Soil organism | biology | dayline.info
Ecological scientists study organism-environment interactions across that inhabit almost every crevice of the Earth; tiny worms that help build soils; and insects . such as coevolved relationships between specialized pollinators and flowers. What types of interactions occur between organisms in soil? Therefore, the potential exists for synergistic relationships to occur between nitrogen-fixing. The Relationship between Micro-organisms and Soil. Aggregation. BY R. J. SWABY. Department of Soil Microbiology, Rothnmsted Experimental Station.
A similar effect was illustrated in a field study in which greater nitrogenase activity was associated with soil in which stubble was retained than in soil in which stubble was burned Roper Where stubble was burnt, a gradual decline in nitrogenase activity was observed this is an indicator of the relative quantity of nitrogen fixed in the two treatments.
Where straw was incorporated into soil, nitrogenase activity remained higher than when straw was burnt. This is because the incorporation of the stubble into the soil adds a large amount of carbon for soil microorganisms to decompose.
The energy released from its decomposition is utilised by other soil organisms, some of which are involved in nitrogen fixation. Interactions between rhizobia during nodulation of clover Many studies have shown that strains of rhizobia interact during the nodulation of legumes and that the strains of bacteria most effective at fixing nitrogen are not always those that form the majority of the nodules on the legumes.
This was demonstrated in a study where the proportion of different strains of the bacteria, Rhizobium leguminosarum biovar trifolii, in an inocula was changed and the identity of the rhizobia in the nodules was determined Triplett In this study, the strains of rhizobia differed in their ability to produce a toxin that inhibits the activity of rhizobial bacteria.
They also differed in and in their sensitivity to the toxin. Three of the bacteria used were: Before assessing the effect of the toxin-producing strain, the study examined the interaction between TA1 andwhich are both highly effective at nodulating clover roots and fixing nitrogen when present alone. As the relative amount of increased in the inoculum the ability of TA1 to form nodules decreased. Therefore, is more competitive than TA1 when they occur together and will form more nodules.
Only when there are far more cells of TA1 than of did TA1 subdue its competitor and form most of the nodules. In contrast, the genetically altered strain of TA1, strain TAIwas much more competitive against When there were only 1.
Therefore, it appears that the insertion of the gene for toxin production into TA1 improved its competitiveness against strain because it was able to reduce the activity of Table However, when outnumbered TA1 by six times regained its competitive advantage.
The toxin produced by TA1 was not enough to inhibit the activity of so many cells of This experiment demonstrates the importance of specific characteristics of rhizobia to their competitiveness in forming nodules. Furthermore, it also shows that competitiveness alone is not sufficient to ensure nodulation.PHC Film: Soil is a living organism
If less competitive bacteria are present in sufficiently high numbers in the soil, they may form the majority of the nodules. Interactions between fungi during the colonisation of wood A succession of fungi colonise dead wood lying on the forest floor during the slow process of degradation and recycling nutrients from the highly lignified wood material.
The fungus Armillaria luteobubalina aggressively colonises old tree stumps. Inoculation of stumps of the tree Eucalyptus diversicolor with selected wood decaying fungi has been trialled as a means of controlling the spread of Armillaria.
The ability of these fungi to prevent colonisation by Armillaria depended on which part of the stump they colonised. An interesting outcome of this investigation was that a naturally occurring fungus was highly effective in excluding Armillaria from the stumps Pearce and Malajczuk This study showed that one species of fungus may be excluded from a tree stump due to its colonisation by another fungus. The mechanism for this type of interaction may be related to differences in i growth rates of the fungi, leading to physical exclusion of a fungus by another fungus, ii the capacity of the fungi to form enzymes that help to degrade the stump material and releasing nutrients, iii the competitiveness of the fungi in obtaining nutrients released during mineralisation, and iv production of toxic molecules by the fungi.
Interactions between soil organisms in soil: Food-web is a term that encompasses all the feeding relationships between organisms in an ecosystem.
Soil organisms that degrade organic matter are the basis of the soil food-web as they provide all of the energy that flows through the rest of the web and these organisms interact in numerous ways. Soil animals feed on the bacteria and fungi that are involved in decomposition, hence there is a link between the numbers of bacteria and fungi in the soil and the numbers of animals. Different species of mites and nematodes have specific food preferences. For example, some mites eat other mites and collembolans, whereas other mites feed on bacteria or fungi.
Similarly, some nematodes eat bacteria and others eat fungi. Interactions between mycorrhizal fungi and small mammals in an Oregon coniferous forest Although the focus of the above case studies has been on the interactions between soil organisms, interactions also occur between soil organisms and larger organisms.
For example, the dependence of many tree species on mycorrhizal associations illustrates the links that occur between organisms of very different size in an ecosystem. Conversely, small mammals can be important for fungi as a way of dispersing fungal spores formed in underground fruiting structures.
The spores within the sporocarps that are eaten by animals remain undamaged within faecal pellets and are dispersed throughout the forest. Studies of spores in faecal pellets and digestive tracts of small animals allow investigation of the species diversity of the fungi Maser et al. Four species of fungi were found in animals trapped in the forest site and at the edge of the forest, but only two species were present in animals trapped in the burned area.
It is not known whether the animals discriminated by selecting different species of fungi. If there was no feeding discrimination, the study can be used to measure the abundance of sporocarps of fungi in different habitats.
The lower diversity of fungi recorded in the burnt area is probably temporary. How can land management influence interactions between soil organisms?
Soil organisms are commonly divided into five arbitrary groups according to size, the smallest of which are the protists —including bacteriaactinomycetes, and algae. Next are the microfaunawhich are less than microns in length and generally feed upon other microorganisms. The microfauna include single-celled protozoans, some smaller flatworms, nematodes, rotifers, and tardigrades eight-legged invertebrates.
The mesofauna are somewhat larger and are heterogeneousincluding creatures that feed on microorganisms, decaying matter, and living plants.
The category includes nematodes, mites, springtails wingless insects so called for the springing organ which enables them to leapthe insectlike proturans, which feed on fungiand the pauropods.
The fourth group, the macrofaunaare also quite diverse. The most common example is the potworm, a white, segmented worm that feeds on fungi, bacteria, and decaying plant material.
The group also includes slugs, snails, and millipedes, which feed on plants, and centipedes, beetles and their larvae, and the larvae of flies, which feed on other organisms or on decaying matter.
Soil Health - part5
Megafauna constitute the largest soil organisms and include the largest earthwormsperhaps the most important creatures that live in the topsoil. Earthworms pass both soil and organic matter through their guts, in the process aerating the soil, breaking up the litter of organic material on its surface, and moving material vertically from the surface to the subsoil.
This is extremely important to soil fertility, and it develops the structure of the soil as a matrix for plants and other organisms. It has been estimated that earthworms completely turn over the equivalent of all the soil on the planet to a depth one inch 2.
Some vertebrates are also in the megafauna category; these include all sorts of burrowing animals, such as snakes, lizards, gophers, badgers, rabbits, hares, mice, and moles.
One of the most important roles of soil organisms is breaking up the complex substances in decaying plants and animals so that they can be used again by living plants. This involves soil organisms as catalysts in a number of natural cycles, among the most prominent being the carbon, nitrogen, and sulfur cycles.
The carbon cycle begins in plants, which combine carbon dioxide from the atmosphere with water to make plant tissues such as leaves, stems, and fruits.
Animals eat the plants and convert the tissues into animal tissues. The cycle is completed when the animals die and their decaying tissues are eaten by soil organisms, a process that releases carbon dioxide. Proteins are the basic stuff of organic tissues, and nitrogen is an essential element of all proteins.