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Response of Field Grown Alfalfa to Root Waterlogging and Shoot Removal. II. Nitrogen and Fermentation Metabolism

Dep. of Agronomy, Ohio Agric. Res. and Dev. Ctr., Wooster, OH 44691

^* Corresponding author.

Shoot removal and root hypoxia are two stresses to which alfalfa (Medicago sativa L.) roots are often exposed. Because shoots are the primary energy source for all higher plant metabolism, clipping may have severe consequences on anoxic root metabolism. The objective of this study was to characterize aspects of N metabolism, especially polyamine accumulation, and fermentation metabolism when waterlogged roots are further stressed by shoot removal 2 or 12 d before soil saturation. Experiments were conducted on a fine, loamy, mixed mesic Typic Fragiudalf soil water-saturated for up to 14 d. Seedling plants of ‘Vernal’ and ‘Answer’ alfalfa were used at the flowering stage of growth. There was no relationship between flooding injury and root N content or amino-N concentration, although both were significantly affected by flooding. Putrescine concentrations increased significantly with flooding, but there was no correlation with flooding injury among the shoot treatments. Root ethanol concentrations increased in all flooded treatments but were not correlated with root injury. Glucose-6-P concentration increased under hypoxia and did not appear rate limiting for fermentation. Root ATP concentrations were significantly reduced by both clipping and root flooding, while the ATP/ADP ratio was affected only by flooding. Because both the ATP concentrations and the ATP/ADP ratios were similar in tissues with differing flooding injury, a quantitative relationship between energy availability and flooding tolerance is not a probable characteristic of the tolerance mechanism.

Received for publication September 11, 1987.