NIKLAS, K. J.1*, F. MOLINA-FREANER2, C. TINOCO-OJANGUREN2, and D. J. PAOLLILO, JR.1. 1Department of Plant Biology, Cornell University, Ithaca, NY 14853; 2Instituto de Ecologia UNAM, Hermosillo, Sonora CP83000, Mexico. - Biomechanics and anatomy of Pachycereus pringlei root systems.
We report the morphology, anatomy, and biomechanics of Pachycereus
pringlei root systems and explore the hypothesis that anchorage and
nutrient absorption/storage are functionally specialized and spatially
partitioned in response to selection in windy and arid habitats. The
root systems of 18 plants were excavated, and root samples were
anatomically and biomechanically examined. Our analyses indicate that
anchorage is provided by a large bayonet-like root that typically
emerges from the stem base in conjunction with the woody proximal
elements of a horizontally extensive, shallow lateral root system that
absorbs and stores water. Wood stiffness and strength correlated with
the volume fraction of axial tissues, which dramatically increased
toward the base of lateral roots. Calculations indicate that the
ability to resist wind-throw decreases with increasing plant size, due
to a disproportionate increase in stem size with respect to the depth
of burial and size of the bayonet-like root. In contrast, the capacity
of more distal lateral root elements to provide for nutrient
absorption/storage increases. These and other lines of evidence
support our hypothesis that the root system of this species is highly
compartmentalized with respect to anchorage and nutrient
absorption/storage.
Key words: biomechanics, Cactaceae, plant anatomy, roots, wind drag, wood