Temperature Requirements for Seed Germination in an Annual‐Type Rangeland Community1

Abstract

AbstractGermination as affected by constant and alternating temperatures was investigated in four species of annual grasses, soft chess (Bromus mollis L.); ripgut (B. rigidus Roth); slender oat (Avena barbata Brot.) and foxtail fescue (Vulpia megalura (Nutt.) Rydb.), and in their replacement forage species, seven cultivars and one naturalized population of rose clover (Trifolium hirtum All.); hardinggrass (Phalaris tuberosa var. stenoptera (Hack.) Hitchc.); and perlagrass (P. tuberosa var. hirtiglumis Bott. & Trobut). Temperature combinations were alternated through a 16 hr (night) and 8 hr (day). All combinations were used for −4, −2, 0, 2, 5, and 5‐degree increments through 40 C. The annual grasses germinated under a very broad range of temperatures above a minimum night temperature of 0 C. The rose clover cultivars germinated at lower temperatures, including subzero C (−4 C and −2 C) alternating with 15 to 25 C day temperatures. Seeds of rose clover from a naturalized population had lower germination at low temperatures and higher germination at high temperatures than the seven cultivars tested. In comparison with the annual grasses and rose clover, the perennial grasses were relatively restricted in the temperature regimes that permitted germination. Interpretation of the ecological significance of the results of monitoring seedbed temperatures during germination periods and the juvenile growth rate of the various species is dependent on the results of this investigation.