Root Effects On Soil Properties and Processes: Synthesis and Future Research Needs.

As roots growth through soil, they may create pores or grow through the existing pore structure, extending the life of the pores or fractures. Actively growing roots may plug the pores through which they are growing, but the pores are re-opened as the roots die back. The pores may remain partially open if roots are smaller than the pores. As roots take up water and dry the soil, the fractures are re-inforced or re-created. When not plugged, these macropores facilitate rapid movement of water and air through soil, and provide pathways for future roots to grow. Bypass flow occurs through continuous macropores, transporting solutes through the soil without much mixing of existing soil solution within peds. This can result in rapid leaching of chemicals applied at the surface, but reduced leaching of chemicals contained within the peds. Since roots are concentrated in biopores and fractures, they are able to utilize some of the water that drains through these pores. Less energy is expended to take up water from larger pores than smaller pores, so roots intercept more of the drainage water than is intercepted under a bare area without plants. Soil disturbance destroys the developed macropore system though new, unstable pores are created by the disturbance. Traffic can compress these unstable macropores, and destroy the continuity of the pores. Future research needs include 1) defining clustered root distribution or function for models of water flow and uptake and of solute transport, and 2) defining the dynamic role of roots in modifying biopores and fractures in the soil.