The nature of the link between plant and microbial diversity reveals information about the ecological drivers of community structure and function.
The nature of the link between plant and microbial diversity reveals information about the ecological drivers of community structure and function. Although the functional interactions of soil microbial communities with plants differ, they can increase plant community diversification through a variety of processes.
Symbiotic mutualists, for example, can promote plant community variety by improving nutrient availability or promoting niche partitioning. While soil pathogens can directly infect and kill plant seedlings, they can also restrict beneficial microbial interactions with plant hosts, which both help hetero-specifics survive and increase plant variety.
Plants also serve as the primary source of energy for decomposers, symbionts, and pathogens, hence governing the niche space in which different soil bacteria can thrive. Thus, the variety of plant communities and soil microbial communities has long been considered to be tightly connected.
Nitrogen (N) is not a rare element on Earth, although the most abundant forms (N2 gas in the atmosphere and N fixed in the earth’s crust and sediments) are inaccessible to plants.
As a result, N is frequently a limiting element in agricultural productivity, particularly for maize and hay crops, which require substantial levels of N. Through symbiosis, a mutually beneficial interaction between microbes and legumes, N2 in the atmosphere can become plant-accessible.
Nitrogen fixation is the process of converting atmospheric N2 to ammonia and ultimately to N-containing organic molecules that can be used by all kinds of life. Non-biological processes, such as lightning or the Haber-Bosch process used to generate fertiliser products such as urea, can fix nitrogen.
The most common N-fixation method, however, is biological N-fixation. Each year, an estimated 193 x 106 tonnes of N are fixed through biological N fixation around the world.
Biological Nitrogen Fixation
Nitrogenase is an enzyme that is required for biological N fixing. This N fixation process necessitates a significant amount of energy (adenosine triphosphate, or ATP) in order to break the triple bond that exists between the N atoms in N2.
N2 + 8H+ + 16 Mg ATP → (Nitrogenise) → 2NH3 + 2H+ + 16 Mg ADP + 16 Pi
As previously stated, substantial amounts of N can be fixed through the symbiotic relationship of microbes with legumes. Plants generate energy (through photosynthesis), and microbes use this energy to repair N2. Biological N fixation is performed by a variety of bacteria that are either free-living, in loose partnerships with plants, or in symbiotic relationships with plants (Rhizobium and Actinomycetes).
Soil Microorganisms in the Suppression of Plant Pathogens
Soil is a complex mixture of organic and inorganic substances containing hundreds of distinct species, the great majority of which are still unknown. Some of the species are pests that cause notable agricultural losses, while others provide ‘environmental services such as biological pest management, aeration, drainage, nutrients, and water cycling.
Soil, as a dynamic living resource, is the foundation of sustainable agriculture as well as the physical support for the majority of human activities.
Disease-suppressive soils have been known for over a century, and the mechanisms that cause disease suppression have been studied for nearly four decades. Disease-suppressive soils are soils in which the pathogen does not establish or persist, the pathogen establishes but causes no damage, or the pathogen causes some disease damage but the disease becomes progressively less severe despite the pathogen persisting in the soil.
Antibiosis, competition, parasitism, and predation are all examples of soil suppression mechanisms. Though some argue that the word disease suppressive should only be used in instances where there is a definite biological component.
There is a lot of proof that both biotic and abiotic soil factors play a role in disease suppression. By influencing soil microbial activities, soil chemical and physical properties, such as pH, organic matter, and clay content, can directly or indirectly inhibit plant diseases.
Although these abiotic soil properties can help suppress illness, soil suppressiveness is often caused by the action of soil microorganisms or microbial metabolites.
The degree of suppressiveness is related to soil physical characteristics, fertility level, biodiversity, populations of soil organisms, and soil management.
The soil environment influences crop growth both indirectly and directly by influencing weed growth, pests, and diseases, as well as by delivering water and nutrients. While fundamental principles are understood, there is a paucity of particular knowledge regarding soil components and soil environmental conditions that affect the severity of plant diseases.
Advantages of Suppressive Soil
- Reduces legal, environmental, and public concerns.
- Chemical safety hazards.
- Control should be comparable to the finest.
- Currently available via alternative ways.
- Can be used in organic or reduced pesticide applications.
- Systems that provide value to the product.
Disadvantages of Suppressive Soil
- Early on, flexibility may be limited.
- It necessitates more rigorous administration and planning.
- New abilities are required.
- Disease control does not happen overnight.
Incorporation of Root Colonizing Rhizosphere Microorganisms
These organisms can improve plant health by making the plant’stronger through phytostimulatory and biofertilizing activities. Many rhizosphere bacteria can cause a systemic reaction in the plant, activating plant defence mechanisms.
Better Agronomic Practices
Cultural practice adaptation has been offered as a strategy to reduce soil inoculum potential or boost disease suppressiveness. Crop rotation, bio-fumigation, intercropping, residue destruction, organic supplements, tillage management practices, and a mix of these regimes have all been used to reduce disease.
Bio-Fumigation
This technique, which is better suited to cooler regions of the world, involves the fermentation of organic materials under plastic, which results in anaerobic conditions in the soil and the generation of hazardous metabolites. Both of these processes help to inactivate or destroy harmful fungi.
Many Brassicaceae (Cruciferae) plants produce glucosinolates, a class of organic compounds that may be used to combat different soilborne plant diseases.
Soil amendments, including Brassica napus seed meal, for example, prevented root infection by Rhizoctonia spp. and the worm Pratylenchus penetrans. Similarly, the breakdown of garlic, onion, and leek tissues releases sulphurous volatiles such as thiosulfate and zwiebelanes, which are transformed into disulfides with biocidal activity against fungus, nematodes, and arthropods.
Soil Solarisation
Solarization, often known as solar heating, is a technology that harnesses sun energy to raise soil temperatures to levels where many plant pathogens are killed or sufficiently weakened to control the illnesses.
Residue Management
Plant residues left on or near the soil surface may help to promote disease suppression by promoting general microbial activity. However, in other circumstances, the debris not only increases microbial activity but also serves to preserve infections, avoiding a decline in inoculum density.
This is true for Macrophomina phaseolina, which causes charcoal rot in soybean; Fusarium sp., which causes root and crown rot in maize; and R. solani, which causes crown and root rot in sugar beetroot.
This article is jointly authored by Hafiz Muhammad Bilal from the Department of Horticulture, Auburn University, AL, USA; Saleem Sajjad from the Department of Soil and Environmental Sciences, College of Agriculture, University of Sargodha; Amanullah Baloch from the National Key Lab of Crop Genetic Improvement and the College of Plant Science and Technology, Huazhong Agricultural University, China; Irum Shahzadi from the National College of Business Administration & Economics, Lahore; and Hadi Ahmad Mansoor from Air Base Inter College Mushaf, Sargodha.