Agriculture Reference
In-Depth Information
The “arable” layer of the soil is where the absorbing roots of plants are
concentrated, becoming the primary habitat and reservoir of AMF propagules in
ecosystems. Any factor impacting this layer will exert a great influence on the AMF
community. Weissenhorn et al. (
1993
) and Weissenhorn et al. (
1994
) evaluated the
tolerance of isolates of
Glomus mosseae
obtained from adjacent areas that were
polluted or not polluted with heavy metals (Cd and Zn), and also in relation to a
reference isolate maintained in the laboratory. Germination tests showed that the
isolates obtained from contaminated areas showed greater tolerance to heavy met-
als than the isolates from adjacent uncontaminated areas. This result demonstrates
that different isolates of the same “species” are functionally distinct and suggest that
AMF have the ability to adapt to anthropogenic changes.
The
AMF responses to heavy metals are diverse at the fungus species level (Hil-
debrandt et al.
2007
). For example,
Glomus etunicatum
was more sensitive to Cd,
Pb and Zn than
G. intraradices
(Pawlowska and Charvat
2004
), and the
G. mosseae
isolated from soils polluted with heavy metals was more tolerant to Cd than the
same species isolated from a non-polluted substrate (Weissenhorn et al.
1994
). An
adequate understanding of the AMF community under stress by heavy metals could
contribute to the recognition of the interactions between fungi and heavy metals
and future revegetation or phytoremediation of regions polluted by heavy metals
(Hildebrandt et al.
2007
). Studies indicate that many species of plants growing well
in areas polluted by a single heavy metal, such as
Fragaria vesca
,
Viola calaminar-
ia
,
Veronica rechingeri
,
Solidago giante
,
Thymus polytrichus
and
Thlaspi praecox
,
were colonised by various AMF and AMF isolates that can positively act to regulate
plant resistance to heavy metal stress (Zarei et al.
2008
; Sonjak et al.
2009
).
Studies conducted with AMF in preserved and disturbed areas show the impor-
tance of these fungi in the studied areas (Silva et al.
2005
). Silva et al. (
2005
) identi-
fied 15 species of AMF in an area of preserved caatinga and an area degraded by
copper mining and observed a strong reduction in plant diversity and AMF species
community; the community was quantitatively and qualitatively affected by mining
activity. In areas of high salinity, Yano-Melo et al. (
2003
) identified 21 taxa of AMF,
especially
G. mosseae
and
G. intraradices
, which favoured sporulation in the first
cycle of multiplication in a trap culture and decreased from the second cycle.
Salinity stress negatively affects the formation and function of mycorrhizal sym-
biosis by inhibition of spore germination, plant colonisation and formation of new
spores (Juniper and Abbott
2006
; Giri et al.
2007
; Abdel Latef and Chaoxing
2011
).
Other environmental factors such as soil water content, concentrations of available
phosphorus, organic matter content in the soil, soil pH and vegetation coverage
affect levels of colonisation in plants through AMF. AMF in wetland habitats are
periodically exposed to anaerobic conditions and high salinity in soils (Bohrer et al.
2004
; Carvalho et al.
2004
). Depending on the AMF species, soil salinity levels
can affect spore production and germination (Carvalho et al.
2004
). The presence
of heavy metals in toxic concentrations in the soil also exert great influence on the
AMF, and the excess metal reduces spore germination, mycelial growth, degree of
colonisation, and sporulation of these fungi, which might have a significant impact
on their ecology and diversity (Klauberg-Filho et al.
2005
).
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