12 Endophytic Rhizobacteria for Mineral Nutrients …
269
and protein contents, root and shoot lengths, yield, and tolerance to abiotic stresses
(Verma et al. 2013, 2015). The rhizobia which are the best-understood endophytes
are critical for Nitrogen (N) nutrition in leguminous plants (Santoyo et al. 2016).
Although endophytic rhizobacteria have widely been investigated, their significance in improving plant mineral nutrient acquisition has emerged quite recently
(Harman and Uphoff 2019), and literature propounds that they could be better plant
growth promoters and possess certain advantageous traits that give them an edge over
their external counterparts (Coutinho et al. 2015; Asaf et al. 2017). However, this
theory is not yet clearly understood as both are similar to their facilitation of plant
mineral nutrients acquisition. This chapter reviews the potential functions of endophytic rhizobacteria in the acquisition of certain plant mineral macronutrients such
as N, P, K and micronutrients like Zn and Fe. The putative advantageous traits that
facilitate these functions and make them suitable candidates for enhancing mineral
nutrients acquisition in plants are also discussed. Such information will enrich our
knowledge on these important plant endophytic microbiome and possibly pave the
way for their complete understanding and utilization as biofertilizers for sustainable
crop production.
12.2 Putative Functions of Endophytic PGPR for Mineral
Nutrients Acquisition in Plants
Several studies demonstrate the diversity and functions of endophytic rhizobacteria
toward plant mineral nutrients acquisition and general PGP activities. In this section,
we outline some of these studies and functions to demonstrate the importance of
these bacteria in plant mineral nutrition.
12.2.1 Endophytic Rhizobacteria and Nitrogen Acquisition
in Plants
Nitrogen is the most important nutrient required for plant growth (Verma et al. 2019).
Although the atmosphere contains about 78% N, most of this is present in inert form
and inaccessible to plants, making it a major plant-limiting nutrient. Artificial Nfertilizers are commonly applied to supply N to plants. However, out of every 100
Tg of N applied in agricultural fields globally, only about 17 Tg are utilized by
plants and the rest is either lost or accumulates in the environment with serious
implications to the soil and environment (Erisman et al. 2008; Howarth 2008). The
microorganisms can convert excess ammonium or nitrate in the soil into nitrous
oxide (N 2 O), a potent greenhouse gas (GHG) (Kandel et al. 2017), whose effects are
reportedly much worse than that of CO 2 (Ramaswamy et al. 2001).
269
and protein contents, root and shoot lengths, yield, and tolerance to abiotic stresses
(Verma et al. 2013, 2015). The rhizobia which are the best-understood endophytes
are critical for Nitrogen (N) nutrition in leguminous plants (Santoyo et al. 2016).
Although endophytic rhizobacteria have widely been investigated, their significance in improving plant mineral nutrient acquisition has emerged quite recently
(Harman and Uphoff 2019), and literature propounds that they could be better plant
growth promoters and possess certain advantageous traits that give them an edge over
their external counterparts (Coutinho et al. 2015; Asaf et al. 2017). However, this
theory is not yet clearly understood as both are similar to their facilitation of plant
mineral nutrients acquisition. This chapter reviews the potential functions of endophytic rhizobacteria in the acquisition of certain plant mineral macronutrients such
as N, P, K and micronutrients like Zn and Fe. The putative advantageous traits that
facilitate these functions and make them suitable candidates for enhancing mineral
nutrients acquisition in plants are also discussed. Such information will enrich our
knowledge on these important plant endophytic microbiome and possibly pave the
way for their complete understanding and utilization as biofertilizers for sustainable
crop production.
12.2 Putative Functions of Endophytic PGPR for Mineral
Nutrients Acquisition in Plants
Several studies demonstrate the diversity and functions of endophytic rhizobacteria
toward plant mineral nutrients acquisition and general PGP activities. In this section,
we outline some of these studies and functions to demonstrate the importance of
these bacteria in plant mineral nutrition.
12.2.1 Endophytic Rhizobacteria and Nitrogen Acquisition
in Plants
Nitrogen is the most important nutrient required for plant growth (Verma et al. 2019).
Although the atmosphere contains about 78% N, most of this is present in inert form
and inaccessible to plants, making it a major plant-limiting nutrient. Artificial Nfertilizers are commonly applied to supply N to plants. However, out of every 100
Tg of N applied in agricultural fields globally, only about 17 Tg are utilized by
plants and the rest is either lost or accumulates in the environment with serious
implications to the soil and environment (Erisman et al. 2008; Howarth 2008). The
microorganisms can convert excess ammonium or nitrate in the soil into nitrous
oxide (N 2 O), a potent greenhouse gas (GHG) (Kandel et al. 2017), whose effects are
reportedly much worse than that of CO 2 (Ramaswamy et al. 2001).