Soil bacteria: A dynamic pool of soil organic matter and catalysts of key belowground processes

Bacteria are key components of the soil ecosystem forming the basis for the soil food web and mediating important biogeochemical reactions. Bacteria a re the most numerous soil organisms in terms of numbers of individuals, but in most wildland ecosystems bacteria comprise a smaller portion of the mic robial biomass than the fungi. The bacterial biomass is a portion of the so il organic matter that has a relatively rapid turnover time and therefore h as the potential for releasing quantitatively important plant available nut rients during turnover (death). The active soil bacteria can be distinguish ed from inactive by their ability to respire and process carbon, but micros copic methods for this differentiation are too labor intensive or expensive for most ecosystem level (field) studies. The active bacteria have an incr edible metabolic diversity and their metabolic types may be classified on t he basis of their sources of energy, carbon and reducing power. The types o f bacterial metabolism present in the soil are dependent on the oxygen stat us (redox potential) in the soil environment. Specific bacterial metabolic products are indicators of anaerobic (oxygen deprived) soil conditions. The presence of active bacteria with a specific metabolic potential combined w ith the appropriate environmental conditions results in the activity of bac teria as catalysts for key soil processes. The chemolithotrophic bacteria a re especially important for their major role in the biogeochemistry of nitr ogen, sulfur and iron.