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Three-Dimensional Modeling of Hydrotropism Effects on Plant Root Architecture along a Hillslope

^a Div. of Fluvial and Marine Disaster, Disaster Prevention Research Institute, Kyoto Univ., Gokasyo, Uji, Kyoto 611-0011, Japan
^b Div. of Forest Science, Graduate School of Agriculture, Kyoto Univ., Oiwakecyo, Kitashirakawa, Sakyoku, Kyoto 606-8502, Japan

View larger version (77K): [in a new window]   Fig. 1. Schematic of possible environmental effects on root elongation: (a) tropism of gravity (gravitropism), (b) tropism of soil water (hydrotropism), (c) deflection by an obstacle (thigmotropism), and (d) tropism of soil mechanical resistance.

View larger version (27K): [in a new window]   Fig. 2. Soil hydraulic properties for the soils of Slopes 1 and 2. The equations in the figures represent the lognormal model, where the function Q represents the complementary cumulative distribution function.

View larger version (30K): [in a new window]   Fig. 3. Schematic showing the differential growth of three-dimensional root elongation of a root segment. The root elongation rate has a minimum (ERmin) and maximum (ERmax) at points P1 and P2, respectively.

View larger version (46K): [in a new window]   Fig. 4. Elongation behavior of a root that is forced to change its direction because of an obstacle.

View larger version (21K): [in a new window]   Fig. 5. Branching model showing (a) the branching interval and angle and (b) branching direction and order around a parent root (N is the branching order number).

View larger version (25K): [in a new window]   Fig. 6. Weather conditions used for the simulation: (a) monthly mean temperature, (b) evapotranspiration, and (c) rainfall intensity.

View larger version (46K): [in a new window]   Fig. 7. Soil domain and selected finite element grid.

View larger version (13K): [in a new window]   Fig. 8. Observed architecture of actual root systems of 2-yr-old pine trees: (a) Slope 1 (slope angle = 31°, soil layer thickness = 25 cm), and (b) Slope 2 (slope angle = 37°, soil layer thickness = 53 cm). Dashed lines indicate the soil surface.

View larger version (24K): [in a new window]   Fig. 9. Calculated cumulative values of the potential and actual (a) evaporation and (b) transpiration rates.

View larger version (28K): [in a new window]   Fig. 10. Simulated root architectures: (a) upslope, (b) midslope, and (c) downslope for Slope 1.

View larger version (28K): [in a new window]   Fig. 11. Simulated root architectures: (a) upslope, (b) midslope, and (c) downslope for Slope 2.

View larger version (32K): [in a new window]   Fig. 12. Simulated root architectures for Slopes 1 and 2 with no hydrotropism, downslope only.

View larger version (32K): [in a new window]   Fig. 13. Averaged angle, av of the simulated and observed root systems for (a) Slope 1 and (b) Slope 2.