不同强度采伐5年后杉阔混交人工林土壤呼吸速率差异

【目的】比较不同采伐强度下闽北杉阔混交人工林土壤及其各组分的呼吸速率差异,揭示土壤总呼吸速率季节变化的主要影响因子,以期为区域森林采伐对土壤呼吸速率的影响研究提供科学依据。【方法】以闽北杉阔混交人工林为研究对象,2011年8月实施了不同蓄积量采伐强度(中度择伐34.6%、强度择伐48.6%、极强度择伐67.6%、皆伐)作业试验,并与未采伐对照;2016年7月—2017年7月运用Li-8100 A土壤碳通量自动测量系统,对土壤及其各组分的呼吸速率、土壤5 cm深处的温度和湿度开展了为期1年的定位观测。【结果】未采伐和各种强度择伐5年后,土壤总呼吸速率最大值都出现在7月份,最小值出现在1—3月份;皆伐5年后,土壤总呼吸速率最大值出现在6月份,最小值出现在11月份;各种强度采伐林地的矿质土壤呼吸速率与未采伐林地无显著差异( P >0.05);各种强度择伐林地的凋落物和根系呼吸速率都与未采伐林地无显著差异( P >0.05),而皆伐林地的凋落物和根系呼吸速率都显著低于未采伐林地( P <0.05),分别比未采伐林地(1.45和1.11 μmol ·m^-2 s^-1 )减少了0.93和0.53 μmol ·m^-2 s^-1;各种强度择伐林地的土壤总呼吸速率与未采伐林地无显著差异( P >0.05),而皆伐林地的土壤总呼吸速率显著低于未采伐林地( P <0.05),比未采伐林地(4.39 μmol ·m^-2 s^-1 )减少了1.64 μmol ·m^-2 s^-1;中度、强度和极强度择伐林地5 cm深处的土壤温度与未采伐林地没有显著差异( P >0.05),而皆伐使林地土壤温度显著升高( P <0.05),比未采伐林地(18.52 ℃)增加了4.7 ℃;中度、强度择伐林地的5 cm深处土壤湿度与未采伐没有显著差异( P >0.05),而极强度择伐和皆伐使林地土壤湿度显著降低( P <0.05),分别比未采伐林地(30.67%)减少了2.17%和3.98%;土壤总呼吸速率的土壤温度指数模型拟合效果最优,能解释未采伐和各种强度择伐林地土壤总呼吸变化的77.8%~83.3%以及皆伐林地土壤呼吸变化的35.5%;未采伐、中度、强度和极强度择伐林地土壤总呼吸的温度敏感性参数Q 10 为1.77~2.72,皆伐林地的 Q 10 为1.49。【结论】不同强度采伐5年后,各种强度择伐林地土壤及其各组分的呼吸速率与未采伐林地没有显著差异;皆伐使凋落物呼吸速率、根系呼吸速率和土壤总呼吸速率都显著降低;各种强度择伐没有改变土壤总呼吸速率的季节变化规律,但皆伐使土壤总呼吸速率最大和最小出现时间有所提前;研究区土壤温度是土壤总呼吸速率季节变化的主要影响因子。

Difference in Soil Respiration Rates of the Mixed Plantations of Cunninghamia lanceolata and Broadleaved Trees 5 Years after Harvesting at Different Intensities

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^-2 s^-1 and 0.53 μmol·m^-2 s^-1 under clear harvesting (P < 0.05) compared to the non-harvesting (1.45,1.11 μmol·m^-2 s^-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^-2 s^-1),the total soil respiration rate significantly increased by 1.64 μmol·m^-2 s^-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 (Q 10) 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.