Figure 1.

Key Figure

Schematic Overview of Research at the Different Levels of Organization and the Processes Studied in Mycorrhizal Biology in the Context of (A) Inorganic Phosphorous (P_i) Uptake and (B) Multitrophic Interactions

Each drawing depicts one level of organization covering the cellular, plant physiological, plant community, and ecosystem level. Each level with its processes is nested within the next higher level, as indicated by the magnifying circles. (A) The P cycle of an ecosystem and the contribution of plant communities (top of figure). Zooming into these contributions, mycorrhizal interactions within the plant community and their diverse mycelial networks become visible. Plant physiological responses to mycorrhizal fungi, such as altered plant growth and altered susceptibility to antagonists, drive plant community responses. At the base, subcellular and cellular processes of P_i transport at the interface of the fungus and the plant root cell determine plant physiological responses. (B) Organismal interactions at the whole ecosystem level (top figure). Zooming into the interactions among mycorrhizal plants, multitrophic interactions via signaling pathways (induced by herbivore attack and subsequent parasitoid recruitment) become apparent as well as signaling of herbivore attack within the plant community via common mycelial networks. The processes by which the plant allocates defense compounds to its leaves (fostered by the association with mycorrhizae), which prevent the herbivore from feeding, become apparent at the next level. At the base, mycorrhizal fungi modulate plant immunity to establish the symbiosis, leading to a defense signaling cascade that can enhance plant immunity against herbivores. Abbreviations: AMF, arbuscular mycorrhizal fungus; MTI, microbial-associated molecular pattern (MAMP)-triggered immunity; PRR: pattern-recognition receptors.