TABLE 1.
Summary of 13CO2 field respiration assays conducted in the agricultural field test plots
| Substratea | Treatmentb | Total evolved 13CO2 (μm) | 13CO2 blankc (μm) | Net 13CO2 (μm) | % of added 13C respired | Initial rate (μm/h) |
|---|---|---|---|---|---|---|
| Glucose | Soil cover | 3.4 ± 0.3 | 2.3 ± 0.37 | 1.1 | 6.8 | 0.25 |
| Sealed chamber | ||||||
| Intact ped | 7.4 ± 10 | 4.5 ± 6.3 | 2.9d | 20d | 0.28d | |
| Core | 4.8 ± 1.9 | 1.7 ± 0.39 | 3.1 | 22 | 0.27 | |
| Crushed soil | 16 ± 3.7 | 5.7 ± 1.2 | 9.8 | 68 | 1.2 | |
| Phenol | Soil cover | 8.1 ± 0.8 | 5.7 ± 1.0 | 2.5 | 9.1 | 0.2 |
| Sealed chamber | ||||||
| Intact ped | 7.2 ± 4.1 | 1.8 ± 0.63 | 5.4 | 20 | 0.2 | |
| Core | 5.5 ± 3.7 | 1.2 ± 1.1 | 4.2 | 16 | 0.1 | |
| Crushed soil | 13.5 ± 1.2 | 3.5 ± 0.56 | 9.5 | 37 | 0.5 | |
| Naphthalene | Soil cover | 2.6 ± 0.45 | 2.4 ± 0.43 | 0.11d | ||
| Sealed chamber | ||||||
| Intact ped | 0.87 ± 0.73 | 0.87 ± 0.69 | 0d | |||
| Core | 0.81 ± 0.34 | 0.79 ± 0.34 | 0.02d | |||
| Crushed soil | 2.0 ± 0.26 | 1.9 ± 0.25 | 0.1d | |||
| Caffeine | Soil cover | 3.2 ± 1.6 | 3.0 ± 1.5 | 0.13d | ||
| Sealed chamber | ||||||
| Intact ped | 1.4 ± 0.84 | 1.4 ± 0.81 | 0.03d | |||
| Core | 1.1 ± 0.45 | 1.0 ± 0.42 | 0.09d | |||
| Crushed soil | 2.5 ± 0.51 | 2.4 ± 0.49 | 0.08d |
a
Aqueous substrates (glucose, phenol, and caffeine) were added as 450 μg in 0.1 ml. Naphthalene was added as 0.5 ml of a 20-ppm aqueous solution.
b
Four treatments were prepared. “Soil cover” designates field release with open-bottom chamber cover installed to trap 13CO2. The three sealed chamber treatments were incubated in the field alongside the soil cover experiment. All treatments were prepared in triplicate.
c
Blank was interpolated from 12CO2 evolved simultaneously with 13CO2.
d
Net was not significantly different from zero as judged by Student's t test comparing final total and background 13CO2.