| Forest soil respiration is an important part of the soil respiration in terrestrial ecosystems, the dynamic changes of which will bring far-reaching influence on the global carbon cycling. Different degrees of soil compaction were caused by frequently human activities in urban forest in recent years, and thus affected forest productivity and soil carbon balance. During the growing season in 2009(May to October), soil CO2 emission rates with different compaction degrees of larch (L. gmellinii) and birch (B. platyphylla) plantations were measured with Li-8100 automatic instrument in NEFU experimental forest field, the temperature, humidity and soil physical properties were also measured. Using statistical analysis software SPSS15.0, the variations of soil respiration rates with different treatment in two stands were analyzed. Then the temperature and humidity, and compaction impacted on soil respiration rates were discussed. The results as follow:The diurnal variations of soil respiration rates in two stands showed a single peak curve, which were consistent with the temperature. In larch plantation, the occurrence time of diurnal variation peak value was at 15:30-17:30, and the valley value appeared at 01:30-05:30; and the peak was at 13:30-15:30, and the valley appeared at 01:30-03:30 in birch plantation. The diurnal variations of soil respiration rates had significant difference (P<0.01), but the soil respiration rates had no significant correlation (P>0.05) with the surface moisture. The regression model fitted by temperature and moisture can explain 86.4% of the diurnal changes of soil respiration in larch plantation, and 97.4% of birch plantation.Meanwhile, the seasonal trend of soil respiration rates in larch plantation was consistent with birch plantation, and the seasonal variations of soil respiration rates also had significant difference (P<0.05). They had significant correlation (P<0.01) with the surface temperature and the temperature underground 10cm. The sensitivity of temperature was presented by Q10 values, which were calculated with the surface temperature and the temperature underground 10cm. they were 2.21 and 3.21 respectively in larch plantation, and birch plantation were 2.33and 2.64. The seasonal soil respiration rates had significant correlation (P<0.01) with the surface moisture. It could explain 85.6% of larch seasonal variation of soil respiration, and 83.1% of birch soil respiration. The interaction of temperature and humidity could explain 86.8% of larch seasonal variation of soil respiration,96.3% of birch seasonal variation of soil respiration.The soil respiration by each compaction treatment had the same trend with the control plots, and the occurrence time of diurnal variation maximum and minimum values were earlier than those of the control. The soil respiration rate became lower with the compaction degree increased. Our experiment applied that the diurnal variation of soil respiration had reduced about 70% in main road Y1, and about 40% in branch road Y2ï¼›while the seasonal variation of soil respiration had reduced about 55% in main road Y1, and about 30% in branch road Y2.The diurnal variation of soil respiration rate by different compaction degrees had significant differences (P<0.01). But the seasonal variations of soil respiration were effected by the compaction degrees. The Q10 values and the rate of soil respiration which could explain by the interaction of temperature and humidity became lower with the compaction degree increased. |
