Agriculture Reference
In-Depth Information
decomposing maple litter through the application of the insecticide carbofuran reduced
its decomposition rate by 40 % (Weary and Meriam, 1978).
In microcosm studies, decomposition is always accelerated by the addition of litter
invertebrates in comparison with situations where micro-organisms are the only decom-
posers present. Increases of 14.6 to 32 % in carbon dioxide evolution from decomposing
birch (
Betula
sp.) litter have been recorded following the addition of epigeic animals
(Setälä
et al.,
1988). Over eight months, Seastedt (1984) observed an increase of
ca.
75 %
in the decomposition rate and Anderson
et al.
(1983a) found increases of 1.6, 2-3 and
10-15 times in the ammonium released from Oak leaf-litter in the L, F and H layers,
respectively, in the presence of the millipede
Glomeris marginata.
The biomass of the
epigeic fauna is therefore a critical factor in the modeling of decomposition processes.
However, this effect is generally delayed in time (by
ca.
2 months in the case of a British
deciduous woodland), and only significant when the biomass comprises at least 10 %
of the weight of the decomposing litter. In the latter case, cumulative losses of mineral
nitrogen are given by the equation:
where NA is nitrogen mineralised (g N resource), T is temperature (°C) and B is
the invertebrate biomass (g fresh weight) to resource quotient (Anderson
et al.,
1985).
In similar field experiments, Anderson
et al.
(1983a) found increases in ammonium
leaching of 23 % during the first 32 weeks of decomposition but followed by a decrease
of 38 % over the subsequent 32 weeks of the experiment (Figure IV.25). Where the same
experiment included living roots, the amount of ammonium leached diminished by 12
to 48 %. Such experiments have shown that, in addition to increased mineralisation
through faunal activities, interactions with other biological components and/or the
decrease in mineralisation rates within faecal pellets may lead to a net immobilisation
(Hanlon and Anderson, 1980).
