Some Thoughts about Micro-Organisms and Epiphytic Life Concerning Orchids
(A report and interpretation of nutrient cycles between autotrophic and heterotrophic entities) written by O. Möller, published in “Die Orchidee” Nov. 2002, translated by I. Ostrander.
If there had not been any living forms that were capable of breaking down autotrophic plants at the same time as chlorophyll came into being, there would be no life on earth now. All plants would have suffocated from their own products and thus there would be no soil. Any metabolism of nutrients would have been impossible and the plants would have starved, together with all other life forms. A forced coexistence, after a struggle for balance, led to the relationship between autotrophic plants and other (heterotrophic) life forms, as they exist today. The opinion of some scientists, who say that the first life forms (on earth) had been heterotrophic bacteria or similar organisms that materialized out of the primal hydrocarbon atmosphere, cannot be refuted. Heterotrophic life forms, bacteria, fungi, mushrooms and animals fulfill an important task in nature and are not the only beneficiaries of (autotrophs) the green plants. Several secretions of the microphytes not only support the growth of plants in higher orders but under certain conditions, only these secretions make higher plant life possible. Plants are not altruistic creations; they do not want to be helpful. It is therefore incorrect to explain any symbiosis of different life forms in these terms, even though both partners may benefit from such an arrangement.
During the Carbon age, about 345 – 280 million years ago, there already existed saprophytes, parasites and even micorrhizae in the carbon forests. During the Jurassic age, about 125 million years ago, through the development of angiosperms (flowering plants) the plant forms changed and began to crowd out conifers and ferns. The micro-organisms either had to adapt to the new conditions or evolve into new species. During the course of all plants’ development, they continue to form new substances, which they can utilize in their struggle to create a labile balance. Many scientists are of the opinion that symbiotic relationships are derived from parasitic ones, where the subjected plant has developed substances that either weaken or destroy the attacker (two-way tolerant parasitism). With orchids, the symbiosis with fungi has developed so far, that only through the presence of fungi on the root surfaces the antifungal orchinol is formed, which suppresses fungal growth within the orchid. If this antifungal substance existed in the orchids earlier, the growth of any fungus on the root surface would not be possible. If the supply of orchinol is too weak, the plant dies. (A similar relationship occurs with the sweet potato, Ipomoea batatas, where the protective substance ipomoeamaron is present only after cell damage.) Even farther developed is the germination symbiosis of orchids. Substance increase is particularly high during the first year and can only be explained by the constant supply of nutrients. So far, it is not known what causes the fungi to supply the seedlings with nourishment. This germination symbiosis is rather different from the presence of micorrhizae in the adult orchid, where the fungi are capturing carbohydrates.
It is fairly easy to learn what a fully autotrophic plant needs in order to grow and to be able to fulfill these needs, knowing the condition of its natural soil. This, however, changes drastically when a plant is no longer capable any more to synthesize its food from the soil (nutrition-heterotrophy). This plant will then only grow in soils that can readily supply all its requirements. One cannot expect to improve the plant’s growth by fertilizing it with chemicals. That might only be possible by supplying certain supplements to those organisms that secrete the materials needed by the plant. Possibly, there could also be organic substances which secrete these materials. Plants that have been removed from their correct habitats will only live in different soils until all the needed materials have been exhausted. There are also fungi which cannot synthesize food and are therefore useless to orchids unless the orchids can utilize materials from the fungi to synthesize into substances which both the orchids and the fungi can use. The mycologist E. Gäumann writes: “In the real fungi, the vegetative body normally consists of cell-covered hyphae. They probably have evolved polypletically from autotrophic algae, which have lost their assimilation colour by mutation and thereby lost the capability to live autotrophically from carbohydrates. Some of them have even lost the ability to synthesize their own growth-substances and are therefore growth-substance heterotrophs. In this carbohydrate- and growth-heterotrophy they are, in a nutritional sense close to the animal kingdom.” This kind of nutrition for the fungi makes the symbiosis with orchids even more of a puzzle, because they are still feeding the plant.
When there are no growth-regulating substances in their food, all life forms’ growth will stagnate. These infinitesimally small substances are generated by a life-form itself and are called enzymes. Within each single cell, there are over 100 enzymes and enzyme systems, depending in their effect on the presence of a sufficient supply of trace elements. When these substances with their catalytic effect have to be taken up externally, they are called vitamins. One of these substances, which is critical in the germination of orchids, is B1=Thiamine (earlier Aneurine). Since that is also important for humans and its absence can have devastating results, its formation has been thoroughly investigated. The biosynthesis of Thiamine is important for epiphytes and perhaps also for the growth of the simple heterotrophic orchids. This synthesis is another example how different relationships between plants simply were forced to develop. Thiamine consists of two substances, namely pyrimidine and thiazol; each one separate is (usually) ineffective. Plants of the higher orders can produce sufficient Thiamine in their chlorophyll-bearing organs, especially under high light. On the other hand, plant embryos and roots have only a limited capacity for this. Their growth is supported when micro-organisms manufacture Thiamine for them. Roots are even capable of utilizing the separate parts. Tests have shown that fungi, even yeast react differently from each other, although they may belong to the same genus. This is also true for bacteria. Soil organisms that live in a symbiotic relationship can also produce Thiamine. There are five separate groups of micro-organisms that react differently to Thiamine or its synthesis.
- Those that need it as a vitamin but cannot produce it.
- Those that can build it from both of its components, which must first be absorbed.
- Those that can only manufacture pyrimidine and must absorb the other part.
- Those that can only manufacture thiazol and must absorb the other part.
- Those that can generate both these substances and manufacture Thiamine from them.
