Oxygen Transport in the Salt Marsh GenusPuccinelliawith Particular Reference to the Diffusive Resistance of the Root—Shoot Junction and the use of Paraffin Oil as a Diffusive Barrier in Plant Studies

Results are presented which contradict previous reports that in the graminaceous genus Puccinellia the root-shoot junction has a high diffusive resistance which severely restricts oxygen transfer from shoot to root. No such restriction was evident in P. maritima, P. festuciformis var.festuciformis, and P. festucfformis var.intermedia(= P. peisonis) and the plants produced well-developed root systems in permanently flooded soils. The evidence obtained supports the view that, whether the root systems are wholly or only partially submerged by soil flooding the shoot is the major source or entry point for oxygen required by the roots; also, that oxygen passes more readily from shoot to root than it does through the wall cells of the root base. It is pointed out that paraffin oil is an undesirable product to employ as a diffusion barrier in studies of root aeration.