The SARS-CoV-2 pandemic reminded humanity of the power of a microorganism. Such a tiny virus managed to change the world. However, current molecular techniques show us that the diversity of microorganisms is immense, and only a small fraction of them is capable of causing diseases. On the contrary, they are responsible for sustaining life on the planet.
In this context, soil microorganisms play a significant role. They carry out nutrient cycling, degrade recalcitrant organic matter, and even contribute to soil decontamination. All of this is thanks to the immense metabolic potential they possess and the interactions they provide.
Understand how microbial interactions can revolutionize agriculture!
Soil Structure
The soil matrix is a complex composed of macroaggregates and microaggregates. The interaction of soil components forms the microaggregates and the macroaggregates result from the combination of several microaggregates, organomineral complexes, organic matter, fungi, and plant roots.
These arrangements, combined with organic matter content and water channels (which can assume different forms and sizes) formed between them, constitute the basic unit of structure and function in most soils. Maintaining this soil structure is crucial as it directly relates to its functions.
Functions of Soil Microorganisms
What functions do they perform? Several! Let's consider some examples. Microorganisms are responsible for the decomposition of organic matter, partially or wholly, adding organic matter to the soil.
The decomposition of organic matter forms volatile organic compounds (VOCs) directly related to promoting plant growth.
Soil microorganisms can also consume and produce other atmospheric gases such as hydrogen, CO₂, nitric oxide, nitrous oxide, and methane. Thus, they play a role in climate regulation. Methane, produced by methanogenic archaea, also plays an essential role in the carbon cycle by linking the two processes involved in carbon cycling.
Another example of the importance of microorganisms in nutrient cycling is nitrogen fixation. In this stage of the nitrogen cycle, it is crucial to turn this nutrient available to plants by only a few species of microorganisms are capable of.
Additionally, microorganisms perform processes such as photosynthesis, respiration, and fermentation, which are responsible for carbon cycling.
Microbe-Plant Interactions
Microorganisms engage in various interactions with other organisms present in the soil. These interactions can have harmful and beneficial consequences for the soil and crops. Why exactly do plants interact with microorganisms?
Microorganisms benefit from the shelter and compounds released by plants that serve as a source of nutrients for them. For plants, the interaction is essential for nutrient acquisition and the production of interesting compounds such as phytohormones.
Furthermore, these associations provide essential services to the ecosystem, promoting plant growth, controlling pathogens, reducing the impact of abiotic stress, and more.
Microbe-plant interactions often involve a communication system. One well-known example is quorum sensing. Based on chemical signalling, this system is related to different microbial processes and may employ various strategies for its implementation.
However, the fundamental concept requires a high population density to succeed because the activity in question would not yield satisfactory results at low population densities.
Applications of Microbe-Plant Interactions in Crop Improvement
By understanding the mechanisms governing these interactions, we can utilize them for crop improvement. Thus, beneficial interactions themselves present biotechnological potential that can be applied to increase productivity. There are many possibilities. Here are some examples:
It is possible to manipulate soil microorganisms through management techniques or the addition/activation of signalling molecules that attract desired microorganisms, thereby stimulating and strengthening mutualistic relationships.
Another possibility is to inoculate the soil with microbial strains of interest. Called consortia, these can function as biofertilizers or biopesticides and may consist of various microorganisms with different and complementary functions that promote plant growth.
A feasible way to select plants involves indirect selection based on the propagation of a host phenotype significantly affected by the microbiome (microorganisms + surrounding environment). In other words, it means selecting plants that do not exhibit symptoms even when exposed to stress. Therefore is possible to identify, isolate, and inoculate bacteria responsible for resistance in other plants.
Production of transgenic plants. The plant's genotype is essential in determining and shaping the rhizosphere microbiome. Thus, it is possible to develop plants that can attract beneficial microorganisms. These plants can release specific hormones or exudates to attract and maintain the desired beneficial microbiota.
Exploring beneficial interactions between microorganisms and plants represents a sustainable way to reduce dependence on agrochemicals and fertilizers. Ultimately, this data allows us to understand how agricultural practices influence the microbiome, develop strategies to modulate the microbiome in a desired direction, produce biotechnologies that promote plant development, and more. These efforts combined to ensure food security and reduce environmental impacts.
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