Root Processes Affecting Soil Moisture Patterns in Ecohydrology

Soil moisture patterns arise from the combined processes induced by vegetation, soil properties, climate, topography, parent material, and time. In this chapter, we focus on how vegetation induces soil moisture patterns, particularly how plant root processes affect the soil moisture distribution. Four different mechanisms were identified as potential drivers of soil moisture variability: root growth, root water uptake and transpiration, plant competitions, and rhizosphere properties. High transpiration, root growth, and root water uptake generally increase the soil moisture variability for drying conditions. On the other hand, other mechanisms reduce the soil moisture variation under drying condition including (1) compensation, which plants extract water in the wettest part of the soil; (2) hydrotropism, which roots tend to grow toward wetter zone of the soil; and (3) plant competition, which different plants try to segregate the depths at which they take up water. In addition, rhizosphere-specific properties tend to increase the variability when the soil is wetted from dry condition or to decrease it under wet conditions. We used a plant architecture model to illustrate how soil and root properties combine to generate or destroy soil moisture relations.