Table 3.
Rice root characteristics determined in the lab experiment (top) and root system properties derived from CRootBox simulations of growing virtual 3-D root systems, which could not be observed directly (bottom). Root architectural parameters extracted from the lab experiment (top) were used to define input parameters for CRootBox (Table 2). The mass fraction distribution measured in the lab experiment was used to simulate equal volume fractions in the corresponding layers at a similar time. For both the laboratory experiment and the simulations, rice was grown on a P-deficient soil with three P treatments in the topsoil [no P amendment (NoP), a sub-optimal rate (SubP) and a non-limiting rate (PlusP)] and two water levels [field capacity (FC) and drying periods (DP)]. The L-type laterals only emerge in deeper layers, and their interbranch distance was not measured but was calibrated as presented in Table 2.
| Lab experiment | Total root mass |
Mass fraction A
(0–15 cm) |
Mass fraction B
(15–30 cm) |
Mass fraction C
(>30 cm) |
Nodal number | Nodal diameter | S-type radius | L-type radius | S-type distance | Secondary distance | |||
| (g) | (%) | (%) | (%) | (mm) | (µm) | (µm) | (cm) | (cm) | |||||
| NoP | DP | 1.6 (0.3) | 44.0 (4.4) | 26.9 (1.0) | 29.1 (4.0) | 43 (6) | 1.045 (0.13) | 118.8 | 206.3 | 0.35 | 0.51 | ||
| FC | 2.0 (0.2) | 56.2 (2.0) | 20.6 (1.7) | 23.2 (2.7) | 60 (1) | 1.080 (0.07) | 131.3 | 187.5 | 0.35 | 0.93 | |||
| SubP | DP | 2.7 (0.2) | 41.3 (5.6) | 24.6 (3.6) | 34.1 (3.7) | 55 (7) | 1.055 (0.07) | 112.5 | 150.0 | 0.30 | 0.32 | ||
| FC | 3.0 (0.1) | 49.4 (3.7) | 26.5 (1.3) | 24.1 (2.5) | 69 (5) | 1.075 (0.06) | 118.8 | 175.0 | 0.19 | 0.81 | |||
| PlusP | DP | 3.0 (0.3) | 42.0 (2.0) | 28.6 (1.8) | 29.4 (3.4) | 69 (6) | 1.250 (0.09) | 100.0 | 209.4 | 0.27 | 0.38 | ||
| FC | 4.5 (0.7) | 55.6 (0.8) | 28.7 (0.7) | 15.7 (0.9) | 100 (8) | 1.350 (0.06) | 106.3 | 168.8 | 0.29 | 0.63 | |||
| Water | * | ** | n.s. | *** | *** | n.s. | n.s. | * | * | ** | |||
| P | *** | n.s. | * | n.s. | *** | * | n.s. | *** | * | n.s. | |||
| Water × P | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. | ** | n.s. | n.s. | |||
| CRootBox | Total root surface | Root volume | Total root length | Surface topsoil | Surface subsoil | Root tips | Tips-volume ratio | Surface-volume ratio | Halfmean distance | Root tips in topsoil | Root tips in subsoil | ||
| (cm2) | (cm3) | (cm) | (cm2) | (cm2) | (n) | (cm–3) | (cm–1) | (cm) | (n) | (n) | |||
| NoP | DP | 863 | 11.09 | 7622 | 439 | 424 | 4663 | 420 | 77.87 | 0.680 | 2323 | 2340 | |
| FC | 957 | 13.25 | 7828 | 560 | 397 | 4579 | 346 | 72.27 | 0.671 | 2427 | 2152 | ||
| SubP | DP | 1597 | 18.53 | 16539 | 689 | 908 | 8116 | 438 | 86.20 | 0.461 | 3129 | 4987 | |
| FC | 1678 | 19.82 | 16472 | 882 | 796 | 7836 | 395 | 84.68 | 0.462 | 4074 | 3762 | ||
| PlusP | DP | 1644 | 21.63 | 15504 | 750 | 894 | 8238 | 381 | 76.00 | 0.476 | 3608 | 4630 | |
| FC | 1831 | 30.10 | 17047 | 1111 | 720 | 7992 | 266 | 60.83 | 0.454 | 4862 | 3130 |
Significance was based on a P-level of *P < 0.05, **P < 0.01, and ***P < 0.001; n.s. = not significant.