Growth and growth rate characteristics of diffuse knapweed and bluebunch wheatgrass seedlings were evaluated under two temperature regimes, 10 and 16 C, and two moisture regimes, − 0.01 and − 0.03 MPa, in an environmental chamber. Intra- and interspecific interference were evaluated at 10 C and at either − 0.01 or − 0.03 MPa. Root–leaf ratios for bluebunch wheatgrass were greater than for diffuse knapweed at − 0.01 MPa. Under moist conditions, root penetration was greater for diffuse knapweed than for bluebunch wheatgrass roots; penetration was equal in warm or dry conditions. Wheatgrass root length was greater than knapweed length under dry conditions. Intraspecific interference was greater than interspecific interference for both species. Leaf area data and root–leaf ratios suggest that diffuse knapweed is the faster-growing species under moist conditions.
Nomenclature: Bluebunch wheatgrass, Pseudoroegneria spicata (Pursh) Scribn. & Smith; diffuse knapweed, Centaurea diffusa Lam. #3 CENDI.
Additional index words: Competition, growth rate.
