Table 2.

Percent survival, maximum efficiency of photosystem II (F_v/F_m) and electrolyte leakage at − 9 °C and temperature for 50% electrolyte leakage (TEL₅₀) of two individual populations of Arabidopsis lyrata ssp. petraea after exposure to sub-zero temperatures for one night

	Cold acclimation duration (days)	Helin (Norway)	Leitrim (Ireland)
% survival after exposure to − 9 °C	0	0	8
	2	27	46
	14	81	76
Fv/Fm after exposure to − 9 °C	2	0.35 (± 0.06)	0.57 (± 0.04) **
	14	0.43 (± 0.02)	0.48 (± 0.03) ns
Electrolyte leakage (%) at −9 °C	0	96.0 (± 2.0)	97.3 (± 0.2) ns
	2	99.3 (± 1.0)	89.2 (± 2.6) *
	14	48.2 (± 13.0)	74.8 (± 17.0) ns
TEL50 (°C)	0	−4.2	−4.5
	2	−6.7	−7.6
	14	−9.2	−7.8

Sub-zero temperatures were applied at a rate of − 2 °C per hour after 0, 2 or 14 days cold acclimation at 2 °C. Statistically significant differences between populations are indicated by * = P ≤ 0.05; ** = P ≤ 0.01; ns = not significant