Readers are requested to refer the article ENDOMYCORRHIZAE for a better understanding of the present article.
Forest trees are an integral part of the coffee ecosystem. In fact, all shade grown Indian coffee farms are a mosaic of coffee plants and natural forests. The characteristic feature of Indian coffee Plantations is that they are shade grown under the canopy of tall evergreen forests.
The coffee farms are home to a variety of trees and not just confined to a monoculture of selective trees (Single species). The biological diversity reaches its zenith inside the coffee mountain. These vast mountains are microcosms of insects, plants and animals. Only a handful of countries in the world grow coffee in an ecofriendly manner like the way India does.
Building a coffee farm in India is like embarking on a voyage of discovery. Challenges are in plenty. The first challenge is to break stereo types regarding modern day chemicals and poisons and to develop sustainable technologies keeping one’s ears and eyes close to the ground. The journey, this far has been strewn with technological, social and scientific challenges. The key in overcoming these hurdles was through constant perseverance and a belief and passion for one’s work.
As a matter of fact, in any Indian Coffee Plantation, whether Arabica or Robusta, there is a likelihood of a standing tree population of approximately 150 to 300 trees per hectare. These tall evergreen trees with their deep rooted system require large amounts of water and nutrients for their growth and survival. The interesting point to note here is that coffee farmers do not apply any external inputs in the form of chemicals or manure for improving the increment of individual trees because they believe in the self regulating forces of nature.
Instead their focus is on getting better yields of coffee and allied crops by way of split application of fertilizer. In spite of this age old practice of not fertilizing the trees, the health of the forest remains excellent and the question that comes to mind is how does the forest retains its health and vigor. Surprising, yet true; nature comes to the rescue of the forest trees.
Invisible microbial agents in symbiotic association with the forest trees provide the necessary nutrition and water uptake. Most forest trees have roots infected with fungi that increase nutrient and water uptake and also aid in the protection from certain root pathogens. These friendly fungi are known as ECTOMYCORRHIZAE. The balance of this cooperation is in favor of the coffee plantation. They nourish the trees creating opportunities for new life.
Scientists have observed four main types of mycorrhizae.
- ERICOID MYCORRHIZAE
- ORCHIDACEOUS MYCORRHIZAE
This article throws light on ectomycorrhizae and its profound influence on coffee plantation ecology.
The ectomycorrhizae (EM) sometimes termed ectotrophic mycorrhizae is the second most common type of mycorrhizae. The fungal symbiont is very closely associated with forest trees belonging to the families Pinaceae, Fagaceae, Betulaceae and Myrtaceae, including many gymnosperms and angiosperms.
The fungi involved in this symbiotic association are grouped under Basidiomycetes from the families, Amanitaceae, Boletaceae, Cortinariaceae, Russulaceae, Tricholomataceae, Rhizopogonaceae and Sclerodermataceae. They cannot grow and reproduce unless they are in association with the roots of a tree host. Over 4000 fungal species belonging primarily to the Basidiomycotina and a few belonging to Ascomycotina are known to form ectomycorrhizae. In North America alone there are more than 2,100 species of ectomycorrhizal species.
The fungus has evolved over the years and has specialized structures and mechanisms which facilitate the easy and effective spread over a large area. These fungal fruiting bodies release microscopic spores, which are finer than dust and are carried great distances by wind dispersal. Basidiomycetous fungi producing mushroom (Amanita, Boletus) or puff ball (Rhizopogon, Pisolithus) type fruiting bodies as their reproductive structures are useful in isolation of pure cultures.
Ectomycorrihizal (EM) Characteristics
- The ectomycorrhizal infected roots are devoid of root hairs.
- The fungus does not invade the living cells of the root.
- The dominance of fungal growth on short feeder roots forming a fungal mantle which looks like the host tissue. This sheath is commonly referred to as parenchymatous sheath. The fungus forms a conspicuous mantle and can be seen by the naked eye.
- The fungus only penetrates the intercellular spaces of the cortical cells and forms the hartignet. ( so named after the German scientist )
- The fungal mantle absorbs the nutrients and transports it to the host tissue through the Hartignet.
- The fungal sheath acts as a reservoir of phosphorus and releases it during deficiency conditions.
- During favorable conditions the EM provides a steady supply of nutrients.
- The feeder roots are morphologically differentiated into branched and elongated structures.
- Metabolites produced by EM have a marked influence on the morphology and structure of the tree roots.
- EM is not celluloytic or lignolytic. Even though some are capable of producing cellulose enzymes their activity is suppressed within the host plants and the roots are safe.
