The ecology of myxomycetes within decaying wood
The interiors of 72 decaying branches from a range of tree
species were investigated for the presence of myxomycetes.
Tree species whose decaying wood yielded myxomycetes included
oak, ash, birch, sycamore, silver birch, hazel, .pine and spindle.
The only phase of the life cycle isolated directly from within
the wood was the uninucleate phase, although aphanoplasmodia
did on occasions form on the isolation plates. It was therefore
concluded that the uninucleate trophic phase was the most
prolonged feeding phase as opposed to the plasmodial phase.
Also the predominant type of myxomycete within the decaying wood
sampled was the aphanoplasmodial-type.
A numerical investigation of the uninucleate myxomycetous
cells, flagellates and ciliates yielded by the interior wood of
121 decaying branches, collected from the ground or "aerially"
at Leigh Woods, Avon; Wetmoor, Avon; and Weston Big Wood, Avon,
revealed numbers of myxomycetous cells up to 64,100 per cm 3 in
oak and up to 13,200 per cm 3 in lime. The numbers of uninucleate
myxomycetous cells per cm 3 were found to be inversely related to
3 the numbers of non-myxomycetous flagellates and ciliates per cm ,
possibly reflecting direct competition for bacterial food.
The state of decay of the branches was determined by
measuring the density and C:N ratio of the wood. These two
variables were found to be directly related. No direct relationship
between the density of the wood or C:N ratio (as measures
of decay) and the numbers of myxomycete uninucleate cells was
found. However myxomycetes, non-myxomycetous flagellates and
ciliates were more frequently isolated from the lower density
(more decayed) wood.
A microcosm system representing decaying wood was developed
to investigate the position of the myxomycetes in food chains
within decaying branches. The uninucleate myxomycetous cells
of Ceratiomyxa fruticulosa were found to feed on the bacteria
(Aerobacter aerogenes) in the microcosm. There was no evidence
that they could directly utilize the cellulose carbon source
provided. The fungus (Peniophora guercina) was not noticeably
affected by the presence of the other two organisms, although
it appeared to have a" deleterious effect on the myxomycete cell
numbers. This effect may have been specific to the species of
myxomycete and fungus involved.
The terminology used to refer to the flagellate and nonflagellate
uninucleate trophic cells of myxomycetes is discussed
and a new term "myxomonads" is introduced to refer to both the
flagellate and non-flagellate cells. The identification of
myxoflagellates is also discussed and criteria for their
identification listed. The identification of typical myxoflagellates
was found to be necessary for their enumeration.