Effect of Environmental Conditions on the Growth of Four Perennial Grasses. I. Response to Controlled Temperature1

The growth of timothy (Phleum pratenseL.), bromegrass (Bromus inermisLeyss.), orchardgrass (Dactylis glomerataL.), and Kentucky bluegrass (Poa pratensis,L.) was studied under controlled temperatures varying by 3.3 C intervals from 18.3 to 34.8 C during the day and from 1.8 to 18.3 C during the night. A day temperature between 18.3 and 21.6 C was optimum for top growth with timothy, orchardgrass, and bluegrass. With bromegrass, the optimum day temperature was between 18.3 and 24.9 C. As the day temperature was increased from these optimum ranges to 34.8 C, all of the species decreased in yield, but the decrease in bromegrass yields was less than in any of the other species. In some cases, night temperature also affected yields; but the optimum night temperature depended upon the species and the day temperature. The dry weight of etiolated growth indicated that the level of food reserves varied greatly. The species ranked orchardgrass > bromegrass > bluegrass > timothy for level of reserves. The most important factor affecting the level of reserves in a particular species was night temperature. In general, the food reserves decreased as the night temperature was increased from 1.8 to 18.3 C.