A Re-examination of the Functional Significance of Aerenchyma

Model roots of known length and internal porosity were assayed for ROL (radial oxygen loss) by the cylindrical Pt electrode technique and a series of curves were obtained which express the inter-relationships between ROL and diffusion path length over a wide range of internal porosity levels. The results indicate that internal porosity can exert considerable control on the amount of oxygen lost from roots, the more so the narrower the root. Because radial oxygen loss is necessary for survival and competitiveness, doubt is therefore cast on the currently held view that aerenchyma formation furnishes the wetland plant with an oxygen diffusion pathway excessive to its requirements. The results also suggest that cellular partitions and diaphragms in wetland species may impede gas transport far less than has hitherto been thought.