Germination response to temperature in tropical and subtropical pasture legumes. 2. Alternating temperature

Abstract

The germination response of 8 promising and commonly used tropical and subtropical legumes in northern Australia was tested at a range of alternating temperatures. Except at temperatures <20°C or >36°C, total germination was largely unaffected by different alternating temperatures. Although there were statistically significant differences between constant and alternating temperatures, overall, these differences were <2% and hence of no biological importance. Increasing amplitude of fluctuation in temperature decreased the rate of germination for some species. At 8°C amplitude Glycine latifolia, Macroptilium atropurpureum and Lablab purpureus showed no difference in the time taken to reach 50% of germination while Chamaecrista rotundifolia, Stylosanthes scabra and Desmanthus virgatus took 1.5-2 times as long as at constant temperature. Predicted germination against real time, using 2 different models, fitted the observed data poorly. In particular, prediction of the commencement of germination was poor for C. rotundifolia and S. scabra. This failure at more extreme or highly fluctuating temperatures indicates that further development is required before the models would be sufficiently reliable for inclusion in simulation models of legume persistence. In particular, the rate of death of seeds at temperatures distant from the optimum range needs to be included. The ability to germinate at a broad range of temperatures indicates that the species are well adapted to northern Australia. Some species may be susceptible to large fluctuations in temperature during germination, and this should be considered in criteria for selecting future species.