Soil microbiota

How changes in. soil microbiota affect the root exudation... 

Ricci MS, De Almeida DL, Ribeiro RD, Aquino AM, Pereira JC, Polli D, Reis VM, Eklund CR (2000) Cyperus rotundus control by solarization. Biol Agric Hort 17 151-157 Rieger M, Krewer G, Lewis P (2001) Solarization and chemical alternatives to methyl bromide for preplant soil treatment of strawberries. HortTechnology 11 258-264 Ristaino JB, Perry KB, Lumsden RD (1991) Effect of soil solarization and Gliocladium virens on sclerotia of Sclerotium rolfsii, soil microbiota, and the incidence of southern blight in tomato. Phytopathology 81 1117-1124... 

Jjemba P.K. (2002b). The effect of chloroquine, quinacrine, and metronidazole on both soybean Glycine max) plants and soil microbiota. Chemosphere 46 1019-1025. 

As said above, plant root chemistry may also influence deeply alpine soil microorganism s biomass. It turns out that the particular chemical composition of exudates is a strong selective force in favour of bacteria that can catabolize particular compounds. Plants support heterotrophic microorganisms by way of rhizodeposition of root exudates and litter from dead tissue that include phenolic acids, flavonoids, terpenoids, carbohydrates, hydroxamic acids, aminoacids, denatured protein from dying root cells, CO2, and ethylene (Wardle, 1992). In certain plants, as much as 20-30% of fixed carbon may be lost as rhizodeposition (Lynch and Whipps, 1990). Most of these compounds enter the soil nutrient cycle by way of the soil microbiota, giving rise to competition between the myriad species living there, from microarthropods and nematodes to mycorrhiza and bacteria, for these resources (e.g. Hoover and Crossley, 1995). There is evidence that root phenolic exudates are metabolized preferentially by some soil microbes, while the same compounds are toxic to others. Phenolic acids usually occur in small concentration in soil chiefly because of soil metabolism while adsorption in clay and other soil particles plays a minor role (Bliun et al., 1999). However, their phytotoxicity is compounded by synergism between particular mixtures (Blum, 1996). 

The proteome of soil microbiota has been elucidated recently using 2D gel and spectrometry at the University of California. These investigators have examined the community of soil microorganisms in a biofilm from a mine. They have identified about 1200 proteins one important protein identified among them is a novel cytochrome that is responsible for the oxidation of iron and for the formation of the biofilm itself. The metapro-teomics of microbial communities involved in the bioremediation of soil and water, particularly those in ground and estuaries, are difficult. 

Contents indude contaminant vapors, adherence of Squids to "Water-dry" and "Water-wet" soil particles, contaminants in pore spaces, floating contaminants, dissolved contaminants, contaminants sorbed onto colloidal particles, diffusion into mineral grains or rock, contaminants sorbed onto or into soil microbiota, and fractured or karstic limestone. 

Data on arsenic effects to soil biota and insects are limited. In general, soil microorganisms are capable of tolerating and metabolizing relatively high concentrations of arsenic. This adaptation seems usually to be due to decreased permeability of the microorganism to arsenic. Tolerant soil microbiota can withstand concentrations up to 1600.0 mg/kg however, growth and metabolism were reduced in sensitive species at 375.0 mg As/kg and, at 150.0-160.0 mg As/kg, soils were devoid of earthworms and showed diminished quantities... 

Mycological analysis of the ions concentration effect was performed on the following test cultures in the complex soil microbiota ... 

Activation of the soil microbiota leads to rapid cascades of decomposition of below- and aboveground litter produced during the previous growing season, and active fluxes of gases derived from soil respiration (CO2, NO, NjO) (Matson and Vitousek, 1995). In these processes significant amounts of nutrients are released which can be leached or taken up by newly formed fine roots. Much research is still required to understand the synchronization of events related to water supply, particularly processes of decomposition and release of nutrients and trace gas fluxes. 

---