- EM are known to produce growth promoting substances like auxins, isobutanol, isobutyric acid, indole acetic acid, gibberellins ,cytokinins , vitamins , antibiotics and fatty acids.
- The symbiosis has a marked influence on the growth and development of both the symbionts.
The two partners, namely the tree and the fungus have a perfect understanding of each others needs. At no time is the relationship parasitic. This perfect understanding between two partners signifies the delicate strands of evolution interwoven not only on the surface of the forest floor of the coffee mountain but also the invisible net work that lies hidden underneath the soil. The EM derives its nutritional needs like carbohydrates, simple sugars and vitamins from the host tree.
The main benefit that the fungus derives is absence of competition for nutrients from soil microorganisms. The tree in turn is benefited with increased uptake of nitrogen, phosphorus and potassium along with water. The fungus also protects the trees from pathogens.
Isolation & Inoculation
The fungus produces fruiting bodies on soil surface close to tree trunks. These fruiting bodies are subsequently used in preparation of pure cultures. The draw back with these fruiting bodies is that they grow slowly in pure culture and require special nutrients such as thiamine, simple amino acids and other unidentified ( collectively known as M-FACTOR ) root exudates.
Inoculation can be carried out by any one of the following techniques:
- Soil inoculation
- Inoculation by spores and sporocarps
- Mass multiplication by pure culture.
Coffee Forest Ecology
The relevance of EM in coffee plantations is particularly demonstrated by the fact that during establishment of new plantations, coffee farmers practice the slash and burn method to clear the land of shrubs, undergrowth and weeds. This method is followed because it saves on labor costs. Even though, it is an easy way out, it causes irreparable damage to the soil in the long run.
Basically, the slash and burn method can be adopted for field crops, but not for plantation crops. The burning increases the soil temperature in the top six inch layer of soil which houses most of the beneficial micro flora. Prolonged high temperatures destroy and kill the entire micro flora of the region and the subsequent rejuvenation takes ages. In such ecosystems, application of EM becomes mandatory.
The abundant tree growth inside the plantation is always taken for granted. Planters are of the opinion that these native trees do not require any internal or external inputs other than a healthy soil system. However, we have observed for the past 15 years that the growth, girth and development of various tree species requires a uniform and sufficiently high degree of nutrient availability and the same can be harvested from the forest floor, provided a sound ecological balance is maintained. It is easy said than done, but a thorough understanding of the elements of nature provides a glimpse in providing the necessary inputs.
Both forest trees as well as young forest seedlings have a high energy requirement. Especially in the case of young seedlings on account of their comparatively weakly developed root system they demand a good supply of the necessary mineral substances. External inputs can be supplied at the nursery stage, but under field conditions it becomes an expensive preposition and goes contrary to the fundamental value of sustainable farming.
The best bet in such a situation is to conserve humus on the floor of the forest. Accumulation of humus is a long drawn process and takes time. The build up of humus changes the entire ground scenario firstly by improving the structural properties of the soil and build up of billions of beneficial microbes. This in turn leads to a better utilization of the nutrients present by the plants, as well as of soil moisture.
Farmyard manure and compost should be periodically applied to the coffee farm, for this accelerates the decomposition of plant residues and at the same time provides a steady supply of nutrients. All these cumulative factors aid in the easy establishment and multiplication of EM.
New Clearings or Replanting in Arabica Plantations
It is quite common to open up new plantations in virgin forests. Also, due to the short life span of certain varieties of Arabica coffee coupled with the heavy infestation of white stem borer, periodic replanting of different varieties of coffee is undertaken. Once the replanting is done, the coffee farmers invariably transport large quantities of humus and leaf litter from an established plantation block and cover the new clearings as well as the replanted blocks.
This practice is scientifically unsound and detrimental to the coffee mountain. The planters need to be educated about such harmful practices because harvesting of humus and biomass in large quantities can drastically bring down the population of beneficial microbes and such areas are easily susceptible to pest and disease incidence. Instead, the solution is to add farmyard manure and compost to new clearings and replanted blocks. This practice maintains a healthy level of EM inside the coffee forest.
The standing tree population in Robusta plantations is very less compared to an Arabica plantation. The number of trees is approximately, 125 trees per hectare. Hence, at any given point of time the available biomass and organic matter on the forest floor is considerably less.
