Phylogenetic tree of nirK sequences. BB denotes Broadbalk sequences from DGGE bands either common to all plots (BB 1– BB 38) or unique to one treatment (BB FYM-1, etc.). Information on environmental sequences (Swedish soil, etc.) or cultured bacterial genera and species names preceding accession numbers were obtained from NCBI. Bootstrap values: open circles, 70–80%; grey circles, 80–90%; black circles, 90–100%.