Effects of Temperature on the Elongation of Seedling Roots of Some Grasses and Legume1

Rate of root elongation of small seeded range plants Agropyron desertorum (Fish, ex Link) Schult.; Agropyron elongatum (Hort.) P.B.; Medicago polymorpha L.; Medicago truncatula Gaertn.; Oryzopsis holciformis (M.B.) Hack, and Phalaris tuberosa L. was slow (0.5–2 cm/day) as compared to the large seeded Avena sterilis L. and Vicia dasycarpa Ten., wheat and barley (2–7 cm/day). all species the rate of root elongation increased two‐ to three‐fold over the 10–20C temperature range. Over this range the rate increased faster in the upper soil layer (2–12 cm depth) than in the deeper layer (12–22 cm). Between 20–25C changes in the rate of root elongation varied with species and depth. The optimal temperature for root elongation near the soil surface (2–12 cm depth) was generally higher than in the 12–22 cm depth. Root‐elongation was positively correlated to seed weight.