Population variation in germination traits and its implications for responses to climate change in a fire-prone plant species complex

Abstract

Many plants in fire-prone environments have limited dispersal ability and thus rely on in situ mechanisms such as evolutionary responses to persist through climate change. The regenerative phases of the plant life cycle, such as seed dispersal, germination and seedling establishment, are likely to be critical to defining species’ environmental niches and, in fire-prone environments, are cued to fire events. Adaptive potential in traits that regulate these processes is key to in situ persistence, yet variability in fire adaptive traits at the population level remains largely unexplored. To investigate adaptive potential, we quantified population-level variability in the thermal germination niche of a widespread fire-prone species complex, the Banksia spinulosa group. In one of the first studies of rising temperatures on germination in serotinous plants, we sampled seeds from 12 source populations spanning seven degrees of latitude and more than 1000 m of elevation and tested germinability over a range of incubation temperatures in common laboratory conditions. Thermal germination niches varied appreciably among source populations, suggesting local adaptation or other mechanisms of differentiation. Some of this variation was explained by current taxonomic boundaries, but germination responses also varied within recognised taxa and within populations. A small but significant portion of the interpopulation variation was related to thermal conditions at the source populations. As well, intrapopulation variation was greater within source populations of taxa from warm climates than those from cooler climates. The expected effect of warming is to narrow the window for germination to the cooler months of the year. The development of fire management strategies that reduce risks of post-fire mortality of seeds and seedlings, and exploit adaptive potential to promote in situ persistence as the climate changes, should therefore be a priority for climate adaptation research.