plants, soil, soil microbes, and PGPR. It is known that bacteria are the highest
number of microbial population in the rooting system (Antoun and Kloepper
2001). Rhizoplane bacteria colonize and reproduce themselves on the root surface
area, and endophytic bacteria can enter and live in the root tissue (Bacon and Hinton
2007; Ali 2013; Compant et al. 2005b); Rhizobacteria (Rhizoplane bacteria and
Endophytic bacteria) that colonize on/in plant roots and are able to stimulate plant
growth when Rhizobacteria are inoculated into seeds, roots, or tubers are known as
plant growth-promoting rhizobacteria (PGPR) (Klopper et al. 1980).
According to Bloemberg and Lugtenberg (2001), PGPR is not only taking
advantage of acquiring nutritions (such as carbohydrates) secreted by plants, but
also reciprocally to benefit the plant for its growth both directly and indirectly.
Ahemad and Kibret (2014) further suggested that PGPR shows the following
properties: (1) bacteria can colonize plant roots, (2) bacteria are able to survive,
reproduce themselves, and compete with other microbes, able to produce growth
promoters and metabolites or enzymes to protect plants from pathogens, and
(3) these bacteria are able to stimulate plant growth. If PGPR is applied for
improving plant production, it will be possible to reduce the use of inorganic
synthetic agrochemicals. Moreover, PGPR can also increase plant tolerance to biotic
and abiotic stress (Compant et al. 2005a).
9.2 Review of PGPR Function
There are many PGPR functions in natural conditions. Therefore, in this section the
main functions related to “AeroHydro Culture” technology in tropical peatland are
summarized as (1) nutrient acquirement and (2) plant growth factors. There are
several mechanisms on how PGPR influences plant growth. PGPR induces plant
growth through changes in the microbial community in the rhizosphere to produce
various kinds of organic compounds. In general, PGPR can directly influence growth
plants through their abilities to increase the availability of nutrients (nitrogen,
phosphorus, potassium, and other elements) and indirectly control pests and diseases
by producing antibiotics, colonizing plant root tissue, and dominating the rhizosphere environment so that the plant pathogens will be suppressed. The direct and
indirect grouping mechanisms of plant growth promotion by PGPR were suggested
by Goswami et al. (2016).
9.2.1 Direct Influence of PGPR
Along with understanding the role of PGPR in plants, until now the direct effect
which is actually a classic definition is still commonly used. The mechanism of
PGPR’s direct influence is the mechanism that affects the physiological balance for
9 Plant Growth-Promoting Rhizobacteria (PGPR) and Compost Materials for. . .
303
number of microbial population in the rooting system (Antoun and Kloepper
2001). Rhizoplane bacteria colonize and reproduce themselves on the root surface
area, and endophytic bacteria can enter and live in the root tissue (Bacon and Hinton
2007; Ali 2013; Compant et al. 2005b); Rhizobacteria (Rhizoplane bacteria and
Endophytic bacteria) that colonize on/in plant roots and are able to stimulate plant
growth when Rhizobacteria are inoculated into seeds, roots, or tubers are known as
plant growth-promoting rhizobacteria (PGPR) (Klopper et al. 1980).
According to Bloemberg and Lugtenberg (2001), PGPR is not only taking
advantage of acquiring nutritions (such as carbohydrates) secreted by plants, but
also reciprocally to benefit the plant for its growth both directly and indirectly.
Ahemad and Kibret (2014) further suggested that PGPR shows the following
properties: (1) bacteria can colonize plant roots, (2) bacteria are able to survive,
reproduce themselves, and compete with other microbes, able to produce growth
promoters and metabolites or enzymes to protect plants from pathogens, and
(3) these bacteria are able to stimulate plant growth. If PGPR is applied for
improving plant production, it will be possible to reduce the use of inorganic
synthetic agrochemicals. Moreover, PGPR can also increase plant tolerance to biotic
and abiotic stress (Compant et al. 2005a).
9.2 Review of PGPR Function
There are many PGPR functions in natural conditions. Therefore, in this section the
main functions related to “AeroHydro Culture” technology in tropical peatland are
summarized as (1) nutrient acquirement and (2) plant growth factors. There are
several mechanisms on how PGPR influences plant growth. PGPR induces plant
growth through changes in the microbial community in the rhizosphere to produce
various kinds of organic compounds. In general, PGPR can directly influence growth
plants through their abilities to increase the availability of nutrients (nitrogen,
phosphorus, potassium, and other elements) and indirectly control pests and diseases
by producing antibiotics, colonizing plant root tissue, and dominating the rhizosphere environment so that the plant pathogens will be suppressed. The direct and
indirect grouping mechanisms of plant growth promotion by PGPR were suggested
by Goswami et al. (2016).
9.2.1 Direct Influence of PGPR
Along with understanding the role of PGPR in plants, until now the direct effect
which is actually a classic definition is still commonly used. The mechanism of
PGPR’s direct influence is the mechanism that affects the physiological balance for
9 Plant Growth-Promoting Rhizobacteria (PGPR) and Compost Materials for. . .
303