Book of Abstracts (PDF) - International Mycological Association

IMC7 Monday August 12th Lectures
94 - Weathering, a new role of ectomycorrhizal fungi in
ecosystems
R. Landeweert 1* , E. Hoffland 1 , M. Smits 2 , L. van Schöll 1 ,
T.W. Kuyper 1 & N. van Breemen 2
1 Wageningen University, Sub-dept. of Soil Quality.,
P.O.Box 8005, NL-6700 EC Wageningen., The
Netherlands. - 2 Wageningen University, Laboratory of Soil
Science and Geology., P.O.Box 37, NL-6700 AA
Wageningen., The Netherlands. - E-mail:
renske.landeweert@bb.benp.wag-ur.nl
Ectomycorrhizal fungi play a major role in the nutrient
acquisition of trees. Mycelial uptake and transport of
dissolved nutrients as well as fungal access to organic N
and P sources have received much attention. Recent
research suggests a third role of ectomycorrhizal fungi:
mobilisation of P and other essential plant nutrients directly
from minerals through excretion of organic acids. The
mobilised cations are subsequently translocated to the
ectomycorrhizal trees and thus by-pass the soil exchange
complex. The primary source of all essential plant nutrients
except nitrogen is the weathering of minerals. Low
molecular weight organic acids excreted by plant roots and
microorganisms are considered to be the most important
biological weathering agents in soils. Commonly released
into their environment by different fungal species are
oxalic and citric acid, both strong chelators of trivalent
metals such as Al3+. As the concentration of Al3+ in the
soil solution diminishes through chelation, weathering rates
of Al silicates such as feldspars increase. The awareness
that ectomycorrhizal fungi contribute to this process has
increased since the discovery of hypha-shaped tunnels
inside mineral grains. The contribution of ectomycorrhizas
to mineral weathering may change traditional ideas on
nutrient cycling and soil formation in forest systems. Latest
results on measurements of fungal weathering activities
will be presented and ecological implications will be
discussed.
95 - Decomposition of humic substances, lignin and
organopollutants by soil-litter decomposing
basidiomycetes
M. Hofrichter 1* , K.T. Steffen 2 & A. Hatakka 2
1 International Graduate School Zittau, Unit Environmental
Biotechnology, Markt 23, D-02763 Zittau, Germany. -
2 University of Helsinki, Dept. Applied Chemistry &
Microbiology, Viikki Biocenter 1, PO box 56, FIN-00014
Helsinki, Finland. - E-mail: Martic@gmx.net
Humic substances (HS) are ubiquitous nonliving organic
materials in all terrestrial and aquatic environments, and
represent the major fraction of organic matter in soils and
sediments. Consequently, microbial degradation of HS is
essential for maintaining the carbon cycle. Despite this
fact, only less is known about the particular
microorganisms which decompose humic matter. Our main
objective has been to examine the potential of litterdecomposing
basidiomycetes colonizing forest soils to
disintegrate HS and other recalcitrant compounds (lignin,
organopollutants). Within the scope of several screening
test, we have selected Nematoloma frowardii, Collybia
dryophila, Stropharia coronilla and Agrocybe praecox as
particularly active species degrading different HS, lignin
and/or several organopollutants in liquid as well as in
sterile and nonsterile solid-state cultures. These agaric
fungi produce manganese peroxidase (MnP) as the
predominant oxidative enzyme which is secreted into their
microenvironment in response to high Mn 2+ titers. In
combination with certain low-molecular mass effectors,
isolated MnP was found to attack recalcitrant aromatic
substances unspecifically via one-electron abstractions
giving rise to instable radicals, which tend to disintegrate
spontaneously into polar fragments and CO2.
96 - Arbuscular mycorrhizal communites in rare and
common Pulsatilla spp.: towards restoration of
endangered plant species
R. Sen 1* , M. Öpik 2 , M. Moora 2 , U. Kõljalg 2 & M. Zobel 2
1 Department of Biosciences, Division of General
Microbiology, P.O. Box 56, FIN-00014 University of
Helsinki, Finland. - 2 Institute of Botany and Ecology, Tartu
University, 40 Lai Str., Tartu-51005, Estonia. - E-mail:
robin.sen@helsinki.fi
In the context of plant conservation it can be hypothesized
that the presence of compatible arbuscular mycorrhizal
fungi (AMF) directly contribute to the growth and survival
of endangered plants. Here, we investigated a congeneric
rare vs. common species pair, Pulsatilla patens and P.
pratensis, in Estonian soils. Seeds were sown in soil
inocula from four localities and germination, seedling
establishment and root colonizing AMF species
communities were assessed. A lack of soil treatmentrelated
differences in P. pratensis germination and seedling
establishment rates strongly contrasted with the
significantly higher establishment rates of the rare P.
patens in soil inoculum from a Scots pine forest where both
target species co-exist in the understorey. Distinct
communities of AMF species, identified following rDNA
(SSU) sequence and phylogenetic analyses, were detected
in roots of established plants and test seedlings grown in
soil inocula from an agricultural landscape and a Scots pine
forest. In seedling roots of both species exposed to forest
soil inoculum, SSU sequences exhibited high homology to
woodland Glomus sequences, earlier detected on
Hyacinthoides non-scripta in a deciduous UK woodland
site. The data provides support for the involvement of
specific AMF in early seedling establishment of Pulsatilla
species. Greater host species-linked dependency towards
particular AMF may explain the loss of the rare P. patens
in mycobiont limited disturbed or managed landscapes.
Book of Abstracts 31