For the germination symbiosis of orchids only those fungi can be of use, which can deliver the vitamins of the B-complex to the seed. Of optimum use are those fungi that can also supply materials which the seedlings can turn into starch. It is possible that the Coral Root Orchid (Corallorhiza) with its large root mass has developed a different symbiotic arrangement. Coral Root always grows in places that show high biologic activity, where the groundwater contains minerals as well as organic supplies. Tests have shown that the root is able to absorb liquids on its total surface. Coral Root, grown in pure perlite have sprouted and flowered. Since plant roots are able to absorb thiamine and manufacture from it vitamin B1, that might be a reason why fungi that cannot manufacture B1 like to grow on the roots of Corallorhiza (vitamin symbiosis?)
A process that is hardly noticed, but is of great value to the germinating orchid, is the guttation (Latin: gutta = drip). For terrestrial orchids the secretions of its companion plants, for epiphytic orchids that of their host, is most important – even critical. Plants have developed special parts to facilitate the necessary (for them) secretion of liquids. In grasses, they are found at the leaf tips, other leaves have them around the edges. The physiological importance of guttation for the plants lies in maintenance of the circulation of their fluids during periods of impaired transpiration. It is an activity similar to bleeding (after damage) and can be considerable, especially during long, tropical nights. It is said that the leaves of Colocasia secrete up to 190 drops per minute. During one 10 hour night, this comes to 8.16 litres of fluids. This fluid contains, besides minerals and sugars, also amines, which will be different depending on what tree (or other plant) they they are from In European trees, the Elm fluid contains mainly aspargine, walnut trees drip mainly glutamine, whereas Alder and Birches drip cibulline, which is an important by-product of amino-acid metabolism and can provide either storage or transportation. In plant fluids with high amounts of cibulline, orchids germinate particularly well.
The different combinations contained in tree sap must of course influence the growth of the epiphytic orchids growing on them. One importer related that the native collectors make cuts at the bottom of a tree to decide from the look of the sap whether it is worth their while to climb a tree in order to get orchids. Weather conditions in the humid tropics have helped to create a relationship between trees and micro-organisms that grow on them, which is of benefit to both. Prerequisite for this is the regular guttation daily as well as during a year’s cycle. Autotrophic plants generally have an abundance of sugars. This contrasts with a general lack of nitrogen because only few lower forms can bind atmospheric nitrogen. Higher plant forms, even fungi are not capable of this. It may be opportunistic to tie the growth of orchids to that of the fungi; it is not realistic. The sources of nitrogen in tropical trees lie in bacteria like Actobacter and Beijerincka and perhaps algae like Nostocacea which grow on the trees. (Natives call them and the epiphytic orchids “parasitos”). Otherwise typical ground dwellers, these organisms have taken to the trees in the tropics. With a large supply of sugars, such bacteria can bind 15 mg of nitrogen for each gram of sugar. Algae only need minerals and light, they are completely autotrophic.
There is little exact data for the amounts of substances that are washed down by rain. During tests with radio-active minerals, in a three-hour period, the leaves of a plant subjected to heavy rain, lost 27% of its sulphur, 20% of its calcium and 12.5% of its phosphorus. Someone figured out that in a one hectare apple orchard, the ground receives annually 800 kg of water-soluble substances, mostly as sugars, which contribute greatly to the nourishment of soil organisms.
Fungi, like yeast and others from the family Sarcharomycetaceae have their homes mainly on leaves and fruit; they can also be found in upper layers of soil, when there are sufficient sugars that can easily be dissolved. Their fermenting capabilities are considerable. (In human medicine, these yeast fungi are the main source of vitamin B complex). These fungi are ubiquitous and cause the fermentation of sugary plants, (as in wine). It is noticeable that huge masses of Orchis mascula grow underneath Hawthorn trees (Crataegus laevigata). The guttation fluid from the Hawthorns contains sugar (measurable with test strips for diabetes). Does the dripping of sugars support the germination directly or the production of vitamin B by the fungi? Are these fungi receiving an optimum diet and is their production of vitamins encouraged?
There are, besides the described organisms others, which can grow so thick on the leaf surfaces, that this growth has been called “phyllosphere”. The majority of the organisms that grow during one hot, tropical night will die again the next day. Their substance is therefore available as food to the tree and the orchids on it. It is easy to underestimate the mass of bacteria in action. During their growth (doubling within 15 minutes), it can be reckoned that (even with a doubling time of only 30 minutes), in a 10 hour night one gram will increase to one kilogram (1000 gram). It is of course unrealistic to count on unlimited growth and a constant supply of food, but this possibly huge increase shows the importance of micro-organisms in nature’s pantry.
There exists one of the true symbioses (eusymbiosis) between trees and the nitrogen fixers living on them. The bacteria receive the necessary nourishment from the tree’s guttation fluid and in return, deliver to it the nitrogen the tree cannot manufacture. Taken together, the products of the tree, the nitrogen fixers and the yeast fungi may result in a mixture which will help the orchid to germinate, perhaps without micorrhizae? From the close cycle of nourishment between trees and their micro organisms as well as those on the ground, it becomes obvious why soil fertility is lost through tree-cutting.
The relationship between host (tree) and orchid can only be called commensalism (table company – the orchid is nourished by the tree without harming it), if there are not too many orchids growing on a tree. This relationship changes when the epiphytes increase beyond a certain number. For instance, if orange trees in a plantation are not regularly stripped of the epiphytes growing on them, they stop bearing fruit. Later, the trees die off. All those epiphytes, bromeliads and orchids clearly damage the tree and are really “parasitos”. Of course, in a botanical sense they are not really parasites – they do not penetrate their hosts to rob their food. This is mainly a question of definition.
Ingrid Schmidt-Ostrander - Canadian Orchid Congress