Do belowground bud-bearing organs share secondary xylem traits with roots in Cerrado woody resprouters?

Xylopodia and woody rhizomes are highly lignified belowground bud-bearing organs (BBOs) reaching extensive depths in soil, persisting through a viable belowground bud bank over many years. In this context, maintaining hydraulic functionality and storing resources are essential secondary xylem functions for their survival in environments prone to disturbances such as fire and drought. Here, we examine how secondary xylem traits vary between roots and both BBOs (woody rhizomes and xylopodia) in resprouting woody species from Cerrado.

We evaluated cross-sections of secondary xylem from two BBO types and their taproots of ten native woody species in a Cerrado area under regeneration after decades of pine cultivation. We applied linear mixed models (LMMs) to test whether secondary xylem traits differ between roots and BBOs.

Xylopodium-type BBOs had narrower, dense vessels, a higher fiber fraction, and lower hydraulic potential conductivity than their roots. Woody rhizome-type BBOs had narrower vessel diameters and lower densities than their roots. Woody rhizome-type BBOs had narrower vessels and a higher density than xylopodia. Xylem fractions (vessels, rays, and axial parenchyma) were not statistically different between roots and BBOs.

BBOs share similar strategies regarding storage capacity and mechanical support. Storage is a key trait for belowground bud bank resourcing during unfavorable periods and supporting resprouting after fire and drought. Fibers are essential for the mechanical stability of new branches. In addition, high lignification could help prevent wood decay and herbivory in the soil, as BBOs remain buried throughout the species' lifespan.