15
Available nutrient levels are commonly low at unfertile/contaminated sites and
resource competition, especially for nitrogen, phosphorus, potash, zinc, iron, etc.,
which become limiting factors for growth of the plants (de-Bashan et al. 2012).
Microbial interactions with plant roots can improve soil quality in degraded, marginal, and unfertile land. Beneficial microbiota are a subset of the rhizospheric
microorganisms that make the soil suppressive to soil-borne disease through production of iron chelators and antibiotics, controlled colonization of the root tissues,
inter-species resource competition, immobilisation, and biodegradation of hazardous compounds, production of the signalling molecule salicylic acid, which induces
systemic resistance in plants and enzymes such as ACC-carboxylase that degrades
the ethylene precursor repressing the plant stress response to various stress factors
(Nadeem et al. 2014; Lehman et al. 2015). The association of plants with arbuscular
mycorrhizae also helps in improving soil quality as the produced glycoprotein
“Glomalin” helps in soil aggregate formation. Plants also improve the soil quality
by addition of readily available carbon inputs belowground as a distinct rhizosecretion of the simpler form of compounds (mono-saccharides, low-carboncontaining amino and organic acids), mucilage, root debris (Philippot et al. 2013).
Freshly added carbon could enhance the turnover of soil organic matter to increase
nutrient availability (Trivedi et al. 2013), enhance fertility, provide the nutrient
source to the soil microorganisms, and shape the soil microorganism community
structure in the rhizosphere. Addition of root exudates at 32.75 mg kg
−1
total organic
carbon concentration was reported to enhance the xenobiotic (pyrene) degradation,
shape the community structure of soil microorganisms, and enhance the activities of
the enzymes catalase, dehydrogenase, and phosphatase in degraded soils (Xie et al.
2012; Sasse et al. 2018). Still, knowledge regarding how the different components
of the root exudates shape community structure of soil microbes to promote plant
health or restore degraded land is limited. Thus, we need to have an in-depth analysis of the molecular mechanisms of root exudation and plant–microorganisms interactions for successfully exploiting these to understand ecosystem services (Zhalnina
et al. 2018).
2.7 Microbially Assisted Extensification for Improving
Agricultural Production from Degraded Lands
Marginal lands are lands where cost-effective agricultural production is not possible
(Edrisi and Abhilash 2016). Hence, beneficial plant–microbe interactions and soil
biodiversity become critically significant in such lands to improve plant health
(Tripathi et al. 2014a; Rillig et al. 2018). Experiments on the reclaimed desert lands
significantly supported canola plant (Brassica napus L.) growth when amended
with different microbial strains (El-Howeity and Asfour 2012). The amendments
included Azotobacter chroococcum, Azospirillum brasiliense, and Paenibacillus
polymyxa. Maximum yield was observed by the inoculation of Azospirillum brasilense supplemented with 60 kg N/fed as compared to other bacterial strains and the
2.7 Microbially Assisted Extensification for Improving Agricultural Production…
Available nutrient levels are commonly low at unfertile/contaminated sites and
resource competition, especially for nitrogen, phosphorus, potash, zinc, iron, etc.,
which become limiting factors for growth of the plants (de-Bashan et al. 2012).
Microbial interactions with plant roots can improve soil quality in degraded, marginal, and unfertile land. Beneficial microbiota are a subset of the rhizospheric
microorganisms that make the soil suppressive to soil-borne disease through production of iron chelators and antibiotics, controlled colonization of the root tissues,
inter-species resource competition, immobilisation, and biodegradation of hazardous compounds, production of the signalling molecule salicylic acid, which induces
systemic resistance in plants and enzymes such as ACC-carboxylase that degrades
the ethylene precursor repressing the plant stress response to various stress factors
(Nadeem et al. 2014; Lehman et al. 2015). The association of plants with arbuscular
mycorrhizae also helps in improving soil quality as the produced glycoprotein
“Glomalin” helps in soil aggregate formation. Plants also improve the soil quality
by addition of readily available carbon inputs belowground as a distinct rhizosecretion of the simpler form of compounds (mono-saccharides, low-carboncontaining amino and organic acids), mucilage, root debris (Philippot et al. 2013).
Freshly added carbon could enhance the turnover of soil organic matter to increase
nutrient availability (Trivedi et al. 2013), enhance fertility, provide the nutrient
source to the soil microorganisms, and shape the soil microorganism community
structure in the rhizosphere. Addition of root exudates at 32.75 mg kg
−1
total organic
carbon concentration was reported to enhance the xenobiotic (pyrene) degradation,
shape the community structure of soil microorganisms, and enhance the activities of
the enzymes catalase, dehydrogenase, and phosphatase in degraded soils (Xie et al.
2012; Sasse et al. 2018). Still, knowledge regarding how the different components
of the root exudates shape community structure of soil microbes to promote plant
health or restore degraded land is limited. Thus, we need to have an in-depth analysis of the molecular mechanisms of root exudation and plant–microorganisms interactions for successfully exploiting these to understand ecosystem services (Zhalnina
et al. 2018).
2.7 Microbially Assisted Extensification for Improving
Agricultural Production from Degraded Lands
Marginal lands are lands where cost-effective agricultural production is not possible
(Edrisi and Abhilash 2016). Hence, beneficial plant–microbe interactions and soil
biodiversity become critically significant in such lands to improve plant health
(Tripathi et al. 2014a; Rillig et al. 2018). Experiments on the reclaimed desert lands
significantly supported canola plant (Brassica napus L.) growth when amended
with different microbial strains (El-Howeity and Asfour 2012). The amendments
included Azotobacter chroococcum, Azospirillum brasiliense, and Paenibacillus
polymyxa. Maximum yield was observed by the inoculation of Azospirillum brasilense supplemented with 60 kg N/fed as compared to other bacterial strains and the
2.7 Microbially Assisted Extensification for Improving Agricultural Production…