Radial oxygen loss

In water logged soils radial oxygen loss from the root raises the redox potential in the rhizosphere as a consequence of which iron oxide plaques are seen to develop on root surfaces. Bacha and Hossner (1977) removed the coatings on rice roots growing under anaerobic conditions. The coatings were composed primarily of the iron oxide mineral lepidocrocite (y-FeOOH) as the only crystalline component. St-Cyr and Crowder (1990) studied the iron oxide plaque on roots of Phragmites and detected both Fe and Mn. The Fe Mn ratio of the plaque resembled the ratio of Fe Mn in substrate carbonates. The plaque material also contained Cu. 

Cohner, T.D. 2003. Long-distance transport of gases in plants a perspective on internal aeration and radial oxygen loss from roots. Plant Cell Environ. 26 17-36. 

Connell, E. L., Colmer, T. D., and Walker, D. I. (1999). Radial oxygen loss from intact roots of Halophila ovalis as a function of distance behind the root tip and shoot illumination. Aquat. Bot. 63, 219-228. 

Armstrong, W. (1971). Radial oxygen losses from intact rice roots as affected by distance from the apex, respiration, and waterlogging. Physiol. Plant. 25, 192-197. 

FIGURE 7.24 Experimental apparatus used to estimate radial oxygen loss from wetland plant roots into titanium citrate buffer solution. (Redrawn from Kludze et al., 1994a.)... 

Relationship of Reduction Intensity with Root Porosity and Radial Oxygen Loss... 

FIGURE 7.35 Root porosity and radial oxygen loss in Spartina patens gvov/n under various soil redox intensity for 50 days. (Modified from Kludze and DeLaune, 1994.)... 

FIGURE 7.38 Radial oxygen loss (ROL) in Spartina patens grown nnder various soil reduction capacities while the reduction intensity was maintained at -200 mV. Values followed by the same letter are not significantly different at the 0.05 level. (From Kludze and DeLaune, 1995b.)... 

What is the relationship of soil reduction intensity to the root porosity and radial oxygen loss (ROL) ... 

The presence of iron oxyhydroxide coatings (i.e., Fe plaque, often dominated by ferrihydrite) on the surface of wetland plant roots is visual evidence that subsurface iron oxidation is occurring in otherwise anoxic wetland soils and sediments. Oxygen delivered via radial O2 loss may react with reduced iron in soil pore spaces to form oxidized iron that can be deposited on the plant roots as Fe plaque. Despite a long history of observing Fe plaque on wetland plant roots and understanding the basics of plaque formation [i.e., reaction of plant-transported O2 with Fe(II) in soils and sediments], it was largely assumed that plaque formation is predominately an abiotic (i.e., chemical) process because the kinetics of chemical oxidation can be extremely rapid (Mendelssohn et al., 1995). However, recent evidence has demonstrated that populations of lithotrophic FeOB are associated with Fe plaque and may play a role in plaque deposition. 

Armstrong W, Beckett PM. 1987. Internal aeration and the development of stelar anoxia in submerged roots. A multishelled mathematical model combining axial diffusion of oxygen in the cortex with radial losses to the stele, the wall layers and the rhizosphere. New Phytologist 105 221-245. 

---