Long‐term exposure to elevated zinc concentrations induced structural changes and zinc tolerance of the nitrifying community in soil

Abstract

A series of long-term Zn-contaminated soils was sampled around a galvanized pylon. The potential nitrification rate (PNR) was unaffected by the soil total Zn concentrations up to 25 mmol Zn kg(-1) whereas spiking the uncontaminated control soil with ZnCl(2) to identical total concentrations completely eliminated nitrification. The larger sensitivity of the PNR to spiked ZnCl(2) than to the Zn added in the field was equally found when relating the PNR to the Zn concentrations in the pore water of these soils, suggesting differences in Zn tolerance of the nitrifying communities. Zinc tolerance in the long-term Zn-contaminated soil was demonstrated by showing that (i) the nitrifying community of long-term Zn-contaminated soil samples was less sensitive to Zn than that of the uncontaminated control soil when both communities were inoculated in sterile ZnCl(2)-contaminated soil samples, and, that (ii) addition of ZnCl(2) to the long-term Zn-contaminated soil samples affected nitrification less than equal additions of ZnCl(2) to uncontaminated control samples. Denaturing gradient gel electrophoresis fingerprinting of polymerase chain reaction amplified 16SrRNA gene fragments of ammonia-oxidizing bacteria showed that the community structure in uncontaminated and long-term contaminated soil samples was different and could be related to soil Zn concentrations.

Effects of mercury on the activity and community composition of soil ammonia oxidizers

“…Therefore, PNRs could be a sensitive parameter in the soil Hg pollution diagnostics as well, especially in the early diagnostics since there were no dose-response relations found in the treatments over 1 week incubation in this study. Mertens et al (2006) mentioned the same phenomena in the study using Zn as a stressor, stating that the long-term Zn pollution could hardly change the PNRs in the soil.…”

“…It was also reported that there was no significant difference in the number of 16S rRNA gene fragment of AOB using most probable number method (Mertens et al 2006). Phylogenetic analysis of the bacterial amoA gene sequences indicated that Nitrosospira cluster 3 was the dominant AOB group and the community composition changed with different soil Hg concentrations.…”

“…It was reported that the AOB were completely inhibited in the heavy metal-contaminated soil according to the measurement of the potential ammonia oxidation (Gremion et al 2004). However, AOB populations from long-term contaminated soil samples were able to tolerate higher Zn concentrations than those from uncontaminated soil samples (Mertens et al 2006). Recent study also found that the ammonia-oxidizing population had a trend of resilience after the relief of heavy metal stress although the soil remained depressed microbial activities (Frey et al 2008).…”

Bacteria, not archaea, restore nitrification in a zinc-contaminated soil

“…It has been hypothesized that recovery of nitrification following Zn exposure is due to the development of Zn-tolerant AOB populations (Mertens et al, 2006). However, the recent insights into the role of AOA in soil ammonia oxidation (Leininger et al, 2006) place the role of AOB in nitrification restoration in doubt.…”

“…Zn tolerance was tested in the unexposed and the Zn-exposed soil samples at T0 to T3 using the spikeon-spike test of Mertens et al (2006). In short, ZnCl 2 was added to duplicate suspensions of soil samples (1:10 soil/CaCl 2 0.01 M ratio) to final concentrations of 0, 0.77, 1.5 and 3.1 mM added Zn.…”