Soils biotic

Soil microorganisms (fungi, bacteria and actinomycetes) play a major role in the degradation of organic matter, ultimately releasing nutrient elements— about 98% nitrogen, 5-60% phosphorus and 10-80% sulphur to the soil nutrient pool—along with micronutrients such as boron and molybdenum, into the soil for reuse by plants and animals. The role of biotic soils as sources of N and CH4... 

This chemistry has been investigated and implemented for wastewater minerahza-tion by oxidizing the organic pollutants. The process is very efficient, not selective and, as a consequence, almost all carbon matter can be removed. Topical areas also include soil and aquifer treatments, sometimes in combination with a secondary biotic process [145]. 

Mercury (Hg) contamination is widespread in water, in surficial soils and sediments, and in the tissues of plants and animals in ecosystems around the globe. Once deposited to terrestrial and aquatic ecosystems, some inoiganic mercury is transformed into methylmercury (MeHg), a highly toxic compoimd that bioaccumulates efficiently in food webs (Wiener et al. 2003). As a result of the toxicity of MeHg to wildlife and humans, many nations are interested in reducing environmental mercury contamination and associated biotic exposure (UNEP 2002). 

Plant survival and crop productivity are strictly dependent on the capability of plants to adapt to different environments. This adaptation is the result of the interaction among roots and biotic and abiotic components of soil. Processes at the basis of the root-soil interaction concern a very limited area surrounding the root tissue. In this particular environment, exchanges of energy, nutrients, and molecular signals take place, rendering the chemistry, biochemistry, and biology of this environment different from the bulk soil. 

In addition to the interactions between plants and microorganisms, a third factor, the soil, also plays a role in determining root exudation and the activity and diversity of rhizosphere microbial populations. In this section, physical and structural aspects of the soil are discussed in relation to their effects on root exudation and microbial populations. Consideration is also given to the role of agricultural management practices on rhizosphere processes. In addition, the role of other biotic factors, such as microfaunal predation, is discussed in relation to nutrient cycling in the rhizosphere. 

The time of year in which a pesticide is applied significantly affects its dissipation rate due to temperature, moisture, and solar-irradiance effects on abiotic and biotic dissipation processes. For example, dissipation rates for agrochemical applications made in the springtime are normally greater than those observed for fall (autumn) applications. Thus, the timing of agrochemical applications made in field soil dissipation studies should closely match those occurring under acmal-use conditions. 

Biotic Transport Biotic transport can be defined as the actions of plants and animals that result in the transport of a radioactive material or other substance from a waste site to locations where it can enter pathways that may result in exposure to humans. Small mammals are ubiquitous and inhabit areas containing radioactive contamination or radioactive waste sites. Mammals inhabiting these areas may become contaminated with americium by consuming contaminated soil or plants and disturb americium-contaminated soil through their burrowing and excavating activities. These animals may therefore affect the distribution of americium within the waste site or transport americium to previously uncontaminated areas. In addition, small mammals may be consumed by animals higher in the food chain such as hawks and coyotes, which would add to the dispersal of americium from disposal areas. However, results of... 

Actinomycetes are typically most abundant in well drained, circumneu-tral to alkaline soils having abundant organic matter. Water-logging and low pH may reduce populations (37, 38). The numbers of actinomy-cetous organisms isolated from the various soil samples in our study follow this pattern. No clear trend emerged as to a particular edaphic or biotic factor causing an increase in the proportion of inhibitory isolates in a soil sample. 

To which phase is the substance likely to migrate will a pesticide applied to soil leach or be volatile will a chemical accumulate in the biotic compartment and so on. 

The ammonium dynamics showed that the initial concentrations of N were reduced after the first 3 days, and after that, a release of the mineral occurred from day 3 up to day 14. Later still, the concentration of ammonium decreased by up to < 14 mg N kg 1 dry soil for all the treatments in both the Otumba and Texcoco soils, and the ammonium concentration decreased by up to < 2 mg N kg 1 dry soil for all treatments, except for the soil treated with sterilized sludge, < 31 mg N kg 1 dry soil. The contour of the ammonium dynamics was similar in both the Otumba and Texcoco soils. Many abiotic and biotic processes might affect the concentration of NH4+ in soil, such as NH4+ fixation in the soil matrix, volatilisation of NH3, and immobilization or oxidation of NH4+. Some soil processes were occurring at too low a level to be detectable, such as NH4+ fixation and the volatilisation of NH3. The nitrate dynamics were similar in both soils. The concentration of N03 was 120 mg N kg 1 dry soil in the control treatment in both soils. The ammonium concentration was similar in both soils, > 200 mg N kg 1 dry soil, treatments with sludge reached > 255 mg N kg 1 dry soil and > 300 mg N kg 1 dry soil in the Texcoco and Otumba soils respectively, and soils treated with sterilized sludge increased the concentration... 

The most important and most particular biological activity is that by microorganisms which concentrate by preference on surface stones and rocks, where they are called lithophytes. The number of these micro-biota in various deserts throughout the world is in the order of 103 to 106 per gram of soil, and in the Sahara alone French microbiologists have described more than 45 types of cyanophyceae, 70 chlorophyceae, 90 lichens and more than 300 diatoms. Hence, deserts cannot be considered an a-biotic environment. 

Saprophytic, dark pigmented fungi such as Alternaria spp. can infect a wide range of plant species, especially tissues that are exposed to other biotic or abiotic stressors and older and senescing plant tissues. Also, wet weather conditions favour attack by Alternaria spp. Inoculum of Alternaria and potentially production of altemariol is further enhanced when cereal straw and stubble is left on the soil surface and not sufficiently incorporated into the soil after harvest (direct seeding and minimum tillage systems). 

The discovery of homochirality on a planet such as Mars could be an excellent biomarker and strengthen the argument for life on Mars. With an EE in the solar nebula there should be an EE on the surface of Mars of order 9 per cent but remains of ancient life on Mars would show a greater excess. The interchange of enantiomers occurs naturally in a process called racemisation and for the most labile amino acid, aspartic acid, the half-life for the racemisation is 800 years at 300 K in 800 years, half of the non-biotic aspartic acid would racemise and the EE would go to zero. In dry conditions, however, the half-life is much longer, perhaps as large as 5 x 104 years at 300 K. Extrapolation of the racemisation rate to 215 K, the equatorial temperature of Mars, extends the half-life further to 3 x 1012 years and to 1027 years at 150 K, Martian polar temperatures. Hence, discovery of a considerable EE in the Martian soil would be a strong indicator of ancient Martian life. 

Ferrara, R., B.E. Maserti, and R. Breder. 1991. Mercury in abiotic and biotic compartments of an area affected by a geochemical anomaly (Mt. Amiata, Italy). Water Air Soil Pollut. 56 219-233. 

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