Recovery of soil nitrification after long-term zinc exposure and its co-tolerance to Cu in different soils.

Soils sampled from different locations of China were used to manipulate soil microbial diversity and to assess the effect of the diversity of the soil nitrifying community on the recovery of the soil nitrification to metal stress (zinc). Ten treatments were either or not amended with ZnCl2. Subsequently, a spike-on-spike assay was set up to test for the tolerance of soil nitrification to zinc (Zn) and copper (Cu). Initially, Zn amendment completely inhibited nitrification. After a year of Zn exposure, recovery of the potential nitrification rate in Zn-amended soils ranged from 28 to 126% of the potential nitrification rate in the corresponding Zn-nonamended soils. This recovery was strongly related to the potential nitrification rate before Zn amendment and soil pH. Increased Zn tolerance of the soil nitrification was consistently observed in response to corresponding soil contamination. Co-tolerance to Cu was obtained in all 1,000-mg kg(-1) Zn-amended soils. This tolerance was also strongly related to the potential nitrification rate before Zn amendment and soil pH. Our data indicate that inherently microbial activity can be a significant factor for the recovery of soil functioning derived from metal contamination.