9.1 Microorganisms in nature ecosystem
1. Microorganisms and microenvironment 2. Terrestrial Environments 3. Freshwater Environments 4. Marine Environments
Metabolically related populations constitute groupings called guilds.
Sets of guilds conducting complementary physiological processes interact to form microbial communities.
9.2 Microbial population interactions
1， neutralism (中性关系 ) 2， commensalism (偏利关系 ) 3， synergism (协同关系 ) 4， mutualism (互惠关系 ) 5， competition (竞争关系 ) 6， antagonism (拮 抗关系 ) 7， parasitism (寄生关系 ) 8， predation (捕食关系 )
Numbers / g
Biomass (g / m3）
Bacteria
108
160
Fungi
105
200
Actinomycetes
105 - 106
160
Algae
104 - 105
32
Protozoa
104
38
Main types of soil microorganisms
Agrobacterium Arthrobacter Caulobacter Clostridium Flavobacterium Mycobacterium Staphylcoccus
Microbial populations in the rhizosphere may benefit the plant by:
(1) removing hydrogen sulfide, which is toxic to the plant roots
(2) increasing solubilization of mineral nutrients needed by the plant for growth
Community 3
Microbial communities then interact with communities of macroorganisms to define the entire ecosystem.
The distribution of microorganisms in nature ecosystem depends on the resources (nutrients) available and on the growth conditions.
Within the rhizosphere, the plant roots exert a direct influence on the soil bacteria. This influence is known as the rhizosphere effect.
In the rhizosphere, microbial populations reach much higher densities in the rhizosphere than in the free soil.
Carbon cycle
Carbon cycle
Carbon dioxide is incorporated, or fixed, into organic compounds by such photoautotrophs as cyanobacteria, green plants, algae, and green and purple sulfur bacteria.
Parasitism, the parasite population is benefited and the host population is harmed.
Predation is a widespread phenomenon where the predator engulfs or attacks the prey. The prey can be larger or smaller than the prey, and this normal results in the death of the prey.
9.1.2. Terrestrial Environments
Proportion of different soil microorganisms in soil
Microbial number and biomass in cultivated field soil（15 cm）
Microbes
Competition occurs when two populations are striving for the same resource of nutrients or the habitat.
Antagonism occurs when one population produces a substrate inhibitory to another population.
Competition
-
-
Amensalism
0 or +
-
Parasitism
+
-
Predation
+
-
0, No effect; +, positive effect; -, negative effect.
9.3 Biogeochemical cycles
1. Carbon cycle 2. Nitrogen cycle 3. Sulfur cycle 4. Iron cycle
Classification of population interaction
EFFECT OF INTERACTION
NAME OF
POPULATION
POPULATION
INTERACTION
A
B
Neutralism
0
0
Commensa#43;
+
Mutualism
+
+
Alcaligenes Bacillus Cellulomonas Corynebacterium Micrococcus Pseudomonas
Rhizosphere Effect ( R/S ratio )
The rhizosphere is the soil region in close contact with plant roots.
A soil aggregate composed of mineral and organic components, showing that localization of soil microbes. Very few microorganisms are found free in the soil solution; most of them occur as microcolonies attached to the soil particles.
Synergism indicates that both populations benefit from the relationship but the association is not obligatory. Both populations are capable of surviving independently.
Microbial ecology is the the study of the behavior and activities of microorganisms in their natural environments.
Environmental microbiology, in comparison, relates primarily to all- over microbial processes that occur in a soil, water or food, as examples. It is not concerned with the particular microenvironment where the microorganisms actually are functioning, but with the broader-scale effects of microbial presence and activities.
9.1.1 Microorganisms and microenvironment
populations guilds communities ecosystem
In a microbial ecosystem individual cells grow to form populations.
Temperature, pH, water availability, light, oxygen of a habitat define the niche for each particular microorganism.
Soil particles are not homogeneous in terms of their oxygen content. The outer zones of a small soil particle may be fully oxic, whereas the center, only a very short distance away, can remain completely anoxic.