight and photosynthesis is reduced except on the soil surface. They are highly susceptible to soil disturbance. Some algae fix atmospheric nitrogen and produce mucigel that contributes to soil aggregation.
Now lets discuss the major symbionts of plants mycorrhizal fungi. Over 95 percent of the green plants of the world form symbiotic relationships with mycorrhizal fungi. These unique, root-inhabiting fungi colonize either the outside of fine absorbing roots (ectomycorrhizae) or the inside of the roots (endomycorrhizae). Ectomycorrhizae occur on about 10 percent of the world flora or about 2000 species of woody plants. Pine, fir, larch, spruce, hemlock, oak, chestnut, beech, alder, birch, basswood, poplar, willow, hickory and pecan, Eucalyptus, Arbutus, and a few others form ectomycorrhizae. In North America there are more than 2,100 species of fungi that form ectomycorrhizae with specific trees; worldwide, there are over 5,000 species. Most of these fungi produce mushrooms or puffballs. Billions of spores are disseminated by wind, insects, and small animals from these fruiting bodies that spread the fungi to new locations. Ectomycorrhizae are only found on trees; they dont occur on nonwoody plants. Most ectomycorrhizae can be recognized with the naked eye since they occur in different shapes, sizes and colors.
Endomycorrhizae are the most widespread of all mycorrhizal types and comprises three general groups. Ericaceous endomycorrhizae occur on four or five families in the Ericales and include Rhododendron, mountain laurel, cranberry and blueberry. Orchidaceous endomycorrhizae are another type that occurs only in the plant family Orchidaceae. These two groups will not be discussed further. Vesicular- arbuscular mycorrhizae (VAM) is the third group of endomycorrhizae. Vesicles and/or arbuscules are structures produced by these fungi in or on colonized roots. VAM have been observed in roots of over 1,000 genera of plants representing some 200 plant families. It has been estimated that over 85 percent of the 300,000 species of vascular plants in the world form VAM. These include agricultural crops (except the cabbage family Brassica), most wild and cultivated grasses, fruit and nut trees (except pecan), many hardwoods, vines, desert plants, flowers, and most ornamentals. VAM fungi are ubiquitous in all natural soils that are or have recently supported their host plants. However, their population density (i.e. number of spores and other propagules) and species diversity vary greatly in different soils supporting different plants. Degraded soils like those in our urban landscapes are low in organic matter, have poor physical structure, and are usually compacted. These characteristics limit plant growth and cannot support significant populations of VAM fungi. Healthy forest, desert and grassland soils with high plant density contain many of them. There are about 150 total species of VAM fungi identified, to date, worldwide. More are being discovered every year. VAM roots are not changed in either color or shape from nonmycorrhizal roots as are ectomycorrhizae. VAM can only be confirmed microscopically and thus, cannot be identified with the unaided eye. These fungi produce large spores on their vegetative threads (mycelia) either in or growing from roots in the soil. Because of their location and large size, spores are disseminated very slowly to new areas by soil animals and insects. VAM fungal spores are 10 to 20 times larger in diameter and volume than the smaller spores of ectomycorrhizal fungi produced in puffballs and mushrooms.
The host plants supply mycorrhizal fungi with organic carbon in the form of sugars and other essential organics, such as certain vitamins and amino acids derived directly or indirectly from photosynthesis. Since these mycorrhizal fungi cannot obtain these essential dietary carbon nutrients from any other source they are totally dependent on the photosynthates translocated to roots of their plant hosts for their survival and growth. This means, very simply, that the mycorrhizal fungi cannot grow and develop unless they obtain their dietary carbon from the roots of their plant hosts thats their restaurant! In return, the fungi extend mycelia far into the soil, significantly increasing the surface area of the roots (up to 700 % more) to improve absorption of water, nitrogen and essential mineral elements for its plant host. Thats why its called a symbiosis both partners give and take in the association.
Lets put this another way. In order to develop and maintain a significant complement of mycorrhizae, a plant will allocate between 4 and 15 % of its sugar made in photosynthesis to satisfy the sugar needs of the fungi in the symbiotic association. The expense of this sugar tax assures the plant of longer-lived (several months) mycorrhizal roots capable of satisfying the plants requirements of essential soil resources. A plant with few or no mycorrhizae will spend as much or more sugar tax producing and replacing (rapid turnover rate) the short-lived (1 6 wks.) nonmycorrhizal absorbing roots which are also significantly less efficient than mycorrhizae in acquiring these essential resources from the soil for the plant. Without significant mycorrhizal development the plant would waste carbon energy theyre too efficient to do this, thus mycorrhizae! Few plants in their native habitat are without mycorrhizae. Research has shown that most plants, especially trees, have an obligate requirement for mycorrhizae without them they die!
Recently, VAM fungi were reported to produce a glycoprotein exudate while in the mycorrhizal association. This organic chemical, called glomalin after the VAM fungal genus Glomus, plays a significant role in soil aggregate stability and can represent 4 to 5 % of total soil carbon and nitrogen in forest soils. This glycoprotein can form a continuous bridge between essential elements in soil solution in the rhizosphere and the plant root. This organic adds to the total rhizodeposition.
