Figure 5.

Average relative abundances of AOA, AOB, NOB and MOB 16S rRNA genes in fractionated DNA from microcosms regularly amended with low ((a–c) 15 μg NH₄⁺-N per g dry soil added initially; 7.5 μg NH₄⁺-N per g dry soil on days 7, 14 and 21) and high ((d–f); 150 μg NH₄⁺-N per g dry soil added initially; 75 μg NH₄⁺-N per g dry soil on days 7, 14 and 21) levels of ammonium and 5% ¹³CO₂ sampled on day 14 (a, d) and day 28 (b, c, e, f) of incubation. Microcosms were incubated in the absence (a, b, d, e) and presence (c, f) of 1% ¹³CH₄ from day 14 onwards. The relative frequencies are expressed as the percentage of 16S rRNA genes from the respective functional group to total 16S rRNA genes of each DNA fraction. Data plotted are mean values and s.e. from DNA obtained from gradient fractions of duplicate nonlabeled ¹²C (open symbols) and labeled ¹³C (closed symbols) microcosms.