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Living Soils: The Role of Microorganisms in Soil Health
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Soil viruses are of great importance, as they may influence the ecology of soil biological communities through both an ability to transfer genes from host to host and as a potential cause of microbial mortality.

Consequently, viruses are major players in global cycles, influencing the turnover and concentration of nutrients and gases. Despite this importance, the subject of soil virology is understudied. To explore the role of the viruses in plant health and soil quality, studies are being conducted into virus diversity and abundance in different geographic areas ecosystems.

It has been found that viruses are highly abundant in all the areas studied so far, even in circumstances where bacterial populations differ significantly in the same environments. Soils probably harbour many novel viral species that, together, may represent a large reservoir of genetic diversity.

Some researchers believe that investigating this largely unexplored diversity of soil viruses has the potential to transform our understanding of the role of viruses in global ecosystem processes and the evolution of microbial life itself. Not microorganisms strictly speaking , nematode worms are typically 50 microns in diameter and one millimetre in length.

Species responsible for plant diseases have received much attention, but far less is known about much of the nematode community, which play beneficial roles in soil. An incredible variety of nematodes have been found to function at several levels of the soil food web. Some feed on the plants and algae the first level , others are grazers that feed on bacteria and fungi second level , and some feed on other nematodes higher levels.

Free-living nematodes can be divided into four broad groups based on their diet. Fungal-feeders feed by puncturing the cell walls of fungi and sucking out the internal contents.

Predatory nematodes eat all types of nematodes and protozoa. Like protozoa, nematodes are important in mineralising, or releasing, nutrients in plant-available forms. When nematodes eat bacteria or fungi, ammonium is released because bacteria and fungi contain much more nitrogen than the nematodes require. Nematodes may also be useful indicators of soil quality because of their tremendous diversity and their participation in many functions at different levels of the soil food web.

Collectively, soil microorganisms play an essential role in decomposing organic matter, cycling nutrients and fertilising the soil. Without the cycling of elements, the continuation of life on Earth would be impossible, since essential nutrients would rapidly be taken up by organisms and locked in a form that cannot be used by others. The reactions involved in elemental cycling are often chemical in nature, but biochemical reactions, those facilitated by organisms, also play an important part in the cycling of elements.

Soil microbes are of prime importance in this process. Soil microbes are also important for the development of healthy soil structure. Soil microbes produce lots of gummy substances polysaccharides and mucilage, for example that help to cement soil aggregates.

This cement makes aggregates less likely to crumble when exposed to water. Fungal filaments also stabilise soil structure because these threadlike structures branch out throughout the soil, literally surrounding particles and aggregates like a hairnet.

It must be stressed that microbes generally exert little influence on changing the actual physical structure of the soil; that is performed by larger organisms. Soil microorganisms are both components and producers of soil organic carbon, a substance that locks carbon into the soil for long periods. Abundant soil organic carbon improves soil fertility and water-retaining capacity. There is a growing body of research that supports the hypothesis that soil microorganisms, and fungi in particular, can be harnessed to draw carbon out of the atmosphere and sequester it in the soil.

Soil microorganisms may provide a significant means of reducing atmospheric greenhouse gasses and help to limit the impact of greenhouse gas-induced climate change.

We can see that healthy soils contain enormous numbers of microbes and substantial quantities of microbial biomass. The potential for activity must be stressed because, under normal situations, the microbial population does not receive a constant supply of readily-available substrates to sustain prolonged high rates of growth.

Almost all soil organisms except some bacteria need the same things that we need to live: They eat a carbon-based food source, which provides all their nutrients, including nitrogen and phosphorus. They require a moist habitat, with access to oxygen in the air spaces in soil.

These reasons explain why 75 per cent of soil organisms are found in the top five centimetres of soil. It also explains, however, why many of our agricultural soil microorganism populations are depleted.

Unfortunately, some of the agricultural practices that were standard in Australia up until the s, such as excessive land clearance, the burning of stubble, inappropriate fertiliser application and over-tillage, have degraded soils and produced conditions such as salinity, acidification, soil structural decline and desertification.

While in many areas, our agricultural soils are still considered to be under threat, in recent decades, changes to the farming practices detailed above are helping to create healthier soils. Until recently, this was considered the only way to improve biological fertility. Creating the right conditions and microbes will come and, alternatively, if the conditions are not correct, efforts to introduce beneficial microbes are doomed to fail. Recently, however, scientific research has achieved significant success in the inoculation of soils and seeds with beneficial bacterial and, in particular, mycorrhizal fungi to improve yields and to promote healthier soils.

While still in an early stage of development, field trials have been positive and may, in the future, lead to a wide range of benefits based upon improved soil biological fertility.

In the past, soil microbiological science has focussed upon the harmful or pathogenic threat posed by a small number of soil-dwelling microorganisms. This is has skewed our understanding away from most of soil microorganisms that pose no threat to human health or to agricultural production and that perform essential roles in mechanisms that are fundamentally important to the sustainability of human civilisation and life on the planet generally.

This emphasis, however, is changing. Rose Corinne Graham-Maar, M. Andrew Grossman Philadelphia PA Claudia Gruss CT , Gastroenterology http: Tupelo MS , Gastroenterology http: Hamden CT , Gastroenterology http: Hirotsugu Imaeda , Gastroenterology http: Strongsville OH Louis Children's Hospital http: Mark Henry Kasowitz, M. Luke's Medical Center https: Nicholas Kennedy , Gastroenterology http: Houssam Al Kharrat, M.

Lubbock TX , Gastroenterology http: Littleton CO Barbara S Kirschner, M. Troy MI Boys Town NE Jonathan Landy , Gastroenterology http: San Diego CA , Gastroenterology http: Morristown NJ Jimmy Limdi , Gastroenterology http: Stony Brook NY , Research http: John hospital Pediatric Gastroenterology https: Downey CA , Gastroenterology http: Cleveland OH , Gastroenterology http: Vineland NJ , Gastroenterology http: Wilmington DE Berman, MD Building, 5th Floor Minneapolis MN Orange CA Darnall Army Medical Center http: Worcester MA , Gastroenterology http: Robert Hal Pittman, M.

Glen Loy Portwood, M. We used DisMod-MR 2. For some causes, we used alternative modelling strategies if incidence or prevalence needed to be derived from other data. YLDs were estimated as the product of prevalence and a disability weight for all mutually exclusive sequelae, corrected for comorbidity and aggregated to cause level. We updated the Socio-demographic Index SDI , a summary indicator of income per capita, years of schooling, and total fertility rate.

Despite mostly stagnant age-standardised rates, the absolute number of YLDs from non-communicable diseases has been growing rapidly across all SDI quintiles, partly because of population growth, but also the ageing of populations.

The largest absolute increases in total numbers of YLDs globally were between the ages of 40 and 69 years. Iron-deficiency anaemia, migraine, Alzheimer's disease and other dementias, major depressive disorder, anxiety, and all musculoskeletal disorders apart from gout were the main conditions contributing to higher YLD rates in women.

Men had higher age-standardised rates of substance use disorders, diabetes, cardiovascular diseases, cancers, and all injuries apart from sexual violence.

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