It is known that soil water flow has two main types, i.e., preferential flow and soil matrix flow. These two behaviors show two contrary effects on soil infiltration, which in further take part in the regulation of soil hydrology. The spatial distribution of preferential flow and soil matrix flow at the soil profiles is extremely heterogeneous, and, could be affected by root systems.
Root systems, as an important component within the soils, could support plants to absorb water and nutrients. So, more water could return to the atmosphere through the transpiration.
However, we must also realize that more complex macropores (especially root channels themselves) could form during root growth. On the one hand, those pores could promote the loss of water and nutrients by preferential flow, which could result in inefficient water use and weaker soil and water conservation. On the other hand, the increasing complex of the pores at the root-soil interface indicates a large interfacial area between soil pores and the surrounding soil matrix, allowing more water infiltration into the matrix.
Based on this contradiction, we need to reconsider the dual function of root systems in balancing water flow in soil, i.e., when root systems promote water flow, and when they restrict it.
Therefore: When do root systems promote water flow by facilitating preferential flow, or when do they restrict water flow by facilitating soil matrix flow? How do different root system types influence this? Is the threshold for this effect different across vegetation types? These questions should be discussed as follows.
Using high-tech techniques (e.g., X-ray CT) to quantify the spatio-temporal distribution of different soil water flow behavior under the regulation of root systems.
- Discussing the mechanism or new hydrological model about root induced soil water flow (preferential flow or soil matrix flow) under different conditions.
- Linking root systems traits (architectural or biological, living roots or dead roots) to the soil water flow characteristics.
- Detecting the transfer between root-induced preferential flow and soil matrix flow using process-based hydrological models or machine learning.
- Exploring the profound effects of root systems on soil water flow from macroscales, such as watershed hydrology, groundwater allocation, atmospheric water cycle, and so on.