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INVITED SPEAKERS
A LOCAL PERSPECTIVE ON BENEFICIAL
MICROFLORA: MYCORRHIZAL
FUNGI
L.K. Abbott
School of Earth and Environment, The University of Western Australia; Email:
Lynette.Abbott@ @uwa.edu.au
ABSTRACT. Arbuscular mycorrhizal fungi are ubiquitous in soils of
south-western Australia in both agricultural and natural
ecosystems. They have potential to increase the efficiency of use of phosphorus fertiliser and to contribute to improving soil
structure via their role in soil aggregation. The extent to which this is likely to occur in agricultural soils depends on
management practices ncluding fertiliser application
(both N and
P), soil type,
plant speciess and rotation. In natural
ecosystems, arbuscular mycorrhizal fungi are integral components of root and rhizosphere habitats and re-establish
gradually
in rehabilitated sites following major disturbance events such as mining. These fungi occur in
communities with little
physiological host specificity. Ecological specificity can occur in response to differences in fungal life cycles and factors that
alter the abundance and
infectivity of
propagules. There are significant challenges to quantifying the contributions of
arbuscularr mycorrhizal fungi in both natural and agricultural ecosystems, and assumptions about
their importance may be
either over- or under-estimated. In agricultural soils, arbuscular mycorrhizal fungi have potential to be used as indicators of
sustainable
management practice based on an understanding the dynamics of their communities in roots and in soil.
INTRODUCTION
Arbuscular mycorrhizal (AM) fungi are ubiquitous soil
organismss with well-recognized
roles. However,
quantification of their contributions in either natural or
disturbed environments is experimentally difficult. Thus,
predictions about AM function in agricultural or other
ecosystems may or may not reflect their full potential.
Procedures for re-introducing
effectively
functioning
communities of AM fungi have been considered but this
may not be practical in Western Australian soils. The
dominance
of species of
AM fungi within soil and roots is
influenced
by plant and soil conditions, as well as season
and their life cycles. Bioassays are effective for interpreting
the state of communities
of AM fungi by determining
their
infectivity
over time. In agricultural soils, AM fungi
have
potential to be used as indicators of sustainable management
practice based on an understanding the dynamics of
their
communities in roots and
in soil.
METHODS AND RESULTS
Plant bioassays have been used to detect variation in
infectivity
of species of AM fungi from
WA soils and this
illustrates (i) seasonal dynamics within communities that
can lead to changes in dominance of fungi present within
roots (Figure 1) and (ii) relatively low diversity of AM
fungi
and their spatial heterogeneity (Figure 2).
Figure 1. Seasonal variation in colonisation of roots of
three cycles of Trifolium
subterraneum
by three species of
arbuscularr mycorrhizal fungi when inoculated with a
composite
inoculum of each fungus with
equal infectivity in
Cycle 1 (Sutarman, Abbott and Solaiman, unpublished) ).
Glomus invermaium was initially dominant in roots of
subterranean clover even when inoculated with a mixed
inoculum containing three AM fungi of similar infectivity
(Figure 1) ). However, after three cycles
of plants grown in
the same soil (in a pot experiment), its dominance declined
and was overtaken by Acaulospora laevis.
In a second example, bioassays demonstrated differences in
infectivity of AM fungi in undisturbed field soil under two
plant
species, Acaciaa cochlearis and Olearia axilaris (Figure
2). Morphological and molecular quantification of
AM fungi
in roots may differ due to sampling
discrepencies 1 .
Figure 2. Relative abundance of morphotypes of
AM fungi
in roots of bioassay
bait plants grown in undisturbed soil
cores
collected under three Acaciaa cochlearis plants (A4 to
A6) and three Olearia axilaris plants (O1 to O3) in a coastal
dune near Mandurah, WA. Overlap areas indicate co-
related to
colonisation of roots (unpublished
additional dataa
study
by Shi et al. 2012).
DISCUSSION
Species of AM fungi differ in the extent to which they
colonise roots alone and in competition with other AM
fungi
1 . They also differ in their ability to
transport
phosphorus from soil to roots, in the extent to which they
form hyphae in soil, and in their sensitivity to changes in
soil conditions. However, the significance of colonisation of
roots by AM fungi
is still contested and remains largely
unknown 2 . Despite difficulties in defining the contributions
of AM
fungi, knowledge of the dynamics of communities of
AM fungi in response to management of agricultural soils
has potential to be used to identify unsustainable land
management practices. Identifying
this potential
would be
based
on an understanding how AM
fungi contribute both to
nutrient cycling and
to soil structure. Capturing the benefits
of AM
fungi has potential to maximise the efficiency of use
of nutrient resources in agriculture and there is even
potential to use knowledge of AM
fungi as an indicator of
sustainable use of nitrogen as well as phosphorus fertilisers.
REFERENCES
1. Shi, P., Abbott, L.K., Banning, N.C. and
Zhao, B.
(2012) Mycorrhiza (DOI) 10.1007/s00572-011-0425-8)
2. Smith, F.A. and Smith, S.E. (2011) Plant Soil 348: 63–
79.
7th Australasian Soilborne Diseases Symposium
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