5.5 Reclamation of Alkaline and Saline Soil
Alkaline and saline soil sets an unfavourable condition for plant growth; hence,
reclamation of such soil could increase the cultivation area, thereby increasing the
crop production. Cyanobacteria could tolerate and thrive on high pH and saline
condition and thus promote plant growth under unfavourable conditions.
Merely, the agricultural soils are in the different physiochemical combined state
of alkaline, saline, abundant nutrients, rich cations and a high percentage of organic
matter. Diversified heterocyst and non-heterocyst cyanobacterial species occupy
different kinds of agricultural soil condition. Spirulina platensis and Spirulina
maxima were reported to thrive in alkaline lakes of Africa and Mexico at pH ranging
from 8.0 to 11.0, which made them cyanobacterial monospecies devoid of other
cyanobacteria. Thus, these cyanobacteria could be used in alkaline agricultural soil
to improve fertility (Alghanmi and Jawad 2019; Habib 2008).
Salinity is one of the most prevalent agricultural problems in the arid and semiarid regions of the world, affecting approximately 1 billion ha of land (Latef and
Chaoxing 2011). Estimations indicate that increased salinization of arable land will
result in 30% land loss within the next 25 years, and up to 50% within the next
40 years (Porcel et al. 2012). High salt depositions in the soil generate a low water
potential zone in the soil, making it increasingly difficult for the plant to acquire both
water and nutrients. In Tamil Nadu, 4.7 lakh ha is salt-affected saline soil in which
2.0 lakh ha is alkali soil confined to inland. The ESP of soils range between 26 and
45. In general, higher sodicity (>15%) leads to severe structural degradation due to
high degree of dispersion of clay particles. The basic physiology of high salt stress
and drought stress overlaps with each other. Therefore, salt stress essentially results
in a water-deficit condition in the plant and takes the form of a physiological drought
(Mahajan and Tuteja 2005). Most of the crops, commonly used for food production,
are sensitive to salinity stress and vary in their response to salt stress tolerance
(Flowers and Colmer 2008). Among cereals, rice (Oryza sativa) is the most sensitive, while barley (Hordeum vulgare) is regarded as the most tolerant. Bread wheat
(Triticum aestivum) is comparatively more tolerant than durum wheat (Triticum
turgidum ssp. durum). High salt concentrations lead to a decline in soil fertility by
adversely affecting the soil microbial flora, including nitrogen-fixing cyanobacteria
and therefore further decreasing rice productivity.
Cyanobacteria are capable of not only surviving but thriving in conditions which
are considered to be inhabitable, tolerating desiccation, high temperature, extreme
pH and high salinity with high sodicity, illustrating their capacity to acclimatize to
extreme environments. Until recently, the responses of cyanobacteria to salinity
stresses were poorly documented as compared to heterotrophic bacteria and
phototrophic eukaryotic algae. These organisms evolved about 3000 million years ago
and are considered to be the primary colonizers of the inhospitable ecosystems. The
physiological aspects for the adaptation of cyanobacteria to high salinities include
(a) synthesis and accumulation of osmoprotective compounds, (b) maintenance of
low internal concentrations of inorganic ions and (c) expression of a set of salt-stress
5 Cyanobacteria-Mediated Bioremediation of Problem Soils
147
Alkaline and saline soil sets an unfavourable condition for plant growth; hence,
reclamation of such soil could increase the cultivation area, thereby increasing the
crop production. Cyanobacteria could tolerate and thrive on high pH and saline
condition and thus promote plant growth under unfavourable conditions.
Merely, the agricultural soils are in the different physiochemical combined state
of alkaline, saline, abundant nutrients, rich cations and a high percentage of organic
matter. Diversified heterocyst and non-heterocyst cyanobacterial species occupy
different kinds of agricultural soil condition. Spirulina platensis and Spirulina
maxima were reported to thrive in alkaline lakes of Africa and Mexico at pH ranging
from 8.0 to 11.0, which made them cyanobacterial monospecies devoid of other
cyanobacteria. Thus, these cyanobacteria could be used in alkaline agricultural soil
to improve fertility (Alghanmi and Jawad 2019; Habib 2008).
Salinity is one of the most prevalent agricultural problems in the arid and semiarid regions of the world, affecting approximately 1 billion ha of land (Latef and
Chaoxing 2011). Estimations indicate that increased salinization of arable land will
result in 30% land loss within the next 25 years, and up to 50% within the next
40 years (Porcel et al. 2012). High salt depositions in the soil generate a low water
potential zone in the soil, making it increasingly difficult for the plant to acquire both
water and nutrients. In Tamil Nadu, 4.7 lakh ha is salt-affected saline soil in which
2.0 lakh ha is alkali soil confined to inland. The ESP of soils range between 26 and
45. In general, higher sodicity (>15%) leads to severe structural degradation due to
high degree of dispersion of clay particles. The basic physiology of high salt stress
and drought stress overlaps with each other. Therefore, salt stress essentially results
in a water-deficit condition in the plant and takes the form of a physiological drought
(Mahajan and Tuteja 2005). Most of the crops, commonly used for food production,
are sensitive to salinity stress and vary in their response to salt stress tolerance
(Flowers and Colmer 2008). Among cereals, rice (Oryza sativa) is the most sensitive, while barley (Hordeum vulgare) is regarded as the most tolerant. Bread wheat
(Triticum aestivum) is comparatively more tolerant than durum wheat (Triticum
turgidum ssp. durum). High salt concentrations lead to a decline in soil fertility by
adversely affecting the soil microbial flora, including nitrogen-fixing cyanobacteria
and therefore further decreasing rice productivity.
Cyanobacteria are capable of not only surviving but thriving in conditions which
are considered to be inhabitable, tolerating desiccation, high temperature, extreme
pH and high salinity with high sodicity, illustrating their capacity to acclimatize to
extreme environments. Until recently, the responses of cyanobacteria to salinity
stresses were poorly documented as compared to heterotrophic bacteria and
phototrophic eukaryotic algae. These organisms evolved about 3000 million years ago
and are considered to be the primary colonizers of the inhospitable ecosystems. The
physiological aspects for the adaptation of cyanobacteria to high salinities include
(a) synthesis and accumulation of osmoprotective compounds, (b) maintenance of
low internal concentrations of inorganic ions and (c) expression of a set of salt-stress
5 Cyanobacteria-Mediated Bioremediation of Problem Soils
147