Soil-plant microcosms

Lichtenstein, E.P., T.T. Liang, and M.K. Koeppe. Effects of Fertilizers, Captafol, and Atrazine on the Fate and Translocation of [ "ClFonofos and [ C]Parathion in a Soil-Plant Microcosm, J. Agric. Food Chem., 30(5) 871-878 (1982). 

Megonigal J. P., Whalen S. C., Tissue D. T., Bovard B. D., Albert D. B., and Allen A. S. (1999) A plant-soil-atmosphere microcosm for tracing radiocarbon from photosynthesis through methanogenesis. Soil Sci. Soc. Am. J. 63, 665-671. 

Microcosms are composed of large chambers, terreria, aquaria, or artificial pools aquatic mesocosms include artificially constructed ponds or streams, while terrestrial mesocosms are large containers filled with soil, plants, and (sometimes) leaf litter. Microcosms and mesocosms typically contain more than one species of test organism, are located outdoors (but may also be located indoors), and often contain sediment and/or vegetation. The rationale is to produce a test system with similarities to the natural environment, but is more controllable. End points examined may include acute toxicity, suble-thal effects, or community/population level effects. 

The soil core microcosm (SCM) is one of the first test vehicles developed for the evaluation of xenobiotics on an agroecosystem with it accompanying plants, soil invertebrates, and microbial processes. Table 4.16 summarizes the basic protocol. 

Organisms were selected based on their tendency to influence the distribution of the chemical between soil, plant, and other organisms, the ease with which they can be maintained in the laboratory and their compatibility. Inputs into the microcosm are summarized in Table 10.2. The development, construction and operation of such a system is quite complex and very expensive. It thus becomes important to review the data generated and to evaluate the extent to which it provides a reasonable representation of the natural environment and whether this information justifies the expense. 

In conclusion, the behavior of the molecular signals can be markedly different in soil with respect to that observed in microcosm experiments involving only the ho.st plant and the infecting microorganism or a mixed microbial population, both without soil particles. Studies are needed to compare the diffusion of molecular signals in the presence of clay and/or humic barriers. 

However, relatively few studies have included growing plants in their experimental systems. In order to mechanistically understand the effects of pine roots on microbial N transformations rates under conditions of N limitation, l-year-old pine seedlings were transplanted into Plexiglas microcosms (121) and grown for 10-12 months. Seedlings were labeled continuously for 5 days with ambient CO concentration (350 iL L ) with a specific activity of 15.8 MBq g C. Then, soils at 0-2 mm (operationally defined as rhizosphere soil) and >5 mm from surface of pine roots (bulk soil) of different morphology and functional type (coarse woody roots of >2 mm diameter fine roots of <2 mm diameter ... 

The simplest system devised comprises a microcosm where seedlings with roots sandwiched between Millipore membranes are in contact with agar containing plant nutrients (25). The shoots can be exposed to CO, and the loss of C into the agar via the roots is then monitored. The design enables the effect of microorganisms on rhizodeposition to be examined easily (26) but really lacks the complexity of substratum to allow data obtained to be related to rhizodeposition in soil. 

Endrin released to water will adsorb to sediments or bioaccumulate in fish and other aquatic organisms. Both bioaccumulation and biomagnification of endrin were reported to occur in an aquatic laboratory microcosm system (Metcalf et al. 1973). In terrestrial ecosystems, endrin transformation products (endrin ketone, endrin aldehyde, and endrin alcohol) have been measured in plants grown on endrin-treated soil (Beall et al. 1972 Nash and Harris 1973). 

Microbial mutagenesis Cytotoxicity Fish acute toxicity Algal bioassay Soil microcosm Plant stress ethylene... 

Two bioassays are employed to evaluate the effect of samples on terrestrial life forms. For gas samples, the plant stress ethylene test is presently recommended. This test is based on the well-known plant response to environmental stress release of elevated levels of ethylene (under normal conditions plants produce low levels of ethylene). The test is designed to expose plants to various levels of gaseous effluents under controlled conditions. The ethylene released during a set time period is then measured by gas chromatography to determine toxicity of the effluent. For liquid and solid samples, a soil microcosm test is employed. The sample is introduced on the surface of a 5 cm diameter by 5 cm deep plug of soil obtained from a representative ecosystem. Evolution of carbon dioxide, transport of calcium, and dissolved oxygen content of the leachate are the primary quantifying parameters. 

Soil microcosms with radish seeds planted on top... 

Ectomycorrhizal plants and non-mycorrhizal control plants have been grown in pots and microcosms by many researchers to investigate the role of EM colonization on dissolution of minerals. In such experiments it is usually not possible to separate effects of the fungus itself and effects of other microorganisms in the soil that might be influenced by the presence of the EM fungus. 

In laboratory microcosms, ira 5-permethrin was selectively degraded compared to the other diastereomer, cw-permethrin, by six bacterial strains [19]. These strains also preferentially biotransformed 15-cw-bifenthrin over their antipodal l/ -cw-enantiomers, which were more toxic to daphnids [19]. Enantioselectivity was more pronounced for cw-permethrin than for cw-bifenthrin, and was strain-dependent. The (—)-enantiomer of both pyrethroids was preferentially depleted in sediments adjacent to a plant nursery, suggesting that in situ microbial biotransformation was enantioselective [20]. Although all enantiomers of permethrin were hydrolyzed quickly in C-labeled experiments in soils and sediments, the degradates of both cis- and irara-permethrin s -enantiomers were mineralized more quickly than those of the 5-enantiomer, while degradation products of cA-permethrin were more persistent than those of the trans-isomex [185]. Enantioslective degradation of fenvalerate in soil slurries has also been reported [83]. These smdies underscore how enantiomer-specific biotransformation can affect pyrethroid environmental residues, the toxicity of which is also enantiomer-dependent [18-20]. 

Bosse U. and Frenzel P. (1997) Activity and distribution of methane-oxidizing bacteria in flooded rice soil microcosms and in rice plants (Oryza sativa). Appl. Environ. Microbiol. 63, 1199-1207. 

Lu Y., Watanabe A., and Kimura M. (2002) Contribution of plant-derived carbon to soil microbial biomass dynamics in a paddy rice microcosm. Biol. Fertility Soils 36, 136-142. 

Terrestrial microcosms also see a comparable range in size and complexity. A microbial community living within the soil in a test tube can be used to examine biodegradation. A soil core is comparable in size and utility to the laboratory microcosms described above. In some cases terrestrial microcosms can be established with a variety of plant cover and include small mammals and insects. Field plots are the terrestrial equivalent of the larger outdoor... 

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