Exam 11: Organisms and Ecology of the Soil

The total number of microorganisms in a hectare of soil is far greater than the number of macroorganisms, but the reverse is true for biomass of the two groups.

Actinomycetes tend to dominate soils that are either very acid, very cold, or very dry.

Compared to the rest of the soil, the rhizosphere is kept relatively sterile by the action of plant roots.

Fungi tend to be the dominant group of microorganisms in acid, sandy soils.

Soil microorganisms often compete with higher plants for mineral nutrients, such as nitrogen.

Compared to the bulk soil in which the earthworms live, earthworm casts contain ____.

Which group of soil organisms includes the largest number of autotrophic species?

Where conditions are favorable, earthworms are known to add several hundred kg/ha of several important nutrients to the soil system.

The fungal symbiont generally benefits from the mycorrhizal relationship by obtaining ____ from the higher plant.

Meso- and macrofauna contribute to organic matter decomposition primarily by ______.

Earthworms generally are most abundant in sandy, acid soils typically under coniferous forest vegetation.

A significant portion of the global production of methane comes from the activity of termites.

Members of this (these) microbial group(s) are responsible for a major proportion of the nitrogen fixed globally in symbiosis with higher plants.

Most soil organisms are heterotrophs.

Mycorrhizae involve a symbiotic combination of certain bacteria and plant cells.

The deeper that they are placed in the soil, the more rapidly organic compounds such as pesticides are decomposed by the soil microflora.

In which situation are the actinomycetes likely to be most dominant?

All but a few nematodes are pests, attacking either economic or wild plants.

Disease suppressive soil often results from _____.

Most anaerobic organisms in soils are bacteria.