Root Aeration Function of Baldcypress Knees (Taxodium distichum)

Abstract

Premise of research. The ability of cypress knees to allow easy diffusion of O2 from the atmosphere to the attached submerged root is supported by a number of past ecomorphological observations yet not by any experimental evidence, despite several past in situ studies that examined this phenomenon.Methodology. O2 concentration of air extracted from submerged roots was compared when attached knees were above water and when they were submerged.Pivotal results. When roots were submerged, the root internal air O2 concentration was much higher when the knee was above water than when both the knee and root were submerged. This result unambiguously supports past assumptions that cypress knees do indeed function as pneumatophores in supplying submerged roots with oxygen.Conclusions. Using a simple but unique experimental approach, the results of this study show that cypress knees function as pneumatophores.