Microbial activity metabolism

In basic soils mepiquat chloride is nonpersistent and is rapidly degraded. There is a half-life of two years in other soil types, but 86—93% is metabolized within 30 days (10). Breakdown does not appear to be a function of microbial activity. 

There has been considerable interest in the use of plants for bioremediation and this merits a rather extensive discussion. Plants can play an important role in bioremediation for several reasons (1) they can transport contaminants from the soil, (2) they can metabolize the contaminants after uptake, or (3) they can produce exudes that support microbial activity for degradation of the contaminants. In addition, bacteria can produce metabolites that counter the effect of toxins produced by fungi, and serve as biocontrol agents that diminish the need for the application of agrochemicals. Plant exudates play an important role in supporting the growth and activity of bacteria that carry out the degradation of contaminants in the rhizosphere and rhizoplane (the external surface of roots... 

Soil microorganisms produce many compounds that are potentially toxic to higher plants. Examples include members of the following antibiotics (1-6), fatty and phenolic acids (7-12), amino compounds (13-15), and trichothecenes (16, 17). "Soil sickness" and "replant problems" have been reported where certain crops or their residues interfere with establishment of a subsequent crop (18, 19). Toxins resulting from microbial activity sometimes are involved, but it is often unclear whether these are synthesized de novo in microbial metabolism or are breakdown products of the litter itself (20). 

These have been ascribed to seasonal variability in organic inputs through rhizodeposition, microbial death and residue inputs and/or seasonal variability in soil microbial activity and thus metabolism of the... 

Zelles L, Bai QY, Ma RX, Rackwitz R, Winter K, Beese F (1994) Microbial biomass, metabolic activity and nutritional status determined from fatty acid patterns and poly-hydroxtbutyrate in agriculturally-managed soils. Soil Biol Biochem 26 439 446... 

Microbial activity requires energy, and all microorganisms generate energy. This energy is subsequently stored as adenosine triphosphate (ATP), which can then be utilized for growth and metabolism as needed, subject to the second law of thermodynamics [2,23,35,41,42,51,54]. 

Biological activity is an important indicator of the decomposition of soil organic matter within the soil. High biological activity promotes metabolism between soil and plants and is an essential part of sustainable plant production and fertiliser management. Earthworms, as a key species for soil macro-fauna, are an appropriate indicator of soil s biological activities due to their sensitivity to any kind of soil disturbance. Microbial activity of soils is an indicator of soil micro-fauna. Both indicators are reviewed below. 

Evidence is accumulating that DOM composition selects specific taxa (see Chapters 9 and 14). Models show that the relative input rates of labile and humic DOM can determine which guilds of bacteria dominate community metabolism (see Chapter 18). Because there may be multiple input sources, varying in magnitude and composition, each community represents a solution to a cacophony of selective pressures. Source heterogeneity in terms of DOM composition or timing probably contributes to greater active diversity, unless response is limited by other environmental factors (e.g., low temperature or low pH). From this perspective, ambient DOM concentration and composition are products of the interaction between input sources and community activity. This conception makes clear the limitations of attempts to model microbial activity in terms of static analyses of DOM abundance or composition. 

---