Chemistry Reference
In-Depth Information
One of the best documented spatial patterns of nutrient distributions in arid and semiarid
ecosystems are the "islands of fertility" associated with shrubs and trees [88].
The components of rhizosphere system which include microorganisms, plant and soil
interact with each other in a way so that the rhizosphere is distinguished from the bulk of
the remaining soil. The activity of root microorganisms is affected by soil environmental
factors or by environmental factors operating indirectly through the plant. Moreover, root
microorganisms can affect the plant and plant nutrient uptake, directly by colonizing the
root and modifying the soil environment around the root. Bacterial growth is stimulated by
a vast range of organic materials released from plant roots, which include carbohydrates,
vitamins, amino acids and enzymes. Organic acids and lipids reduce the pH of the
rhizosphere and also have a role in the chelation of metals [89]. However, direct benefit to
the plant growth is not easy to demonstrate but the activities essential to plant growth,
including mineralization and nitrogen fixation by free-living bacteria are concentrated in
the rhizosphere. Miscellaneous compounds including volatile substances can physiologically
stimulate or inhibit organisms. There are many factors affecting the release of organic
compounds include plant species and cultivars, age and stage of plant development, light
intensity and temperatures, soil factors, plant nutrients, plant injury, and soil microorganisms.
Factors such as light, moisture, and temperature can all cause changes in plant metabolism and
the rhizosphere effect. In summary, rhizosphere populations are dependent on many diverse
interacting factors. In heavy textured soils oxygen become limiting, resulting in reduced
rhizosphere populations compared to the coarse-textured soils.
5. Microorganisms and the outstanding problems
Modern and innovative approaches to solve the problems facing mankind of health,
economy and food security rely mainly on living organisms that can be grown and breed
easily in the lab. Great achievements in the biotechnology have been accomplished using
microorganisms like bacteria, fungi and viruses. For example,
Rhizobium
has been used as
bio-fertilizer, mycorhizae were used to promote the plant growth by uptake minerals from
soil,
Bacillus thuringiensis
is to control the pest, Ti plasmid of
Agrobacterium
in genetic
engineering and the field is opined for more molecules and compounds (proteins, enzymes,
UV-absorbents, etc) extracted from those microorganisms that are adapted to survive the
hostile environmental in the Gulf region. Also, in Qatar there have been a large number of
bacteria strains that have been isolated from soils and being tested against different
pathogens affecting economic plants (data not published). Such approach might be a good
alternative to the classic one of using chemicals.
B. thuringiensis
strains are aerobic, Gram-
positive found broadly distributed in the Qatari soil; produce a protein that has been used to
control insect population. Another challenge to make clean environment in Qatar,
bioremediation is being tested in Qatar to degrade and remove contaminants from
wastewater and soil. Bioremediation processes rely mainly on the activity of those
microorganisms to get rid of organic pollutants including polycyclic aromatic hydrocarbons
(PAHs). This topic will be discussed latter with phytoremediation of contaminated soils and
waters. In Qatar, information about the organic degrading bacteria from soil are scarce.
