The ecological role of mycorrhizal symbiosis and the origin of the land plants.

Abstract

Phosphorus plays an essential role in the regulation and physiology of recent endomycorrhizas, indicating a possible evolutionary mechanism involved in the origin of symbiosis, based on improved phosphorus supply to the first land plants. An evolutionary scenario of the origin of the endomycorrhizal symbiosis ( Glomales , Zygomycetes ) is constructed. Phosphorus was available in coastal anoxic sediments of Devonian and Silurian water reservoirs. At that time, the plants radiating to land lacked an effective mechanism for phosphorus accumulation in the oxidative environment. The cooperation between plants and fungal microorganisms would have resolved this problem. Partners then developed regulatory mechanisms balancing the nutritional relationship between them and formed the integrating structures (arbuscules), responsible for mass and signal interchange.