Ammonia-oxidizing communities in agricultural soil incubated with organic waste residues

The impact of organic compounds present in different kinds of organic fertilizers, i.e., anaerobically digested household waste, composted organic household waste, swine manure, and cow manure, on microbial communities in arable soil was investigated using microcosms. Soil was amended with dried residues or organic extracts of the residues and incubated for 12 weeks at 25 degrees C. The microbial community composition was investigated by phospholipid fatty acid (PLFA) analysis, and the community of ammonia-oxidizing bacteria (AOB) was assessed by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA fragments, followed by sequencing. All dried residues increased the AOB activity, determined as potential ammonia oxidation, whereas the organic extracts from the thermophilically digested waste and the swine manure caused a decreased potential activity. However, no differences in the DGGE banding patterns were detected, and the same AOB sequences were present in all samples treated with the residue extracts. Moreover, the PLFA composition showed that none of the residue additions affected the overall microbial community structure in the soil. We conclude that the AOB community composition was not affected by the organic compounds in the fertilizers, although the activity in some cases was.