Chapter 21: Decomposition and Nutrient Cycling

Question 1

Pathway of an element or nutrient through the ecosystem, from assimilation by organisms to release by decomposition;

See also internal cycling

Answer 1

nutrient cycling

Question 2

Breakdown of complex organic substances into simpler ones

Answer 2

decomposition

Question 3

Recycling of nutrients within a plant

Answer 3

retranslocation or resorption

Question 4

4 major groups of invertebrate detritivores, classified by body width

Answer 4

• Microfauna and microflora
• Mesofauna
• Macrofauna
• Megafauna

Question 5

< 100 micrometers

Includes protozoans and nematodes inhabiting the water in soil pores

Answer 5

microfauna and microflora

Question 6

> 20 millimeters

Dominated by earthworms and snails

Answer 6

megafauna

Question 7

Between 100 micrometers and 2 millimeters

Includes mites, potworms, and springtails that live in soil air spaces

Answer 7

mesofauna

Question 8

Between 2 and 20 millimeters

Includes annelid worms

Answer 8

macrofauna

Question 9

Dead plant tissues

Answer 9

plant litter

Question 10

A widely used approach to examine the rate of decomposition of dead plant tissues (plant litter) using litterbags;

Results are measured as % original mass remaining as a function of time

Answer 10

litterbag experiment

Question 11

Areas of accumulated leaf litter in stream ecosystems;

Term also refers to litterbags used in stream decomposition experiments

Answer 11

leaf pack

Question 12

Organic matter that, upon death, their bodies break up and dissolve within 15 to 30 minutes, too rapidly for any bacterial action to occur;

Provides a source of fixed carbon for decomposition;

Major sources of this organic matter are the free-floating macroalgae, phytoplankton, and zooplankton inhabiting the open water

Answer 12

dissolved organic matter (DOM)

Question 13

Microbial breakdown of humus and other organic matter in soil to inorganic substances

Answer 13

mineralization

Question 14

Conversion of an element from inorganic to organic form in microbial or plant tissue, rendering the nutrient unavailable to other organisms

Answer 14

immobilization

Question 15

Difference between the rates of mineralization and immobilization

Answer 15

net mineralization rate

Question 16

The ratio of carbon to nitrogen (grams of carbon per gram of nitrogen)

Answer 16

C/N ratio

Question 17

Typical C/N ratios of plant litter and bacteria and fungi

Answer 17

For plant litter:
About 50:1 to 100:1

For bacteria and fungi:
About 10:1 to 15:1

Question 18

Describes a region of the soil where plant roots function;

It is an active zone of root growth and death, characterized by intense microbial and fungal activity

Answer 18

rhizosphere

Question 19

Dead organisms and other organic matter that, in the still and open water of ponds and lakes and in the ocean, drift toward the bottom;

On its way, they are constantly ingested, digested, and mineralized until much of the organic matter settles on the bottom in the form of humic compounds

Answer 19

particulate organic matter (POM)

Question 20

Process of supplementing carbon to microbial decomposers in the rhizosphere, enhancing the decomposition of soil organic matter, and subsequently releasing mineral nutrients for plant uptake by microbial grazers

Answer 20

soil microbial loop

Question 21

Farming systems that alternate periods of annual cropping with extended fallow periods;

Also referred to as shifting cultivation;

Fire is used to clear fallow areas for cropping

Answer 21

swidden agriculture

Question 22

Fertilizer composed of organic matter derived from plants or animals

Answer 22

organic fertilizer

Question 23

Fertilizer that provides nutrients in an inorganic or mineral form (referred to as chemical fertilizers when it is of synthetic origin)

Answer 23

inorganic fertilizer