Biomechanical Trade-Offs Between Root Tensile Strength and Porosity in Coastal Marshes

Abstract

Root biomechanics play a fundamental role in stabilizing wetland soils and sustaining coastal ecosystems under increasing environmental stress. This study investigates the tensile strength (TS) and internal porosity (n) of roots from two dominant marsh grasses, Spartina alterniflora and Spartina patens, across four sites in the Mississippi River Delta Plain (MRDP), spanning active (Atchafalaya) and inactive (Terrebonne) basins. Through approximately 300 tensile strength tests conducted on live roots across diameter classes and depths, we observed a consistent decline in strength with increasing root diameter and depth. Fine roots (<2 mm), particularly those in the upper 15 cm, showed the highest tensile resistance, reinforcing their critical role in erosion control. To assess morphological drivers, we employed high-resolution scanning electron microscopy (SEM) with a machine learning (ML) segmentation pipeline to quantify porosity and visualize aerenchyma. Coarse roots exhibited significantly higher porosity due to large central lumens and expanded aerenchyma, while fine roots maintained denser tissue structures. An exponential decay relationship emerged between porosity and tensile strength, indicating a trade-off: increased void space enhances oxygen diffusion in waterlogged soils but compromises mechanical integrity. This inverse relationship was most pronounced in saline environments, suggesting that stress amplifies structural compromises in root traits. This integrative approach, combining precision mechanical testing, advanced imaging, and ML-based analysis, provides a scalable and reproducible framework for characterizing root biomechanics. Findings advance understanding of plant contributions to belowground stability in coastal wetlands and offer practical insights for restoration strategies to enhance shoreline resilience.