The important point here is that unlike Arabica plantations, Robusta plantations are irrigated each year with blossom showers as well as post blossom showers. This increases the losses of nutrients by leaching and hence reduces the fertility status of the soil. This means increased demands for a good humus economy for the proliferation of beneficial microbes. Since Robusta plants are surface feeders the roots require well aerated soils which in turn are possible in humus rich soil systems.
During preparation of nursery beds the practice often followed is soil fumigation to kill harmful pathogens. Unfortunately, this also kills many beneficial microbes. EM application on to such beds significantly, improves the seedling quality.
World wide research has clearly demonstrated that tree seedlings lacking ectomycorrhizae suffer nutrient deficiencies early in the growing season. However, with inoculation of EM the deficiency disappears.
There is a direct correlation in the reduction of EM with increased tree felling. Forests cleared of timber are very low in EM activity and are difficult to reclaim unless inoculated with the right kind of EM. There is every possibility that a particular tree species may be infected by more than one fungal species. Scientists are a long way in identifying the right kind of EM for various tree species inside the coffee mountain.
Fertilizers, Pesticides & Chemicals
Fertilizers, pesticides and chemicals are known to have a inhibitory effect on the growth and development of ecto mycorrhizae.Reduced application of the above mentioned significantly stimulates EM development.
Benefits of Ectomycorrhizae
- EM results in longevity of feeder roots.
- Quite a few forest trees, such as pines, cannot grow beyond the first year without the local presence of mycorrhizae in the soil.
- Increased rate of nutrient uptake.
- Selective absorption of certain minerals.
- Formation of a physical barrier for the entry of pathogens.
- Increased adaptability to wide fluctuations in environmental conditions. Trees with EM are in a position to establish and survive in habitats they otherwise could not.
- Some EM is known to adapt well to extremes of temperature as well as mined sites or stressful sites. Reclaiming such sites becomes easy with the inoculation of EM.
- Production of volatile organic acids which have fungi static effects.
- Production of antibiotics.
- Release of nutrients from leaf litter by production of enzymes involved in mineralization of organic matter.
We keep reminding the Planting Community that the coffee mountain is a sum of many parts. Hence utmost care needs to be taken to minimize the destruction from man made activities. Destruction breaks vital links and wipes out plant, animal and microbial life.
Just two decades back, the luxuriant growth of trees was an integral part of coffee farms. Even though the high density of trees per unit area resulted in a sustainable yield of coffee, from a scientific stand point there was an equitable balance of nature. Today, all that has changed for the worse. The global coffee crisis has put undue pressure on every square inch of the coffee mountain. The primary objective of the coffee farmer is to increase coffee yields at any cost, even if it means the destruction of the coffee forests and the application of very high levels of fertilizers, pesticides and chemicals. In a short span of three to four years these man made changes have resulted in a virtual break down of the energy flow and nature’s equilibrium has tilted in favor of pathogens.
Years of continuous drought, global price crash, and disease spread have left the coffee industry in a state of flux. Destruction of coffee farms by borer and inability to raise fresh loans to refurbish estates; it is a vicious circle of distress and more distress. These factors are directly responsible for the large scale felling of trees planted two generations back. The fabric of the forest is lost due to loss of forest habitat. Despite efforts to save the coffee bush, the forests supporting them are disappearing. All these years it was the forest factor that protected coffee.
However, this scene is shortly going to change with the last remaining tracts of evergreen coffee forests impoverished by the constant removal of timber and especially by the removal of leaf litter from the forest floor. This is robbing the soil of its sustaining ability. This practice results in Disastrous losses of humus and nutrients inside the coffee mountain. Logging of trees from the coffee farms would result in signing the death warrant of coffee plantations. The direct consequence is the build up of both macro and micro temperatures.
Coffee forest soils are a storehouse of sufficiently large stocks of valuable biomass and humus. This itself is the principle source of energy and food for microorganisms.These forests with their great reserve of nutrients support the flora and fauna of the fragile coffee mountain. If logging continues unabated then in such a scenario the EM population will decrease alarmingly. Scientific evidence clearly points out that forest trees infected with EM can meet their nutritional demand from the microsymbiont. Also, forest seedlings grown in soils which are mined and low in nutrients, easily establish with EM application.
In the face of such a huge problem our conscience should analyze the facts more lucidly. It is upon our shoulders,that the next generation of coffee farmers stand. We have a choice. It is up to us which path we take. Let us not forget that the forest trees have been key drivers in harvesting the sunlight (PHOTOSYNTHESIS) and have turned this light into life for sustaining the needs of the coffee mountain. The axe or the chain saw needs to be stopped at any cost before they create an empty world without depth and substance.
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