Laboratory experiments were conducted to determine the effects of oxygen concentration (21, 10, 5 and 2.5%), exposure to light, and osmotic potential on the germination of wheat, canola [rape] and various weed species, i.e. barnyardgrass ( Echinochloa crus-galli), catchweed bedstraw ( Galium aparine), curly dock ( Rumex crispus), dandelion ( Taraxacum officinale), foxtail barley ( Hordeum jubatum), green foxtail ( Setaria viridis), perennial sowthistle ( Sonchus arvensis), wild mustard ( Brassica kaber), wild oat ( Avena fatua) and field pennycress ( Thlaspi arvense). Germination of most species increased as osmotic potential was increased. Seed germination for some species like barnyardgrass was inhibited by the combination of exposure to normoxic (21% oxygen) conditions and light. This combination of conditions may function as a signal to prevent soil surface germination. Wild mustard germination increased with increasing oxygen concentration when seeds were not exposed to light, whereas green foxtail germination was relatively insensitive to oxygen concentration. Wild oat germination increased with increasing osmotic potential, and osmotic potential had a greater influence when the seeds were exposed to light. Dandelion, foxtail barley, curly dock and perennial sowthistle germination was affected more by osmotic potential and light exposure than by oxygen concentration. A better understanding of the mechanisms of depth detection for specific species will lead to a better understanding of their recruitment biology. This information may help model the potential for invasion and proliferation of each species as well as devise improved management strategies.
