Agronomic Management of Indigenous Mycorrhizas

Many benefits that accrue to plants from their association with arbuscular mycorrhizal (AM) fungi are a function of the increased volume of soil that can be explored by the extraradical mycelium. Sieverding (1991) estimates that for each centimeter of colonized root there is an increase of 15 cm³ on the volume of soil explored, this value can increase to 200 cm³ depending on the environmental conditions. The enhanced volume of soil explored, together with the ability of the extraradical mycelium to absorb and translocate nutrients to the plant, results in one of the most obvious and important advantages of mycorrhizal formation: the ability to take up more nutrients. The more important nutrients in this respect are those that have limited mobility in soil, such as phosphorus (P). In addition to nutrient acquisition many other benefits are associated with AM plants (Gupta et al. 2000): alleviation of water stress (Augé 2004; Cho et al. 2006), protection from root pathogens (Graham 2001), tolerance to toxic metals (Audet and Charest 2006), tolerance to adverse temperature, salinity and pH (Sannazzaro et al. 2006; Yano and Takaki 2005), and better performance following transplantation shock (Subhan et al. 1998). The enhanced tolerance to toxic metals provide by arbuscular mycorrhizas can be of benefit in phytoremediation (Göhre and Paszkowski 2006). The extraradical hyphae also stabilize soil aggregates by both enmeshing soil particles (Miller and Jastrow 1990) and as a result of the production of substances that adhere soil particles together (Goss and Kay 2005).