Mycorrhizae are able to absorb, accumulate and transfer essential elements and water to plants more rapidly and for longer periods of time than nonmycorrhizal roots. From a practical perspective, it would require approximately 100 times more sugars and energy from photosynthesis for a tree to form enough nonmycorrhizal absorbing roots to produce the same surface area formed by the mycelia of mycorrhizal fungi and the mycorrhizae. Trees and other plants are simply not able to produce 100 times more photosynthate; thus, they evolved a dependency on mycorrhizae. Mycorrhizae live and function longer than nonmycorrhizal absorbing roots, increase the tolerance of their tree host to drought, soil compaction, high soil temperatures, heavy metals, soil salinity, organic and inorganic soil toxins and extremes of soil pH. They also depress many root diseases caused by pathogenic fungi and nematodes. Recently, mycorrhizal plants were found to suppress the attacks by certain foliar insects by increasing the natural defense chemicals produced by healthy plants. Mycorrhizal fungi of any type do not significantly decompose soil organic matter but may acquire certain elements, such as nitrogen and phosphorus, from the organic matter and share them with their plant host. An important prerequisite to remember for mycorrhizal development is that nonwoody, susceptible roots must be preformed before they can be colonized by the fungi and become mycorrhizae. Susceptibility means that the simple sugars required by these fungi are available to them in these roots. Remember, everything is based on availability of essential carbon.
In natural forests and grasslands, many species of mycorrhizal fungi share common plant hosts and form a continuous, interconnecting network of mycelia on roots between the plants. It has been shown that dominant forest trees in full sunlight will actually transfer sugars through a common ectomycorrhizal fungal mycelial network to roots of adjacent understory trees that are shaded and produce less photosynthate. The dominant trees can function as nurse trees to the understory trees and improve growth and competitive abilities of the smaller trees. Photosynthate transfer between grasses sharing a common VAM fungal mycelial network has also been reported.
TO YOUR UNDERSTANDING
The preceding discussion was an attempt to describe the foliar and soil processes that support normal growth and development of plants in their native habitats. Note that I used the word normal. Thats deliberate. If you dont know what normal is, how can you possibly recognize abnormal? You must be able to recognize a healthy plant before you can judge one to be unhealthy. You also have to identify what contributes to normal growth and what growth looks like without it.
By now you have a better understanding of the importance of the organic carbon cycle to the world. Also, you should have a greater appreciation for the importance of the biological factory that produces most of the worlds energy, oxygen and organic-based sugars green leaves! All life on Earth is dependent on this factory and its products, including the diverse life in the soil. I bet you didnt know you walked over such abundant and diverse populations of soil microbes that are so critically important to soil and plant health thru the soil processes they drive. Even through they represent only about 5% of the total organic carbon (living and dead) in soil, over 95% of the essential inorganic elements (N, P, K, etc.) pass through these microbes before these elements are passed on to plants.
Compared to natural soils, the soils in most manmade landscapes have little periodically renewed and recyclable high quality, native organic matter needed to drive natural soil processes, are compacted with poor aeration and low water storage capacity, and frequently have a creeping soil pH caused by alkaline or effluent irrigation water or fertilizer and lime treatments of turf. Trees and other plants growing on these sites must have the capacity to produce new functional absorbing roots, the soil must contain effective inocula of mycorrhizal fungi needed to form abundant mycorrhizae on the new roots and the soil must contain the proper organic matter and associated microbes to carry out all of the essential natural soil processes. If not, you have abnormal or inhibited growth. You are then forced to maintain these trees with a row crop mentality that involves the abundant use of pesticides and inorganic fertilizers. These chemicals, when used in excess, can inhibit beneficial microbes, delay normal root function and natural soil processes and may actually increase the susceptibility of the tree and other plants to pests. Many states have already banned or have limited the use of many of these synthetic chemicals because of their purported damaging effects to the environment.
We have domesticated forest trees and other plants, by removing them from their natural environments and by growing them in commercial tree plantations, fruit and nut tree orchards, yards in subdivisions, manicured parks and golf courses, roadsides, sidewalk cutouts and other unnatural landscapes. Trees commonly occur in these various manmade landscapes by one of two events. Either they existed as a forest tree in the area before manmade development or they were transplanted after development. Roots of preexisting trees are routinely damaged during construction by trenching utilities, by drain fields, by grading for drainage, by compaction from vehicles, and by the ever-present urban forest floor of concrete/asphalt roads, driveways and sidewalks.
There is an old forestry saying build the roots and the tops will follow. Transplanted trees are routinely moved to their new environment with less than 10 percent of their original root system developed in the nursery but yet they are expected to maintain a normal growth rate on their new planting site. In reality these transplanted trees, if they survive, may need 10 years to replace the original lateral and absorbing root systems, if ever. Roots not only need large soil volumes for proper development but also they must have favorable soil conditions (oxygen, proper temperature, available soil water, soluble nitrogen and essential minerals) that allow them to develop. Remember, that with all of this, these plants must have a healthy green and dense canopy to produce the photosynthates (sugars) and energy needed for growth and respiration. Since photosynthesis and the allocation pattern of the photosynthate is essential to plant growth, it is obvious that the most important single indicator of plant health, especially trees, is the health of the canopy. Protect the factory!!
If your job is to manage trees and other plants then you must understand the belowground traits acquired by these plants from their former natural environment and design management practices in manmade landscapes to satisfy these requirements. Good quality organic matter in soil, an organic mulch over the rooting area of shrubs and trees, the largest possible volume of quality soil (preferred pH, good water storage and physical properties, high reserve of mineral elements) for maximum root expanse, and adequate populations of mycorrhizal fungi and beneficial rhizobacteria are a few prerequisites to healthy and normal root development and function. Inoculants of mycorrhizal fungi and rhizobacteria can be introduced to roots and soil in the nursery, at planting or during maintenance of turf, flowers, shrubs and trees. Use of these microbial and natural inoculants has been shown to improve the establishment and normal growth of these plants and also to improve the below and aboveground health and function of established mature trees in diverse manmade landscapes.
