5115 Microbes in Climate Change Adaptation and Mitigation
Dryland areas—with an aridity index (precipitation/potential evapotranspiration
ratio) below 0.65—are among the most sensitive ecosystems to climate change.
Dryland areas are expected to increase globally by 11–23 % by 2100 and experience
increased aridity and reduced soil moisture (Maestre et al. 2015 ). Low rainfall and
high temperatures are the characteristics of arid or semi-arid regions. Salinity and
low temperatures (in temperate regions) are other stresses that influence dryland
agriculture. Altered climatic conditions and anthropogenic activities are expected to
exacerbate these problems in dryland areas. Different stress factors will signifi-
cantly influence the performance of beneficial microorganisms. If the soil is healthy
and biologically diverse, plants will have a higher chance of surviving stressful
conditions. Under stress, plants or microorganisms need a stronger network to sur-
vive, so their interactions with each other evolve to cope with the stress conditions
(Timmusk and Wagner 1999 ). Compared with higher organisms, microorganisms
can adapt quickly to changing environments. Therefore, the isolation of stress-
tolerant microorganisms from a stressed ecosystem can help in the selection of effi-
cient strains to be used as bioinoculants for abiotic stress management in crop
plants. Rasul et al. ( 2012 ) isolated abiotic stress tolerant rhizobial isolates nodulat-
ing pongamia (Milatta pinnata), from soils of dryland agroecosystems. The isolates
could tolerate a wide pH range (4.0–10.0), salinity (3 % NaCl) and high temperature
(45 °C) conditions, indicating their potential for application under stressed condi-
tions. In the last decade, the number of reports on plant growth promotion by micro-
organisms under different abiotic stress conditions, such as drought, high and low
temperature, salinity and flooding, has increased (Kohler et al. 2009 ; Ali et al. 2009 ;
Sandhya et al. 2009 ; Grover et al. 2011 , Kaushal and Wani 2016 ). The term Induced
Systemic Tolerance (IST) has been proposed for PGPR-induced physical and chem-
ical changes that result in enhanced tolerance to abiotic stress (Yang et al. 2009 ).
Bacteria belonging to different genera including Rhizobium, Bacillus, Pseudomonas,
Pantoea, Paenibacillus, Burkholderia, Achromobacter, Azospirillum,
Microbacterium, Methylobacterium, variovorax and Enterobacter, viruses, fungi
and mycorrhizae have improved the tolerance of host plants under different abiotic
stress environments (Grover et al. 2011 ).
A variety of mechanisms has been proposed behind microbial-elicited stress tol-
erance in plants (Grover et al. 2011 ). Microorganisms produce phytohormones,
solubilize and mobilize nutrients, compete with plant pathogens for nutrients and
space, and antagonize plant pathogens. These properties directly or indirectly help
plants to grow better under normal and stress conditions. The production of stimula-
tory phytohormones, such as indole acetic acid, gibberellins and some unknown
determinants, by PGPR can increase root length, root surface area and the number
of root tips, which enhance the uptake of nutrients to improve plant health under
abiotic stress conditions (Egamberdieva and Kucharova 2009 ). The production of
Application of Microbiology in Dryland Agriculture