Fig. 5. Relationship between the size of the labile carbon pool (C_l) and the decay constant for the labile pool (k_l). These two parameters are simultaneously determined by fitting the curve C_t = C_l (1 – e^–k_lt) + k_rt, where C_t is the known cumulative amount of C respired at sampling period t, and k_r is the mineralization rate for the recalcitrant pool which is set at 3 µg g^–1 soil d^–1 (r² = 0.55, P < 0.0001, y = 0.025 – 0.0000065x).