Projected soil temperature increase and seed dormancy response along an altitudinal gradient: implications for seed bank persistence under climate change

Background and aims Understanding the mechanistic effects of climate change on species key life-history stages is essential for predicting ecological responses. In fire-prone regions, long-term seed banks allow post-fire recovery and persistence of plant populations. For physically dormant species, seed bank longevity depends on the maintenance of dormancy which is controlled primarily by temperature. Successful inter-fire recruitment is rare and dormancy loss between fires produces a net loss to the seed bank. We assessed whether temperature increases related to climate change can affect seed dormancy and, potentially, seed bank longevity. Methods We quantified the relationship between air temperatures and soil temperatures. Seeds of two shrub species, from four populations along an altitudinal gradient, were then exposed to a range of soil temperatures calculated to occur at the end of the 21st century, using projected mean and heat wave scenarios. Alterations to dormancy were assessed via germination. Results For every 1°C increase in air temperature, associated soil temperature increased by 1.5°C. Mean temperature increase had no affect on seed dormancy. However, future heat wave conditions produced soil temperatures that significantly increased dormancy loss. This impact was greatest in seeds from cooler, high elevation populations. Conclusions Projected heat wave events produce conditions that provide a mechanism for seed bank compromise. Dormancy-breaking temperatures for each population were positively related to parental environment temperatures, indicating local adaptation. Whilst heat from fire may govern post-fire recruitment response, we suggest that parental climate is the key selective force determining dormancy-breaking threshold temperatures, ensuring inter-fire seed bank persistence.