Soil ecosystem

Estimates of the diversity of DNA-based soil organisms so far have not been able to answer the questions concerning the functions of soil ecosystem, although, they can serve as an efficient tool for explaining DNA diversity in situ. The presence of a certain microbial gene does not assure that the metabolic process, for which the gene is responsibile, is carried out. The challenge for molecular techniques is to provide quantitative measures for microbial cells and activities rather than Just qualitative measures. To this purpose, DNA-based techniques... 

Handbook of Photosynthesis, edited by Mohammad Pessarakli Chemical and Isotopic Groundwater Hydrology The Applied Approach, Second Edition, Revised and Expanded, Emanuel Mazor Fauna in Soil Ecosystems Recycling Processes, Nutrient Fluxes, and Agricultural Production, edited by Gero Benckiser Soil and Plant Analysis in Sustainable Agriculture and Environment, edited by Teresa Hood and J. Benton Jones, Jr. 

By sharply decreasing biodiversity in the soil ecosystem, pesticides negatively affect all soil organisms on which soil productivity depends. Pesticides affect the biological activity in soil, especially through long-term use and accumulation (or accumulation of their residues). 

Zietz, E., K. Dumpert, and J. Rombke. 1987. Effects of pentachlorophenol and 2,4,5-trichlorophenol on a soil ecosystem. I. Application and residue analysis. Sci. Total Environ. 61 153-165. 

Biotic control over the functioning of soil ecosystems also follows the model described by Chapin et al. (1997) for universal ecosystem. Types of soil biota and their composition are likely to alter soil ecosystem processes through changes in the functional traits (Fig. 10.1). It can alter ecosystem processes, such as phosphorous transformation and availability by plants, which in turn modifies community... 

Fig. 10.1 Model representing components of soil ecosystem processes (Modified from Chapin et al. 1997). It depicts biotic control over the functioning of soil ecosystem. Biotic introductions, land use and atmospheric compositions influences species composition and diversity, which controls the biotic functional traits and ecosystem processes... 

Table 1. The values of biogeochemical cycling (C ), active temperature (Ct) and relative biogeochemival (Ct,r) coefficients in various soil-ecosystem geographical regions of the World (Bashkin and Kozlov, 1999). 

Table 3. The ranges attached to biogeochemical cycling data to assess the migration capacity of soil-ecosystem types.

Bossert, I., and Bartha, R., 1984, The Fate of Petroleum In Soil Ecosystems Petroleum Microbiology (edited by R. M. Atlas), Macmillan Co., New York. 

With maximal densities of 53,000 individuals/m2, springtails (Collembola) are exceedingly abundant and are among the most important consumers in many soil ecosystems. Springtails also represent important and readily avail-... 

Fig. 8.41 Simulated Chernobyl Cs+ distribution in the soil ecosystem (A) in leaf pads and (B) in soil columns when the microbial decomposition of the organic material is enhanced by an increase in ambient temperature. (Tengen et al. 1991)...

The C02 flux at the atmosphere vegetation cover boundary is determined in many respects by the soil processes involved in organic matter transformation. To better understand the biotic and abiotic mechanisms that control C02 emission from the soil, Jassal et al. (2005) compared measured C02 fluxes in a forest with their distribution profile in the soil of a 54-year-old coniferous forest on the eastern coast of Vancouver. It was established that C02 concentration grows at all depths of the soil layer with rising temperature and humidity. This is explained by soil diffusion reduction and changes in soil ecosystem functioning. It was noted that more than 75% of C02 emitted from the soil was generated at a depth of 20 cm, and almost total C02 flux forms from the 0 cm-50 cm layer. 

Standards that are derived using SSDs for the soil ecosystem can in some cases be validated in the held. The overview by Posthuma et al. (2002) reported on some validation studies in which it was shown that the HC5 was lower than the no-effect concentration of studied ecosystems (i.e., in mesocosm or held conditions). An array of further studies has been published since that time. However, held studies are often difhcult to interpret in terms of dose-response relationships. This difficulty in interpreting held data is sometimes due to soil heterogeneity and a highly variable soil ecosystem. Nevertheless, held soils are relevant test systems and represent a more realistic environment. Although causality may be difhcult to assess, the use of pragmatic methods, derived from an expert judgment process, can improve the overall accuracy of standards. 

Knowledge on the functioning of soil ecosystems is to a large extent lacking, and SQSs are for that reason derived using many assumptions. Therefore, there is an urgent need for more systematic validation of SQSs. 

Soil Quality Standards are developed for different purposes (e.g., different land uses and different protection goals) since soils are variable by nature and have various uses and functions that may influence the protection goals. Nevertheless, a minimum level of protection or a base level is needed to guarantee resilience of the soil ecosystem, and this should be incorporated into all approaches to soil standards. Standards can be derived that indicate the presence or absence of certain data. 

Acidification Release of oxides of sulfur and nitrogen (SOx, NOx) Chemical oxidation and deposition of acid compounds Acidic precipitation and lowering of pH in lakes and soils Ecosystem changes and plant/animal death Acidification Potential (AP)... 

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