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Home / Agriculture / Endomycorrhizaeby Dr. Anand Titus and Geeta N. Pereira Page 1 | Page 2 Coffee Plantations are uniquely positioned in the fragile Western Ghats. These lush and verdant biodiverse mountains are filled with surprises. They have only revealed a part of the mystery and today scientist’s world over are trying to unlock the hidden secrets associated with the coffee mountains. Evolution has deliberately created a fundamental niche which makes up the character of the coffee mountain, where in one species does not compete for food and space with the other. In fact all the biotic partners participate in creating a healthy coffee forest. Each plantation is distinct from the other in terms of flora and fauna. Coffee plantations are a tropical paradise with abundant sunlight. Millions of plant cells with the photosynthetic pigment, chlorophyll act as factories converting solar energy into chemical energy. This is one of the key drivers in the sustaining power of planet earth. Somehow, over the years we have had an uneasy relationship with the coffee forest; Technology has been the driving force behind modern day plantations. The present day coffee farmers are aggressively turning towards chemical inputs in the hope of maximizing returns in a short span of time. Trapped by economic necessity, coffee farmers are ready to abandon traditional wisdom and pump in pesticide and poisons to get better yields. Pollution is spilling into the forest floor. This relationship cannot last forever. In the long run there is more damage caused to the ecology of the region and it not only affects the coffee plantation, but the flora and fauna of the region in a number of ways. If this trend continues into the future, it is bound to leave permanent scars in this delicate landscape. Ultimately, the stability of the relationship between coffee and forests is an accurate health barometer for all other biotic communities inside the coffee mountain. Luckily, MYCORRHIZAE has the capacity towards a gentle interaction with several plant species in providing the necessary stability and nutrient uptake.
Role of PhosphorusPhosphorus is a key element in the establishment of new plantations and in the productivity of established plantations. However, in tropical countries where coffee is cultivated, phosphorus is often the limiting nutrient. The scientific truth is that the coffee soils contain abundant phosphorus, but most of it is fixed and unavailable to the plant. However, the coffee mountain is blessed with MYCORRHIZAE which provides a host of benefits to the surrounding biotic community in the uptake of soil phosphorus and other nutrients. There are two main kinds of mycorrhizae, namely ecto and endomycorrhizae. The general term for all mycorrhizae types where the fungus grows within cortical cells of plants is termed ENDOMYCORRHIZAE. This article throws light on only the endomycorrhizae { endotrophic } .
MycorrhizaeMycorrhiza literally means plant roots infected with fungus (FUNGUS ROOTS). It is derived from a Greek word: MYKES-meaning fungus or mushroom and RHIZA –meaning root. This natural relationship was first observed by the German scientist A.B. Frank in 1885. It involves a mutualistic relationship between two partners, namely the fungus and roots of plants. The plant supplies the nutritional requirement of the fungus like amino acids, carbon and vitamins and the fungus in turns aids the plant in the nutrient uptake. This unique association has a tremendous bearing on coffee forests and the amazing biodiversity. Infact researchers are of the opinion that more than 90 % of all plant species in the world have one or the other mycorrhizal association. Hence, it is easy to name a few species of plants which lack the fungal association. At times the plant species involved is called the host and the fungal partner, the microsymbiont. The mycorrhizal association is of a very highly specialized nature where both the partners derive benefit from one another. One important point that has to be borne in mind is that mycorrhizae are not soil microorganisms, but one which are associated with the roots of plants. This complex behavior has been little understood, but the benefits, already exploited in commercial agriculture. The endomycorrhizae fungus establishes itself intracellularly with the mycelium linking the cells of the coffee root and the surrounding soil. The fungus initially grows only between cortical cells and over a small period of time penetrates the host cell wall, but the most important point to bear in mind is that neither the plant cell wall or fungal cell wall are breached. Infact, the host cell wall invites the fungal mycelium and accommodates it by forming an invagination inside the cell and then envelopes it. A new compartment is formed inside the host cell where efficient nutrient transfer takes place between the fungus and plant cell.
Endomycorrhizae are found in species of the family of angiosperms and certain pteridophytes and bryophytes. The fungi involved in endomycorrhizae belong either to Phycomycetes or to Basidiomycetes. Arbuscular mycorrhizae have well defined specialized structures known as ARBUSCULES which aid in the transfer of nutrients from the soil complex to the root, through a direct linkage. Arbuscules are commonly referred to as little trees because of their highly branched structures. Vesicles are also produced which help in storage of nutrients. They can also serve as reproductive propagules for the fungus. Arbuscules are short lived, not more than fifteen days and makes it that much difficult for collection in the field. The criteria to differentiate arbuscular mycorrhizae are based on spore characteristics. Five genera namely, Glomus, Gigaspora, Acaulospora, Sclerocystis and Endogone have been recognized.
Characteristic Features of Vesicular Arbuscular Mycorrhizae
The key element for the establishment of coffee plantations has been the availability of phosphorus in the available form. However, the characteristic feature of tropical coffee plantation soils is phosphorus deficiency. To augment this limitation the governments import synthetic fertilizers like super phosphate and di ammonium phosphate which are not only very expensive but also highly sensitive to high temperatures. A significant amount of these fertilizers is lost at the time of application either by volatilization or by leaching into ground water or by fixation. Secondly, Coffee Plantation regions in India are characterized by heavy rainfall resulting in fertilizer runoff. This transport of synthetic fertilizers along with precious soil to river beds is catastrophic leading to pollution. Soil erosion is a destabilizing factor in all agro ecosystems. Hence, the establishment of both old and new plantations is based on the accumulation of organic matter, humus and leaf litter on the floor of the coffee forest.
Significance of Shade Grown CoffeeIn the Indian context, SHADE GROWN COFFEE makes all the difference to the microbial ecology of the entire coffee zone. It literally provides a hotbed for the proliferation of billions of beneficial microorganisms. This is due to the fact that the floor of the coffee farm is littered with thousands of tons of BIOMASS in the form of leaf litter, organic wastes, humus, which are acted upon by mycorrhizae and converted into energy rich compounds required for maintaining the sustainability of the farm. Mycorrhizal roots are known to break down lignin and cellulose and constantly supply nutrients to the coffee plants as well as to the surrounding biotic community. Mycorrhizal roots are known to assimilate phosphate more readily than in the roots not having the fungus. Without the crucial role played by microorganisms, the entire coffee belt would be a desert of the future. The starting point of any healthy ecosystem is the abundant availability of either raw material or biomass. Luckily the coffee plantations have huge reserves of both due to the fact that any Arabica plantation has a standing tree population of approximately 200 trees per acre and in Robusta , around 50 to 75 trees. These trees belong to different species and on an average the diversity of species is approximately 50 different types. In addition these tree species shed their leaves during different times of the year thereby providing a constant supply of leaf litter for microbial degradation. Death and decay of the trees also adds to the organic matter content of the soil, which in turn is recycled. Most importantly, the biodiversity of the region with thousands of species of shrubs, herbs, climbers with short lifespan are again a rich source of nutrients for microorganisms which improve water and nutrient uptake.
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