Switchgrass Root Composition and Anatomy Vary with Depth, Suggesting Approaches for Trait Enhancement

Plant root cellular architecture and composition influence plant productivity, stress resilience, biotic interactions, and potentially soil carbon storage. This study establishes comprehensive compositional parameters for roots of a lowland switchgrass genotype, DVR3. Root traits were analyzed across four 12.5 cm depth zones, from Zone 1 near the surface to Zone 4 down to 50 cm. Mean values across zones were 170 ± 15 µg/mg lignin, 470 ± 20 µg/mg cellulose, and 35 ± 5 µg/mg total suberin. Composition and cellular anatomy varied with depth, in an uncoordinated manner. Crown root cross sections showed extensive aerenchyma in mature root regions despite greater root mass density, corresponding to abundant lignin and cellulose. Deep roots were enriched for pectin-associated traits, including arabinogalactan II, homogalacturonan, and arabinose-associated linkages. Heteroxylan branching increased with depth (21 to 30 mol%) though xylose was invariable. Suberin content by GC-MS did not vary statistically, though Casparian strip formation, endoderm and exoderm thickening, and suberin surface staining progressed with development, with most exodermal development between Zones 3 and 4. These results suggest that native switchgrass root chemistry can be genetically enhanced to promote soil penetration and carbon storage by reducing variability with development, potentially via cell-type specific adjustments.