Abstract: [Objective] The objective was to explore the differences of respiration rates in the soil and soil components of the mixed plantations of Cunninghamia lanceolata and broadleaved trees in northern Fujian Province in China under different harvesting intensities, to identify the main influencing factors of the seasonal variation in total soil respiration rate, and to provide a scientific basis for studying the impact of regional forest harvesting on soil respiration rate.[Method] Experiments were carried out in a mixed plantation of C. lanceolata and broadleaved trees in northern Fujian Province in August 2011. Selective harvesting at three intensities:medium (34.6%), high (48.6%), and extra-high (67.6%) and clear cutting were performed, and non-harvesting was used as control. The respiration rates of soil and its components, soil temperature and moisture at a depth of 5 cm were measured using a Li-Cor 8100A infrared gas exchange analyzer from July 2016 to July 2017 (5 years after harvesting).[Result] As assessed in 2016, in the non-harvesting control plot and selective harvesting plots, the total soil respiration rate reached its maximum in July and minimum during January to March; 5 years after clear cutting, the total soil respiration rate reached its maximum in June and minimum in November. There was no significant difference (P > 0.05) in respiration rate in the mineral soil between the harvested plots at different intensities and the non-harvested control. The respiration rates of litter and roots did not differ significantly between the selective harvesting and the non-harvesting (P > 0.05), but significantly decreased by 0.93 μmol·m^-2s^-1 and 0.53 μmol·m^-2s^-1 under clear harvesting (P < 0.05) compared to the non-harvesting (1.45, 1.11 μmol·m^-2s^-1). The total soil respiration rate did not differ significantly between the selective harvesting at different intensities and non-harvesting plots (P > 0.05), but compared to non-harvesting (4.39 μmol·m^-2s^-1), the total soil respiration rate significantly increased by 1.64 μmol·m^-2s^-1 under clear harvesting (P < 0.05). Soil temperature did not differ significantly between the selective harvesting at different intensities and the non-harvesting (P > 0.05), but compared to the non-harvesting (18.52℃), the soil temperature significantly increased by 4.7℃ under clear harvesting (P < 0.05). Soil moisture did not differ significantly among medium intensity, high intensity, and non-harvesting conditions (P > 0.05), but compared to non-harvesting (30.67%), the soil moisture significantly decreased by 2.17% and 3.98% at the extra-high intensity of harvesting and the clear cutting (P < 0.05). The total soil respiration rate could be best described by the exponential model of soil temperature. The model that fit temperature best explained 77.8%-83.3% of the variation in the total soil respiration rate under selective harvesting and non-harvesting conditions, and 35.5% of the variation in total soil respiration rate under clear harvesting. The temperature sensitivity (Q₁₀) of the total soil respiration rate was in the range of 1.77-2.72 under selective harvesting and non-harvesting conditions, and it was 1.47 under clear cutting conditions.[Conclusion] 5 years after harvesting, selective harvesting at different intensities and non-harvesting had no significant difference in the respiration rates of soil and its components. The respiration rate of the litter, the root, and the total significantly decreased under the clear cutting. Selective harvesting at different intensities did not change the regularity of seasonal variation in total soil respiration rate. The maximum and minimum values of seasonal variation in total soil respiration rate appeared early under the clear cutting. In the study area, the seasonal variation in total soil respiration was mainly controlled by soil temperature.

Key words: selective harvesting, soil respiration rate, soil temperature, soil moisture, mixed plantation of Cunninghamia lanceolata and broadleaved trees