The Development of Waterlogging Damage in Young Wheat Plants in Anaerobic Solution Cultures

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Abstract
Anaerobic (anoxic) solution cultures were used to investigate the effect of a restricted oxygen supply to roots on the development of symptoms of waterlogging damage in young wheat plants, especially effects on growth and nutrient uptake by the shoots. Anaerobic conditions produced by bubbling solutions with oxygen-free nitrogen gas caused premature senescence of the lower leaves, slowed shoot fresh weight accumulation, and arrested the growth of the seminal roots. However the shoot dry weight initially increased above that of the aerobic controls. Nutrient accumulation by the shoot was severely inhibited by anoxia, the uptake of nitrate, phosphate, and potassium being more affected than that of calcium and magnesium. The calculated concentrations in the xylem stream of all these ions (except nitrate) were equal to, or less than, those in the external solution, suggesting that the slow but continuous accumulation of nutrients in the shoot could have occurred passively by the mass flow of solution across damaged roots in response to transpiration. Aerenchymatous nodal roots extended into the anoxic solutions to a maximum length of 12 cm but there were few produced, and the size of the root system remained small and may have limited shoot growth. Inclusion of carbon dioxide (10 kPa partial pressure) in the nitrogen gas stream had little additional effect on plants to that caused by anoxia alone. All the responses of wheat to the anaerobic solutions were similar to those observed previously in waterlogged soil, indicating that many of the early symptoms of waterlogging damage to wheat can be caused simply by the direct effects of inadequate oxygen supply to the roots. The results are discussed in relation to current views of the mechanisms contributing to waterlogging damage to plants.