Table 1.
Number, mass and leghaemoglobin content of root nodules in the 0–10 cm layer (Root1) and visual ranking (1–5; lowest to highest and smallest to largest) of root nodules in the 10–55 cm layer (Root2) of field pea grown for 15 weeks under either an aCO2 or eCO2 concentration and with 5, 25, 50 or 90 mg NO3–-N kg–1 soil
| Factor | N rate (mg kg–1) | Primary root1 nodules (per plant) | Lateral root1 nodules (per plant) | Root1 nodule mass (mg per column) | Root1 nodule size (mg per nodule) | Root2 nodule ranking (1–5) |
Root1 leghaemoglobin concentration (µmol) |
||
|---|---|---|---|---|---|---|---|---|---|
| n | Size | g–1 | Per nodule | ||||||
| N rate (mg kg–1) | 5 | 28·0 | 127·9 | 512 | 1·26 | 3·4 | 4·0 | 628 | 1·66 |
| 25 | 27·2 | 103·8 | 327 | 1·29 | 3·1 | 3·5 | 575 | 2·42 | |
| 50 | 27·7 | 70·4 | 267 | 1·01 | 2·5 | 2·8 | 557 | 2·27 | |
| 90 | 25·8 | 93·4 | 108 | 0·42 | 1·2 | 1·5 | 616 | 2·77 | |
| CO2 level | aCO2 | 27·1 | 97·7 | 272 | 0·97 | 2·4 | 2·9 | 567 | 2·5 |
| eCO2 | 27·2 | 100·0 | 335 | 1·02 | 2·8 | 3·0 | 621 | 2·1 | |
| N rate | n.s. | * | * | *** | ** | *** | n.s. | n.s. | |
| LSD (P = 0·05) | – | 31 | 236 | 0·32 | 0·38 | 0·73 | – | – | |
| CO2 level | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. | |
| LSD (P = 0·05) | – | – | – | – | – | – | – | – | |
No CO2 × N interactions were observed (P > 0·05).
n.s., P > 0·05; *P < 0·05; **P < 0·01; ***P < 0·001.
–, not applicable; LSD, least significant difference.