Table 1.

Root length responses near the low temperature limit. RERs during the 12-h interval with the lowest temperature in the cold treatment, the deepest single root tip position and the mean maximum root tip depths (averaged across cylinders per species ± SD) at harvest. Corresponding root tip temperatures were derived from the temperature gradients (polynomial functions, calculated for 12 h for RER and for the last five treatment days prior to harvest). ^#Hourly minimum and maximum temperatures for n = 26–30 single roots per species during root formation.

	Rumex	Ranunculus	Tussilago	Poa
RER (mm per 12 h)	0.4	0.2	0.3	0.6
Temperature (°C) during 12-h interval (hourly min–max per 12 h)	0.9 (0.8–1.1)	0.9 (0.7–1.2)	0.7 (0.6–1.1)	0.7 (0.7–1.0)
Single deepest root tip position (mm)	73.7	77.3	87.6	105.8
Root tip temperature (°C; hourly min–max)	1.2 (1.1–1.4)	1.0 (0.8–1.2)	1.0 (0.9–1.3)	1.0 (0.8–1.3)
Mean of maximum root tip positions (mm; ±SD)	54.4 ± 11.9	61.5 ± 12.3	65.5 ± 14.5	91.7 ± 13.1
Number of deepest root tips (n)	n = 26	n = 30	n = 26	n = 29
Mean of root tip temperatures (°C; ±SD):	2.4 ± 1.1	2.0 ± 0.9	1.9 ± 0.8	1.5 ± 0.3
Hourly min/max temperatures#	1.1/5.3	0.8/5.1	0.9/4.7	0.8/2.8