plant surface microbiology.pdf

Population 1
Population 2
Population 3
Population 4
Population 5
cycles (Fig. 2). An example is the cellulolytic functional group; if the soil suspension
is inoculated in Petri dishes with selective culture media for cellulolytic
microorganisms, where cellulose is the only carbon source, and the
culture is incubated at 28 °C for 3 days, some colonies will form halos around
the colonies after staining with Congo red. If we count the different organisms
by decreasing order of numbers, we can observe colonies forming units
of fungi, actinomycetes and then bacteria. Many species will be observed
within the fungi group, as will also occur with actinomycetes and bacteria
populations.
The number of colony forming units (CFU) and the ratio between colony
size and degradation halo diameter should be considered in an evaluation
study, while assessing the cellulolytic activity. These parameters determine
the community size and/or the activity of the individuals that compose it. The
biodiversity of the fungi, actinomycetes and bacteria that form this functional
group are secondary parameters when assessing the functionality of the biogeochemical
cycle under study.
3 Carbon Cycle Functional Groups
4 Microorganisms on the Rhizosphere Microcosm 53
Celulase
producers
Protease
producers
Functional
group of
celulolytic
Functional
group of
Proteolytic
Fig. 2. Many populations of microorganisms may participate in one or more
biogeochemical cycling
C cycle
N cycle
The largest carbon reservoir is present in the sediments and rocks of the
Earth, but the turnover time is so long that flow from this compartment is relatively
insignificant on a human scale. From the viewpoint of living organisms,
a large amount of organic carbon is found in land plants. This represents
the carbon of forests and grasslands and constitutes the major site of photosynthetic
CO 2 fixation. However, more carbon is present in dead organic
material, called humus, than in living organisms (Madigan et al. 2000)
Plant residues are the largest fraction of all organic carbon entering the
soil. Plants contain 15–60 % cellulose, 10–30 % hemicellulose, 2–30 % lignin,