Department of Land and Environmental Management, College of Nyiregyhaza, Nyiregyhaza, Hungary. Introduction The heavy metals or toxic elements are posing serious problems in the various soil-plant ecosystems of the world (Mathe-Gaspar et al. 2006). In case of the beneficial microbes, such as the nitrogen-fixing Rhizobium bacteria, or the phoshorus-mobilising arbuscular mycorrhizal fungi (AMF), however there is a discrepancy in the literature regarding their metal tolerant abilities and their functions in the plant performance and plant fitness (Biro et al. 1998, Takacs et al. 2006). The trustable long-term field experiments, which are not so frequent in Europe, can serve therefore, as valuable tools to study those effects and the behaviour of the heavy metals among the natural conditions (Kadar and Nemeth, 2005). Other studies can show mainly the direct effect of the metals, but due to the multifactorial manner of the environmental conditions, only the long-term experiments can show both the abundance and the functioning of the plant-microbe interactions. It is also known, that the effect of heavy metals can be different, if other amendments, such as the organic or inorganic additives, or soil conditioners are given to the metal-polluted soils (Posta, Fuleky 1997; Simon, Biro 2005). In such soils the introduction of the higher plants can be more successful by increasing the relevance of the soil-technological and phytoremediation techniques (Lakatos et al. 2001). The combination of those procedures with the metal-tolerant beneficial microbes and/or microsymbionts can have further benefits, ie. stabilising the metals in the rhizosphere and improve the nutrient supply or the growth and fitness of the higher plants (Simon, Biro 2005; Vivas et al. 2006). Among the field conditions a particular pattern of the metal- or salt-tolerant abilities was found seasonally and annually (Biro et al. 1999, Naar and Biro 2006, Fuzy et al. 2006). Depending on the severity of the stress the beneficial microbes could confer the stress-tolerant abilities toward the macrosymbiont hosts (Vivas et al. 2006), more particularly if they are well-adapted to the certain environment. Other findings with non-adapted fungi have shown also the potential applicability of the symbiosis in the other way of the phytoremediation, such as the phytoextraction (Takacs and Voros 2003). Some of the toxic elements, i.e. the As and Se could even more intensify the microbial functioning of the nitrogen-fixing abilities of the rhizobium bacteria (Biro et al. 1999). At the different Cd loads, the role of the AM fungi was found to be the part of the surviving mechanism, as well. But how the adaptation process is developed in a particular population (among the most sensitive nitrogen-fixing rhizobia), when applying the same heavy metal loads within a shorter or a longer application periods? How the known essential Zn micronutrient become a toxic element in the sewage sludge treated soil? Those questions are addressed in the study.