六盘山林区几种土地利用方式土壤呼吸时间格局

测定分析了六盘山林区典型的天然次生林灌木林、山杨(Populus davidanda dode)林和辽东栎(Quercesliaotungensis koiz)]林、农田、草地和人工林13a、18a和25a华北落叶松(Larix principis-rupprechtil mayr)]土壤呼吸时间格局.结果显示:随着温度升高,土壤呼吸速率逐渐升高,温度最高值在13:00～15:00点钟、最低值在凌晨4:00～8:00点钟,土壤呼吸速度最高和最低值也在这个时间范围.5～10月,土壤呼吸速率呈现增加而又降低的趋势,在8～9月达最大值,10月下降,这种变化主要与土壤温度变化基本一致.农田和草地土壤呼吸速率的昼夜或月变化幅度比天然次生林和人工林中大,且农田和草地土壤呼吸速率在昼夜或月变化中的最高值比天然次生林和人工林高、最低值比天然次生林和人工林低.天然次生林土壤年呼吸量平均在3.96～4.51 t/(hm²·a)、农田在1.91 t/(hm²·a)、草地在5.08 t/(hm²·a)、人工林在4.11～5.55t/(hm²·a).结果说明天然次生林变成农田或草地后,将使土壤呼吸速率的昼夜或月变化幅度增大,而农田或草地上造林后又将使这些变化幅度减小.另外,土地利用变化也将使土壤的年呼吸量改变.

The Temporal Variations of Soil Respiration Under Different Land Use in Liupan Mountain Forest Zone

The temporal variations of soil respiration under cropland, rangeland, natural secondary forest (brushwood, nature secondary forest dominated by Querces liaotungensis koiz or Populus davidiana dode) and the plantation of larch (13, 18 and 25-year-old Larix principis-rupprechtil mayr) in Liupan Mountain forest zone was studied. It was found that the rate of soil respiration increased with increasing soil temperature during diurnal variation and the highest temperature was from 13:00 o'clock to 15:00 o'clock, the lowest temperature was from 04:00 o'clock and 08:00 o'clock, the variation of soil respiration rate appeared same trend. The daily rate of soil respiration increased from May to October and which was the highest from August to September and declined on October. The diurnal or seasonal variation of soil respiration rate mainly consisted with the diurnal or seasonal variation of soil temperature and its range under cropland or rangeland was greater than which under forestland (natural secondary forest, plantation or brushwood). The highest rate of soil respiration for diurnal or seasonal variation of soil CO2 efflux under cropland or rangeland was higher than which under the forestland, while the lowest rate of soil respiration under cropland or rangeland was lowered than which under forestland. Annual rate of respiration for natural secondary forest, cropland, rangeland and plantation was 3.96-4.51 t/(hm2.a), 1.91 t/(hm2.a), 5.08 t/(hm2.a) and 4.11-5.55 t/(hm2.a) respectively. The results shows that the diurnal or seasonal variation range of soil respiration rate would increase with conversion from natural forests to cropland or rangeland, while which would decrease following afforestation under cropland or rangeland. In addition, the annual respiration rate would also change with change in land use.