Microbes in Agriculture and Environmental Development

Chhatarpal Singh, Shashank Tiwari, Jay Shankar Singh, Ajar Nath Yadav, Chhatarpal Singh, Shashank Tiwari, Jay Shankar Singh, Ajar Nath Yadav

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000204445
• Edition: 1
• Topic: Biowissenschaften
• Subtopic: Umweltwissenschaft

The collection of essays in Microbes in Agriculture and Environmental Development explores the applications of microbes for the improvement of environmental quality and agricultural productivity through inoculants and enzymes. These are useful for the conservation and restoration of degraded natural and agricultural ecosystems, crop yield extension, soil health improvement, and other aspects of agriculture and the environment. It discusses the effective use of microbial technology, wastewater treatment, and recycling of agricultural and industrial wastes. It provides detailed accounts of recent trends in microbial application in plant growth promotion, soil fertility, microbial biomass and diversity, and environmental sustainability through bioremediation, biodegradation, and biosorption processes

Features:

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• Discusses microbes and their applications for sustainable agriculture and environmental protection in agro-environmental circumstances

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• Presents innovative and eco-friendly approaches for the remediation of contaminated soil and wastewater

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• Focuses on green technologies and sustainability

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• Includes chapters on sustainable agriculture development through increasing soil fertility, physico-chemical properties and soil microbial biomass in nutrient-deprived soils

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• Defines the role of microbial bio formulation-based consortia in the productivity improvement of agricultural crops

It will be an invaluable addition to the bookshelves of researchers and graduate students in agriculture and environmental engineering, soil science; microbiology, sustainable agriculture, and ecosystems.

Dr. Chhatarpal Singh is presently the President of Agro Environmental Development Society (AEDS), Majhra Ghat, Rampur, Uttar Pradesh, India.

Dr. Tiwari is currently working in the field of methanotrophs ecology (methane oxidizing bacteria), which is sole entity responsible for the oxidation of potent greenhouse gas CH4.

Dr. Jay Shankar Singh is presently working as a faculty member in the Department of Environmental Microbiology at Babasaheb Bhimrao Ambedkar University in Lucknow, India.

Dr. Ajar Nath Yadav is currently serving as an assistant professor in the Department of Biotechnology, Akal College of Agriculture, Eternal University, Baru Sahib, Himachal Pradesh, India.

1 Plant–Microbe Association Leading to a Sustainable Agroecosystem

Rajeswari Das, Subhrajyoti Mishra, and Mukesh Kumar

CONTENTS

1.1 Introduction

1.2 Impact of Microbial Ecology of Rhizosphere on Terrestrial System

1.3 Factors Affecting Rhizospheric Microbial Association

1.4 Interaction between Beneficial Microorganisms and Crop Plants

1.4.1 Interactions Leading to Atmospheric Dinitrogen Fixation

1.4.1.1 Symbiotic Nitrogen Fixation

1.4.1.2 Asymbiotic Nitrogen Fixation

1.4.2 Interactions Leading to Nutrient Dynamics and Crop Growth

1.4.2.1 Plant-Soil-Microbe Interaction in Phosphorus Dynamics

1.4.2.2 Potassium-Solubilizing Microbes Activity in the Rhizosphere

1.4.2.3 Interaction of PGPRs Resulting Micronutrient Availability via Redox Mechanism in Phytomicrobiome

1.4.2.4 Enhancement in Crop Growth – Consequence of Plant Growth-Promoting Activities of Microbes

1.4.2.5 Nutrient Acquisition by PGPR

1.4.2.6 Plant Hormones Produced by PGPR

1.4.3 Microbe-Mediated Induced-Stress Tolerance in Crop Plants

1.4.3.1 Contribution to Phytoremediation

1.4.3.2 Contribution of Rhizospheric Microbe Towards Rhizomediation

1.4.3.3 Microbial Association Improving Tolerance of Crops to Abiotic and Biotic Stress

1.4.4 Concept of Bioremediation Microbial Role in Soil Quality Enhancement

1.5 Sustainable Agroecosystem: An Outcome from Healthy Plant–Microbe Association

1.6 Potential of Plant–Microbe Interaction for Developing a Low-Input Sustainable Agriculture

1.7 Conclusion

References

1.1 Introduction

There is a need to understand precisely the way in which microbes are associated with plants (metaorganisms) and their interactions. Plants secret root exudates which contain enzymes, water, H⁺ ions, mucilage, and carbon-containing primary and secondary compounds, and help develop a microbial colony. It has been observed that microbial density is several times greater in the rhizosphere as compared to soil (Mendes et al. 2013; Baetz and Martinoia 2014). Plants are specific in the selection of a rhizosphere microbial colony, which may be the reason behind their coexistence (Ciccazzo et al. 2014; Lareen et al. 2016).

Since the dawn of the Industrial Revolution, and various associated human activity, there has been an aggravation of the climate, which directly or indirectly affects crop production worldwide. Biotic and abiotic stress factors also contribute to crop loss in terms of millions of dollars (Hua 2013; Suzuki et al. 2014). Abiotic stress involves extreme temperature, drought, waterlogging, light, and salinity as major parameters (Majeed et al. 2015). Infection and damage by various insect pests, pathogens, and other organisms are covered under biotic stress. Many plant-associated microbes play a crucial role in reducing crop losses by mitigating various stresses. They enhance plant growth and physiology by various means, such amelioration is regarded as promoting rhizobacteria (PGPR). PGPR are often found to produce 1-aminocyclopropane-1-carboxylate (ACC) deaminases, indole acetic acid, siderophore, and solubilizing phosphorus and thereby enhancing nutrient uptake and the growth of plants (Egamberdieva et al. 2015). As the role of PGPR is very prominent in the plant lifecycle in enhancing its physiology and growth aspects by providing tolerance of various forms of environmental stress, there is a need to focus attention on the study of plant microbiomes (Prashar et al. 2013; Ho et al. 2015). This chapter therefore explores the plant–microbe relationship. Several reports have discussed the effect of plant microbiomes on growth, productivity, and host survival in various symbiotic associations. This knowledge will guide efforts to move towards a sustainable agroecosystem by understanding plant–microbe intercommunication.

