Soil respiration during freeze-thaw cycles in a temperate Korean Larch (Larix olgensis herry.) plantation

Successive effects of freeze-thaw cycles (FTCs) on soil respiration rate (Rs) were explored in a Korean Larch (Larix olgensis Herry.) plantation during the winter to spring season. In March 2014, laboratory incubation with severe FTCs at the extreme minimum temperatures of -16 degrees C and mild FTCs (-8 degrees C) and field-based methods through five days continuous measurements of Rs at eight time points in one day were applied to determine the diurnal and seasonal Rs variations during FTCs, and to analyze the effects of FTCs regimes on Rs. The Rs increased rapidly as thawing proceeded, generating two peaks during severe FTCs, but with no obvious CO2 peaks in mild FTCs or field-based measurements. In severe FTCs, the Rs in first three FTCs changed dramatically, subsequently tended to stabilize. The diurnal Rs dynamics both followed unimodal type, with no fixed peak in laboratory study but the maximum value at 14:00 in field study. Laboratory- and field-based FTCs studies both highlighted the significant effects on soil carbon release. Initial response of soil respiratory bursts during early FTCs appeared to be driven by extreme minimum temperatures, while response of soil carbon release in late cycles was controlled by reduction in soil organic matter during early cycles.