Symbiotic Report

The Symbiotic Relationship between

Mycorrhizas and their Associated Bacteria

Introduction

Context

The majority of terrestrial plants are known to form specialised mycorrhizal structures with symbiotic fungi (Read et al., 2000).More than 450 Mya, certain plants established an intimate association with filamentous fungi that have been identified, on the basis of morphological features detectable in the fossils, as the ancestors of today’s mycorrhizal fungi (21, 82). Hypogeous plant organs, mostly roots, are in fact the preferred niche for soil fungi, which live in the rhizosphere as saprotrophs or are directly associated with photosynthetic plants as mycorrhizal symbionts. The latter represents a vital component in plant ecosystems: they are

AM fungi are able to enhance plant water and nutrient uptake. They can increase the solubility and the hence the uptake of different macro- and micronutrients by the host plant. For example, P is among the most important nutrients, whose absorption is considerably increased by the host plant. The reason is the production of phosphatase enzymes by AM fungi. Phosphorus (P) is mostly present in the form of insoluble phosphates in the soil and so plants cannot utilise it. Plant roots are often associated with mycorrhizal fungi and other microorganisms that effectively can absorb P and other elements from the soil. Phosphorous is the second major nutrient next to nitrogen required by plants. However, many soils throughout the world are P deficient while nearly 95 to 99 % of soil P is present in the form of insoluble phosphates (Vassileva et al., 1998) and only 1 to 5 % is available in the form of soluble, plant-available form (Molla et al. 1984). MASSE MER OM