Simulating the germination response to diurnally alternating temperatures under climate change scenarios: comparative studies on Carex diandra seeds

Background and Aims Environmental temperature regulates plant regeneration via seed in several superimposed ways, and this complex regulation will be disrupted by climate change. The role of diurnally alternating temperatures (Delta T) in terminating dormancy will be a major factor in this disruption, as its effects on seed germination are immediate. Methods The effect of Delta T on seed germination was modelled using two populations of the wetland sedge Carex diandra, one from a montane site and one from a subalpine site. A cardinal-temperature model was fitted to germination results obtained from a thermal gradient plate, and the model was used to simulate changes in germination under two possible future climate scenarios (RCP2.6 and RCP8.5, for representative concentration pathways) as defined by the Intergovernmental Panel on Climate Change. Key Results Scenario RCP2.6 projected moderate increases in average temperatures and Delta T, whereas RCP8.5 projected greater warming and higher Delta T. Increasing Delta T decreased the base temperature for seed germination and the thermal time required for germination. The effect of higher Delta T together with the higher temperatures increased germination under both climate scenarios. Conclusions Carex diandra germination is highly responsive to potential changes in Delta T, and thus this study highlights the role of Delta T in seed responses to climate change. Comprehensive cardinal-temperature models, encompassing the different effects of temperature on seed germination, are needed to understand how climate change will affect plant regeneration.