Fig 1.
A conceptual visualization of the study system.
A: The cross-section of the soil profile shows a hydrophobic zone in the topsoil (light brown). This zone is hypothesized to be induced by root mucilage, which becomes hydrophobic after drying. The inset B is taken from [20]. It shows the soil water distribution ranging from reddish–yellowish colors for dry soil to blue color tones for wet soil areas. Re-wetting after a drying period is inhibited in topsoil and only occurs in lower soil areas.
Fig 2.
Root systems at different developmental stages.
(A) Fibrous roots at intermediate stage show seven short adventitious root branches. (B) At final root growth stage, fibrous-rooted plants have 13 rootbranches. (C) Tap-roots after seven days show a principal vertical root reaching final depth already. Secondary root branches are restricted to one pair next to the surface. (D) The fully developed tap root system consists of the principal vertical root and seven pairs of lateral branches with a higher density in the topsoil. The root/soil system is capped by a impermeable barrier for water (red line) with one raster cell exit to the shoot/above ground system. For the first root growth stage (1–6 days) no water uptake was assumed and, hence, no sketch was drawn.
Fig 3.
A global process (Initialization) is colored in red, (soil-)water related processes are filled in blue, and plant processes are given in green.
Fig 4.
Quantification of water-uptake by plants according to hydraulic resistances at different soil water saturation levels.
In the top row total hydraulic resistances of plants at different root system developmental stage (columns) in relation to total soil water saturation Θtotal (without hydrophobicity) are displayed. Note the logarithmic y-axis. In the bottom row normalized inverse of the resistance values are displayed as they were used to fit a vitality function (line). Reference value for normalization was the second highest resistance value at Θtotal = 0 (black circle).
Fig 5.
Quantification of water-uptake by plants at hydrophobic soils according to hydraulic resistances at different soil water saturation levels.
In the top row total hydraulic resistances of plants with different root system architectures (columns, development stage 3) in relation to subsoil water saturation Θsub and to different strengths of hydrophobicity affecting the water saturation of the topsoil (Θtop). Note the logarithmic y-axis. In the bottom row normalized inverse of the resistance values are displayed as they were used to fit a vitality function (line).
Table 1.
Best estimates for parameters of Eq 8.
Fig 6.
Impact of precipitation on plant populations with and without hydrophobicity in the soil.
Columns show different precipitation sums. Rows show population indices total biomass (top panel) and total abundance (bottom panel). Precipitation frequency is seven days. Values are differences between tap-rooted to fibrous rooted plants. Differences are normalized by the total sum. Positive values are in favor of tap-rooted plants. Thin lines are results of 100 simulation runs with either hydrophobicity trait activated (violet) or deactivated (green). Thick lines are smoothed (spline) averages.
Fig 7.
Scale-dependent spatial interactions between taproots and fibroots.
Each panel shows the relative frequency of the outcomes of 199fold simulations of the pair-correlation functions. In each simulation run, the actual point pattern is tested against the null model of complete spatial randomness (green). Red colors indicate significant avoidance and blue colors show attraction compared to the null model. Statistics were run for four simulation steps: 500, 1000, 1500, and 3500 (columns) and two scenarios (without and with hydrophobicity (rows)). Precipitation frequency was seven days with an annual sum of 700mm.