Environmental Engineering Reference
In-Depth Information
can benefi t nonleguminous crops through the
transfer of N via common mycelia network
(CMN) (Simard and Durall
2004
). This CMN
aids nutrient transfer between different host
plants, thereby acting as an extension of the root
systems, and also provides signalling molecules
(Xiaolin and Shang
1997
). For example, the
cocultivation of citrus (
Citrus tangerine
) which is
highly dependent on AM fungal association due
to the poor root development (Wu and Xia
2006
),
along with a leguminous herb,
Stylosanthes grac-
ilis
, consequently increased both soil quality and
citrus yield in Southern China (Yao et al.
2008
).
Other features of intercropping like the nutri-
ent cycling and organic matter turnover can max-
imize the resource use by plants, thereby
improving soil fertility. For example, Li et al.
(
2007
) showed that the root exudates of faba bean
containing organic acids and protons increased P
content of maize plants in a maize-faba bean
(
Vicia faba
) intercropping system. The CMN of
AM fungi also enhances P balance as well as the
N and P levels between plants (Giovannetti et al.
2004
). Each AM fungal species tends to have dif-
ferent effects in relation to plant systems. For
instance, AM fungal taxa that reduce plant growth
in one plant species can enhance it in another
(Klironomos
2003
). Recently, Hu et al. (
2013
)
examined the effect of intercropping
Sedum
alfredii
with
Ipomoea aquatica
inoculated with
two different AM fungal species ([Funneliformis
caledonium
(
=Glomus caledonium
)
90036
,
Glomus versiforme
HUN02B)] in cadmium (Cd)-
contaminated soil. The AM fungus
F. caledonium
90036 increased P acquisition and plant biomass
of
S. alfredii
, whereas
G. versiforme
HUN02B
had the same effect on
I. aquatica
. Some of the
studies also suggest that intercropping is benefi -
cial and far better than monoculture system
(Harinikumar et al.
1990
; Ishii et al.
1996
).
in response to AM symbiosis (Smith et al.
2003
;
Gamalero et al.
2004
); the shoot/root ratios of
AM plants are usually higher in AM plants than
in their corresponding non-AM controls (Smith
1980
). It has also been recently recognized that
AM colonization could affect a wide range of
morphological parameters in developing root
systems including root branching (Atkinson et al.
1994
; Berm et al.
1995
). Enhanced root prolifera-
tion in response to AM fungal inoculation has
been reported in black pepper (
Piper nigrum
)
(Anandaraj and Sarma
1994
; Thanuja et al.
2002
)
and cashew (
Anacardium occidentale
) (Krishna
et al.
1983
). Therefore, it has been speculated
that changes in the plant hormonal balance and
meristematic activity in response to AM associa-
tion were responsible for the AM-induced effects
on root development.
Changes in root morphology and P uptake
alter the rhizosphere through predominantly
affecting the microbial community (Linderman
1988
). The variation in the root architecture of
mycorrhizal plants from that of a non-mycorrhizal
plant clearly indicates the involvement of some
compounds from root system responsible for
these traits. For example, Wu et al. (
2010
) showed
that polyamines in addition to improving plant
growth could also signifi cantly alter the root sys-
tem architecture in AM plants.
4
Management of AM Fungi
In agroecosystems, various management practices
such as the degree and type of fertilization, plant
protection, fallow period and soil tillage could
infl uence AM association.
4.1
Fertilizer
3.2.2.4 Rooting
Nutrient supply by the AM mycelium activity
exerts a feedback regulation, especially in the
aerial parts of the plant like photosynthesis and
the translocation of the photosynthates. Generally,
fewer photosynthetic products are allocated to
the root due to an increased effi ciency of the roots
Crops require adequate nutrients especially P
during early stages of growth for optimum crop
production (Grant et al.
2001
). Limited P supply
frequently limits crop production and P fertilizer
is commonly applied to ensure that suffi cient P
is available for optimal crop yield and maturity
(Grant et al.
2005
). The total soil P usually
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