There are billions to hundreds of billions of soil microorganisms in a mere handful of a typical, garden soil. That single handful might well contain thousands of different species of bacteria (most of whom have yet to be classified), hundreds of different species of fungi and protozoa, dozens of different species of nematodes plus a goodly assortment of various mites and other microarthropods. Almost all of these countless soil organisms are not only beneficial, but essential to the life giving properties of soil.
The work of these soil microorganisms is exceedingly complex and extends into nearly every section of this FAQ. The ways the soil bacteria and fungi break down plant and animals residues and wastes are addressed inSection C, "Composting & Use of Compost". The ways the soil bacteria and fungi breakdown and then convert materials into plant nutrients as well as the ways the soil bacteria, fungi, and amoeba hold these nutrients in place and then make them available to the plants are addressed in Section D, "Plant Nutrition". The ways some of the soil microorganisms assist the plants in their physiology are addressed in Section F, "Botany for the Home Gardener". The ways some of the soil bacteria and SOME of the fungi both cause and control plant disease are addressed in Section G, "Plant & Soil Disease; Treatment and Prevention" and the ways some of the nematodes, some of the soil insects, and some of the various micro-arthropods such as mites attack and/or protect plants are addressed in Section H, "Plant & Soil Pests; Prevention and Treatment". This sub-section is limited to the ways the soil microorganisms impact on the physical, chemical, and bio-chemical properties of soil.
Animals as large as whales and as small as plankton ingest plastics as a matter of course (see image above). Microbes and mussels live on floating plastics. “Cleaning up” these plastics, even if it were technologically possible, would disrupt and destroy the ecosystems we would be trying to save in the first place.Some of these ecosystems are unique and exist only because of ocean plastics.
A new study published in Environmental Science and Technology have dubbed this flotilla of plastic-based ecologies the “Plastisphere.” Using scanning electron microscopy and gene sequencing, the scientists found more than one thousand types of bacterial cells on plastic samples. The tiny plastic pieces they investigated were home to plants, algae, and bacteria, the animals and larger bacteria that feed on them, predators that feed on these, and other organisms that establish synergistic relationships. Some of these complex communities are the size of a head of a pin, matching the scale of their hosting microplastic. The report likens ocean plastics to “artificial microbial reefs” with more and different biodiversity than the surrounding sea water.
What is the soil foodweb? Per gram of healthy soil, which is about a teaspoon of soil plus organic matter, the following organisms are found: of which are mostly unknown to scientists. Bacteria break down easy to-use organic material, and retain the nutrients, like N. P and S. in the soil. About 60% of the carbon in those organic materials are respired as carbon dioxide, but 40% of that carbon is retained as bacterial biomass. The waste products bacteria produce become soil organic matter. This "waste" material is more recalcitrant than the original plant material, but can be used by a large number of other soil organisms, exemplifying the classic statement that "One man's garbage is another's treasure". Productive garden soil should contain more bacteria than any other kind of organism, although care must be taken to make sure beneficial bacteria, instead of disease-causing bacteria, are most prevalent.- S to 60 000 meters of fungal hyphae. Fungi break down the more recalcitrant, or difficult-to-decompose, organic matter, and retain those nutrients in the soil as fungal biomass. Just like bacteria, fungal waste products become soil organic matter, and these waste materials are used by other organisms. Gardens require some fungal biomass for greatest productivity, but in order for best crop growth, there should be an equal biomass of bacteria as compared to fungi. Most grasslands or pastures have less fungi than bacterial, while all conifer forests have much more fungal, as compared to bacterial, biomass. As with bacteria, some fungi cause disease and the soil must be managed to prevent these fungi from being a problem.
-100 to 100,000 protozoa. These organisms are one-celled, highly mobile organisms that feed on bacteria and on each other. Because protozoa require 5 to 10-fold less nitrogen than bacteria, N is released when a protozoan eats a bacterium. That released N is then available for plants to take up. Between 40 and 80% of the N in plants can come from the predator-prey interaction of protozoa with bacteria.
- 5 to 500 beneficial nematodes. Beneficial nematodes eat bacteria, fungi, and other nematodes. Nematodes need even less nitrogen than protozoa, between 10 and 100 times less than a bacterium contains, or between 5 and 50 times less than a fungal hyphae contains. Thus when bacterial- or fungal-feeding nematodes eat bacteria or fungi, nitrogen is released, making that N available for plant growth. However, plant-feeding nematode are pests because they eat plant roots. These "bad" nematodes can be controlled bacteria, fungi, and other nematodes. Nematodes need even less nitrogen than protozoa, between 10 and 100 times less than a bacterium contains, or between 5 and 50 times less than a fungal hyphae contains. Thus when bacterial- or fungal-feeding nematodes eat bacteria or fungi, nitrogen is released, making that N available for plant growth. However, plant-feeding nematode are pests because they eat plant roots. These "bad" nematodes can be controlled biologically, as they are in natural systems, by fungi that trap nematodes, by having fungi that colonize root systems and prevent nematode attack of roots, or by predation of nematodes by arthropods. In cases of extreme outbreaks, however, the only answer may be the use chemicals to control these plant-feeding nematodes. However, once a chemical is used which kills the beneficial nematodes as well as the plant-feeding ones, the beneficial nematodes need to be replaced through inoculation.
- A few to several hundred thousand microarthropods. These organisms have several functions. They chew the plant leaf material, roots, stems and boles of trees into smaller pieces, making it easier for bacteria and fungi to find the food they like on the newly revealed surfaces. The "comminuting" arthropods can increase decomposition rates by 2- to 100- times, although if the bacteria or fungi are lacking, increased decomposition will not occur. In many cases, however, the arthropods carry around an inoculum of bacteria and fungi, making certain the food they want is inoculated onto the newly exposed surfaces! Arthropods then feed on bacteria and fungi, and because the C:N ratio of arthropods is 100 times greater than the bacteria and fungi, they release nitrogen which then is available for plant growth. Some arthropods eat pest insects, while others eat roots. Again, it's important to encourage the beneficial ones and discourage the ones that eat plants!
Just a few millimetres across, Daphnia pulex is the first crustacean to have its genome sequenced. With 30,907 genes, it has more than any other species sequenced so far, including nearly 5000 more than humans.
Many of the genes are newly evolved to help the water fleas survive climatic changes and exposure to pollutants.
The nature of the process of species formation has been the subject of debate since before the time of Darwin. Allopatric speciation through geographical separation is by now reasonably well understood, but the prevalence and mechanics of sympatric speciation are still a matter of debate . Underlying this dilemma is the perhaps even more fundamental question of precisely what constitutes a species. For prokaryotic organisms, it is accepted that complications such as horizontal gene transfer pose a significant challenge to the traditional understanding . Even in metazoa, the picture is not completely clear: the extreme biodiversity of meiofaunal organisms makes it difficult to distinguish between inter- and intraspecific genetic differences.
Welcome to Lens on Leeuwenhoek -- the life, times, and accomplishments of Antony van Leeuwenhoek, who lived during the Dutch Golden Age and discovered the microscopic world of protozoa and bacteria with tiny hand-made lenses.
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