1.2 Impact of Microbial Ecology of Rhizosphere on Terrestrial System

Dynamic changes in soil microbial ecology, as a result of functional alteration of the ecosystem, have an impact on crop ecology. A few stabilizing mechanisms have been postulated for the maintenance of species diversity and coexistence (Cheson 2000). Microbially mediated positive and negative feedback might play a crucial role in the whole plant ecosystem and contribute to plant–microbe intercommunication (Bever et al. 2010). Rhizospheric microbes have the potential to alter the nutrient uptake from soil to plant and can affect plant–plant interaction (competition) through resource partitioning which drives plant community dynamics.

The coexistence of plant species can be affected by an indirect feedback mechanism (i.e., competition or inhibition of symbionts) of rhizospheric microbes (Figure 1.1). To explain the mechanism that produces low diversity plant communities, a few hypotheses have been proposed, among which the empty niche hypothesis and degraded mutualist hypothesis are explained here. The former suggests the inhabitation of novel symbionts in the areas invaded by invasive plants, whereas the latter suggests the inhibiting ability of both the invasive plant and their symbionts towards a native symbiotic community to acquire resources, indirectly reducing the performance of native plants (Stinson et al. 2006; Vogelsang and Bever 2009). Ecological linkages of plant-soil feedbacks might enhance the growth and survival of exotic seedlings near efficient native symbionts.

FIGURE 1.1 Schematic figure showing feedback mechanism among plant soil community.

A plant microbiome is a complex network, demonstrating the inhabitation of plant-associated microbes (Berendsen et al. 2012; Bulgarelli et al. 2012). Thorough research and analysis are a prerequisite for dealing with the impact of rhizospheric microbes on the terrestrial ecology.

1.3 Factors Affecting Rhizospheric Microbial Association

A compatible phyto-microbial interaction is key to successful endophyte colonization in plants. A host plant recognizes the endophyte invading it through the crosstalk of signal molecules (plant–microbe intercommunication). Various studies have shown the response of endophytes to various chemical secretions from the plant root viz., chemotactic movement of endophytes in response to root exudates. Several other chemoattractants are secreted by plants (flavonoids). This plays an important role in endophytic interaction with root hair also being used as bioformulations, including the successful infection of legume roots by rhizobia. Flavonoids are also found to be crucial in non-rhizobial endophytes. Other than chemoattractants, there are known to be only a few signal molecules, including lipo-chitooligosaccharides (LCOs) and strigolactones (SLs), which initiate and enhance microbial colonization with the roots of a higher plant. LCOs are also known as nod-factors, which activate a common symbiotic pathway in both rhizobium legume association and arbuscular mycorhizal association (Compant et al. 2010; Brader et al. 2014).

In contrast, such plant–microbe intercommunication is frequently affected by various factors (Figure 1.2). These include various forms of abiotic and biotic stress (Nguema-Ona et al. 2013; Chagas et. al. 2017; Majeed et. al. 2015). Extreme temperature, drought, waterlogging, and salinity are major parameters included in abiotic stress factors, whereas pathogen infection and insect pest attack in plants are categorized as biotic stress factors (Arora and Mishra 2016). Biotic stress is found to be controlled by a few PGPRs, as bioagents and abiotic stress are mitigated by root and shoot growth promotion. This is due to the secretion of plant hormones (IAA), nutrient solubilization and the uptake by production of siderophores, the solubilization of the phosphorus, and the fixation of nitrogen and performance of other plant growth-promoting activity (Prashar et. al. 2013).

FIGURE 1.2 Factors affecting plant–microbe association in the agroecosystem.

1.4 Interaction between Beneficial Microorganisms and Crop Plants

The study of the interaction between beneficial microorganisms and crop plants is crucial for predicting their role in the development of a sustainable agroecosystem. Microorganisms and plants interact with each other in a number of ways: for nutrient availability, growth promotion, survival, and many more benefits for both plant and microbe. For this reason, there is subsequently less impact on both plant–microbe interaction and intercommunication.

1.4.1 Interactions Leading to Atmospheric Dinitrogen Fixation

Nitrogen, being a key macro element, is utilized in a broad spectrum by all living organisms. Higher plants and bacteria can utilize diverse organic and inorganic nitrogenous compounds, and some prokaryotic organisms can use N₂ via biological N₂ fixation. Biological nitrogen fixation (BNF) is carried out by a specialized group of prokaryotes, which utilize the nitrogenase enzyme as a catalyst for the conversion of atmospheric dinitrogen (N₂) to ammonia (NH₃), thence readily assimilated by plants to synthesize nitrogenous biomolecules. Prokaryotes responsible for nitrogen fixation are further categorized as aquatic organisms (i.e. cyanobacteria), free-living soil bacteria (i.e. Azatobacter), associative soil bacteria (Azospirillum) and most importantly symbiotic bacteria (i.e. Rhizobium and Bradyrhizobium).

1.4.1.1 Symbiotic Nitrogen Fixation

Symbiotic nitrogen fixation, which is one of the crucial biological processes for the develo...