Root Exudates Explained: How Plants Recruit Beneficial Soil Microbes for Healthier Growth

In the soil, the plants are not growing naturally. Rather, they communicate actively with billions of microorganisms that inhabit around their roots. Plants draw beneficial microbes on their roots by means of special chemical substances called root exudates, which aid in making nutrients more readily available and produce extra strength and resilience under stress to build healthy plant growth. This important biological relationship is a key element in today's sustainable agriculture where understanding and maintaining soil biology is just as critical as providing nutrients. This relationship is further sustained by healthy levels of soil organic matter which supplies food and habitat for soil microbial populations that are important for long term soil productivity.

Know all about root exudates and explain their functions as to why plants exude them

A complex cocktail of sugars, amino acids, proteins, enzymes, organic acids and signals are constantly exuded from roots into the soil. The different collectively named root exudates act as bio-messages regulating the activity of microbes in the root zone.

Plants do not invest their resources in attracting all the microorganisms to them, but select some special populations of beneficial microbes that would help them meet their nutrient needs. This process is working more effectively in soils containing high amounts of soil organic matter and therefore high diversity of soil biota and biological activity.

Selecting and recruiting beneficial soil microbes – how plants do it?

During plant growth, the range of microorganisms that attach to the roots can be modified by the plants, which, to some extent, affect the characteristics of the microorganisms in their neighbourhood. It is a selective process that enables the crops to gain beneficial organisms like plant growth promoting microorganisms, possess threats to the plant diseases and provide endurance to stress. The composition of beneficial microbes attracted toward the crops depends on their demanding requirements, and environmental conditions. Thereby each crop creates its own unique rhizosphere microbiome in its root zone, impacting on crop performance and overall soil health.

Plant Growth Promoting Microorganisms (PGPMs): An emerging solution for a longer growing season

Many of these microorganisms that are recruited by roots are part of a micro organism group called plant growth promoting microorganisms. They enhance the productivity of crops in several ways, including solubilisation of nutrients, production of hormones, suppression of biological diseases and stress tolerance. Typically, these are species of Bacillus, Pseudomonas and Trichoderma. The activities they perform play a significant role in creating a healthy rhizosphere microbiome and stabilize the microbial community assembly that grows around plant roots. Numerous studies continue to demonstrate their correlation to a good establishment and yield stability.

Role of the Arbuscular Mycorrhizal Fungi

One of the most important root associated organisms is the arbuscular mycorrhizal fungi (AMF). They partner with the roots of various plants in a mutually beneficial relationship that develops when plants grow a network of soil borers known as mycorrhizal fungi and the beneficial microbes grow together.

As part of this association, arbuscular mycorrhizal fungi aid plants in the availability of elements like water and nutrition they might otherwise not be able to obtain. They also play a role in increasing the biological activity of the soil near the rhizosphere microbiome and better aggregation of soil. If soils provide a good soil organic matter, then good long-term soil and crop benefits are expected from the use of mycorrhizal fungi.

The importance of Soil Organic Matter for beneficial microbe recruitment

Soil Organic Matter has a strong impact on the abundance and diversity of soil microbial populations. Many microorganisms use organic residues as a main source of energy, and healthy microbial community assembly in agricultural soil. Well-balanced soil organic matter (SOM) content is likely to lead to more abundant populations of beneficial microbes, which in turn should be a more active and resilient rhizosphere microbiome. The greater the microbial activity, the better the cycling of nutrients, aggregation of soil particles, and functions of the root zone biology, which lead to better crop growth and soil long-term fertility.

The impact of Mycoryx on Root-Microbe Relationships

Novobac is known for its expertise in providing biological crop nutrition, microbial technologies and sustainable agriculture solutions for farmers in the most agricultural areas all over the world. One of its biological products, Novobac Mycorrhizal Inoculant offers a means of placing beneficial arbuscular mycorrhizal fungi into the root zone, thus encouraging beneficial relationships between the crop and the microbial world.

Mycoryx helps to promote root colonization, provides an extra source of rhizosphere microbiome, enhances nutrient uptake, improves water absorption, and overall boosts root function. The product will co-exist with naturally occurring beneficial microbes and plant growth promoting microorganisms; this will provide a more biologically active zone around the roots. Mycorrhizal technologies are currently being incorporated into sustainable crop management programs for farmers in Canada, the United States, Mexico, Europe, India and other agricultural areas that seek to achieve optimal soil biology and productivity in the long-term. Moreover the imbalances of microbial populations may improve the bio-attraction of beneficial species which favour the growth of crops via root exudates.

Establishing an LTSP for the recruitment of beneficial microbes

Practices of building a healthy root and soil biology system are the first means of a successful microbial recruitment system. Improving populations of beneficial microbes can be achieved by the supply of additional organic matter, minimizing over tillage, adjusting to a cover cropping system, and using a biological inoculant (where appropriate). These practices have the potential to lower the risk of microbial community assembly changes and encourage diverse structure of the rhizosphere microbiome over time.

One of the best management techniques to maintain soil organic matter levels for promoting soil microbial activity and soil health in the root zone is one of the most important management techniques. In partnership with biologically oriented technologies like inoculants with mycorrhizal fungi (MAM), growers can set the stage for sustained microbial recruitment, nutrient-use efficiency, and long-term resilience of the crops. The importance of plant recruitment of beneficial microorganisms in the context of sustainable agriculture will continue to grow as agriculture advances into new directions and solutions for enhancing productivity and the health of soils for generations to come.

Reference:

• Xu, Yunjian, et al. "Mycorrhizal fungi alter root exudation to cultivate a beneficial microbiome for plant growth." Functional Ecology 37.3 (2023): 664-675.
• Liu, Hongwei, et al. "Evidence for the plant recruitment of beneficial microbes to suppress soil‐borne pathogens." New Phytologist 229.5 (2021): 2873-2885.