thermophile(maximum about 55°C, optimum about
50°C) might start earlier than H. insolens(maximum
about 55°C, optimum about 37°C), and these two
fungi are known to recolonize before A. fumigatus
(maximum 52°C, optimum 37°C). During the pro-
longed warm-temperature phase after peak-heating
a compost can lose up to half of its original dry
weight, and nearly two-thirds of the main plant
wall components such as cellulose and hemicelluloses
(mixed polymers of arabinose, xylose, mannose,
and glucose). The mitosporic fungus, Thermomyces
lanuginosus(see Fig. 8.3) has a temperature maximum
of about 62°C, and optimum of about 47°C. It
grows during the high temperature phase and is one
of the commonest fungi in all types of compost.
However, it is noncellulolytic, and it seems to
grow as a commensal, utilizing some of the sugars
released by the enzymes of other fungi (see later).
3 As the temperature falls below 35– 40°C, the ther-
mophilic fungi start to decline but A. fumigatus
remains active. The compost is then colonized
progressively by mesophilic fungi, including some
mitosporic fungi (e.g. Fusarium, Doratomyces) and
Basidiomycota such as Coprinus cinereus (max. about
40°C but its optimum is much lower). Coprinusspp.
represent the degraders of recalcitrant polymers.
They utilize lignocellulose and are highly antagonistic
to many other fungi, damaging their hyphae on
contact by a process termed hyphal interference
(Chapter 12). Spores of the commercial mushroom,Agaricus bisporus, can be introduced into the com-
post once this has cooled to below 30°C. It cannot
be added earlier because of its temperature require-
ments, but it must be added before Coprinus
becomes established or it will be antagonized. In
practice, this problem is overcome (and the whole
commercial composting process is accelerated) by
pasteurizing commercial composts soon after peak
heating so that most of the resident fungi are killed
before Agaricusis introduced (Chapter 5).The central role of nitrogen in the
composting processAn adequate supply of mineral nutrients is essential
for composting and for the decomposition of organic
matter in general. A supply of nitrogen is particularly
important, and can often be the rate-limiting factor.
The availability of nitrogen is often expressed in terms
of the carbon-to-nitrogen (C : N) ratio– the ratio of
elemental nitrogen to elemental carbon, assuming
that both the nitrogen and the carbon are available in
usable forms.
To appreciate the significance of this, we must make
two points:1 Fungal hyphae typically have a C : N ratio of
approximately 10 : 1, although it can vary depend-
ing on the age of the hyphae and other factors.224 CHAPTER 11
Fig. 11.12 (a) Thermoascus aurantiacusproduces a thick, crusty, golden-brown colony on agar. (b) The crusty appear-
ance is due to the presence of many cleistothecia (closed ascocarps) which contain asci. (c) Within each ascus is a
cluster of eight ascospores, shown in different stages of maturity.(a)
(b)(c)