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Chapter 11

Fungal ecology: saprotrophs

This chapter is divided into the following major sections:

• a theoretical model: the concept of life-history
  strategies


• the biochemical and molecular toolbox for fungal
  ecology


• a “universal” decomposition sequence


• the fungal community of composts


• fungal decomposers in the root zone


• fungal communities in decaying wood

The importance of fungi in ecosystem processes is unde-

niable. Fungi are the main agents of decomposition

in many terrestrial and aquatic environments. They are

particularly important in the breakdown and recycl-

ing of cellulose and hemicelluloses, which together

account for nearly 70% of all the plant wall material

that is recycled annually. In addition, fungi have a

unique role in degrading woody substrates, which

contain cellulose intimately complexed with lignin

(lignocellulose). And, fungi degrade many other

natural and manmade materials, causing serious

economic losses.

In previous chapters we dealt with the physiology,

growth, genetics, and dispersal of fungi – the basis

for understanding fungal ecology. But when we turn

to fungi in natural environments we face a major

problem, because natural communities are extremely

complex: they contain many types of substrate,

interacting species, and microhabitats. Therefore, at

a practical level we need to find well-defined com-

munities that can be dissected to provide key insights

into fungal behavior. We will do this by focusing on

a few natural “model” systems that have been well

researched – the leaf zone, leaf litter, the root zone,

self-heating composts, and wood decay. The principles

derived from these natural model systems apply more

generally across the fungal kingdom. We will also

explore the biochemical and molecular toolboxthat

enables us to track and identify fungi in complex

natural materials.

A theoretical model: the concept of

life-history strategies

Ecology lends itself to theoretical models as a basis for

synthesizing complex information. The references at the

end of this chapter cite some key publications in this

field. Here we will briefly discuss one of these models,

first developed by animal ecologists, then applied to

plants and later to fungi – the concept of life-history

strategies(Fig. 11.1).

Initially, ecologists developed the concept of r-

selectedand K-selectedorganisms, these being the two

extreme expressions of the life history of an organism.

The r-selected organisms (ruderals) establish themselves

and grow rapidly in suitable conditions, but after a short

phase of growth they produce many offspring, each of

which has only a low chance of reproductive success.

Weed plants are classic examples of this strategy, as are

many of the fast-growing fungi of the Zygomycota

(Mucor, Rhizopus, etc. – see Chapter 2). At the other

extreme, K-selected organisms typically establish and

develop slowly, live for a long time, and produce few

offspring, but each of these offspring has a significant