Two soil microorganisms can act together to help plants obtain iron. Researchers studied a fungus, Trichoderma brevicompactum TB2, and a bacterium, Pseudomonas fluorescens PSE180.
Iron is essential for photosynthesis and several cellular reactions. Yet it can be present in large amounts without being usable by roots. In calcareous soil, the high pH keeps part of this iron in poorly soluble forms.
Iron is essential for photosynthesis.
Illustration image: Pixabay.
The researchers first added the fungus TB2 to two types of soil. The first soil retained its natural microorganisms. The second soil had been sterilized to remove most of them. This comparison was intended to determine whether the fungus acted alone or with the help of other microbes naturally present in the soil.
In the natural soil, TB2 improved plant growth and iron content more. Its effect diminished in the sterilized soil. This result showed that the fungus probably benefited from the presence of certain bacteria living around the roots.
The team then analyzed the bacterial DNA present in this area, called the rhizosphere. They looked for bacteria that had become more abundant after the addition of the fungus. A genetic signature named ASV49 stood out particularly in the treated samples.
The researchers isolated several soil bacteria to find the one corresponding to ASV49. A strain of Pseudomonas fluorescens, named PSE180, showed a genetic match. They then cultured this bacterium with the fungus to check their compatibility. These tests showed no significant inhibition between the two organisms.
Finally, the plants received the fungus alone, the bacterium alone, or both together. The combination produced the best results for growth and iron accumulation under the studied conditions. The fungus seems to favor the bacterium, which then helps release iron around the roots.
These trials were carried out with specific strains and in a controlled environment. The researchers still need to verify their effectiveness on other plants, in different soils, and over several seasons. They will also need to measure the stability of this cooperation in response to variations in temperature, humidity, and fertilization.