Long-term exposure to Zn-spiked sewage sludge alters soil community structure

An 8 year study to investigate the effects of Zn-spiked sewage sludge additions on the microbial community structure and microbial processes was carried out in a field soil under pasture. The microbial community structure was evaluated using a combination of multiplex-terminal restriction fragment length polymorphism (M-TRFLP) and T-RFLP fingerprinting approaches. Soil respiration, microbial biomass and enzymatic activities were measured as indicators of soil microbial processes. Changes in the microbial community structure, with Zn additions were evident in all the microbial groups investigated (bacteria, fungi, archaea, actinobacteria and rhizobia/agrobacteria). The fungal community showed the greatest response to Zn additions compared to the other microbial communities measured. The relative abundance of several fungal terminal restriction fragments (TRFs) significantly increased in high Zn treated treatments, at the expense of others, some of which were lost from T-RFLP profiles completely. These results indicate that metal-spiked sludge application can have long-lasting impacts on the composition of the microbial community in pasture soils. Despite notable changes in community structure there was no significant long-term impact of Zn-spiked sludge applications on microbial respiration, biomass or enzyme activities.