Endophytes and Rhizosphere Bacteria of Plants Growing in Heavy Metal-Containing Soils

Abstract

As a consequence of industrialization during the last centuries, the heavy metal concentration of soils has increased worldwide (Adriano 2001). Hot spots of soil contamination are located in areas of large industrial activities, where surrounding agricultural areas are affected by atmospheric deposition of heavy metals. Also, agricultural practices, such as the application of sewage sludge or phosphate fertilisers, has led to increased metal concentration in soils (Puschenreiter et al. 2005a). Metal contamination of soils may also derive from geogenic sources. These natural metalliferous soils are the classical habitats for metal-accumulating plants and may be divided into four different main groups, depending on the parent rock materi- als (see Section 15.2). Most of these naturally contaminated soils are quite infertile, which is particularly true for Ni-rich serpentine soils (which are characterized by low NPK levels and a low Ca:Mg ratio; Baker et al. 2000). Indigenous soil contamination may be restricted to either very small spots of only a few square meters or may affect large areas of several square kilometers such as those found in Cornwall and Devon (UK), where up to 700 km2 are contaminated with As (Mitchell and Barr 1995).