Wheat Responses to Seminal Root Geometry and Subsoil Water1

Abstract

AbstractRapid drying of the topsoil following germination has been shown to restrict the depth of penetration of the nodal roots of wheat (Triticum aestivum L.). In such instances, the supply of subsoil water to the plant through the seminal root system assumes great importance.A glasshouse experiment was designed to assess the effects of altering the number of seminal root axes of wheat plants dependent on subsoil water and to examine characteristics of the metaxylem vessels in the seminal axes of two cultivars. Deep pots (12.7 ✕ 12.7 ✕ 120 cm) containing soil with a partially reconstructed profile were planted with seedlings of ‘Warimek’ and ‘Manitou’. Plants grew normally in a fully watered soil profile for 5 weeks; thereafter only the subsoil was watered. At stemelongation, all roots other than one, three, or five seminal roots on each plant were severed just below the crown. One set of plants was harvested 10 days after the treatments began and two additional sets, one with the subsoil water maintained at field capacity and the other with a subsoil that received no further water, were harvested at maturity.Five days after the root treatment was imposed, Warimek plants with one, three, or five seminal axes had lost 28, 26, and 17% of their leaves, respectively; corresponding values for Manitou were 40, 31, and 24%. Plants with fewer seminal roots had lower water potentials 4 days after the roots were cut. The rate of water use was greater for plants with more seminal roots. The different rates of water use resulted in leaf water potentials of −29, −39, and −43 bar for plants with one, three, or five seminal roots, respectively, in the drying subsoil 26 days after the treatments began. Grain yield was positively related to the amount of water available after anthesis. With the wet subsoil, yield increased with increasing number of seminal roots per plant; with the drying subsoil, yield decreased. The results showed that the yield response of wheat plants depended on the interaction of the root geometry and the availability of the subsoil water. It was also shown that the metaxylem vessel increased in radius along the seminal axis towards the apex and that all seminal axes within a cultivar had similar vessel radii.