25th International Meeting on Organic Geochemistry IMOG 2011

P-497
Decomposition of wheat straw buried in a grassland soil: the
fungi involved and the products obtained
Rachel Muito-Kabuyah 1 , Clare Robinson 1 , Bart van Dongen 2
1 University of Manchester, School of Earth, Atmospheric and Environmental Sciences, Manchester, United
Kingdom, 2 University of Manchester, Williamson Research Centre for Molecular Environmental Science,
Manchester, United Kingdom (corresponding author:rachel.muitokabuyah@postrgrad.manchester.ac.uk)
Decomposition of dead plant material in soils is a
process of equivalent importance to primary
production in ecosystem functioning, and is driven
partly by saprotrophic fungi. Basidiomycete fungi are
particularly important in lignin degradation [1] but their
contribution is still a matter of ongoing debate. The
aims of this project are, using a combination of
mycological and organic geochemical techniques, to
characterise the diversity of saprotrophic
basidiomycete, ascomycete and zygomycete mycelia
in a representative sandy grassland soil and to
determine their influence on the fate of soil organic
matter, particularly lignin and cellulose.
Bait bags of winter wheat straw (Triticum aestivum
var. Swatham) were buried at two defined depths and
several defined horizontal distances in the field at a
UK coastal grassland (Ainsdale National Nature
Reserve) in May 2005. These baits were retrieved
approximately 4 years later. Visual analyses of the
retrieved bags indicated substantial degradation of
the wheat straw buried (not shown). The fungi present
in the degraded straw were isolated using two types
of selective media: one medium to isolate the general
fungi and a second lignin-rich medium specifically to
isolate basidiomycete fungi. Fungal isolates obtained
showed, that at both soil depths, the fungal
community was dominated by the cellulose
decomposing fungi Trichoderma species and lignin
modifying fungi (Fig. 1a & b). Interestingly,
basidiomycetes were not observed. Pyrolysis GC-MS
analyses of both upper and lower layer samples
showed a substantial degradation of the wheat straw
confirming the earlier visual observations [2].
Acid/aldehyde (Ad/Al) ratios were used as a relative
decomposition state proxy for the syringyl lignin
monomer and describe the ratio of 3,4,5trimethoxybenzoic
acid, methyl ester (S6) to 3,4,5trimethoxybenzaldehyde
(S4) (Fig. 1c). Results
suggest that although no basidiomycetes could be
observed in the fungal frequency analyses,
basidiomycetes were present and must have played
an important role in straw decomposition as the
results infer that the fungi in the soil had induced
oxidative cleavage following degradation of lignin, in a
manner similar to numerous previous laboratory
studies with basidiomycetes [e.g. 3].
Future research will include a combination of
mycology and organic geochemistry to explore
hypotheses developed from the field experiment in a
mechanistic way.
12%
[Ad/Al]S
A
12%
C
10
5
0
0%
6%
70%
B
38%
8%
0%
15%
39%
0 2 4 6 8 10
Distance (m)
Cellulolytic
Lignin modifier
Weakly
cellulolytic
Not
cellulolytic/lign
inolytic
Unidentified
fungi
lower
upper
original straw
Fig.1a & b Fungal frequency of isolation and their
primary enzymatic capabilities from a lowert depth
isolated on media. Fig.1c. Acid/aldehyde ratio
([Ad/Al]S) in THM products from wheat straw. The
original straw, buried in 2005, had an [Ad/Al]S ratio in
the range of 0.6- 1.5 represented by the rectangle.
References:
[1]Kirk, T.K. & Farrell, R. L.
Annu Rev Microbiol 41, 465-505 (1987).
[2]Filley, T.R. et al. Org Geochem 30, 607-621
(1999).
[3] Vane, C. H. et al. J Anal Appl Pyrol 60: 69-78
(2001).
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