Daffodils and Snowdrops react differently to warming seasons

For seeds to become plants, they need to germinate. Some will do so at any opportunity. Some need a cold shock in order to wake them. Wild daffodils, Narcissus pseudonarcissus, and snowdrops, Galanthus nivalis, need something more complicated. They need warm summers and then cooler autumns to germinate. What happens when the climate becomes less stable and warmer? Rosemary Newton and colleagues have been looking at how daffodil and snowdrop seeds germinate to find out.

Knowing how these plant seeds react to changing temperatures could be an important asset to forest management, the authors write. “Sustainable forest management can reduce (and indeed sometimes reverse) land degradation and can support mitigation and adaptation to climate change, slowing a decline in biodiversity. These geophytes represent an important component of temperate woodland understorey species, typified by complex seed dormancy-breaking requirements and poor ability to disperse to and colonize new habitats, and are thus a focal constituent of temperate woodland ecology.”

The team gathered the seeds from Kew’s properties at Loder Valley and Wakehurst. “When investigating seed dormancy and ecology, fresh seeds are vital to ensure that it is the ecology of seed dormancy on shedding which is considered,” write Newton and colleagues. “This is because physiological changes may occur during storage which reduce seed dormancy and alter germination requirements… This is particularly so in the moist temperate woodland species N. pseudonarcissus (daffodil) and G. nivalis (snowdrop).”

The team found that both daffodil and snowdrop were almost like anti-weeds. Far from being rapid to germinate and take advantage of a habitat, germination in some seeds took over five hundred days. They found that seeds did not germinate in their first summer but, given the complex dormancy of daffodil and snowdrop, they weren’t expected to. However, warmer autumns affected the two plants in different ways.

“Warming increased the germination of both N. pseudonarcissus and G. nivalis in the current study, but with key seasonal differences due to different optimal temperatures for seed germination for each species. Warming in autumn improved germination in that season in G. nivalis (optimum germination temperature of 15 °C) but reduced it in N. pseudonarcissus (optimum germination temperature of 10 °C), whilst warming in the winter promoted germination in N. pseudonarcissus but not in G. nivalis.”

“The origin of both species from regions with warmer climates than the UK may explain why the best germination is observed at warmer rather than average autumn temperatures for West Sussex,” say Newton and colleagues. Yet coming from warmer climes doesn’t mean future warming climate will always be kind. They note that instability of climate is also a problem. “[E]ven though their origin and germination temperature optima may suggest that these species will fare better in future, given that the soil seed bank is likely to be depleted more quickly, they may be at greater risk of one-off events such as extreme rainfall.