Bài giảng Soil ecology

The soil is the home of  innumerable forms of  plant, animal, and  microbial life.   Life in the soil is  amazingly diverse,  ranging from microscopic  single‐celled organisms  to large burrowing  animals.  

All ecosystems have two types of organisms based

on carbon source:

(1) producers, and

(2) the consumers and decomposers

The producers use (fix) inorganic carbon from carbon

dioxide, and are autotrophs

The consumers and the decomposers use the carbon fixed by the producers, such as glucose, and are

heterotrophs

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Estimates of Amount of Organic

Matter and Proportions, Dry Weight, and Number

of Living Organisms

in a Hectare

of Soil to a Depth of 15 Centimeters

in a Humid Temperate Region

activity of bacteria is limited to surface

erosion in place, fungi readily extend their tissue and penetrate into the surrounding environment

The most common fungi are molds and mushrooms Mold mycelia are commonly seen growing on bread, clothing, or leather

goods Rhizopus is a common mold that

grows on bread and in soil

Mushroom fungi have an

underground mycelium that

absorbs nutrients and water,

and an above-ground

mushroom that contains

reproductive spores Many

mushrooms are collected for

food, such as the shaggy-mane

mushroom shown in Figure:

Mushroom fungal caps that

contain spores-an edible type

!

The actinomycetes resemble bacteria in that they have a very simple cell structure and are about the same size in cross section

They resemble filamentous fungi in that they produce a branched

filamentous network.

Actinomycetes are in great abundance in soils, as shown in Table They make up as much as 50 percent of the colonies that develop

on plates containing artificial media and inoculated with a soil

extract The numbers of actinomycetes may vary from 1 to 36

million per gram of soil Although there is evidence that

actinomycetes are abundant in soils, it is generally concluded they that are not as important as bacteria and fungi as decomposers It appears that actinomycetes are much less competitive than the

bacteria and fungi when fresh additions of organic matter are

added to soils Only when very resistant materials remain do

actinomycetes have good competitive ability

Vertical Distribution of Decomposers in the Soil

The surface of the soil is the interface between the

lithosphere and the atmosphere At or near this

interface, the quantity of living matter is greater than at any region above or below As a consequence, the A horizon contains more organic debris or food sources than do the B and C horizons Although other factors besides food supply influence activity and numbers of microorganisms, the greatest abundance of

decomposers typically occurs in the A horizon

Distribution of microorganisms in the A, B, and C horizons of

a cultivated grassland soil All values refer to the number of organisms per gram of air-dry soil

EARTH MOVING BY SOIL ANIMALS

All soil animals participate as consumers and play a

minor role in the cycling of nutrients and energy Many of the larger animals move soil to such an extent that they affect soil formation

Earthworm Activity

Earthworms are probably the best known earth

movers This activity produces thicker than normal,

dark-colored surface layers in soils

As a result of their earth-moving activities, earthworms leave channels Where these channels are open at the soil surface, they can tranport water very rapidly into and through the soil

Ants and Termites

The activities of ants and termites are, perhaps, more important than the activities of earthworms Ants

transport large quantities of material from within the soil, depositing it on the surface Some of the largest ant mounds are about 1 meter tall and more than 1 meter in diameter The effect of this transport is

comparable to that of earthworms in creating thick A horizons and in burying objects lying on the soil

surface

Rodents

Many rodents, including mice, ground

squirrels, marmots, gophers, and prairie dogs

inhabit the soil

Ant (Formica

cinera) in a

Prairie soil in

southwestern Wisconsin The sketch shows soil horizons and location of ant channels;

numbers refer to the number of channels

observed at the depth indicated

SUMMARY

Higher plants are the major producers contribut- ing to the supply of soil organic matter The microorganisms (bacteria and fungi) are the major decomposers and are mainly responsible for the cycling of nutrients and energy in soil ecosystems

Soil animals play a minor role in the cycling of nutrients and energy, but play an important role in earth-moving activities

Nutrient cyling results in reuse of the nutrients in an ecosystem Nutrients are efficiently recycled in natural ecosystems Interference of the cycle, such as cropping and removal of nutrients in food, results in reduced soil fertility Manures and fertilizers are used to maintain soil fertility in

agriculture

Soil organisms and higher plants engage in many interactions related to disease, mycorrhiza, and nitrogen fixation, and soil organisms and higher plants compete for the same growth factors

A zone adjacent to plant roots with a high population of microorganisms is the rhizosphere

Microorganisms play important environmental quality roles, such as

detoxification of chemicals and decomposition of oil from spills

Earthworms, ants, termites, and rodents move large quantities of soil and may greatly alter the nature of soil horizons

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