Arbuscular mycorrhizal fungi are soil fungi that form a close symbiosis with the roots of many plants. Inside the root they form tree-like branched structures through which they supply the plant with nutrients and water, and in return receive lipids and carbohydrates. For plants the fungus is beneficial.

The exhibition bed shows maize plants with and without arbuscular mycorrhiza. The plants without a fungal partner are the negative control: they remain smaller and are slightly chlorotic, sometimes also turning purple through the accumulation of anthocyanins.

As a partnership between microbes and plants, arbuscular mycorrhiza can support the achievement of several UN Sustainable Development Goals.

Goal 2 (Zero Hunger): the AM symbiosis could in future improve the nutrient and water supply of many crop plants, stabilise yields and thus — particularly on nutrient-poor soils — contribute to food security and sustainable agriculture.

Goal 12 (Responsible Consumption and Production): through more efficient uptake of phosphorus and other nutrients, the symbiosis can lower the need for mineral fertilisers.

Goal 13 (Climate Action): by incorporating plant carbon into stable soil structures and reducing greenhouse gas emissions from soils, AM fungi may contribute in the long term to carbon storage in soil.

Goal 15 (Life on Land): the AM symbiosis can improve soil structure, soil fertility and the resilience of plants to stress such as drought.

Arbuscular mycorrhizal fungi are soil fungi that form a close symbiosis with the roots of many plants. Inside the root they form tree-like branched structures, the arbuscules. Nutrients and water pass through them into the plant; in the opposite direction, lipids and carbohydrates flow to the fungus. Because the exchange of substances benefits both partners, this is called a mutualistic symbiosis. For plants the fungus is beneficial.

Fine, thread-like hyphae run through the root tissue. The arbuscules inside the plant cells are the central sites of exchange in the symbiosis — hence the name "little trees". The fungus extends the plant's capacity to take up nutrients such as phosphate. Hyphae also grow in the intercellular spaces between the root cells. These spaces are not empty gaps but highly dynamic contact zones between plant and microorganism. The fungus colonises the root not as a harmful intruder but as a symbiont.

The symbiosis is studied, among other systems, in Lotus japonicus with the mycorrhizal fungus Rhizophagus irregularis. A green fluorescent dye makes the fungal structures visible within the root tissue; electron-microscopic cross-sections show individual hyphae between neighbouring plant cells. Both images were taken in this model plant, not in a crop species.

The exhibition bed places maize plants with and without arbuscular mycorrhiza side by side. The plants of the negative control, that is those without a fungal partner, remain smaller and are slightly chlorotic; sometimes they also turn purple through the accumulation of anthocyanins. The comparison shows the difference under the conditions of the exhibition, not under those of a field trial.