overall plant growth improvement which can induce plant metabolism and ultimately increase plant adaptation and production.
9.2.1.1 N 2 -Fixation
Nitrogen is a vital element that affects plant growth and productivity. The amount of
N 2 in the atmosphere is about 78%, but plant species alone cannot be able to use it
for growth. N 2 in the atmosphere is enzymatically converted by N-fixing bacteria to
become a form that plants can use. N 2 -fixing bacteria provide nitrogen to plants
through symbiotic and non-symbiotic N 2 -fixation. In the symbiotic mechanism, the
bacterial cells enter the root tissue and form nodules such as the Rhizobia group
(Ahemad and Kibret 2014). Rhizobium, Bradyrhizobium, Sinorhizobium, and
Mesorhizobium are the members of Rhizobia groups. In general, these bacteria
interact symbiotically with legumes. The non-symbiotic mechanism is generally
known as diazotroph. The non-symbiotic bacteria include the genus of Burkholderia,
Diazotrophicus, Enterobacter, Gluconacetobacter, Azoarcus, Azotobacter,
Acetobacter, Azospirillum, Pseudomonas, and Cyanobacteria (Bhattacharyya and
Jha 2012; Vejan et al. 2016a, b).
The diversity of non-symbiotic N 2 fixing microorganisms is very high. It is an
indication of their important role in supporting plant growth. It was estimated that the
contribution of N 2 fixation to total N assimilation was between 23% and 32%
(Bairamov et al. 2001). Bacteria such as Enterobacter, Klebsiella, Burkholderia,
and Stenotrophomonas have been gaining attention in recent years because of their
association with important crops and the potential to enhance plant growth (Ramirez
and Mellado 2005).
In the field research in peatland of Central Kalimantan, Hashidoko et al. (2006)
found that plants Melastoma malabathricum grow very well not only in peatland,
but also in acid sulfate soil (extremely acidic) and sandy podzolic soil (extremely
poor nutrients content), without applying N fertilizer. As it was found that the
microbes of the rhizosphere of Melastoma malabathricum fix N 2 , and the N 2 fixing
microbes exude ammonium to neutralize pH in the rhizosphere.
Under unfavorable environmental conditions, microbes will synergize with each
other, even though they are from different groups, for example, N 2 fixing bacteria
will interact with the fungus Arbuscular Mycorrhiza (AM) (Bona et al. 2017; Puppi
et al. 1994). AM fungi that are in the root tissue of plants will help to provide
phosphorus (P) for N-fixing microbes, which can ultimately bring benefits to host
plants. Some bacterial co-inoculation in AM treatments can increase N fixation,
although this does not necessarily mean increasing plant agronomic parameters
(Ibijbijen et al. 1996; Bona et al. 2015; Rashid et al. 2016). AM mycelium has the
opportunity to protect the N-fixing Burkholderia that exists in the intra-cell, as a
shelter from oxygen and nitrogenase enzyme synthesis. The existence and benefits of
Burkholderia in N 2 fixation are very meaningful for the ecological function of the
soil (Minerdi et al. 2001).
304
S. Antonius et al.
9.2.1.1 N 2 -Fixation
Nitrogen is a vital element that affects plant growth and productivity. The amount of
N 2 in the atmosphere is about 78%, but plant species alone cannot be able to use it
for growth. N 2 in the atmosphere is enzymatically converted by N-fixing bacteria to
become a form that plants can use. N 2 -fixing bacteria provide nitrogen to plants
through symbiotic and non-symbiotic N 2 -fixation. In the symbiotic mechanism, the
bacterial cells enter the root tissue and form nodules such as the Rhizobia group
(Ahemad and Kibret 2014). Rhizobium, Bradyrhizobium, Sinorhizobium, and
Mesorhizobium are the members of Rhizobia groups. In general, these bacteria
interact symbiotically with legumes. The non-symbiotic mechanism is generally
known as diazotroph. The non-symbiotic bacteria include the genus of Burkholderia,
Diazotrophicus, Enterobacter, Gluconacetobacter, Azoarcus, Azotobacter,
Acetobacter, Azospirillum, Pseudomonas, and Cyanobacteria (Bhattacharyya and
Jha 2012; Vejan et al. 2016a, b).
The diversity of non-symbiotic N 2 fixing microorganisms is very high. It is an
indication of their important role in supporting plant growth. It was estimated that the
contribution of N 2 fixation to total N assimilation was between 23% and 32%
(Bairamov et al. 2001). Bacteria such as Enterobacter, Klebsiella, Burkholderia,
and Stenotrophomonas have been gaining attention in recent years because of their
association with important crops and the potential to enhance plant growth (Ramirez
and Mellado 2005).
In the field research in peatland of Central Kalimantan, Hashidoko et al. (2006)
found that plants Melastoma malabathricum grow very well not only in peatland,
but also in acid sulfate soil (extremely acidic) and sandy podzolic soil (extremely
poor nutrients content), without applying N fertilizer. As it was found that the
microbes of the rhizosphere of Melastoma malabathricum fix N 2 , and the N 2 fixing
microbes exude ammonium to neutralize pH in the rhizosphere.
Under unfavorable environmental conditions, microbes will synergize with each
other, even though they are from different groups, for example, N 2 fixing bacteria
will interact with the fungus Arbuscular Mycorrhiza (AM) (Bona et al. 2017; Puppi
et al. 1994). AM fungi that are in the root tissue of plants will help to provide
phosphorus (P) for N-fixing microbes, which can ultimately bring benefits to host
plants. Some bacterial co-inoculation in AM treatments can increase N fixation,
although this does not necessarily mean increasing plant agronomic parameters
(Ibijbijen et al. 1996; Bona et al. 2015; Rashid et al. 2016). AM mycelium has the
opportunity to protect the N-fixing Burkholderia that exists in the intra-cell, as a
shelter from oxygen and nitrogenase enzyme synthesis. The existence and benefits of
Burkholderia in N 2 fixation are very meaningful for the ecological function of the
soil (Minerdi et al. 2001).
304
S. Antonius et al.