Roots oxygenation

Bodelier, P. L. E., Lihochant, J. A., Blom, C. W. P. M., and Laanbroek, H. J. (1996). Dynamics of nitrification and denitrification in root-oxygenated sediments and adaptation of ammonia-oxidizing bacteria to low-oxygen or anoxic habitats. Appl. and Environ. Microbiol. 62, 4100-4107. 

FIGURE 4.22 Redox potential of soil planted with rice, showing the influence of root oxygenation. (From Reddy and Patrick, 1984.)... 

Saturated soil conditions in wetlands affect plant growth and productivity in several ways. The abundance of water seriously interferes with plant root metabolism, creating root oxygen deficiency. In addition, microbial processes in wetland soils can produce reduced substances potentially toxic to wetland plants. Saturated soil conditions in wetlands affect the reactivity of many inorganic redox-mediated processes, thus influencing adaptations of wetland plants. 

Under prolonged flooded conditions or in wetland soils with high intensity of reduction, the amount of oxygen transported by plants may not be snfficient to snpport aerobic respiration. When this situation arises, certain wetland plants may snrvive by anaerobic metabolism. ADH activity, which is induced under anaerobic conditions, has been nsed as an indicator of root oxygen... 

Acceleration of airspace formation is attributed to production of ethylene and increased cellu-lase activity in the tissue (Kawase, 1981). The sequential processes in aerenchyma development are presented by McLeod et al. (1987). They suggest that flooding first results in soil oxygen depletion, followed by depletion of root oxygen. This results in ACC (1-aminocyclopropane-l-carboxylic acid) production that requires ATP. Ethylene is produced from ACC, and this process requires oxygen and is sensitive to temperature. Ethylene produced accelerates cellulase activity that softens tissue, resulting in the formation of aerenchyma tissue. 

The relative importance of each of the processes described above is difficult to ascertain because all the processes function simultaneously and independently, and various interactive factors regulate each process. Humidity-induced pressurization is usually the most dominant process, regulating convective flows in many wetland plants. Species with cylindrical culms and linear leaves usually have internal pressurization potential (Brix et al., 1992) and may be able to grow in deeper water than species dependent on root oxygenation due to diffusion only (Brix et al., 1992). 

Root oxygenation in flooded plants is essential in the maintenance of aerobic respiration. In the absence of oxygen, the less energy-efficient anaerobic fermentation occurs. Decreasing oxygen... 

Oxygen microelectrodes, similar to those described by Revsbech (1989), have been used to determine the ROL and thickness of aerobic layers around the roots. Oxygen-depleted hydroponic soln-tions used in many ROL experiments are, however, a poor analog of wetland soil, because they do not mimic the high oxygen demand and low redox potentials found in wetland soil (DeLanne et al.,... 

Kludze, H. K., S. R. Pezeshki, and J. H. Pardue. 1990. An oxidation-reduction buffer for evaluating the physiological responses of plants to root oxygen stress. Environ. Exp. Bot. 30 243-247. 

DeLaune, R. D., A. Jugsujnda, and K. R. Reddy. 1999. Effect of root oxygen stress on phosphorus uptake by cattail. J. Plant Nutr. 22 459-466. 

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