Changes in growth, porosity, and radial oxygen loss from adventitious roots of selected mono- and dicotyledonous wetland species with contrasting types of aerenchyma

Growth in stagnant, oxygen-deficient nutrient solution increased porosity i n adventitious roots of two monocotyledonous (Carex acuta and Juncus effusu s) and three dicotyledonous species (Caltha palustris, Ranunculus sceleratu s and Rumex palustris) wetland species from 10 to 30% under aerated conditi ons to 20-45%. The spatial patterns of radial oxygen loss (ROL), determined with root-sleeving oxygen electrodes, indicated a strong constitutive 'bar rier' to ROL in the basal root zones of the two monocotyledonous species. I n contrast, roots of the dicotyledonous species showed no significant 'barr ier' to ROL when grown in aerated solution, and only a partial 'barrier' wh en grown in stagnant conditions. This partial 'barrier' was strongest in C. palustris, so that ROL from basal zones of roots of R. sceleratus and R. p alustris was substantial when compared to the monocotyledonous species. ROL from the basal zones would decrease longitudinal diffusion of oxygen to th e root apex, and therefore limit the maximum penetration depth of these roo ts into anaerobic soil. Further studies of a larger number of dicotyledonou s wetland species from a range of substrates are required to elucidate the ecophysiological consequences of developing a partial, rather than a strong , 'barrier' to ROL.