Agriculture Reference
In-Depth Information
symbiosis with a legume. Furthermore,
Rhizobium
protein and plasmid profiles were
evaluated, in order to identify variability and to relate it with salt tolerance.
To accomplish these goals isolates were grown in YEM supplemented with NaCl (25
to 1800 mM). According to their growth responses isolates were classified in three
groups: sensitive (0-50 mM NaCl), tolerant (100-500 mM NaCl) and extremely tolerant
(600-1800 mM NaCl). Salt tolerance was a reflex of the conditions experienced in their
natural habitats. Forty-one polypeptides were separated by SDS-PAGE. Salt conditions
induced differences in protein profiles when compared with controls. Extremely tolerant
strains were the less affected, suggesting the putative presence of constitutive
mechanisms conferring tolerance to NaCl. Strains displayed different plasmid profiles
and classification analysis suggests that the presence of certain plasmids (828, 734, 147
and 82 MDa) can be correlated to salt tolerance. Finally, tolerant strains were
demonstrated to efficiently nodulate
Pisum sativum
plants, in the absence of salt, and
more importantly in the presence of moderate levels of sodium chloride, which, due to
the announced climate changes, could be important in a near future to maintain the
present areas of legume cultivation. This is of particular importance because it points out
the need of further studies to predict the influence of climate alterations on soil microbial
populations. Under this context, because
Rhizobium
is important to several natural and
agricultural communities, it may be potential use as an indicator and enabler of
agricultural sustainability in affected soils.
1.
I
NTRODUCTION
The impact of climate changes on biota has recently gained prominence, given the
significant concern towards global warming and impending climate changes. According to the
Third Assessment Report of Working Group I of the Intergovernmental Panel on Climate
Change (IPCC, 2007) the global average surface temperature has increased over the 20
th
Century by about 0.6ºC and for 2100 estimates predict increases between 1.4 and 5.8 ºC,
depending on natural changes and human activities. With the predicted climate alterations of
increasing temperature and rainfall distribution is expected that this problem will not only be
intensified but also be spread worldwide in a very near future. The resulting land degradation
is a major constraint of crop yield worldwide, with erosion, salinization, and desertification as
important consequences (Rozelle et al., 1997). About one-third of the world's irrigated land is
salt affected (Shannon et al., 1984), and up to 40% of world's land surface shows potential
salinity problems (Bouhmouch et al., 2005). Being a Mediterranean country, Portugal is
strongly affected by high temperature (which frequently surpass 40ºC) and reduced rainfall,
specially in late Spring and Summer, constraining agriculture production, particularly in the
southern areas.
In many developing countries, the effective management of nitrogen (N) in the
environment is an essential element for agricultural sustainability (Rehman and Nautiyal,
2002). The 6 billion people on earth consume an average of nearly 11 g of N per person per
day (Fink et al., 1999). Plant sources satisfy up to 80% of dietary needs in much of the tropics
and sub-tropics. With the earth's population increasing 1.4% annually, and expected to reach
8.3 billion in 2025 (Mannion, 1998), unprecedented increases in crop production will be
needed if the current levels of dietary proteins and caloric intake are to be maintained.
Furthermore, leguminous plants are frequently used for degraded soil sites in arid and
semiarid regions because they can grow in barren soils that are unsuitable for most crops.
