The Biology Of Soil Health 2

A "microbiome" is simply a population of organisms in a given environment (in this case, the rhizosphere, or root zone). There is growing evidence that plants release exudates designed specifically to attract and grow certain types of microbes, so as to create a distinctive microbiome. The purpose of this is to have a population of microbes nearby that will help the plant prevent or fight diseases and pests, optimize nutrition, and generally support plant health. This has a parallel in human (and animal) health, where medical scientists are growing more and more interested in the potential of the human gut microbiome to prevent and cure disease.

As mutualists, mycorrhizal fungi cannot survive without a "host", which comes in the form of a plant "root". They form an attachment with the root through which they exchange water and nutrients in return for carbon-rich substances (photosynthate).

As a class of organism, this is true. Nematodes are specialized, however, and some types eat bacteria, others eat fungi, some are predators that eat other nematodes, and some feed on plant roots.

Photosynthesis is the fundamental process of converting the sun's energy into biochemical energy, in the form of sugars. Plants (and a few other organisms, such as algae and some microorganisms) are able to use the sun's energy to break down carbon dioxide from the atmosphere (CO2) and water (H2O) and to use the carbon and hydrogen this liberates to synthesize sugars, which then become the building blocks for many organic compounds. Living organisms use the energy embodied in these organic molecules to drive their metabolisms.

The word comes from the Greek word for root - "rhizo" and the Old English word "sphere", which originally meant "globe" but has come to mean "area" or "region".

Biological glues are produced by several organisms, including bacteria, fungi, and earthworms. These glues are the substances that allow particles of sand, silt, clay or organic matter to stick together in clumps. These clumps are a key factor in soil aggregation. Frequent ploughing breaks up aggregates and adds oxygen to the soil, promoting high populations of decomposer microbes that can consume the glues and destroy the aggregates. High moisture or fertility levels can affect aggregation over time, but unless these factors are extreme, they are not key to the process of aggregate formation.

All of the organisms listed among the potential answers above are eukaryotes. This means that the cells of their bodies have nuclei and a higher level of organization than do prokaryotes (bacteria and archaea). However, the only organisms in this group that are ALWAYS single-celled are the protozoa. Nenatodes and earthworms are always multi-celled and fungi can be single-celled (e.g., yeast) but are usually multi-celled.

Protozoans in soil generally eat bacteria, although they may also eat other (smaller) protozoa, soluble organic matter, and occasionally fungi.

Fungi are eukaryotes, which means that their cells have nuclei and a high level of organization. Prokaryotes (bacteria, archaea) are single-celled organisms with no nuclei and little internal organization. Animalia is a kingdom (animals) within the domain of Eukaryota.

One millionth of a metre is a ten-thousandth of a centimetre, or one thousandth of a millimetre.

The word "micro" on the front of "Microarthropods" just means "very small" (less than 2 millimeters) and NOT microscopic. Amost all soil arthropods are visible to the naked eye, even though microarthropods like mites and springtails are very tiny.

Although scientists believe that soils have lost a lot of organic matter over the past 10,000-15,000 years, due to agricultural practices such as clearing the land and ploughing, they still hold more carbon than the atmosphere and the biosphere (the sum of all living things) combined. Because they have lost so much carbon, many people think that they can become an important "sink" (storage area) for carbon in the future, thus helping in the fight against climate change. Soil organisms play an important role in carbon sequestration. They do release carbon back into the atmosphere as CO2 (they "breathe" just as we do), butb they also help to hold carbon in the soil through their work in forming soil aggregates, which can trap carbon and protect it from fast release. Carbon builds in soils if it is released more slowly than it is absorbed, and the best management practices associated with soil health either increase carbon intake, slow its release, or both.

It used to be thought that the carbon sequestered in soil came almost entirely from crop residues. While it is true that these residues do boost carbon sequestration, the latest thinking is that much of the carbon sequestered actually comes from plant roots -- either as exudates (carbon-rich substances released into the soil by plant roots for a variety of purposes) or as root residues.

Turning the soil is actually the opposite of a main soil-health principal -- "minimize soil disturbance". Turning the soil has immediate benefits, including increased nutrient availability, weed suppression, and looser soil for planting. However, over the longer term, turning the soil promotes soil compaction and is detrimental to some of the soil food web organisms, especially fungi. The latter are key to longer-term aggregate formation and stability, as well as higher levels of soil organic matter.

The three categories are "decomposfrers", "mutualists", and "parasites/pathogens". Decomposers get their energy from consuming dead organic materials; mutualists get their energy through excahnges with living organisms; parasites get their energy from attacking living organisms.