Rhizotrophs in Saline Agriculture
The rhizo-deposition provides energy and nutritional inputs to soil with selection of large and distinct community of metabolically active soil microbiota that carries many biochemical transformations. Positive effects of Rhizobium, Pseudomonas, Bacillus,
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Rhizotrophs in Saline Agriculture Faizan Ullah and Asghari Bano
Abstract
The rhizo-deposition provides energy and nutritional inputs to soil with selection of large and distinct community of metabolically active soil microbiota that carries many biochemical transformations. Positive effects of Rhizobium, Pseudomonas, Bacillus, and Azospirillum on the mitigation of salt stress in inoculated plants have been documented. However, information is scarce regarding the mode of action of the beneficial microbes in improving salt tolerance to host plants. This chapter deals with the salt tolerance potential of rhizobacteria and their mechanism in planta. It has been shown that cooperative microbial activities can be exploited as a low input biotechnology. Addition of osmoprotectants increases tolerance of the microbes to salt. Difference in the utilization of C/N sources also makes the difference in the salt tolerance of rhizobia. Field experiments should be conducted with plant growth-promoting rhizobacteria (PGPR) isolated from stressed areas. Furthermore, efficiency of growth regulators previously used to ameliorate salt stress should be monitored in combination with PGPR, which may be useful as future strategy to mitigate salt stress for agriculture productivity and environmental sustainability. The mechanism of salt tolerance in PGPR appears similar to that of growth regulators applied exogenously to plants.
5.1
Introduction
Salt stress is an important environmental stress significantly affecting plant growth as well as deteriorating soil health and productivity. The FAO Land and Plant Nutrition Management Service estimated greater than 6 % of the land globally F. Ullah Department of Botany, University of Science and Technology, Bannu, KP, Pakistan A. Bano (*) Department of Biosciences, Quaid Campus, University of Wah, Wah Cantt, Pakistan e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 S. Mehnaz (ed.), Rhizotrophs: Plant Growth Promotion to Bioremediation, Microorganisms for Sustainability 2, DOI 10.1007/978-981-10-4862-3_5
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Phytohormones Production (µg/g)
Fig. 5.1 Mechanism of the effects of osmotic stress on higher plants 13 12 11 10 9 8 7 6 5 4 3 2 1 0
A B
B C D AB
D
A C AB A
B CD B B
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P.mendocina Khsr2
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D B B C B
P.putida Khsr4
P.stutzeri Khsr3 Pseudo monas species
IAA -Trp
IAA +Trp
GA3 -Trp GA3 +Trp
t-zr-Trp
t-zr+Trp
ABA -Trp
ABA +Trp
Fig. 5.2 Production of phytohormones (μg/ml) by Pseudomonas sp. in culture media supplemented with tryptophan @ μg/ml and without tryptophan. –Trp = without tryptophan, +Trp = with tryptophan. Adapted from Naz and Bano (2010)
affected by either salinity or sodicity (FAO 2008). The first response of salt stress is osmotic adjustment. Mechanism of the effects of osmotic stress on higher plants is given in Fig. 5.1. Plant survival under salt stress depends on maintaining a positive turgor, which is indispensable for the expansion growth of cell and for the stomatal conductance (Jaleel et al. 20
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