[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.