Environmental Engineering Reference
In-Depth Information
Table 1
Interaction of arbuscular mycorrhizal fungi with
benefi cial soil microorganisms
Group of microorganisms
Veresoglou and Rillig
2012
). The two symbionts
act synergistically under low fertile conditions,
resulting in greater N and P content in dually
inoculated plants than when the organisms are
inoculated separately. Even at low water poten-
tial, AM fungal inoculation improves nodulation
and N
2
fi xation by the bacterial symbiont
(Goicoechea et al.
1998
), thereby neutralizing the
effects of salinity. An early association of the
seedling with AM fungi can moderate the stressed
condition of the host (Evelin et al.
2009
). It has
been noted that the premature nodule senescence
in soybean under drought conditions could be
ameliorated through AM fungal inoculation
(Porcel et al.
2003
).
Synergistic interactions have also been
reported between AM fungi and plant growth-
promoting rhizobacteria (PGPR) (Muthukumar
et al.
2001
; Muthukumar and Udaiyan
2006
; Sala
et al
.
2007
). However, the nature and the extent of
benefi t from interaction could vary. For instance,
Chandanie et al. (
2005
,
2006
) noted that co-
inoculation of
Trichoderma
with an AM fungus
(
F. mosseae
) positively stimulated plant growth.
However, no such effect on plant growth was evi-
dent when
Penicillium
was co-inoculated with
the same AM fungus.
Results
Symbiotic and asymbiotic
N
2
fi xers
N
2
fi xation, N cycling, N
transfer
Phosphate solubilizers
P cycling, use of
sparingly soluble P source
Phytostimulators
Increased rooting and
seedling establishment
Biocontrol agents
Increased resistance/
tolerance to root disease
Other fungi and bacteria
related to soil aggregation
Important to soil quality
Adapted from Azcón-Aguilar and Barea (
1997
) with
permission
nematode attack could mask the magnitude of AM
fungal benefi ts to the host plant, but AM fungal iso-
lates could modify the severity of stress on plants to
different levels (Veresoglou and Rillig
2012
).
3.2.2.2 Interaction with Other Soil
Organisms
Arbuscular mycorrhizal fungi interact with a
diverse group of organisms in the rhizosphere.
These interactions can range from positive to
neutral and to negative on the AM association or
a particular component of the rhizosphere
(Azcón-Aguilar and Barea
1992
; Rillig
2004
).
Different types of positive interactions between
AM fungi and other soil microorganisms are pre-
sented in Table
1
. The microfl ora in the rhizo-
sphere of mycorrhizal roots most aptly termed as
the 'mycorrhizosphere' quantitatively and quali-
tatively differs from the non-mycorrhizal roots
(Bansal and Mukerji
1994
). Mainly two groups
of bacteria, namely, saprophytes and symbionts,
interact with AM fungi that may be either detri-
mental, neutral or benefi cial in their response
(Johanson et al.
2004
). 'Mycorrhiza helper
bacteria' (MHB) found mostly in temperate and
tropical ecosystems (Frey-Klett et al.
2007
) initi-
ate AM fungal root colonization, stimulate myce-
lia growth and also assist spore germination
(Gryndler et al.
2000
; Vivas et al.
2006
). The
interaction between AM fungi and nodulating
nitrogen fi xers has received considerable atten-
tion because of the high P demand involved in N
2
fi xation (Barea and Azcón-Aguilar
1984
;
3.2.2.3 Nutrient Transfer in
Intercropping Systems
Intercropping is an ancient technique of growing
more than one crop species simultaneously in the
same fi eld. It plays an important role in agricul-
ture rendering advantages to both soil and plant.
Intercropping improves soil texture and soil
water availability and supplies various organic
matters for most effi cient proliferation of symbi-
otic and non-symbiotic microorganisms (Burner
2003
; Muok et al.
2009
). The wide and diverse
plants in an intercropping favour an increased
and viable population of AM fungi. However, the
capability of legumes to form dual symbiotic
association with both bacteria and AM fungi is
important in intercropping systems from improv-
ing soil fertility point of view (Pagano et al.
2008
;
de Carvalho et al.
2010
). As plants from different
species could be linked by the common AM
mycelia network, intercropping of legume crops
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