Table 1.
Concentrations of ammonium and nitrate, gross nitrification rates and the minimum and maximum contribution of ammonia-oxidizing bacteria (AOB) to the observed gross nitrification rates in different treatments and sampling occasion.
| Treatment | Sampling (Day) | Concentration of ammonium [μg N (g dry soil)-1] | Concentration of nitrate [μg N (g dry soil)-1] | Gross nitrification rate [μg N (g dry soil)-1 day-1] | Lowest AOB contribution to nitrification (%)a | Highest AOB contribution to nitrification (%)b |
|---|---|---|---|---|---|---|
| Sugar | 5 | 1.8 (0.2) | 11.5 (0.3) | 1.3 (0.1) | 100 | 100 |
| 19 | 1.5 (0.1) | 15.9 (1.1) | 8.5 (1.4) | 34 | 60 | |
| 33 | 2.2 (0.4) | 15.9 (0.5) | 4.2 (0.8) | 70 | 100 | |
| Amino acids | 5 | 8.2 (0.1) | 29.6 (1.4) | 2.8 (0.6) | 73 | 100 |
| 19 | 27.0 (1.6) | 36.8 (0.6) | 4.0 (0.4) | 81 | 100 | |
| 33 | 33.8 (0.4) | 34.2 (1.6) | 8.8 (0.6) | 67 | 100 | |
| Ammonium | 5 | 15.7 (0.9) | 28.1 (1.0) | 2.9 (0.6) | 94 | 100 |
| 19 | 30.0 (1.7) | 33.2 (1.3) | 11.4 (0.1) | 69 | 100 | |
| 33 | 32.6 (3.5) | 31.5 (1.0) | 23.1 (1.2) | 76 | 100 | |
| Control | 5 | 2.9 (0.5) | 15.5 (1.0) | 3.0 (0.4) | 100 | 100 |
| 19 | 1.9 (0.3) | 27.7 (3.2) | 11.5 (1.2) | 25 | 44 | |
| 33 | 3.7 (0.3) | 34.6 (2.3) | 11.9 (0.9) | 25 | 44 | |
Values in brackets represent standard error (n = 3).
aBased on the lowest detected AOB specific nitrification rate, which was 1.5 pg N day-1 (AOB amoA copy)-1, found between day 5 and 19 in the amino-acid treatment.
bBased on the greatest detected AOB specific nitrification rate, which was 2.7 pg N day-1 (AOB amoA copy)-1, found between day 19 and 33 in the amino-acid treatment.