Response of Field Grown Alfalfa to Root Waterlogging and Shoot Removal. I. Plant Injury and Carbohydrate and Mineral Content of Roots

Shoot removal represents a significant stress to plants, especially forage legumes subjected to frequent harvest. Since it has been reported that alfalfa (Medicago sativa L.) injury due to flooding is increased after clipping, this study examined cultivar response and root chemical composition (minerals and carbohydrates) in response to increasing duration of flooding and shoot removal stress. The objective was to characterize physiological responses related to flooding-induced injury. Experiments were conducted on a fine, loamy, mixed mesic Typic Fragiudalf soil that was water saturated for up to 14 d. Young plants of ‘Vernal’ and ‘Answer’ alfalfa were used at the flowering stage of growth. Responses of Vernal and Answer alfalfa were not significantly different from each other in terms of growth or root chemical composition. Shoot removal 2 and 12 d prior to initiation of soil flooding reduced regrowth dry matter accumulation 56 and 33%, respectively. Non-clipped plants were not injured with flooding duration up to 14 d. Root K⁺ content was significantly reduced by flooding stress only in the clipped treatments. Significant accumulation of Mn⁺² or Fe⁺² in flooded roots was not observed. Waterlogging had no effect, while clipping significantly reduced root starch concentration. In contrast, concentrations of both sucrose and glucose increased significantly with increased flooding stress for all shoot treatments. However, there was no apparent relationship between availability of soluble carbohydrates, as affected by clipping treatment, and flooding injury. Supply of fermentable carbohydrates does not appear to be limiting for fermentation reactions and is thus probably not a critical factor in flooding tolerance. Salaries and research support provided by state and federal funds appropriated to the Ohio Agric. Res. and Dev. Ctr., The Ohio State Univ. Journal Article no. 173-87.