Root physiological characteristics associated with drought resistance in tall fescue cultivars

Knowledge of root traits associated with drought tolerance is important for further understanding drought tolerance mechanisms of the whole plant. The experiment was designed to investigate effects of drought stress on root physiological activities of six cultivars (Kentucky-31, Falcon II, Houndog V, Phoenix, Rebel Jr., and Bonsai) of tall rescue (Festuca arundinacea Schreb.) varying in drought resistance. Grasses were grown in well-watered or drying (nonirrigated) soil for 35 d in a greenhouse. Drying reduced root length and dry mass in the 0- to 20-cm layer for all six cultivars. Root length and dry mass in the 40- to 60-cm layer was enhanced for Houndog V, Falcon II, and Kentucky-31; was not affected for Phoenix and Bonsai; and was reduced for Rebel Jr. by soil drying. Water uptake rates for Falcon II and Kentucky-31 decreased with soil drying in the 0- to 20cm layer but increased in the 40- to 60-cm layer. Soil drying limited water uptake by Rebel Jr. in both layers. Drought stress increased root mortality in the 0- to 20-, 20- to 40-, and 40- to 60-cm layers, but the increase was most dramatic in the surface soil layer. The increase in root mortality in each soil layer was most severe for Rebel Jr. and least severe for Kentucky-31. Root death of tall fescue cultivars during drought was positively correlated with root desiccation, as evidenced by severe leakage of organic solutes from roots in drying soil. Carbohydrate supply to roots was not a contributor to root death during drought stress. This was supported by the increased or unaffected total nonstructural carbohydrates in both shoots and roots, and the increased C allocation to roots under soil drying conditions.