Agriculture Reference
In-Depth Information
11.1
Introduction
Soil inhabits different life-forms including plants, animals, and microorganisms and
is a nutrient hoarded treasure, a support system (for plant) furnishing with plentiful
crops and yields. Any change in soil conditions eventually affects plant growth.
Human activities and ever-increasing populations are continuously exploiting this
natural system, consequently affecting the growth and productivity of plants.
However, there are certain soil factors which negatively affect plant growth.
These are (1) moisture content, (2) salt, (3) nutrient pool of soils, (4) microbial
composition and their functional variation, and (5) soil pollution especially depo-
sition of toxicants (heavy metal and pesticides) in soil. When deviated from optimal
conditions, these factors cause adverse effects and are specified as stress conditions
for soil. The deleterious impacts of these stresses include dwindling productivity,
burden on delimited resources, and economic fall. Considering these threats,
researchers from different fields are working in unison to avert such problems.
One such area involves the exploitation of microbiological resources of soils.
Microorganisms are known to be omnipresent and possess multifunctional charac-
teristics even though the full potential of microorganisms is still unrevealed. Most
of the chemical reactions occurring in soil leading to nutrient availability are
mediated by different microorganisms like N
2
fixers, P solubilizers, or decomposers
(Powlson et al.
2001
). Considering the available information and application of
microorganisms, there has been greater interest in using such organisms to restrain
the adverse effects also (Vassilev et al.
2012
).
Microorganisms colonizing the rhizospheres are known to have beneficial
effects on the nutrient acquisition, mineral solubilization, disease resistance, and
stress tolerance and are collectively described as plant growth-promoting
rhizobacteria (PGPR) (Kloepper and Schroth
1978
; Vessey
2003
). Reports are
available in the literature on the effectiveness of rhizospheric microorganisms as
plant growth promoters as well as on their potential for imparting stress resistance
or improving stress tolerance in plants, presenting PGPR as viable option to cope
with these problems (Yang et al.
2009
; Zelicourt et al.
2013
; Ahemed and Kibret
2014
). Another aspect of exploiting microbial potential is to combine the attributes
of different microbes to get an outcome encompassing numerous or complementing
beneficial effects. Microorganisms are known to have attributes like cooperation/
mutualism where they benefit each other or other life-forms to enhance the positive
outcomes (Singh et al.
2010
). Multiple properties of resistance/tolerance and plant
growth promotion, therefore, serve as an appraisal and make PGPR one of the most
suitable choices to manage these problems (Bano and Fatima
2009
; Egamberdieva
and Kucharova
2009
; Zelicourt et al.
2013
). Judicial application of the stress-
tolerant PGPR consortium can be a viable solution and need to be further strength-
ened through field trials. The present chapter gathers reports on the experimental
studies done on PGPR consortium helping plant/crops cope with stressful soil
conditions. Also, the focus is given here on soil stress and associated effects
including mechanisms of PGPR in stress alleviation.
