UC Berkeley

Abstract Plant roots stabilize sediment in engineered and natural landscapes, but we lack a general understanding of how root architecture affects anchoring forces. Existing models can accurately simulate root breakage and soil failure, but such models primarily rely on experimentally calibrated empirical relations between root geometry characteristics and the peak force required for uprooting. To address this knowledge gap, we conducted physical experiments uprooting rigid root geometries via pullout from noncohesive sediment. We found that peak pullout force primarily increased with rooting depth and the volume of sediment mobilized during uprooting. We calculated the peak uprooting force for arbitrary rigid root geometries using an anchoring force balance and nondimensionalization and validated this theory with our experimental data. The work required for uprooting increased more than linearly with respect to peak force because both peak force and total displacement increased with root length and depth. To determine which root architectures maximized anchoring forces while minimizing energetic costs for root growth and maintenance, we developed a simple model in which the energetic cost increases linearly with overburden. Model results indicate that branching and growing laterally to increase the sediment overburden at shallow depths are the most energy‐efficient anchoring strategies for plants. Our results yield a general theory for peak pullout force, provide insight into root stabilization of minimally cohesive materials, and could inform erosion prevention strategies and numerical models of plant resource optimization. Plain Language Summary Plants are commonly used as a natural engineering solution since their roots can stabilize soils and prevent riverine, coastal, and hillslope erosion. Therefore, it is important to understand what root network architectures are most effective at stabilizing soil and under what conditions plants grow those networks. To determine the anchoring forces of different root networks, we developed an analytical theory and conducted experiments to measure the force and work required to uproot simplified root geometries. Intuitively, roots that were longer and deeper beneath a heavier sediment load were more difficult to uproot. We used experiments to confirm our analytical theory and proposed an anchoring efficiency relation, where we compared the work required to uproot a plant with the energetic cost to grow and maintain its root network. These results could be incorporated into root growth models to understand and predict environmental controls on root architecture and landscape stability. Key Points Plant roots stabilize soil against erosion, but root networks cost plants significant resources to grow and maintain Deep roots with a heavy sediment overburden are most resistant to uprooting if uprooting force is measured relative to root network volume Root network branching and lateral expansion produce the greatest uprooting force per unit energy invested in plant growth