Symbiotic bacteria and fungi need plants as much as the intestines microbiota need humans. The “right” microbiome helps plants in many ways: it extracts much-needed nitrogen from the air, increases the solubility and availability of nutrients from soil and fertilizers, protects against pathogens, synthesizes substances useful for plants and growth stimulants. In this article, we will talk about the mechanisms of probiotics for plants and how they can benefit them.
Where do beneficial microflora live?
Symbiont microorganisms inhabit the entire surface of the above-ground organs of the plant, in the peri-root space and even in its internal tissues. Based on this, they can be conditionally divided into two groups:
Free-living, which live outside the plant cells and enhance plant growth by releasing beneficial metabolites into the near-root space, on the surface of the roots or above-ground parts of the plant.
Endophytes that live inside plant tissues and/or cells and directly exchange metabolites with the host plant.
The beneficial microflora of plants are called many different names.There are several terms: plant growth promoting microorganisms (PGPM), plant growth promoting bacteria (PGPB) and most specifically plant growth promoting rhizobacteria (PGPR), because most of the plant symbiont bacteria live in the root space (rhizosphere). A specially prepared mixture of such microorganisms is called biofertilizers, or plant probiotics.
To avoid confusion, it is the latter option - probiotics for plants - that we will most often use later in the article!
So how do you get beneficial microorganisms into a plant?
In the natural environment, all plants have a unique microbiota. The task of the scientist and the “green” farmer following in his footsteps is to successfully introduce “useful” microorganisms to the plant and create the most comfortable conditions for mass colonization.To repopulate a plant with beneficial microorganisms, three basic methods are used: seed, root, and/or soil inoculation.
Mechanisms that stimulate plant growth.
So, a well-chosen microflora is extremely beneficial to plants and can greatly improve agricultural efficiency. But how do microorganisms help the plant? What processes are they involved in and where do they live? How and where are plant probiotics used?
Soil is the key to successful crop production, as it is the source of most of the plant's mineral nutrients. Its composition is dynamic and is determined not only by the existing components and fertilizers, but also largely depends on the microorganisms that inhabit it. Their effect on soil and plant growth will be discussed below.
The mechanisms by which bacteria stimulate plant growth and yield can be roughly divided into several types:
participation in nitrogen fixation;
solubilization (increase of water solubility) of phosphates and other salts;
biosynthesis of phytohormones and other biologically active substances;
increasing the plant's resistance to disease or pests.
Let's talk more about each of them in detail.
Nitrogen-fixing bacteria
Biological nitrogen fixation can become a “green” alternative to the use of chemical nitrogen fertilizers and at least partially replace them. Only bacteria can fix atmospheric nitrogen, among which Azotobacter, Bacillus, Paenibacillus (Terra Power Microbial Biofertilizer) are active.
Solubilizing bacteria
Phosphorus (P) is the second most needed plant nutrient after nitrogen. Reducing phosphorus losses during phosphate fertilization by preventing phosphate from quickly changing into a non-degradable form that is not available to the plant is another challenge that bacteria can help with!
Soil bacteria are able to greatly increase phosphate solubilization. In this case, they are called phosphate solubilizing bacteria (PSB). The use of PS-bacteria can cover about 50% of the plant's phosphate requirements, greatly reducing the use of chemical fertilizers. Among soil bacteria, Pseudomonas, Bacillus, Paenibacillus and Azotobacter (Terra Power Microbial Biofertilizer) are effective phosphate solubilizers.
Finally, the third essential mineral element important for plant health is Potassium (K). Here again, bacteria come to our rescue!
There are rather many rhizobacteria that are able to convert insoluble potassium salts into plant-available compounds.
The most active potassium solubilizers include members of Bacillus and Paenibacillus (Terra Power Microbial Biofertilizer).
Bacteria and phytohormones
Many bacteria, among which the most common and well studied are Bacillus, Paenibacillus, etc. (Terra Power Microbial Biofertilizer), are able to synthesize phytohormones - “native” to plants molecules that regulate their growth and development. We only need to “tame” them and make them work for the benefit of our “green” farm.
Bacteria vs. phytopathogens
Plant probiotics can help in controlling pathogens. Various species of Bacillus, Paenibacillus, etc. (Terra Power Microbial Biofertilizer) are active against pathogenic fungi and bacteria.
Mechanisms of disease prevention by bacteria can be direct or indirect. Creation of a competitive habitat, production of antibiotics and enzymes that destroy the cell wall of pathogens are the main mechanisms of participation of “beneficial” bacteria in this struggle.
The use of probiotics for plants does not imply a complete rejection of chemical fertilizers. We will most likely never be able to do away with them, but we don't need to.By correctly applying beneficial microorganisms, we can greatly reduce the use of chemical fertilizers, increase their efficiency, and therefore reduce their harmful effects on human and ecosystem health.