Environmental Engineering Reference
In-Depth Information
hunger facing mankind is far from being realized
(FAO
2004
). Factors that deter maximum crop
productivity include several abiotic and biotic
stresses like unfavourable climate, drought, dis-
eases and pests. Recently, increased crop produc-
tivity has been achieved through crop breeding
along with huge input of chemicals in the form of
fertilizers and biocides. These chemicals not only
disturb agricultural ecosystems but are also detri-
mental to the environment (Chapin et al.
2000
;
Barabasz et al.
2002
; Parmesan and Yohe
2003
;
Zhong and Cai
2007
). The tolerance of crops to
various abiotic and biotic stresses can also be
evolved through the exploitation of the world-
wide abundant endophytic associations, where
microorganisms live in reciprocally benefi cial
relationship with plants.
Sustainable agriculture, by defi nition, is eco-
logically sound, economically viable, and
socially responsible (Siddiqui and Pichtel
2008
). Agroecosystems are characterized by
major dependence on human interference and
therefore are infl uenced by factors that extend
into the system such as energy, agrochemicals
and their residues (Odum
1984
). In contrast to
natural ecosystems, agroecosystems are created
and controlled by humans through the manage-
ment of ecological processes for production and
conservation. Soil is the prime area for manipu-
lation in agroecosystems, because it is a biologi-
cally dynamic resource. Within this soil, the
rhizosphere is the locus of greater role of energy
fl ow and mineral cycling among the physical,
chemical and biological components; it can
therefore be considered as a subsystem (Wright
and Miller
1994
).
Arbuscular mycorrhizal (AM) fungi are one
of the imperative soil microorganisms that
participate mainly in the plant uptake of nutri-
ents, especially phosphorus (P) in diverse agro-
ecosystems (Atkinson et al.
2002
; Gadd
2005
;
Jansa et al.
2008
). In addition, AM fungi can
easily take up and translocate other macronutri-
ents and several micronutrients to plants (Ortas
and Akpinar
2006
; Abo-Rekab et al.
2010
).
Hence, AM fungi are recipients of worldwide
attention as they play an important role in sus-
taining an active and diverse biological community
essential for increasing the sustainability of
agricultural systems (Gianinazzi and Schüepp
1994
). Arbuscular mycorrhizal fungi constitute
around 50 % of soil microbial biomass in agri-
cultural soils due to their profuse growth and
abundance (Olsson et al.
1999
). Most of the
major crops are capable of forming AM associa-
tions naturally and are the most common mycor-
rhizal type involved in agricultural systems
(Barea et al.
1993
). As AM fungal association
can improve plant growth and health, there is an
increasing interest in ascertaining their effec-
tiveness in plant production systems and, conse-
quently, in manipulating them when feasible, so
that they could be successfully incorporated into
plant production systems.
The aim of this review is to discuss the devel-
opments and to provide insights regarding the
potentials of AM fungi in agricultural systems.
Given the overview of benefi cial effects of AM
association on plant growth and health, it is
expected that the development of appropriate
management practices that enable the prolifera-
tion of AM fungi would reduce the chemical
inputs (fertilizers and biocides) in the upcoming
years, a key aspect of sustainable agriculture.
2
General Aspects
The obligate endosymbiont, 'AM fungi' associating
with more than 90 % of terrestrial plants (Graham
2008
), belongs to the phylum Glomeromycota
and acts as a bridge between soil and plants.
Arbuscular mycorrhizal fungal hyphae are coe-
nocytic and aseptate and reproduce asexually by
spores (Kuhn et al.
2001
). Formerly called 'vesic-
ular-arbuscular mycorrhiza' or 'VAM', the name
implies to the production of special structures,
i.e. arbuscules and vesicles (Fig.
1
), within the
host roots. However, the lack of the production of
vesicles within the host roots by certain genera
belonging to the order Gigasporales (
Gigaspora
,
Scutellospora
) resulted in the modifi cation of
term to 'arbuscular mycorrhiza' or 'AM'. At pres-
ent, there are around 249 species in 17 genera of
fungi involved in AM association (Schü
ʲ
ler and
Walker
2010
).
Search WWH ::
Custom Search