Table 2.
Analysis of covariance to test the effects of shoot biomass (S), water heterogeneity (W), nutrient level (N), plant density (D) and block on root biomass
| (A) ANCOVA for all densities | ||||
|---|---|---|---|---|
| Source | d.f. | SS | F-value | P |
| S | 1 | 9·87 | 193·09 | <0·001 |
| W | 1 | 4·23 | 82·76 | <0·001 |
| N | 1 | 8·41 | 164·58 | <0·001 |
| D | 3 | 3·94 | 25·66 | <0·001 |
| W × N | 1 | 0·94 | 18·44 | <0·001 |
| W × D | 3 | 1·17 | 7·64 | <0·001 |
| N × D | 3 | 0·35 | 2·30 | 0·078 |
| W × N × D | 3 | 0·09 | 0·57 | 0·632 |
| Block | 17 | 7·61 | 8·76 | <0·001 |
| Error | 242 | 12·37 | ||
| (B) ANCOVA at each density | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1-plant density | 3-plant density | 6-plant density | 9-plant density | |||||||||
| Source | d.f. | F-value | P | d.f. | F-value | P | d.f. | F-value | P | d.f. | F-value | P |
| S | 1 | 119·12 | <0·001 | 1 | 31·84 | <0·001 | 1 | 28·65 | <0·001 | 1 | 19·46 | <0·001 |
| W | 1 | 0·85 | 0·361 | 1 | 17·87 | <0·001 | 1 | 48·03 | <0·001 | 1 | 31·39 | <0·001 |
| N | 1 | 117·85 | <0·001 | 1 | 59·63 | <0·001 | 1 | 37·69 | <0·001 | 1 | 6·62 | 0·014 |
| W × N | 1 | 7·28 | 0·010 | 1 | 2·39 | 0·129 | 1 | 0·89 | 0·349 | 1 | 11·72 | 0·001 |
| S × W | – | – | – | – | – | – | – | – | – | 1 | 5·37 | 0·026 |
| S × N | 1 | 5·41 | 0·024 | – | – | – | – | – | – | – | – | – |
| Block | 17 | 1·59 | 0·104 | 17 | 3·47 | <0·001 | 17 | 4·01 | <0·001 | 17 | 3·81 | <0·001 |
| Error | 49 | 48 | 48 | 41 | ||||||||
Interaction terms between the covariate and the treatments were removed if P > 0·10.