Table 3.

Modelled double first-order kinetic parameters that describe ¹⁴C-labelled amino acid mineralisation in Arctic and temperate soils subjected to 1 and 3 freeze–thaw (FT) cycles of −7.5 to +5 °C

Amino acids
Soil	Parameter	Control	FT	3 Control	3FT
Meadow mineral	a 1 (%)	11.2 ± 0.8	11.5 ± 0.7	10.8 ± 0.8	12.9 ± 0.2
	k 1 (h−1)	0.37 ± 0.08	0.24 ± 0.04	0.15 ± 0.03	0.14 ± 0.02
	a 2 (%)	88.1 ± 0.8	87.5 ± 0.7	88.4 ± 0.8	86.2 ± 0.2
	k 2 (×10−3 h−1)	0.59 ± 0.06	0.53 ± 0.07	0.47 ± 0.15	0.53 ± 0.03
Meadow organic	a 1 (%)	12.0 ± 0.7	11.2 ± 0.3!	13.3 ± 0.5	13.7 ± 0.5!
	k 1 (h−1)	0.41 ± 0.03!	0.37 ± 0.05	0.22 ± 0.02!	0.19 ± 0.02
	a 2 (%)	87.4 ± 0.7	88.1 ± 0.4!	85.9 ± 0.6	85.5 ± 0.5!
	k 2 (×10−3 h−1)	0.43 ± 0.03	0.44 ± 0.02	0.54 ± 0.04	0.52 ± 0.03
Heath mineral	a 1 (%)	8.6 ± 2.5	12.1 ± 0.5	13.5 ± 0.3	12.9 ± 1.7
	k 1 (h−1)	0.20 ± 0.11	0.10 ± 0.04	0.11 ± 0.04	0.06 ± 0.01
	a 2 (%)	90.9 ± 2.6	87.4 ± 0.4	86.0 ± 0.4	86.9 ± 1.6
	k 2 (×10−3 h−1)	0.39 ± 0.06	0.47 ± 0.04	0.55 ± 0.02	0.45 ± 0.04
Temperate	a 1 (%)	9.9 ± 0.5*	12.4 ± 0.3*	11.0 ± 0.6	12.5 ± 1.0
	k 1 (h−1)	0.22 ± 0.02	0.14 ± 0.00	0.21 ± 0.01*	0.15 ± 0.01*
	a 2 (%)	89.2 ± 0.5*	86.9 ± 0.3*	88.3 ± 0.6	86.9 ± 1.1
	k 2 (×10−3 h−1)	0.46 ± 0.01	0.44 ± 0.01	0.47 ± 0.03	0.50 ± 0.05

The parameters a ₁ and a ₂ are the proportion of substrate mineralised rapidly or slowly, whilst k ₁ and k ₂ are their respective rate constants

* A statistical difference between freeze–thaw treatment and the control (not frozen)

^! Statistical difference over time (i.e. between the first and third control or 1FT and 3FT), (p < 0.05). Values represent mean ± SE (n = 4)