Diffuse knapweed and bluebunch wheatgrass seedling growth under stress

Abstract

Growth characteristics of diffuse knapweed (Centaurea diffusa Lam.) and bluebunch wheatgrass (Pseudoroegneria spicata (Pursch) Scribn. Smith) seedlings were evaluated in 2 temperature regimes, 10 and 16 degrees C, and 2 moisture regimes, -0.01 and -0.03 MPa, in an environmental chamber. In cool, wet conditions, root penetration was greater for diffuse knapweed roots than bluebunch wheatgrass roots, but penetration was equal in warm, dry conditions. Root lengths for both species were equal in cool, wet conditions; but, bluebunch wheatgrass root length was greater in warm, dry conditions. Leaf area of diffuse knapweed was greater than bluebunch wheatgrass in warm, dry conditions. Drier, but not cooler, conditions favored diffuse knapweed leaf area over bluebunch wheatgrass leaf area. Root:shoot ratios for bluebunch wheatgrass were greater than diffuse knapweed in all environmental conditions. Results suggest that bluebunch wheatgrass should be more competitive than diffuse knapweed for nutrients and water at lower depths in warmer, drier conditions. Diffuse knapweed should be more competitive for nutrients and water in wetter conditions.